Turbellarian taxonomic database

Abstract / Notes

"Self-fertilization occurs in a broad range of hermaphroditic plants and animals, and is often thought to
evolve as a reproductive assurance strategy under ecological conditions that disfavour or prevent outcrossing.
Nevertheless, selfing ability is far from ubiquitous among hermaphrodites, and may be constrained in taxa
where the male and female gametes of the same individual cannot easily meet. Here, we report an extraordinary
selfing mechanism in one such species, the free-living flatworm Macrostomum hystrix. To test the hypothesis
that adaptations to hypodermic insemination of the mating partner under outcrossing also facilitate selfing,
we experimentally manipulated the social environment of these transparent flatworms and then observed the
spatial distribution of received sperm in vivo. We find that this distribution differs radically between
conditions allowing or preventing outcrossing, implying that isolated individuals use their needle-like stylet
(male copulatory organ) to inject own sperm into their anterior body region, including into their own head,
from where they then apparently migrate to the site of (self-) fertilization. Conferring the ability to self
could thus be an additional consequence of hypodermic insemination, a widespread fertilization mode that is
especially prevalent among simultaneously hermaphroditic animals and probably evolves due to sexual conflict
over the transfer and subsequent fate of sperm."

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