BAEZA, J.A.; Univ. of Louisiana, Lafayette: Local mate competition does affect sex allocation in a protandric simultaneous hermaphrodite with low risk of sperm competition

For strictly simultaneous hermaphrodites, the local mate competition (LMC) model predicts a positive correlation between the proportion of resources devoted to the male function and mating group size whenever sperm competition plays an important role on their mating systems. LMC should also affect sex allocation of protandric simultaneous hermaphrodites (PSHs), where young individuals reproduce only as male while older individuals reproduce as both male and female. In these PSHs, sex allocation measured as the time individuals spend as males (i.e. male-phases, MPs) before maturing as functional simultaneous hermaphrodites (SHPs) should increase with increases in mating group size. Here, I examined the effect of LMC on sex allocation of the PSH marine shrimp Lysmata wurdemanni when maintaining a single young MP solitarily or with 1, 2, 5, or 10 older SHPs in the same aquarium. The time spent by young shrimps as MPs before maturing as SHPs increased with increases in the number of SHPs on their vicinity, in agreement with the LMC model. Although this adjustment on sex allocation was striking, the risk of sperm competition was found to be low in L. wurdemanni. Parturial SHPs (i.e. SHPs reproducing as female after molting) invariably mated with a single other conspecific reproducing as a male as observed when shrimps were maintained in aggregations. The fact that a species featuring a mixed sexual system (PSH) respond accordingly to predictions of sex allocation theory originally proposed for pure simultaneous hermaphrodites is relevant as indicates the need for a comprehensive theoretical model explaining the evolution of both strict, sequential hermaphroditism, and mixed sexual systems.