Bdelloid rotifers have been veiled in mystery for decades. Despite extensive studies of this class of tiny freshwater invertebrates, no one has observed any trace of sex: no proven males, hermaphrodites, mating, or meiosis. Unlike other asexual organisms, which tend to be short-lived in evolutionary history, the apparently asexual bdelloid rotifers have managed to persist for millions of years and have diverged into hundreds of species. Such persistence without sexual reproduction challenges the view that sex is essential for the long-term evolutionary success of eukaryotes. Do these populations somehow avoid the accumulation of detrimental mutations thought to occur with asexual reproduction, or have we simply been investigating them under the wrong conditions?

A study by Signorovitch et al. published in the June issue of GENETICS sought to answer this question by using a method of population genetics that allowed the investigators to look for evidence of infrequent or atypical sex in bdelloid genomes.

By comparing genome sequences of individuals descended from a common ancestor, researchers are able to find clues to the population’s mode of reproduction. For any two individuals in an asexual population, the phylogenetic distance between a sequence in one individual and its homolog in the other should be the same for all such sequence pairs. That is because all the sequences in these individuals have been evolving independently of each other for the same number of generations. But if genetic material has been transferred between individuals in the population (as in sexual reproduction), two individuals may be closely related at one sequence, but more distantly related at its homolog. Signorovitch et al. searched for evidence of this phylogenetic pattern—called allele sharing— in the genomes of a species of bdelloid collected from geographically diverse sites.

The results clearly demonstrate that three of six individuals sampled from a mitochondrial clade show allele sharing consistent with sexual reproduction. At each of four genomic regions, a particular individual shared one of its alleles with a second individual and shared its other allele with a third individual. This suggests that genetic material was transferred between individuals via a cross.

Provided by Dr. Matthew Meselson

Study species, Macrotrachela quadricornifera, and its eggs at right. Provided by Dr. Matthew Meselson

Finding three closely-related individuals in a small sample of geographically well-separated bdelloids suggests that lines that have experienced recent crossing have a fitness advantage over lines that have not, leading to the predominance of the prior. In support of this possibility, Signorovitch et al. cite a study indicating that the loss of sex in the water flea Daphnia pulex (which cycles between asexual and sexual reproduction) is followed by surprisingly rapid extinction. This is thought to be due to the effects of gene conversion, which allows the expression of accumulated recessive deleterious mutations. If bdelloids are also cyclically sexual, Signorovitch et al. propose, then descendents from recent outcrossing that restores heterozygosity would have enhanced fitness and become predominant in the sampled clade.

The evidence for sexual reproduction seems incompatible with previous work that concluded these organisms lack the homologous chromosome pairs needed for standard meiosis, a necessary process for sexual reproduction. The authors hypothesize that bdelloids may undergo a rare type of meiosis that can function without homologous chromosomes. Observed in plants of the Oenothera genus, this involves parental genomes segregating without assortment or crossing over. In other words, segregation is achieved without side-by-side chromosome pairing and without assortment or crossing over, enabling chromosomes of the same parentage to stay together generation after generation.

Signorovitch et al. discovered that a population previously thought to evolve without sex does in fact experience a unique form of sexual exchange. While these organisms remain enigmatic, the authors provide a glimpse into how bdelloid rotifers may have persisted through time.

CITATIONS:

Signorovitch, A., J. Hur, E. Gladyshev & M. Meselson (2015). Allele Sharing and Evidence for Sexuality in a Mitochondrial Clade of Bdelloid Rotifers, Genetics, 200(2), 581-590. doi: http://dx.doi.org/10.1534/genetics.115.176719 http://www.genetics.org/content/200/2/581.full

Tucker, A. E., M. S. Ackerman, B. D. Eads, S. Xu, and M. Lynch (2013) Population-genomic insights into the evolutionary origin and fate of obligately asexual Daphnia pulex. Proc. Natl. Acad. Sci. USA 110: 15740–15745 http://dx.doi.org/10.1073/pnas.1313388110

Umen, J. G (2015) Lost and Found: The Secret Sex Lives of Bdelloid Rotifers, Genetics, 200(2), 409-412, doi: http://dx.doi.org/10.1534/genetics.115.176388  http://www.genetics.org/content/200/2/409.short?rss=1

 

, , , ,

GSA science writing intern. Grad student in Evolution, Ecology, and Organismal Biology at UNC Chapel Hill.

View all posts by Kayleigh O'Keeffe »

Read more in

  • Collage of 2021 Rosalind Franklin Award recipients

    Where are they now? Rosalind Franklin Young Investigator Award recipients share updates on their research

    Rosalind Franklin Young Investigator Award applications are open–make sure you submit your application or nomination of a colleague by September 30, 2024.

  • University of Minnesota researchers map genome of the last living wild horse species

    The study, published in G3: Genes|Genomes|Genetics, is part of larger conservation efforts to save Przewalski’s horse.

  • Congratulations to the Spring 2024 DeLill Nasser Awardees!

    GSA is pleased to announce the recipients of the DeLill Nasser Award for Professional Development in Genetics for Spring 2024! Given twice a year to graduate students and postdoctoral researchers, DeLill Nasser Awards support attendance at meetings and laboratory courses. The award is named in honor of DeLill Nasser, a long-time GSA supporter and National Science Foundation…

  • Carolyn Damilola headshot

    Carolyn Damilola: an NFS Rising Scientist on a lifelong quest to learn more

    Carolyn Damilola is an NFS Rising Scientist from Nigeria doing respiratory system research and paving the way for scientists from underrepresented communities through mentorship.

  • Text over a blue background image: Apply for up to $2,000 for your project from the Starter Culture Microgrant Program.

    What does a good microgrant proposal look like?

    Members of the Microgrant Review Committee share their tips for a successful proposal.

  • A blurred image of a human face is shown against a dark background.

    The first piece of the facial recognition puzzle

    New research in GENETICS gives a first peek at the molecular pathway involved in recognizing faces.

  • New Senior Editor Amy MacQueen joins GENETICS

    A new senior editor is joining GENETICS in the Genome Integrity and Transmission section. We’re excited to welcome Amy MacQueen to the editorial team.

  • Close up of an adult zebrafish with blue and white stripes in an aquarium with red lighting.

    Block party on the zebrafish sex chromosome

    Research in G3 identifies a gene regulatory block of the zebrafish genome responsible for overseeing the maternal-to-zygotic-transition.

  • Lemna Minor, the common duckweed

    Unraveling the mysteries of duckweed: epigenetic insights from Spirodela polyrhiza

    Research published in G3 offers insight into the impact of DNA methylation on clonal propagation in asexually reproducing plants.

  • Luciano Marraffini headshot

    A microbiologist’s quest to understand CRISPR in bacterial self-defense

    2024 Genetics Society of America Medal recipient Luciano Marraffini determined how CRISPR-Cas systems destroy genetic targets with precision, paving the way for gene editing technology development.

  • Elaine Ostrander headshot

    Unlocking mysteries of trait and disease heritability in dogs

    2024 Edward Novitski Prize recipient Elaine Ostrander, a pioneer of the domestic dog model, discovered numerous genes affecting dog size, morphology, behavior, and disease susceptibility—many of which have relevance in humans.

  • NSF-funded BIO-LEAPS Grant to Support Culture Change in Genetics

    GSA and collaborators Personal Genetics Education & Dialogue and Reclaiming STEM Institute launch NSF-funded BIO-LEAPS project to support culture change in genetics 

    We are thrilled to announce that the Genetics Society of America (GSA) is collaborating with the Personal Genetics Education & Dialogue (PGED) based in the Department of Genetics at Harvard Medical School, and the Reclaiming STEM Institute (RSI) on a Leading Culture Change Through Professional Societies of Biology (BIO-LEAPS) grant from the U.S. National Science…

  • Daman Saluja: Navigating Science and Policy in India

    In the Paths to Science Policy series, we talk to individuals who have a passion for science policy and are active in advocacy through their various roles and careers. The series aims to inform and guide early career scientists interested in science policy. This series is brought to you by the GSA Early Care­er Scientist…

  • Deborah Andrew headshot

    A fly geneticist’s journey into discovering rules of organ development

    2024 George W. Beadle Award recipient Deborah Andrew discovered new genes and pathways in Drosophila salivary gland organogenesis. Now, her work can help optimize cell secretion in therapeutic applications and fight malaria.

  • Małgorzata Gazda's headshot

    Małgorzata Gazda: How receiving the DeLill Nasser Award helped her land her dream job

    Have you ever experienced an event that changes the course of your life, or in this case, your career? Małgorzata (Gosia) Gazda is Assistant Professor at the University of Montreal and in 2022, she received the DeLill Nasser Award for Professional Development in Genetics, which she used to attend and present at the 2022 Population,…

  • Hongyu Zhao joins GENETICS as new Senior Editor

    A new senior editor is joining GENETICS in the Statistical Genetics and Genomics section. We’re excited to welcome Hongyu Zhao to the editorial team.

  • Julio Molina Pineda at TAGC 2024

    GSA Member Julio Molina Pineda Receives DeLill Nasser Award, Shines at TAGC 2024 

    “At any career stage, the GSA membership is an amazing investment for any genetics professional!” Julio Molina Pineda is a PhD Candidate in Cell and Molecular Biology and a Research Assistant at the University of Arkansas, and a Doctoral Academy Fellow at the Lewis Lab. In 2023, Julio was awarded the DeLill Nasser Award for…

  • Ed Grell at his dissecting microscope using ether to anesthetize his flies.

    In Memoriam: Ellsworth Herman Grell (1932–2023), a pioneer of Drosophila genome engineering and annotation

    Ellsworth (Ed) Grell blessed the Drosophila community through three enduring legacies: as a pioneer of chromosome mechanics, as a primary organizer and synthesizer of genetic knowledge in Drosophila, and as a graceful mentor to those fortunate to have known him personally. Ed grew up in rural Nebraska, completed his undergraduate studies at Iowa State, and…

  • Congratulations to the #Fungal24 Poster Award winners!

    We are pleased to announce the recipients of the GSA Poster Awards for posters presented at the 32nd Fungal Genetics Conference! Undergraduate and graduate student members of GSA were eligible for the awards, and a hard-working team of judges made the determinations. Congratulations to all! Felicia Ebot Ojong, The University of Georgia My research is focused…

  • Poster presentation tips for TAGC 2024

    You’ve been selected to present a poster at The Allied Genetics Conference 2024 in March—you’ve celebrated, made plans to attend, now what? This is an exciting opportunity to showcase your research and engage with fellow members of the genetics community, so you want to make sure you’re prepared. We wanted to offer you some tips…

  • Maximize your TAGC 2024 experience 

    A guide to all that National Harbor & DC have to offer Are you joining us for The Allied Genetics Conference 2024 in March? Make the most of your #TAGC24 experience in National Harbor! We know the science will keep you busy, but you deserve to unwind and have some fun, so we’ve curated a…

  • Early Career Leadership Spotlight: Sarah Petrosky

    We’re taking time to get to know the members of the GSA’s Early Career Scientist Committees. Join us to learn more about our early career scientist advocates. Sarah PetroskyMultimedia SubcommitteeUniversity of Pittsburgh Research Interest I am interested in understanding adaptation that has been happening recently in populations by dissecting the ways that genes underlying an adaptation…

  • TAGC 2024 Early Career Award Winners

    GSA is pleased to announce the winners of the early career awards presented at The Allied Genetics Conference 2024. These awards are specific to particular TAGC communities and recognize early career scientists’ outstanding work on their respective research organisms. The awardees will present their talks in keynote sessions at TAGC 2024.  Don’t miss the opportunity…

  • Preeminent geneticists recognized with revamped GSA Awards

    In 2022, GSA’s Board of Directors launched an audit to review the five major awards conferred by the Society. Today, we are thrilled to announce the recipients of the reimagined GSA Awards, including the new Genetics Society of America Early Career Medal. The scientists honored this year are recognized by their peers for their outstanding…

  • Fly Board funds outreach programs to spread the word about Drosophila research

    In 2020, the Fly Board voted to use part of its reserve fund to support efforts to increase trainee participation as well as equity and diversity in the Drosophila community. An awards committee decides how the money will be spent each year, and from 2020–2022, the committee posted a very broad call for applications from…

  • New members of the GSA Board of Directors: 2024–2026

    We are pleased to announce the election of four new leaders to the GSA Board of Directors: 2024 Vice President/2025 President Brenda Andrews Professor, University of Toronto It’s an honor to continue my association with the Society by serving as Vice President of the Board of Directors. I have broad knowledge of the ongoing activities…

  • The Fly Meeting is one-of-a-kind! Dros 2025 organizers share their excitement

    The 66th Annual Drosophila Research Conference promises to be a meeting rich with the latest in Drosophila research as well as opportunities to advance your career and connect with a global community of 1,400+ scientists. The organizers Todd Nystul, Michelle Bland, Leila Rieder, Amanda Crocker, and Justin Crocker are hard at work, planning a conference…

  • Early Career Leadership Spotlight: Olufemi Osonowo

    We’re taking time to get to know the members of the GSA’s Early Career Scientist Committees. Join us to learn more about our early career scientist advocates. Olufemi Adekunle OsonowoCareer Development SubcommitteeDalhousie University Research Interest Metabolomics and genomics are two distinct but complimentary approaches that offer valuable insights into the underlying mechanisms of complex traits, such…

  • Early Career Leadership Spotlight: Hector Mendoza

    We’re taking time to get to know the members of the GSA’s Early Career Scientist Committees. Join us to learn more about our early career scientist advocates. Hector MendozaCommunication and Outreach SubcommitteeUniversity of Michigan Research Interest My research goals converge around the evolution of sexual reproduction. During my doctoral program, I investigated mitochondrial inheritance, a mechanism…