Sexual reproduction evolved 2 billion to 3.5 billion years ago, but hundreds of species have ditched sex in favour of parthenogenesis, in which female embryos develop from unfertilized eggs. New work suggests that a positive feedback loop may have helped to drive some species from sexual reproduction to female-only lineages.
Tanja Schwander at Simon Fraser University in Burnaby, Canada, and her colleagues report this finding from an analytical model, which they verified with data from sexually reproducing Timema stick insects. A few stick-insect species reproduce by parthenogenesis, but most reproduce sexually, although some unfertilized eggs do hatch spontaneously.
The authors showed that this spontaneous hatching increases when females are less able to find mates. This biases the population towards females, causing even more spontaneous hatching, and so on, providing a potential stepping stone towards full parthenogenesis.
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Evolutionary biology: How girls go solo. Nature 463, 272 (2010). https://doi.org/10.1038/463272e