SMBE Conference guidelines

Download a PDF of the Conference Guidelines here.

Statement of diversity

SMBE has a strong commitment to diversity. Organizers should place emphasis on diversity of participants, including gender and geographic diversity, at every level of the meeting, including but not limited to the selection of plenary speakers, symposium organizers, and invited and contributed talks. Please ensure that this criterion is considered throughout the organization of the conference.

Professional Conference Organizer (PCO)

Each conference is organized jointly by SMBE’s contracted Professional Conference Organizer (PCO) and the Local Organizing Committee.  The role of the PCO is described in its contract with SMBE.

Local Organizing Committee (LOC)

The SMBE conference Local Organizing Committee should include Local Organizers and one member of SMBE Council. The role of the Council member on the LOC is to make sure the conference organizers adhere to these guidelines. Additionally, one organizer of the meeting from a previous year and one organizer of the meeting for the next year should be included for the purpose of continuity.

The LOC will be required to sign a formal agreement with SMBE agreeing to its responsibilities.

The LOC should send any presentations it makes – usually their proposal and post-conference feedback – to the SMBE Executive Administrator for archiving.


It is very important that the meeting is fully costed, with costs borne by the meeting and not by the Society.  A rolling budget should be set up with precise costs and with frequent updates on income and expenditure. The Society will provide US$100,000, which is the only funding promised by the Society. While these funds can be made available at any time and used temporarily for other expenditures (such as reserving a venue), it is understood that the US$100,000 will ultimately cover travel costs for 50 invited speakers.  In addition, in the event that a short-term loan is required for down-payments on the venue and suppliers, then this can be arranged. Be aware that this loan will be issued in US dollars and all currency change costs, as well as the danger of currency fluctuations, must be borne by the conference.

Size of conference

The conference can currently expect between 1000 and 1500 delegates, although we have seen considerable fluctuations in this number depending on factors such as convenience and cost of travel. Organizers are advised to make two alternative plans for a smaller and a larger conference - i.e. make plans for a smaller conference but include options to expand if registration numbers seem to indicate the meeting will be large. This should happen at the same location with options for a larger auditorium that can hold the entire conference. Conference attendance should be capped at 2000.

Approximate timelines




Last day of the conference of the preceding year.

Initial website goes live



●       venue

●       opportunities for sponsorship

●       composition of the organizing committee

●       contact information for the conference organizer.

10 months before the date of the conference.

Call for symposia opens

See ‘Call for symposia’ below.

9 months before the date of the conference

Call for symposia closes


8.5 months before the conference

Notification of successful Symposia


8 months before the conference

Titles and short description of all symposia, should be placed on the conference website. Note that these are sometimes worded differently from the original proposals, which sometimes contain information related to the submission process.,.


8 months before the conference

Early bird registration opens

This deadline offers discount on the registration fee. Past experience indicates that 50-75% of delegates will take advantage of this early registration deadline.

Early bird registration should be advertised to the society membership, in the society journals, through the social media, on EvolDir, etc.

7 months before the conference

Abstract submission and award applications open

6 months before the conference

Abstract submission and award applications close (though it is common to extend by one week, depending on number of submissions).

Fitch Symposium, Abstract and travel award deadlines all occur at the same time. Fitch finalists are selected first and present in a separate symposium.

2-3 weeks prior to council decision of travel awards

Deadline for symposium organizers’ talk selection

To allow inclusion of talks in symposia to be considered in selection of travel awards

2 weeks before early bird registration closes

Council decision of travel awards: award applicants notified of success or otherwise

This is essential to allow applicants time to register at Early Bird rate if they haven’t received a travel/registration award. Some individuals who do not receive funding or are not selected for a talk will not register. There can be loss of ~100 participants as a result.

4 months before the conference

Early bird registration closes, full price registration opens


2 months before the conference

Full programme available online

Until the conference begins

Full cost registration

Full cost online registration; allows delegates to submit an abstract, though as an additional encouragement to register early, it should be stipulated that late abstracts can be considered only for poster presentations.

Either on the penultimate day of the meeting or up to two days later

Post-meeting survey

To be emailed to all meeting participants and able to run on a computer OR phone 

Structure of the conference


The preferred conference length is at 3.5 days with the acceptable range from 3 to 4 days (not counting the day of the council meeting/opening reception). The LOC is encouraged but not required to organize Public Lectures on Evolution/Molecular Evolution either immediately before or immediately after the meeting.

Council meeting

One council meeting to be held in a room that accommodates the council plus outside participants (about 16 people altogether).  Light breakfast, lunch, and all day coffee, tea, and light refreshments should be provided. This meeting will usually take place on the first day of the conference, starting at 8 or 9 am and must end at least 15 minutes before the Nei lecture. The main conference usually begins in the late afternoon/early evening with the Nei lecture, followed by the opening reception.

Scientific content

Limit oral presentations per person

Each person is limited to one oral presentation (either invited or contributed) for the entire annual SMBE meeting. If the same person is invited to several symposia, the person is given a choice of in which symposium s/he would like to present.

Presenter information

Each presenter should have clear instructions on where their presentation is going to be held, when they have been allocated a speaking time, and how to upload their slides.

Plenary lectures

There should be 3-4 plenary lectures, which are attended by all delegates, and usually last one hour. The number of plenary lectures should be limited to keep costs down and maximize  the number of multi-speaker symposia. Refer to the ‘Statement of Diversity’ above in the selection of plenary speakers. 

One of these plenary lectures is the Nei Lecture, named in honour of Professor Masatoshi Nei, and is given by the President of the society. Usually this lecture takes place near the beginning of the conference. SMBE has funds for this lecture to be published in MBE. The other plenary lectures are invited by the LOC and the invitees are usually fully funded in terms of the registration fee, travel and accommodation by the meeting.

Special symposia

Fitch Symposium

The Fitch Symposium occurs as an exclusive event when no other events or symposia are taking place.

Graduate students and postdocs in their first year of their first postdoc are eligible to apply to present their work in the Fitch Symposium, which is a plenary symposium, again attended by all delegates at the conference. A committee is convened each year by the Past-President to select the 8 talks from the submitted abstracts. The President-Elect will moderate the Fitch Symposium. The President will convene a committee to select the winner.

Open Symposium

The LOC is strongly encouraged to include an Open Symposium at which ground-breaking work not covered by the accepted symposium topics can be presented, Faculty award recipients can present, and potentially to allow more student/postdoc talks accepted.

Faculty awards symposium

There may also be a separate symposium for recipients of the Allan Wilson, Margaret Dayhoff, Motoo Kimura, and Community Service Awards.  Recipients of these awards should all be given the opportunity at the meeting, either in an ordinary symposium, or the special symposium, or in slots set aside for them in the Open Symposium.  The Council members responsible for these awards should be informed of the latest dates that lectures can incorporated into the programme.

Parallel symposia

The LOC should have a (usually audible) mechanism to ensure that concurrent sessions stay on time and try to minimize similarity in content or theme of overlapping concurrent sessions.

Number of symposia

There should be approximately 20-30 symposia, usually with no more than four parallel sessions (fewer than four is fine). SMBE Council considers that if there are more than four parallel sessions then delegates feel they are missing too many talks, while fewer parallel sessions restrict the diversity of the conference. Moreover, recent experience has shown that more sessions and/or additional plenary speakers can put the meeting into financial jeopardy.

Call for symposia

The call for symposia should indicate that if a symposium is selected, the invited speakers will have all or most of their registration fee, accommodation, and travel covered by the conference (at the level of approximately $2000 per invited speaker against receipts; adjusted reimbursement for intra- and intercontinental travel is allowed. This $2000 support for invited speakers should be maintained by the LOC under all circumstances.

A list of at least two confirmed invited speakers per symposium should be requested in response to the call for symposia.

Selection of the symposia

Most symposia are selected by the LOC on the basis of proposals and depending on whether the same topics were covered by symposia at recent SMBE meetings.

Symposia should reflect the broad diversity of interests in the SMBE community, not simply the most popular topics. Symposium organizers select abstracts for talks, taking speaker diversity into consideration (see Statement of diversity above) as well as diversity of career stage (student/postdoc/junior/senior investigators).

Symposium proposals should include a summary of the topic, why it is timely for the SMBE meeting, and which speakers have been invited and confirmed. If there are two or more proposals on the same topic, the LOC has a choice of selecting one proposal or merging two or more proposals. Merging two or more symposia either reduces the number of invited speakers that can be supported by SMBE or the number of slots available for contributed talks and is therefore discouraged.

Each symposium organizer can only select one talk from her/his own research group. That includes his/her own talk. In the event of too few submissions, exceptions to this rule may permit one additional talk from the organizer’s group, after consultation with the LOC.

The LOC selects the talks for the Open Symposium.


Recent conferences have settled on a structure where a ‘unit’ of time is 15 minutes. This includes time for questions (usually, 12 minutes for the talk and 3 minutes for questions and movement between rooms). This makes it especially important to have rooms in close proximity to each other. Invited speakers can be allocated 15 or 30 mins. It is also prudent to remind symposium organizers that delegates frequently move between symposia, so it is useful to allow one minute of moving time between talks (if adequate for travel between rooms) within the allocated 15 minutes and to be sure that the layout of seating is conducive to movement between rooms.. Some symposium organizers may choose to use the first 15 minutes to provide an overview of the study area at the beginning, but this is subject to time availability.

Selecting speakers

Each symposium of contributed talks will select its preferred speaker list from the list of contributed talk abstracts. It is best if a delegate is allowed to submit their abstract to more than one symposium (though logistically, it is probably best to restrict this to two symposia). When the symposium organizers are given their list of abstracts and delegates who wish to speak in their symposium, they can choose their preferred list of speakers. However, the exact details of this process are to be worked out by the LOC. In the end, the LOC will match delegates and symposia and communicate to both the symposium organizers and the delegates the outcome of this process. This decision should be reached before Early Bird registration closes as it affects many scientists’ travel funding, and no later than 4 months before the conference.

Poster sessions

Poster presenters frequently feel that they do not get adequate opportunity to present their work, so it is important that each poster presenter is given enough time both to talk to other delegates and to have the posters visible (at breaks, etc.). Poster sessions should have accompanying refreshments and each poster should have at least two sessions when they are available to be seen. Although not always possible, it is desirable to have sufficient space that all posters can be viewed throughout the meeting, so that participants (and poster judges) have plenty of opportunity for viewing. The website should also indicate when posters can go up. Poster space should only be made available to participants who have registered and sent payment, to minimize “no-shows.”

Social events

Please provide vegetarian/vegan options with all catering.

Breaks and catering

It is expected that the conference will provide morning coffee break, lunch on all days, afternoon coffee breaks on each day, preferably with some small snack (fruit, cookies, pastry, etc.), and poster sessions.

Welcome reception

This typically provides ample snacks, enough for all participants, in addition to at most one or two drink tickets. Additional drinks can usually be purchased at the bar.

Gala Dinner  (banquet)

Delegates can choose to pay extra for this dinner or choose not to attend.

This is the preferred venue for distributing awards, and awardees present at the meeting, including all Fitch participants, should have free Gala tickets. A few venues include an after-dinner speaker, and some venues include dancing Drink tickets may be provided at registration for the Gala, with additional drinks available for purchase.

Awards Ceremony

The preferred venue for the Awards Ceremony (which lasts about 20 minutes) is the Gala Dinner.

If the awards are not distributed at the Gala Dinner, then 20-30 minutes should be set aside for an Awards Ceremony in the middle of the last morning (to allow enough time for decisions to be made on poster prizes and to maximize attendance). This ceremony is usually combined with an invitation to the next meeting (10-15 minutes), but the Gala is the preferred venue for awards.

While not all poster participants typically attend the Gala, due to cost, unless it is covered in registration, not all participants attend a separate Awards Ceremony, due to other choices on the last day, including packing and checking out of the hotel.

Post-conference survey

Each delegate should be invited to evaluate the conference, either using a paper form that can be dropped into a box onsite or an online form that can be completed either on a computer or smart phone.  The survey should be organized by the PCO and its content checked by the SMBE Council representative before distribution.

Certificates of attendance

Some delegates will require a certificate of attendance for their home institutions or for funding agencies that have supported their travel. These certificates should be provided on request and made available at the conference venue or sent after the meeting.

Post meeting reporting

Meeting organizers are required to provide a summary document to the Council after the

meeting, including the diversity statistics of the meeting participants, (gender, geography, and career stage).

Awards (see

SMBE provides several types of pre-conference awards, which should be administered via the conference abstract submission system. It is essential that time is allowed for awardees to be chosen and applicants notified before Early Bird registration closes so that attendees can make informed financial decisions about registration options and travel.

Those receiving awards that include registration and travel need to pay in the first instance and will then be reimbursed by SMBE.  This applies to all but recipients of Registration-only awards, who need  a code to put in to the online registration system to avoid payment.

SMBE-appointed committees select the recipients of travel awards.  All award applicants should be SMBE members.

SMBE’s Faculty, Best Paper, Fitch, and best poster awards are presented at the Awards Ceremony. All awardess, including all eight Fitch presenters, attending the meeting are eligible for free Gala Dinner tickets.

1.     Faculty awards

Faculty award-winners are reimbursed for registration and travel to the meeting.

Recipients of these awards should all be given the opportunity to present talks at the meeting, either in an ordinary symposium or the special symposium or in slots set aside for them in the Open Symposium.  The Council members responsible for these awards should be informed of the latest dates that lectures can be incorporated  into the programme.

2.     Fitch awards

All those selected to present in the Fitch Symposium are eligible for a free Gala Dinner ticket, and will be reimbursed for travel and accommodation.

The Council will appoint two separate committees, one to review the initial applicants to the Fitch symposium and another to determine the winner among the 8 finalists (see timeline above). Banquet tickets should be reserved for the 8 finalists.

3.     Undergraduate mentoring and diversity travel awards

Award-winners are reimbursed for registration and a contribution toward travel to the meeting.

10 undergraduate mentoring and diversity awards are available each year to undergraduate students that submit abstracts. The total value of each of  these awards is $1500 to $2000, depending whether intercontinental travel is involved. This covers registration, with the rest intended for travel.   Registration fees are to be charged directly to SMBE, so that students do not have to pay themselves (the amount of registration cost being deducted from the final value of their award, and the award recipients informed at time of notification of the value of their award to be used for travel and lodging).

One or two SMBE Councillors assigned by the Council will take charge of this selection, with a recommended bias towards funding those selected to give oral presentations, keeping the Statement of Diversity in mind.

The process consists of finding a mentor for each student so that they can be guided through the conference. In addition, a dinner should be arranged for all 10 students, their 10 mentors and the Council members who organize the activity. The conference organizers should reserve 10 banquet tickets for the awardees (to be charged to SMBE) and liaise with the Councillors in order to find an appropriate restaurant for the mentoring dinner, which is usually on the first full day.). The Councillors will send the list of awardees and their details to the meeting organizers and the PCO so that they can be registered automatically.

All undergraduate awardees should present their posters in the same poster session and their posters grouped together.

4.     Graduate and postdoc travel awards

Award-winners are reimbursed for registration and travel to the meeting.

SMBE provides graduate and postdoc travel awards for the purpose of enhancing gender and geographic diversity. The awards are chosen from eligible applicants who are SMBE members and who have expressed a desire to be considered for such awards. The Past-President, usually in conjunction with the LOC, will head a committee to determine the awards.

5.     Poster awards

The poster prizes will be decided by a committee convened by the President-Elect. Poster prizes consist of up to 9 prizes of $500 each, to be distributed in the 3 categories of postdoc, graduate student, and undergraduate prizes (it does not have to be 3 each).

6.     Best GBE and MBE papers awards

Award recipients receive registration waivers, travel awards to attend the meeting, and a Gala ticket.

7.     Registration awards

These are registration only awards, and there are usually more of these than awards that include travel.

8.     Carer travel awards

SMBE provides additional travel awards for our members who are also primary carers (for example caring for children or dependent adults, including adult children with a disability or an elderly relative). This award can be used in the manner of choosing of the awardee, for example for procuring child care or dependent care at home (e.g., flying a relative to help at home while the delegate is at the meeting; hiring a professional). Priority will be given to early-career scientists and according to need (e.g., younger children, disabled children or adults).

Information about Carer Travel Awards should be included in emails promoting conference registration and applications should be through the registration system. The decision on who is granted an award will be made by a committee of at least one person designated by Council. It shall be noted that people in need of an early decision can email a request to the organizers and/or council member in charge of the Carer Travel Award process.  


Payment for registration

The online registration system should accept all major credit and debit cards using the conventional inputting mechanism.  Credit card fees charged to the conference should be less than 3% per transaction.

Registration fees

SMBE members receive discounted registration. The discount for SMBE members must be at least $30, but a higher differential between member and non-member registration is allowed. Students and postdocs should be given a further discounted registration rate as well; the discount should be larger for graduate students than for postdocs.  The conference registration page should allow conference delegates the opportunity to join SMBE on the spot, e.g. by linking to the SMBE website membership page in a new window (currently Finally, while most registrants will use the website, it should also be possible to register onsite (‘walk-ins’).

Registration data

Registration data, including lists of delegates, should only be given to SMBE officials and used for SMBE business.  Third parties, including organizers of future conferences, should not be given the lists without express permission from SMBE.

This determines eligibility for certain awards and allows SMBE to maintain a participant database with student or postdoc status recorded (this is essential for determining poster and travel award eligibility, for instance). The conference organizers must maintain a database of participants with this information, as well as abstract numbers and titles as separate entries, email addresses, affiliations, etc.

Registration should include declarations of:

·  career stage (faculty, postdoc, graduate student, undergraduate, other)

gender,(with both a write-in option for non-gender conforming participants who prefer to specify and the option omit             this question).

Registration giveaways at the meeting

Printed conference material should be kept to a minimum. Sponsors should be encouraged to provide advertisements and information on the conference website or app or instead of printed flyers.


Each delegate should be provided with a badge. This must not include advertising promotion for any journal or society other than MBE/GBE and SMBE, though non-journal sponsors may sponsor lanyards. It is desirable to have badges that designate Editors and Associate Editors of the journals (sometimes provided by the MBE EiC) as well as a separate designation for Council members, and/or speakers, though this is the option of the organizers.

Other swag (bags, bottles, USB thumb drives, etc.)

Should be kept to a minimum to reduce environmental impact and should avoid advertising for journals directly competing with society journals.  

Conference website, programme, and app

SMBE conference promotion should consider environmental impact and minimize the use of printed materials.


Must include:

promotion of travel and child care awards

SMBE policies on harassment and broadcasting (text in Appendix to this document)

All images either posted online or used in emails related to the conference should be approved by the Council liaison and take gender balance and other demographic issues into consideration, regarding the people shown in the images. When possible, images from previous SMBE meetings should be used.


The timetable should ideally be available in three formats:

●       “at-a-glance” format, simply detailing the session/symposia times and locations.

●       a more detailed version with each speaker shown in column format so that parallel talks are on the same row. This helps         participants plan their schedule. Once the meeting starts, it should be updated live online (or at least daily), since changes       do arise.

●       a detailed online-only booklet with each speaker listed along with all co-authors, affiliations, and abstract.

Be sure that all authors are visible in the complete online program, not just the presenting author, since many people choose to attend a talk based on the laboratory or senior author. It is helpful if this information can be provided in column format.

The programme should include SMBE policies on harassment and broadcasting (text in Appendix) and an email contact to report any violations of these policies. 

The most updated printed or printable conference programme should be the version with concurrent sessions in columns and concurrent talks in rows to make it easy to choose a path.

Additional requirements for the online programme

A participant list should be provided in the web programme.

The entire conference program, complete with timetables, should be made available for download to laptops or mobile devices, usually in PDF or Excel format.

The online programme should also contain all the logistical details for the conference, including the best and most cost-effective means of ground and air transportation to the meeting location.

Essential conference app features

●       Available in both iPhone and Android formats

●       Useable offline, since many travelers do not have a data plan and some hotels charge fees for wifi. Wifi quality can also be unreliable at large meeting venues.

●       If possible should not require registration (unless necessary for those who want  to customize it, for example to create a personalized program)

●       Updateable and updated daily

●       Include first author name, surname, and talk title, hyperlinked to abstract with all authors.

●       Allow announcements

●       Include SMBE policies on harassment and social media (text in Appendix) with quick email link to report violations

●       Include quick link so that a poster presenter can invite another meeting participant to her/his poster. (This should not require composing an email each time.)

●        Include, if possible, the ability to create a personalized schedule, selecting talks and/or abstracts to attend, by clicking on (such as “liking” or saving to schedule) either the talk title, speaker name, or abstract from any of its views.  This may include the option to set reminders. Reminders, alerts, or notifications (for example of poster sessions closing or a talk about to start) should always be inaudible.



The conference venue should have at least one room that can hold at least 80% of delegates. Past experience indicates that for the plenary talks approximately 80% of the delegates will attend. Therefore, it is preferable that there is a room to hold this number. If this is not possible, then there should be a facility to relay the plenary lectures to another comfortable room via video link.

The venue should additionally have enough rooms for all parallel sessions and these should be sufficiently large to accommodate approximately one third of the conference, given the difficulty in predicting the numbers of delegates that attend any given talk. The rooms should be located no more than a 1-2 min walk from each other and have seating or aisles arranged to facilitate movement between sessions.

Kindly ask the venue to refrain from using air freshener during the conference in all locations, including registration desk and lobbies. Some participants are allergic to it and it exposes all participants to poor air quality.

Free, secure wifi should be available throughout the venue.

Onsite child care

Organizers will arrange for onsite (in the same building as the conference) child care, as this is an issue of great importance to the members of the Society. SMBE will help defray the cost of child care. Please communicate early and often with the Society as to the costs, barriers and opportunities for child care. Ideally the onsite location should be no more than a 5 minute walk from the sessions but not right next to a room where there are talks. Parents need quick access but the sound level can be that of a play-room setting.

Speaker set-up

There should be a set-up room for speakers to check their presentations. The preferred presentation file format is pdf, but ideally both Powerpoint and Keynote should be accepted. Both modern (current OS) Apple and PC computers should be provided for presenters.


The LOC is responsible for liaising with SMBE and the PCO to ensure that all insurance requirements are met.

Appendix 1: SMBE policies

Policy on harassment, discrimination and liability
SMBE and the Annual Meeting organizers are dedicated to providing a safe, hospitable, and productive environment for all attendees. Accordingly, the SMBE Annual Meeting prohibits all forms of discrimination and harassment. Behaviour that undermines the integrity of intellectual discourse and interactions will not be tolerated. This applies to all conference participants, including staff, volunteers, and attendees. If a participant engages in harassing or discriminatory behaviour, the SMBE Annual Meeting organizers reserve the right to take action ranging from a simple warning to the offender to expulsion from the conference. If you have a question or concern about this policy or would like to report an incident involving yourself or another person, please contact any member of the Local Organizing Committee or email [email address for the appropriate year’s conference PCO]. We take such issues seriously and will maintain your confidentiality (unless legally compelled otherwise). Neither SMBE nor the SMBE Annual Meeting organizers shall be responsible for any defamatory, offensive, or illegal conduct of Meeting participants, and shall not be held liable for personal injury, property damage, theft or damage of any kind suffered by the participants at or in connection with the SMBE Annual Meeting.

Broadcasting policy
The SMBE Annual Meeting supports the communication and discussion of science. Information presented at the Meeting (in oral or poster format) may be reported and discussed by attendees and science writers via blogs, Twitter, or other formats, unless any of the authors requests otherwise. We do request that communications are respectful and do not directly reproduce visual materials (e.g., no posting of photos of slides or posters) unless permission is obtained from the presenter or if they have already made this information freely available in an open-source forum. If a presenter does not want information from his/her presentation to be photographed at all, or broadcast, they should make this clear in their talk/poster and we ask that attendees respect this. If you have questions or concerns about this policy, or would like to report an abuse of it, please contact any member of the Local Organizing Committee or email [email address for that year’s conference PCO].

Appendix 2: Call for proposals for conference

The President-Elect issues a call for proposals five years (e.g. call issued in 2017 for meeting in 2021) before the conference year, following the rotation below:

●       North America

●       Europe

●       Rest of the World

Applicants will be required to submit written proposals following a standard template to SMBE Council.  Applicants are required to work with SMBE’s designated PCO.

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Neutral Theory, Disease Mutations, and Personal Exomes

Mon, 23 Apr 2018 00:00:00 GMT

Genetic differences between species and within populations are two sides of the same coin under the neutral theory of molecular evolution. This theory posits that a vast majority of evolutionary substitutions, which appear as differences between species, are (nearly) neutral, that is, these substitutions are permitted without a significantly adverse impact on a species’ survival. We refer to them as evolutionarily permissible (ePerm) variation. Evolutionary permissibility of any possible variant can be inferred from multispecies sequence alignments by applying sophisticated statistical methods to the evolutionary tree of species. Here, we explore the evolutionary permissibility of amino acid variants associated with genetic diseases and those observed in personal exomes. Consistent with the predictions of the neutral theory, disease associated amino acid variants are rarely ePerm, much more biochemically radical, and found predominantly at more conserved positions than their non-disease counterparts. Only 10% of amino acid mutations are ePerm, but these variants rise to become two-thirds of all substitutions in the human lineage (a 6-fold enrichment). In contrast, only a minority of the variants in a personal exome are ePerm, a seemingly counterintuitive pattern that results from a combination of mutational and evolutionary processes that are, in fact, broadly consistent with the neutral theory. Evolutionarily forbidden variants outnumber detrimental variants in individual exomes and may play an underappreciated role in protecting against disease. We discuss these observations and conclude that the long-term evolutionary history of species can illuminate functional biomedical properties of variation present in personal exomes.

Neutral Theory, Transposable Elements, and Eukaryotic Genome Evolution

Mon, 23 Apr 2018 00:00:00 GMT

Among the multitude of papers published yearly in scientific journals, precious few publications may be worth looking back in half a century to appreciate the significance of the discoveries that would later become common knowledge and get a chance to shape a field or several adjacent fields. Here, Kimura’s fundamental concept of neutral mutation-random drift, which was published 50 years ago, is re-examined in light of its pervasive influence on comparative genomics and, more specifically, on the contribution of transposable elements to eukaryotic genome evolution.

Neutral Theory, Microbial Practice: Challenges in Bacterial Population Genetics

Thu, 19 Apr 2018 00:00:00 GMT

I detail four major open problems in microbial population genetics with direct implications to the study of molecular evolution: the lack of neutral polymorphism, the modeling of promiscuous genetic exchanges, the genetics of ill-defined populations, and the difficulty of untangling selection and demography in the light of these issues. Together with the historical focus on the study of single nucleotide polymorphism and widespread non-random sampling, these problems limit our understanding of the genetic variation in bacterial populations and their adaptive effects. I argue that we need novel theoretical approaches accounting for pervasive selection and strong genetic linkage to better understand microbial evolution.

Neutral Theory and the Somatic Evolution of Cancer

Thu, 19 Apr 2018 00:00:00 GMT

Kimura’s neutral theory argued that positive selection was not responsible for an appreciable fraction of molecular substitutions. Correspondingly, quantitative analysis reveals that the vast majority of substitutions in cancer genomes are not detectably under selection. Insights from the somatic evolution of cancer reveal that beneficial substitutions in cancer constitute a small but important fraction of the molecular variants. The molecular evolution of cancer community will benefit by incorporating the neutral theory of molecular evolution into their understanding and analysis of cancer evolution—and accepting the use of tractable, predictive models, even when there is some evidence that they are not perfect.

Neutral Theory Is the Foundation of Conservation Genetics

Mon, 16 Apr 2018 00:00:00 GMT

Kimura’s neutral theory of molecular evolution has been essential to virtually every advance in evolutionary genetics, and by extension, is foundational to the field of conservation genetics. Conservation genetics utilizes the key concepts of neutral theory to identify species and populations at risk of losing evolutionary potential by detecting patterns of inbreeding depression and low effective population size. In turn, this information can inform the management of organisms and their habitat providing hope for the long-term preservation of both. We expand upon Avise’s “inventorial” and “functional” categories of conservation genetics by proposing a third category that is linked to the coalescent and that we refer to as “process-driven.” It is here that connections between Kimura’s theory and conservation genetics are strongest. Process-driven conservation genetics can be especially applied to large genomic data sets to identify patterns of historical risk, such as population bottlenecks, and accordingly, yield informed intuitions for future outcomes. By examining inventorial, functional, and process-driven conservation genetics in sequence, we assess the progression from theory, to data collection and analysis, and ultimately, to the production of hypotheses that can inform conservation policies.

DAMBE7: New and Improved Tools for Data Analysis in Molecular Biology and Evolution

Sat, 14 Apr 2018 00:00:00 GMT

DAMBE is a comprehensive software package for genomic and phylogenetic data analysis on Windows, Linux, and Macintosh computers. New functions include imputing missing distances and phylogeny simultaneously (paving the way to build large phage and transposon trees), new bootstrapping/jackknifing methods for PhyPA (phylogenetics from pairwise alignments), and an improved function for fast and accurate estimation of the shape parameter of the gamma distribution for fitting rate heterogeneity over sites. Previous method corrects multiple hits for each site independently. DAMBE’s new method uses all sites simultaneously for correction. DAMBE, featuring a user-friendly graphic interface, is freely available from (last accessed, April 17, 2018).

MitoFish and MiFish Pipeline: A Mitochondrial Genome Database of Fish with an Analysis Pipeline for Environmental DNA Metabarcoding

Sat, 14 Apr 2018 00:00:00 GMT

Fish mitochondrial genome (mitogenome) data form a fundamental basis for revealing vertebrate evolution and hydrosphere ecology. Here, we report recent functional updates of MitoFish, which is a database of fish mitogenomes with a precise annotation pipeline MitoAnnotator. Most importantly, we describe implementation of MiFish pipeline for metabarcoding analysis of fish mitochondrial environmental DNA, which is a fast-emerging and powerful technology in fish studies. MitoFish, MitoAnnotator, and MiFish pipeline constitute a key platform for studies of fish evolution, ecology, and conservation, and are freely available at (last accessed April 7th, 2018).

Neutral Theory: From Complex Population History to Natural Selection and Sociocultural Phenomena in Human Populations

Wed, 11 Apr 2018 00:00:00 GMT

Here, we present a synthetic view on how Kimura’s Neutral theory has helped us gaining insight on the different evolutionary forces that shape human evolution. We put this perspective in the frame of recent emerging challenges: the use of whole genome data for reconstructing population histories, natural selection on complex polygenic traits, and integrating cultural processes in human evolution.

Acceleration of Olfactory Receptor Gene Loss in Primate Evolution: Possible Link to Anatomical Change in Sensory Systems and Dietary Transition

Tue, 10 Apr 2018 00:00:00 GMT

Primates have traditionally been regarded as vision-oriented animals with low olfactory ability, though this “microsmatic primates” view has been challenged recently. To clarify when and how degeneration of the olfactory system occurred and to specify the relevant factors during primate evolution, we here examined the olfactory receptor (OR) genes from 24 phylogenetically and ecologically diverse primate species. The results revealed that strepsirrhines with curved noses had functional OR gene repertoires that were nearly twice as large as those for haplorhines with simple noses. Neither activity pattern (nocturnal/diurnal) nor color vision system showed significant correlation with the number of functional OR genes while phylogeny and nose structure (haplorhine/strepsirrhine) are statistically controlled, but extent of folivory did. We traced the evolutionary fates of individual OR genes by identifying orthologous gene groups, demonstrating that the rates of OR gene losses were accelerated at the ancestral branch of haplorhines, which coincided with the acquisition of acute vision. The highest rate of OR gene loss was observed at the ancestral branch of leaf-eating colobines; this reduction is possibly linked with the dietary transition from frugivory to folivory because odor information is essential for fruit foraging but less so for leaf foraging. Intriguingly, we found accelerations of OR gene losses in an external branch to every hominoid species examined. These findings suggest that the current OR gene repertoire in each species has been shaped by a complex interplay of phylogeny, anatomy, and habitat; therefore, multiple factors may contribute to the olfactory degeneration in primates.

Neutral Theory and Phenotypic Evolution

Thu, 05 Apr 2018 00:00:00 GMT

Although the neutral theory of molecular evolution was proposed to explain DNA and protein sequence evolution, in principle it could also explain phenotypic evolution. Nevertheless, overall, phenotypes should be less likely than genotypes to evolve neutrally. I propose that, when phenotypic traits are stratified according to a hierarchy of biological organization, the fraction of evolutionary changes in phenotype that are adaptive rises with the phenotypic level considered. Consistently, molecular traits are frequently found to evolve neutrally whereas a large, random set of organismal traits were recently reported to vary largely adaptively. Many more studies of unbiased samples of phenotypic traits are needed to test the general validity of this hypothesis.

Neutral Variation in the Context of Selection

Wed, 04 Apr 2018 00:00:00 GMT

In its initial formulation by Motoo Kimura, the neutral theory was concerned solely with the level of variability maintained by random genetic drift of selectively neutral mutations, and the rate of molecular evolution caused by the fixation of such mutations. The original theory considered events at a single genetic locus in isolation from the rest of the genome. It did not take long, however, for theoreticians to wonder whether selection at one or more loci might influence neutral variability at linked sites. Once DNA sequence variability could be studied, and especially when resequencing of whole genomes became possible, it became clear that patterns of neutral variability in genomes are affected by selection at linked sites, and that these patterns could advance our understanding of natural selection, and can be used to detect the action of selection in genomic regions, including selection much weaker than could be detected by direct measurements of the relative fitnesses of different genotypes. We outline the different types of processes that have been studied, in approximate order of their historical development.

New Methods for Inferring the Distribution of Fitness Effects for INDELs and SNPs

Wed, 04 Apr 2018 00:00:00 GMT

Small insertions and deletions (INDELs; ≤50 bp) are the most common type of variability after single nucleotide polymorphism (SNP). However, compared with SNPs, we know little about the distribution of fitness effects (DFE) of new INDEL mutations and how prevalent adaptive INDEL substitutions are. Studying INDELs has been difficult partly because identifying ancestral states at these sites is error-prone and misidentification can lead to severely biased estimates of the strength of selection. To solve these problems, we develop new maximum likelihood methods, which use polymorphism data to simultaneously estimate the DFE, the mutation rate, and the misidentification rate. These methods are applicable to both INDELs and SNPs. Simulations show that they can provide highly accurate results. We applied the methods to an INDEL polymorphism data set in Drosophila melanogaster. We found that the DFE for polymorphic INDELs in protein-coding regions is bimodal, with the variants being either nearly neutral or strongly deleterious. Based on the DFE, we estimated that 71.5–83.7% of the INDEL substitutions that took place along the D. melanogaster lineage were fixed by positive selection, which is comparable with the prevalence of adaptive substitutions at nonsynonymous sites. The new methods have been implemented in the software package anavar.

An Evaluation of Function of Multicopy Noncoding RNAs in Mammals Using ENCODE/FANTOM Data and Comparative Genomics

Tue, 03 Apr 2018 00:00:00 GMT

Mammalian diversification has coincided with a rapid proliferation of various types of noncoding RNAs, including members of both snRNAs and snoRNAs. The significance of this expansion however remains obscure. While some ncRNA copy-number expansions have been linked to functionally tractable effects, such events may equally likely be neutral, perhaps as a result of random retrotransposition. Hindering progress in our understanding of such observations is the difficulty in establishing function for the diverse features that have been identified in our own genome. Projects such as ENCODE and FANTOM have revealed a hidden world of genomic expression patterns, as well as a host of other potential indicators of biological function. However, such projects have been criticized, particularly from practitioners in the field of molecular evolution, where many suspect these data provide limited insight into biological function. The molecular evolution community has largely taken a skeptical view, thus it is important to establish tests of function. We use a range of data, including data drawn from ENCODE and FANTOM, to examine the case for function for the recent copy number expansion in mammals of six evolutionarily ancient RNA families involved in splicing and rRNA maturation. We use several criteria to assess evidence for function: conservation of sequence and structure, genomic synteny, evidence for transposition, and evidence for species-specific expression. Applying these criteria, we find that only a minority of loci show strong evidence for function and that, for the majority, we cannot reject the null hypothesis of no function.

Genomics of Parallel Ecological Speciation in Lake Victoria Cichlids

Mon, 02 Apr 2018 00:00:00 GMT

The genetic basis of parallel evolution of similar species is of great interest in evolutionary biology. In the adaptive radiation of Lake Victoria cichlid fishes, sister species with either blue or red-back male nuptial coloration have evolved repeatedly, often associated with shallower and deeper water, respectively. One such case is blue and red-backed Pundamilia species, for which we recently showed that a young species pair may have evolved through “hybrid parallel speciation”. Coalescent simulations suggested that the older species P. pundamilia (blue) and P. nyererei (red-back) admixed in the Mwanza Gulf and that new “nyererei-like” and “pundamilia-like” species evolved from the admixed population. Here, we use genome scans to study the genomic architecture of differentiation, and assess the influence of hybridization on the evolution of the younger species pair. For each of the two species pairs, we find over 300 genomic regions, widespread across the genome, which are highly differentiated. A subset of the most strongly differentiated regions of the older pair are also differentiated in the younger pair. These shared differentiated regions often show parallel allele frequency differences, consistent with the hypothesis that admixture-derived alleles were targeted by divergent selection in the hybrid population. However, two-thirds of the genomic regions that are highly differentiated between the younger species are not highly differentiated between the older species, suggesting independent evolutionary responses to selection pressures. Our analyses reveal how divergent selection on admixture-derived genetic variation can facilitate new speciation events.

Detecting Signatures of Positive Selection along Defined Branches of a Population Tree Using LSD

Thu, 29 Mar 2018 00:00:00 GMT

Identifying the genomic basis underlying local adaptation is paramount to evolutionary biology, and bears many applications in the fields of conservation biology, crop, and animal breeding, as well as personalized medicine. Although many approaches have been developed to detect signatures of positive selection within single populations and population pairs, the increasing wealth of high-throughput sequencing data requires improved methods capable of handling multiple, and ideally large number of, populations in a single analysis. In this study, we introduce LSD (levels of exclusively shared differences), a fast and flexible framework to perform genome-wide selection scans, along the internal and external branches of a given population tree. We use forward simulations to demonstrate that LSD can identify branches targeted by positive selection with remarkable sensitivity and specificity. We illustrate a range of potential applications by analyzing data from the 1000 Genomes Project and uncover a list of adaptive candidates accompanying the expansion of anatomically modern humans out of Africa and their spread to Europe.

Multiple Factors Confounding Phylogenetic Detection of Selection on Codon Usage

Tue, 27 Mar 2018 00:00:00 GMT

Detecting selection on codon usage (CU) is a difficult task, since CU can be shaped by both the mutational process and selective constraints operating at the DNA, RNA, and protein levels. Yang and Nielsen (2008) developed a test (which we call CUYN) for detecting selection on CU using two competing mutation-selection models of codon substitution. The null model assumes that CU is determined by the mutation bias alone, whereas the alternative model assumes that both mutation bias and/or selection act on CU. In applications on mammalian-scale alignments, the CUYN test detects selection on CU for numerous genes. This is surprising, given the small effective population size of mammals, and prompted us to use simulations to evaluate the robustness of the test to model violations. Simulations using a modest level of CpG hypermutability completely mislead the test, with 100% false positives. Surprisingly, a high level of false positives (56.1%) resulted simply from using the HKY mutation-level parameterization within the CUYN test on simulations conducted with a GTR mutation-level parameterization. Finally, by using a crude optimization procedure on a parameter controlling the CpG hypermutability rate, we find that this mutational property could explain a very large part of the observed mammalian CU. Altogether, our work emphasizes the need to evaluate the potential impact of model violations on statistical tests in the field of molecular phylogenetic analysis. The source code of the simulator and the mammalian genes used are available as a GitHub repository (

Phenomenological Load on Model Parameters Can Lead to False Biological Conclusions

Tue, 27 Mar 2018 00:00:00 GMT

When a substitution model is fitted to an alignment using maximum likelihood, its parameters are adjusted to account for as much site-pattern variation as possible. A parameter might therefore absorb a substantial quantity of the total variance in an alignment (or more formally, bring about a substantial reduction in the deviance of the fitted model) even if the process it represents played no role in the generation of the data. When this occurs, we say that the parameter estimate carries phenomenological load (PL). Large PL in a parameter estimate is a concern because it not only invalidates its mechanistic interpretation (if it has one) but also increases the likelihood that it will be found to be statistically significant. The problem of PL was not identified in the past because most off-the-shelf substitution models make simplifying assumptions that preclude the generation of realistic levels of variation. In this study, we use the more realistic mutation-selection framework as the basis of a generating model formulated to produce data that mimic an alignment of mammalian mitochondrial DNA. We show that a parameter estimate can carry PL when 1) the substitution model is underspecified and 2) the parameter represents a process that is confounded with other processes represented in the data-generating model. We then provide a method that can be used to identify signal for the process that a given parameter represents despite the existence of PL.

The Birth and Death of Olfactory Receptor Gene Families in Mammalian Niche Adaptation

Mon, 19 Mar 2018 00:00:00 GMT

The olfactory receptor (OR) gene families, which govern mammalian olfaction, have undergone extensive expansion and contraction through duplication and pseudogenization. Previous studies have shown that broadly defined environmental adaptations (e.g., terrestrial vs. aquatic) are correlated with the number of functional and non-functional OR genes retained. However, to date, no study has examined species-specific gene duplications in multiple phylogenetically divergent mammals to elucidate OR evolution and adaptation. Here, we identify the OR gene families driving adaptation to different ecological niches by mapping the fate of species-specific gene duplications in the OR repertoire of 94 diverse mammalian taxa, using molecular phylogenomic methods. We analyze >70,000 OR gene sequences mined from whole genomes, generated from novel amplicon sequencing data, and collated with data from previous studies, comprising one of the largest OR studies to date. For the first time, we demonstrate statistically significant patterns of OR species-specific gene duplications associated with the presence of a functioning vomeronasal organ. With respect to dietary niche, we uncover a novel link between a large number of duplications in OR family 5/8/9 and herbivory. Our results also highlight differences between social and solitary niches, indicating that a greater OR repertoire expansion may be associated with a solitary lifestyle. This study demonstrates the utility of species-specific duplications in elucidating gene family evolution, revealing how the OR repertoire has undergone expansion and contraction with respect to a number of ecological adaptations in mammals.

A Model-Based Approach for Identifying Functional Intergenic Transcribed Regions and Noncoding RNAs

Thu, 15 Mar 2018 00:00:00 GMT

With advances in transcript profiling, the presence of transcriptional activities in intergenic regions has been well established. However, whether intergenic expression reflects transcriptional noise or activity of novel genes remains unclear. We identified intergenic transcribed regions (ITRs) in 15 diverse flowering plant species and found that the amount of intergenic expression correlates with genome size, a pattern that could be expected if intergenic expression is largely nonfunctional. To further assess the functionality of ITRs, we first built machine learning models using Arabidopsis thaliana as a model that accurately distinguish functional sequences (benchmark protein-coding and RNA genes) and likely nonfunctional ones (pseudogenes and unexpressed intergenic regions) by integrating 93 biochemical, evolutionary, and sequence-structure features. Next, by applying the models genome-wide, we found that 4,427 ITRs (38%) and 796 annotated ncRNAs (44%) had features significantly similar to benchmark protein-coding or RNA genes and thus were likely parts of functional genes. Approximately 60% of ITRs and ncRNAs were more similar to nonfunctional sequences and were likely transcriptional noise. The predictive framework established here provides not only a comprehensive look at how functional, genic sequences are distinct from likely nonfunctional ones, but also a new way to differentiate novel genes from genomic regions with noisy transcriptional activities.

Evidence of Signaling and Adhesion Roles for β-Catenin in the Sponge Ephydatia muelleri

Wed, 07 Mar 2018 00:00:00 GMT

β-Catenin acts as a transcriptional coactivator in the Wnt/β-catenin signaling pathway and a cytoplasmic effector in cadherin-based cell adhesion. These functions are ancient within animals, but the earliest steps in β-catenin evolution remain unresolved due to limited data from key lineages—sponges, ctenophores, and placozoans. Previous studies in sponges have characterized β-catenin expression dynamics and used GSK3B antagonists to ectopically activate the Wnt/β-catenin pathway; both approaches rely upon untested assumptions about the conservation of β-catenin function and regulation in sponges. Here, we test these assumptions using an antibody raised against β-catenin from the sponge Ephydatia muelleri. We find that cadherin-complex genes coprecipitate with endogenous Em β-catenin from cell lysates, but that Wnt pathway components do not. However, through immunostaining we detect both cell boundary and nuclear populations, and we find evidence that Em β-catenin is a conserved substrate of GSK3B. Collectively, these data support conserved roles for Em β-catenin in both cell adhesion and Wnt signaling. Additionally, we find evidence for an Em β-catenin population associated with the distal ends of F-actin stress fibers in apparent cell–substrate adhesion structures that resemble focal adhesions. This finding suggests a fundamental difference in the adhesion properties of sponge tissues relative to other animals, in which the adhesion functions of β-catenin are typically restricted to cell–cell adhesions.

Network Analysis of Protein Adaptation: Modeling the Functional Impact of Multiple Mutations

Wed, 07 Mar 2018 00:00:00 GMT

The evolution of new biochemical activities frequently involves complex dependencies between mutations and rapid evolutionary radiation. Mutation co-occurrence and covariation have previously been used to identify compensating mutations that are the result of physical contacts and preserve protein function and fold. Here, we model pairwise functional dependencies and higher order interactions that enable evolution of new protein functions. We use a network model to find complex dependencies between mutations resulting from evolutionary trade-offs and pleiotropic effects. We present a method to construct these networks and to identify functionally interacting mutations in both extant and reconstructed ancestral sequences (Network Analysis of Protein Adaptation). The time ordering of mutations can be incorporated into the networks through phylogenetic reconstruction. We apply NAPA to three distantly homologous β-lactamase protein clusters (TEM, CTX-M-3, and OXA-51), each of which has experienced recent evolutionary radiation under substantially different selective pressures. By analyzing the network properties of each protein cluster, we identify key adaptive mutations, positive pairwise interactions, different adaptive solutions to the same selective pressure, and complex evolutionary trajectories likely to increase protein fitness. We also present evidence that incorporating information from phylogenetic reconstruction and ancestral sequence inference can reduce the number of spurious links in the network, whereas preserving overall network community structure. The analysis does not require structural or biochemical data. In contrast to function-preserving mutation dependencies, which are frequently from structural contacts, gain-of-function mutation dependencies are most commonly between residues distal in protein structure.

Shifts in Selective Pressures on Snake Phototransduction Genes Associated with Photoreceptor Transmutation and Dim-Light Ancestry

Thu, 22 Feb 2018 00:00:00 GMT

The visual systems of snakes are heavily modified relative to other squamates, a condition often thought to reflect their fossorial origins. Further modifications are seen in caenophidian snakes, where evolutionary transitions between rod and cone photoreceptors, termed photoreceptor transmutations, have occurred in many lineages. Little previous work, however, has focused on the molecular evolutionary underpinnings of these morphological changes. To address this, we sequenced seven snake eye transcriptomes and utilized new whole-genome and targeted capture sequencing data. We used these data to analyze gene loss and shifts in selection pressures in phototransduction genes that may be associated with snake evolutionary origins and photoreceptor transmutation. We identified the surprising loss of rhodopsin kinase (GRK1), despite a low degree of gene loss overall and a lack of relaxed selection early during snake evolution. These results provide some of the first evolutionary genomic corroboration for a dim-light ancestor that lacks strong fossorial adaptations. Our results also indicate that snakes with photoreceptor transmutation experienced significantly different selection pressures from other reptiles. Significant positive selection was found primarily in cone-specific genes, but not rod-specific genes, contrary to our expectations. These results reveal potential molecular adaptations associated with photoreceptor transmutation and also highlight unappreciated functional differences between rod- and cone-specific phototransduction proteins. This intriguing example of snake visual system evolution illustrates how the underlying molecular components of a complex system can be reshaped in response to changing selection pressures.

GBE | Most Read

Genome Biology & Evolution

Fast Evolution and Lineage-Specific Gene Family Expansions of Aphid Salivary Effectors Driven by Interactions with Host-Plants

Mon, 18 Jun 2018 00:00:00 GMT

Effector proteins play crucial roles in plant-parasite interactions by suppressing plant defenses and hijacking plant physiological responses to facilitate parasite invasion and propagation. Although effector proteins have been characterized in many microbial plant pathogens, their nature and role in adaptation to host plants are largely unknown in insect herbivores. Aphids rely on salivary effector proteins injected into the host plants to promote phloem sap uptake. Therefore, gaining insight into the repertoire and evolution of aphid effectors is key to unveiling the mechanisms responsible for aphid virulence and host plant specialization. With this aim in mind, we assembled catalogues of putative effectors in the legume specialist aphid, Acyrthosiphon pisum, using transcriptomics and proteomics approaches. We identified 3,603 candidate effector genes predicted to be expressed in A. pisum salivary glands (SGs), and 740 of which displayed up-regulated expression in SGs in comparison to the alimentary tract. A search for orthologs in 17 arthropod genomes revealed that SG-up-regulated effector candidates of A. pisum are enriched in aphid-specific genes and tend to evolve faster compared with the whole gene set. We also found that a large fraction of proteins detected in the A. pisum saliva belonged to three gene families, of which certain members show evidence consistent with positive selection. Overall, this comprehensive analysis suggests that the large repertoire of effector candidates in A. pisum constitutes a source of novelties promoting plant adaptation to legumes.

Activity of Genes with Functions in Human Williams–Beuren Syndrome Is Impacted by Mobile Element Insertions in the Gray Wolf Genome

Fri, 01 Jun 2018 00:00:00 GMT

In canines, transposon dynamics have been associated with a hyper-social behavioral syndrome, although the functional mechanism has yet to be described. We investigate the epigenetic and transcriptional consequences of these behavior-associated mobile element insertions (MEIs) in dogs and Yellowstone gray wolves. We posit that the transposons themselves may not be the causative feature; rather, their transcriptional regulation may exert the functional impact. We survey four outlier transposons associated with hyper-sociability, with the expectation that they are targeted for epigenetic silencing. We predict hyper-methylation of MEIs, suggestive that the epigenetic silencing of and not the MEIs themselves may be driving dysregulation of nearby genes. We found that transposon-derived sequences are significantly hyper-methylated, regardless of their copy number or species. Further, we have assessed transcriptome sequence data and found evidence that MEIs impact the expression levels of six genes (WBSCR17, LIMK1, GTF2I, WBSCR27, BAZ1B, and BCL7B), all of which have known roles in human Williams–Beuren syndrome due to changes in copy number, typically hemizygosity. Although further evidence is needed, our results suggest that a few insertions alter local expression at multiple genes, likely through a cis-regulatory mechanism that excludes proximal methylation.

Horizontal Gene Acquisitions Contributed to Genome Expansion in Insect-Symbiotic Spiroplasma clarkii

Fri, 01 Jun 2018 00:00:00 GMT

Genome reduction is a recurring theme of symbiont evolution. The genus Spiroplasma contains species that are mostly facultative insect symbionts. The typical genome sizes of those species within the Apis clade were estimated to be ∼1.0–1.4 Mb. Intriguingly, Spiroplasma clarkii was found to have a genome size that is >30% larger than the median of other species within the same clade. To investigate the molecular evolution events that led to the genome expansion of this bacterium, we determined its complete genome sequence and inferred the evolutionary origin of each protein-coding gene based on the phylogenetic distribution of homologs. Among the 1,346 annotated protein-coding genes, 641 were originated from within the Apis clade while 233 were putatively acquired from outside of the clade (including 91 high-confidence candidates). Additionally, 472 were specific to S. clarkii without homologs in the current database (i.e., the origins remained unknown). The acquisition of protein-coding genes, rather than mobile genetic elements, appeared to be a major contributing factor of genome expansion. Notably, >50% of the high-confidence acquired genes are related to carbohydrate transport and metabolism, suggesting that these acquired genes contributed to the expansion of both genome size and metabolic capability. The findings of this work provided an interesting case against the general evolutionary trend observed among symbiotic bacteria and further demonstrated the flexibility of Spiroplasma genomes. For future studies, investigation on the functional integration of these acquired genes, as well as the inference of their contribution to fitness could improve our knowledge of symbiont evolution.

Phylogenomic Analysis of Lactobacillus curvatus Reveals Two Lineages Distinguished by Genes for Fermenting Plant-Derived Carbohydrates

Tue, 29 May 2018 00:00:00 GMT

Lactobacillus curvatus is a lactic acid bacterium encountered in many different types of fermented food (meat, seafood, vegetables, and cereals). Although this species plays an important role in the preservation of these foods, few attempts have been made to assess its genomic diversity. This study uses comparative analyses of 13 published genomes (complete or draft) to better understand the evolutionary processes acting on the genome of this species. Phylogenomic analysis, based on a coalescent model of evolution, revealed that the 6,742 sites of single nucleotide polymorphism within the L. curvatus core genome delineate two major groups, with lineage 1 represented by the newly sequenced strain FLEC03, and lineage 2 represented by the type-strain DSM20019. The two lineages could also be distinguished by the content of their accessory genome, which sheds light on a long-term evolutionary process of lineage-dependent genetic acquisition and the possibility of population structure. Interestingly, one clade from lineage 2 shared more accessory genes with strains of lineage 1 than with other strains of lineage 2, indicating recent convergence in carbohydrate catabolism. Both lineages had a wide repertoire of accessory genes involved in the fermentation of plant-derived carbohydrates that are released from polymers of α/β-glucans, α/β-fructans, and N-acetylglucosan. Other gene clusters were distributed among strains according to the type of food from which the strains were isolated. These results give new insight into the ecological niches in which L. curvatus may naturally thrive (such as silage or compost heaps) in addition to fermented food.

Cross-Kingdom Commonality of a Novel Insertion Signature of RTE-Related Short Retroposons

Tue, 29 May 2018 00:00:00 GMT

In multicellular organisms, such as vertebrates and flowering plants, horizontal transfer (HT) of genetic information is thought to be a rare event. However, recent findings unveiled unexpectedly frequent HT of RTE-clade LINEs. To elucidate the molecular footprints of the genomic integration machinery of RTE-related retroposons, the sequence patterns surrounding the insertion sites of plant Au-like SINE families were analyzed in the genomes of a wide variety of flowering plants. A novel and remarkable finding regarding target site duplications (TSDs) for SINEs was they start with thymine approximately one helical pitch (ten nucleotides) downstream of a thymine stretch. This TSD pattern was found in RTE-clade LINEs, which share the 3′-end sequence of these SINEs, in the genome of leguminous plants. These results demonstrably show that Au-like SINEs were mobilized by the enzymatic machinery of RTE-clade LINEs. Further, we discovered the same TSD pattern in animal SINEs from lizard and mammals, in which the RTE-clade LINEs sharing the 3′-end sequence with these animal SINEs showed a distinct TSD pattern. Moreover, a significant correlation was observed between the first nucleotide of TSDs and microsatellite-like sequences found at the 3′-ends of SINEs and LINEs. We propose that RTE-encoded protein could preferentially bind to a DNA region that contains a thymine stretch to cleave a phosphodiester bond downstream of the stretch. Further, determination of cleavage sites and/or efficiency of primer sites for reverse transcription may depend on microsatellite-like repeats in the RNA template. Such a unique mechanism may have enabled retroposons to successfully expand in frontier genomes after HT.

Multiple and Independent Phases of Transposable Element Amplification in the Genomes of Piciformes (Woodpeckers and Allies)

Tue, 29 May 2018 00:00:00 GMT

The small and conserved genomes of birds are likely a result of flight-related metabolic constraints. Recombination-driven deletions and minimal transposable element (TE) expansions have led to continually shrinking genomes during evolution of many lineages of volant birds. Despite constraints of genome size in birds, we identified multiple waves of amplification of TEs in Piciformes (woodpeckers, honeyguides, toucans, and barbets). Relative to other bird species’ genomic TE abundance (< 10% of genome), we found ∼17–30% TE content in multiple clades within Piciformes. Several families of the retrotransposon superfamily chicken repeat 1 (CR1) expanded in at least three different waves of activity. The most recent CR1 expansions (∼4–7% of genome) preceded bursts of diversification in the woodpecker clade and in the American barbets + toucans clade. Additionally, we identified several thousand polymorphic CR1 insertions (hundreds per individual) in three closely related woodpecker species. Woodpecker CR1 insertion polymorphisms are maintained at lower frequencies than single nucleotide polymorphisms indicating that purifying selection is acting against additional CR1 copies and that these elements impose a fitness cost on their host. These findings provide evidence of large scale and ongoing TE activity in avian genomes despite continual constraint on genome size.

Conserved Noncoding Elements Influence the Transposable Element Landscape in Drosophila

Tue, 29 May 2018 00:00:00 GMT

Highly conserved noncoding elements (CNEs) constitute a significant proportion of the genomes of multicellular eukaryotes. The function of most CNEs remains elusive, but growing evidence indicates they are under some form of purifying selection. Noncoding regions in many species also harbor large numbers of transposable element (TE) insertions, which are typically lineage specific and depleted in exons because of their deleterious effects on gene function or expression. However, it is currently unknown whether the landscape of TE insertions in noncoding regions is random or influenced by purifying selection on CNEs. Here, we combine comparative and population genomic data in Drosophila melanogaster to show that the abundance of TE insertions in intronic and intergenic CNEs is reduced relative to random expectation, supporting the idea that selective constraints on CNEs eliminate a proportion of TE insertions in noncoding regions. However, we find no evidence for differences in the allele frequency spectra for polymorphic TE insertions in CNEs versus those in unconstrained spacer regions, suggesting that the distribution of fitness effects acting on observable TE insertions is similar across different functional compartments in noncoding DNA. Our results provide evidence that selective constraints on CNEs contribute to shaping the landscape of TE insertion in eukaryotic genomes, and provide further evidence that CNEs are indeed functionally constrained and not simply mutational cold spots.

Comparison of Migratory and Resident Populations of Brown Trout Reveals Candidate Genes for Migration Tendency

Tue, 29 May 2018 00:00:00 GMT

Candidate genes associated with migration have been identified in multiple taxa: including salmonids, many of whom perform migrations requiring a series of physiological changes associated with the freshwater–saltwater transition. We screened over 5,500 SNPs for signatures of selection related to migratory behavior of brown trout Salmo trutta by focusing on ten differentially migrating freshwater populations from two watersheds (the Koutajoki and the Oulujoki). We found eight outlier SNPs potentially associated with migratory versus resident life history using multiple (≥3) outlier detection approaches. Comparison of three migratory versus resident population pairs in the Koutajoki watershed revealed seven outlier SNPs, of which three mapped close to genes ZNF665-like, GRM4-like, and PCDH8-like that have been previously associated with migration and smoltification in salmonids. Two outlier SNPs mapped to genes involved in mucus secretion (ST3GAL1-like) and osmoregulation (C14orf37-like). The last two strongly supported outlier SNPs mapped to thermally induced genes (FNTA1-like, FAM134C-like). Within the Oulujoki, the only consistent outlier SNP mapped close to a gene (EZH2) that is associated with compensatory growth in fasted trout. Our results suggest that a relatively small yet common set of genes responsible for physiological functions associated with resident and migratory life histories is evolutionarily conserved.

Recurrent Loss, Horizontal Transfer, and the Obscure Origins of Mitochondrial Introns in Diatoms (Bacillariophyta)

Tue, 29 May 2018 00:00:00 GMT

We sequenced mitochondrial genomes from five diverse diatoms (Toxarium undulatum, Psammoneis japonica, Eunotia naegelii, Cylindrotheca closterium, and Nitzschia sp.), chosen to fill important phylogenetic gaps and help us characterize broadscale patterns of mitochondrial genome evolution in diatoms. Although gene content was strongly conserved, intron content varied widely across species. The vast majority of introns were of group II type and were located in the cox1 or rnl genes. Although recurrent intron loss appears to be the principal underlying cause of the sporadic distributions of mitochondrial introns across diatoms, phylogenetic analyses showed that intron distributions superficially consistent with a recurrent-loss model were sometimes more complicated, implicating horizontal transfer as a likely mechanism of intron acquisition as well. It was not clear, however, whether diatoms were the donors or recipients of horizontally transferred introns, highlighting a general challenge in resolving the evolutionary histories of many diatom mitochondrial introns. Although some of these histories may become clearer as more genomes are sampled, high rates of intron loss suggest that the origins of many diatom mitochondrial introns are likely to remain unclear.

Expression of Novel Gene Content Drives Adaptation to Low Iron in the Cyanobacterium Acaryochloris

Tue, 29 May 2018 00:00:00 GMT

Variation in genome content is a potent mechanism of microbial adaptation. The genomes of members of the cyanobacterial genus Acaryochloris vary greatly in gene content as a consequence of the idiosyncratic retention of both recent gene duplicates and plasmid-encoded genes acquired by horizontal transfer. For example, the genome of Acaryochloris strain MBIC11017, which was isolated from an iron-limited environment, is enriched in duplicated and novel genes involved in iron assimilation. Here, we took an integrative approach to characterize the adaptation of Acaryochloris MBIC11017 to low environmental iron availability and the relative contributions of the expression of duplicated versus novel genes. We observed that Acaryochloris MBIC11017 grew faster and to a higher yield in the presence of nanomolar concentrations of iron than did a closely related strain. These differences were associated with both a higher rate of iron assimilation and a greater abundance of iron assimilation transcripts. However, recently duplicated genes contributed little to increased transcript dosage; rather, the maintenance of these duplicates in the MBIC11017 genome is likely due to the sharing of ancestral dosage by expression reduction. Instead, novel, horizontally transferred genes are responsible for the differences in transcript abundance. The study provides insights on the mechanisms of adaptive genome evolution and gene expression in Acaryochloris.

Meiosis Leads to Pervasive Copy-Number Variation and Distorted Inheritance of Accessory Chromosomes of the Wheat Pathogen Zymoseptoria tritici

Tue, 29 May 2018 00:00:00 GMT

Meiosis is one of the most conserved molecular processes in eukaryotes. The fidelity of pairing and segregation of homologous chromosomes has a major impact on the proper transmission of genetic information. Aberrant chromosomal transmission can have major phenotypic consequences, yet the mechanisms are poorly understood. Fungi are excellent models to investigate processes of chromosomal transmission, because many species have highly polymorphic genomes that include accessory chromosomes. Inheritance of accessory chromosomes is often unstable and chromosomal losses have little impact on fitness. We analyzed chromosomal inheritance in 477 progeny coming from two crosses of the fungal wheat pathogen Zymoseptoria tritici. For this, we developed a high-throughput screening method based on restriction site-associated DNA sequencing that generated dense coverage of genetic markers along each chromosome. We identified rare instances of chromosomal duplications (disomy) in core chromosomes. Accessory chromosomes showed high overall frequencies of disomy. Chromosomal rearrangements were found exclusively on accessory chromosomes and were more frequent than disomy. Accessory chromosomes present in only one of the parents in an analyzed cross were inherited at significantly higher rates than the expected 1:1 segregation ratio. Both the chromosome and the parental background had significant impacts on the rates of disomy, losses, rearrangements, and distorted inheritance. We found that chromosomes with higher sequence similarity and lower repeat content were inherited more faithfully. The large number of rearranged progeny chromosomes identified in this species will enable detailed analyses of the mechanisms underlying chromosomal rearrangement.

A Comparative View on Sex Differentiation and Gametogenesis Genes in Lungfish and Coelacanths

Tue, 29 May 2018 00:00:00 GMT

Gonadal sex differentiation and reproduction are the keys to the perpetuation of favorable gene combinations and positively selected traits. In vertebrates, several gonad development features that differentiate tetrapods and fishes are likely to be, at least in part, related to the water-to-land transition. The collection of information from basal sarcopterygians, coelacanths, and lungfishes, is crucial to improve our understanding of the molecular evolution of pathways involved in reproductive functions, since these organisms are generally regarded as “living fossils” and as the direct ancestors of tetrapods. Here, we report for the first time the characterization of >50 genes related to sex differentiation and gametogenesis in Latimeria menadoensis and Protopterus annectens. Although the expression profiles of most genes is consistent with the intermediate position of basal sarcopterygians between actinopterygian fish and tetrapods, their phylogenetic placement and presence/absence patterns often reveal a closer affinity to the tetrapod orthologs. On the other hand, particular genes, for example, the male gonad factor gsdf (Gonadal Soma-Derived Factor), provide examples of ancestral traits shared with actinopterygians, which disappeared in the tetrapod lineage.

Well-Annotated microRNAomes Do Not Evidence Pervasive miRNA Loss

Fri, 18 May 2018 00:00:00 GMT

microRNAs are conserved noncoding regulatory factors implicated in diverse physiological and developmental processes in multicellular organisms, as causal macroevolutionary agents and for phylogeny inference. However, the conservation and phylogenetic utility of microRNAs has been questioned on evidence of pervasive loss. Here, we show that apparent widespread losses are, largely, an artefact of poorly sampled and annotated microRNAomes. Using a curated data set of animal microRNAomes, we reject the view that miRNA families are never lost, but they are rarely lost (92% are never lost). A small number of families account for a majority of losses (1.7% of families account for >45% losses), and losses are associated with lineages exhibiting phenotypic simplification. Phylogenetic analyses based on the presence/absence of microRNA families among animal lineages, and based on microRNA sequences among Osteichthyes, demonstrate the power of these small data sets in phylogenetic inference. Perceptions of widespread evolutionary loss of microRNA families are due to the uncritical use of public archives corrupted by spurious microRNA annotations, and failure to discriminate false absences that occur because of incomplete microRNAome annotation.

Evolution of Gustatory Receptor Gene Family Provides Insights into Adaptation to Diverse Host Plants in Nymphalid Butterflies

Fri, 18 May 2018 00:00:00 GMT

The host plant range of herbivorous insects is a major aspect of insect–plant interaction, but the genetic basis of host range expansion in insects is poorly understood. In butterflies, gustatory receptor genes (GRs) play important roles in host plant selection by ovipositing females. Since several studies have shown associations between the repertoire sizes of chemosensory gene families and the diversity of resource use, we hypothesized that the increase in the number of genes in the GR family is associated with host range expansion in butterflies. Here, we analyzed the evolutionary dynamics of GRs among related species, including the host generalist Vanessa cardui and three specialists. Although the increase of the GR repertoire itself was not observed, we found that the gene birth rate of GRs was the highest in the lineage leading to V. cardui compared with other specialist lineages. We also identified two taxon-specific subfamilies of GRs, characterized by frequent lineage-specific duplications and higher non-synonymous substitution rates. Together, our results suggest that frequent gene duplications in GRs, which might be involved in the detection of plant secondary metabolites, were associated with host range expansion in the V. cardui lineage. These evolutionary patterns imply that the capability to perceive various compounds during host selection was favored during adaptation to diverse host plants.

Robustness of Transposable Element Regulation but No Genomic Shock Observed in Interspecific Arabidopsis Hybrids

Fri, 18 May 2018 00:00:00 GMT

The merging of two divergent genomes in a hybrid is believed to trigger a “genomic shock”, disrupting gene regulation and transposable element (TE) silencing. Here, we tested this expectation by comparing the pattern of expression of transposable elements in their native and hybrid genomic context. For this, we sequenced the transcriptome of the Arabidopsis thaliana genotype Col-0, the A. lyrata genotype MN47 and their F1 hybrid. Contrary to expectations, we observe that the level of TE expression in the hybrid is strongly correlated to levels in the parental species. We detect that at most 1.1% of expressed transposable elements belonging to two specific subfamilies change their expression level upon hybridization. Most of these changes, however, are of small magnitude. We observe that the few hybrid-specific modifications in TE expression are more likely to occur when TE insertions are close to genes. In addition, changes in epigenetic histone marks H3K9me2 and H3K27me3 following hybridization do not coincide with TEs with changed expression. Finally, we further examined TE expression in parents and hybrids exposed to severe dehydration stress. Despite the major reorganization of gene and TE expression by stress, we observe that hybridization does not lead to increased disorganization of TE expression in the hybrid. Although our study did not examine TE transposition activity in hybrids, the examination of the transcriptome shows that TE expression is globally robust to hybridization. The term “genomic shock” is perhaps not appropriate to describe transcriptional modification in a viable hybrid merging divergent genomes.

Differences in Performance among Test Statistics for Assessing Phylogenomic Model Adequacy

Fri, 18 May 2018 00:00:00 GMT

Statistical phylogenetic analyses of genomic data depend on models of nucleotide or amino acid substitution. The adequacy of these substitution models can be assessed using a number of test statistics, allowing the model to be rejected when it is found to provide a poor description of the evolutionary process. A potentially valuable use of model-adequacy test statistics is to identify when data sets are likely to produce unreliable phylogenetic estimates, but their differences in performance are rarely explored. We performed a comprehensive simulation study to identify test statistics that are sensitive to some of the most commonly cited sources of phylogenetic estimation error. Our results show that, for many test statistics, traditional thresholds for assessing model adequacy can fail to reject the model when the phylogenetic inferences are inaccurate and imprecise. This is particularly problematic when analysing loci that have few informative sites. We propose new thresholds for assessing substitution model adequacy and demonstrate their effectiveness in analyses of three phylogenomic data sets. These thresholds lead to frequent rejection of the model for loci that yield topological inferences that are imprecise and are likely to be inaccurate. We also propose the use of a summary statistic that provides a practical assessment of overall model adequacy. Our approach offers a promising means of enhancing model choice in genome-scale data sets, potentially leading to improvements in the reliability of phylogenomic inference.

Ca. Endozoicomonas cretensis: A Novel Fish Pathogen Characterized by Genome Plasticity

Thu, 03 May 2018 00:00:00 GMT

Endozoicomonas bacteria are generally beneficial symbionts of diverse marine invertebrates including reef-building corals, sponges, sea squirts, sea slugs, molluscs, and Bryozoans. In contrast, the recently reported Ca. Endozoicomonas cretensis was identified as a vertebrate pathogen, causing epitheliocystis in fish larvae resulting in massive mortality. Here, we described the Ca. E. cretensis draft genome, currently undergoing genome decay as evidenced by massive insertion sequence (IS element) expansion and pseudogene formation. Many of the insertion sequences are also predicted to carry outward-directed promoters, implying that they may be able to modulate the expression of neighbouring coding sequences (CDSs). Comparative genomic analysis has revealed many Ca. E. cretensis-specific CDSs, phage integration and novel gene families. Potential virulence related CDSs and machineries were identified in the genome, including secretion systems and related effector proteins, and systems related to biofilm formation and directed cell movement. Mucin degradation would be of importance to a fish pathogen, and many candidate CDSs associated with this pathway have been identified. The genome may reflect a bacterium in the process of changing niche from symbiont to pathogen, through expansion of virulence genes and some loss of metabolic capacity.

Comparative Transcriptomics in Two Bivalve Species Offers Different Perspectives on the Evolution of Sex-Biased Genes

Fri, 20 Apr 2018 00:00:00 GMT

Comparative genomics has become a central tool for evolutionary biology, and a better knowledge of understudied taxa represents the foundation for future work. In this study, we characterized the transcriptome of male and female mature gonads in the European clam Ruditapes decussatus, compared with that in the Manila clam Ruditapes philippinarum providing, for the first time in bivalves, information about transcription dynamics and sequence evolution of sex-biased genes. In both the species, we found a relatively low number of sex-biased genes (1,284, corresponding to 41.3% of the orthologous genes between the two species), probably due to the absence of sexual dimorphism, and the transcriptional bias is maintained in only 33% of the orthologs. The dN/dS is generally low, indicating purifying selection, with genes where the female-biased transcription is maintained between the two species showing a significantly higher dN/dS. Genes involved in embryo development, cell proliferation, and maintenance of genome stability show a faster sequence evolution. Finally, we report a lack of clear correlation between transcription level and evolutionary rate in these species, in contrast with studies that reported a negative correlation. We discuss such discrepancy and call into question some methodological approaches and rationales generally used in this type of comparative studies.