RPG: The Evolution of Mixed Sex Allocation Patterns: A Comparative, Phylogenetic Approach

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Colette M. St. Mary 9707609 ABSTRACT Sex allocation theory has provided a powerful conceptual framework from which to understand allocation patterns in a wide range of organisms, included those that have separate sexes, as well as those that are hermaphroditic. However, there are some organisms for which current theory is clearly inadequate. Individuals of two temperate species of fish (gobies) in the genus Lythrypnus (L. dalli and L. zebra) simultaneously devote energy to both male and female functions, although they reproduce via only one sex at a time. Further, gonadal allocation varies with body size (i.e., ontogenetically). This overall pattern of sex allocation cannot be explained by reference to existing theory. The PI's recent theoretical work in this area suggests that costs of changing sex plays an important role in the evolution of these mixed strategies. To examine this hypothesis the PI will conduct a detailed examination of the pattern of sex allocation throughout the genus Lythrypnus. This will be done in an explicitly historical context, integrating studies focused on phylogenetic reconstruction and field and lab experiments designed to quantify the costs of reallocation and associated patterns of allocation and behavior. The genus Lythrypnus includes 20 species, which range over both temperate and tropical seas, including the eastern Pacific, the Atlantic and the Caribbean. Five species have been recently examined histologically. All are simultaneous hermaphrodites; however, they differ significantly in sexual pattern. Within the context of this proposal the PI will initate collection of the additional data needed to understand the evolution of complex allocation patterns in hermaphroditic organisms. The overall program goals include 1) development of a phylogeny for Lythrypnus based on molecular data; 2) documentation of variation in sexual patterns in Lythrypnus (i.e., ontogenetic and among-individ ual variation in sex allocation); and 3) application of field and laboratory experiments to quantify the degree of sexual flexibility, the costs and benefits of each sexual function, and the costs of reallocation. Ultimately, the PI will map sexual patterns and potential selective factors onto the phylogeny to provide an integrated test of the hypothesis generated from the PI's dynamic model. This work and studies of this sort provide a basic understanding of sex allocation patterns in hermaphroditic species. Many fishes, invertebrates and plants are hermaphroditic and our management, harvesting and control of such species is predicated on an understanding of their sexual and mating systems.