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Related Experiment Videos

How ancient are ancient asexuals?

Koen Martens1, Giampaolo Rossetti, David J Horne

  • 1Koninklijk Belgisch Instituut voor Natuurwetenschappen, Afdeling Zoetwaterbiologie, Vautierstraat 29, 1000 Brussels, Belgium.

Proceedings. Biological Sciences
|April 26, 2003
PubMed
Summary
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Darwinuloid ostracods, ancient asexual animals, likely lost sexual reproduction over 208 million years ago. Fossil evidence suggests Jurassic and Cretaceous darwinuloids were exclusively female, supporting long-term asexuality.

Area of Science:

  • Paleontology
  • Evolutionary Biology
  • Zoology

Background:

  • Ancient asexual animal groups, like bdelloid rotifers and darwinuloid ostracods, offer insights into long-term asexuality.
  • The precise duration of asexuality in these groups is often overlooked.
  • Darwinuloid ostracods show a decline in sexual reproduction after the Permian-Triassic extinction (245 million years ago), but Mesozoic male records complicate the timeline.

Purpose of the Study:

  • To re-examine Mesozoic darwinuloid fossil records to determine their reproductive modes.
  • To establish the timeframe of obligate asexuality in darwinuloid ostracods.
  • To test the hypothesis of bisexual populations in Mesozoic darwinuloid assemblages.

Main Methods:

  • Utilized three criteria to identify males in fossil populations: absence of a brood pouch, muscle scar position, and size dimorphism.

Related Experiment Videos

  • Analyzed a well-preserved latest Jurassic assemblage of Darwinula leguminella (now Alicenula).
  • Re-evaluated other putative dimorphic Mesozoic darwinuloid records using the same criteria.

    • Main Results:

    • The latest Jurassic Darwinula leguminella assemblage (145 million years ago) was determined to be entirely female, despite size and shape variability.
    • This species was re-assigned to the extant genus Alicenula due to exceptional preservation.
    • The hypothesis of bisexual populations was rejected for all post-Triassic (208 million years ago) Mesozoic darwinuloid records.

    Conclusions:

    • Darwinuloid ostracods likely ceased sexual reproduction entirely by the post-Triassic period.
    • The study provides strong evidence for obligate asexuality in darwinuloids for at least the last 208 million years.
    • This research refines our understanding of the evolutionary history of asexuality in animals.