WEEKS, Stephen C.; The University of Akron: The evolution of androdioecy in the ephemeral pool clam shrimp, Eulimnadia texana

In androdioecious species, males coexist with hermaphrodites. Androdioecy is rare, found in only a handful of species, and is thought to be a short-lived mechanism for species transitioning from hermaphroditic to gonochoristic reproduction. Most androdioecious species are recently derived from either hermaphroditic or gonochoristic ancestors. However, one well studied androdioecious species, the clam shrimp Eulimnadia texana, appears to have maintained androdioecy for millions of years, which suggests that these shrimp have found a balance between these two forms of reproduction. We use an integrative approach to understanding androdioecy in E. texana by examining genetic, behavioral, and ecological aspects of these shrimp to determine whether these parameters are consistent with a model of androdioecy in this system. We have identified significant inbreeding depression in E. texana that should select for gonochorism. We have noted that there is no evidence for sperm limitation in hermaphrodites, and that males have higher mortality than hermaphrodites, both of which should select for hermaphroditism. Laboratory estimates of male mating success suggest that males can fertilize from one to ten times the amount of eggs a hermaphrodite can produce in a lifetime, but that this ability is tempered by physiological and ecological conditions. Currently, it is difficult to explain the observed sex ratios of males and hermaphrodites in E. texana given the above data. However, we are further examining male mating success, using both laboratory and field studies, to better understand the relative merits of hermaphroditism versus gonochorism in this species.