Determinants of female fecundity in a simultaneous hermaphrodite: the role of polyandry and food availability |
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Authors: | Tim Janicke Peter Sandner Lukas Schärer |
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Institution: | (1) Evolutionary Biology, Zoological Institute, University of Basel, Vesalgasse 1, 4051 Basel, Switzerland |
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Abstract: | Classical sexual selection theory assumes that the reproductive success of females is primarily limited by the resources available
for egg production rather than by the number of mating partners. However, there is now accumulating evidence that multiple
mating can entail fitness costs or benefits for females. In this study we investigated the effect of polyandry (i.e., the
mating with different mating partners) and food availability on the reproductive output of the female sex function in an outcrossing
simultaneous hermaphrodite, the free-living flatworm Macrostomum lignano. We exposed virgin worms to different group sizes, a treatment that has previously been shown to affect the level of polyandry
in this species. Moreover, we manipulated the food availability throughout the subsequent egg laying period, during which
the worms were kept in isolation. The number of offspring produced was used as an estimate of female fecundity. We found that
food availability, but not group size, had a significant effect on female fecundity. Additionally, female fecundity was positively
correlated with the number of stored sperm in the female sperm-storage organ at the time of isolation, but it was not correlated
with body or ovary size of the worms. Our results suggest that female fecundity in M. lignano is primarily determined by the resources available for egg production, and not by the level of polyandry, confirming classic
sexual selection theory for simultaneous hermaphrodites. |
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