Turbellarian taxonomic database

Abstract / Notes

"Sex allocation theory for simultaneous hermaphrodites predicts an influence of the mating group size on sex
allocation. Mating group size may depend on the size of the group in which an individual lives, or on the
density, but studies to date have not distinguished between the two factors. We performed an experiment in
which we raised a transparent simultaneous hermaphrodite, the flatworm Macrostomum sp., in different group
sizes (pairs, triplets, quartets and octets) and in different enclosure sizes (small and large). This design
allows us to differentiate between the effects of group size and density. After worms reached maturity we
determined their reproductive allocation patterns from microscopic images taken in vivo. The results suggest
that the mating group size is a function of the group size, and not of the density. They support the shift to
higher male allocation in larger mating groups predicted by sex allocation theory. To our knowledge, this is
the first study that unambiguously shows phenotypically plastic sex allocation in response to mating group
size in a simultaneous hermaphrodite."

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