Variation in Sex Expression in a Marine Bryozoan

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Hermaphroditism is poorly understood in sessile marine Bryozoa that release of sperm externally for fertilization and reproduction. This project is designed to explore in a marine bryozoan how male reproductive success is related to male reproductive effort, and ultimately to the evolution of hermaphroditism. The hermaphroditic marine bryozoan Celleporella hyalina displays extensive variation in the expression of male and female gender in populations studied along the mid-coast of Maine. Individual colonies vary quantitatively in the allocation of anatomical structures to male relative to female reproductive functions. This investigation will use this polymorphism to test theoretical mechanisms for evolutionary maintenance of hermaphroditism. The study will address three specific objectives: (1) to develop genetic markers in the bryozoan that can be used in paternity analysis, (2) to determine whether gender variation has any measurable reproductive success, and (3) to use naturally-occurring "female" variants of the bryozoan in independent assays for fertilization success. This study will represent the first attempt to test sex allocation models for the presence of simultaneous hermaphroditism in benthic marine animals. Although this study will not isolate the mechanism of combined gender in bryozoans, it will provide an evaluation of the validity of this mechanism, a poorly understood aspect of benthic invertebrate reproductive ecology.