The Effect of Gamete Competition on Levels of Gamete Production in a Marine Invertebrate

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Previous work suggests that high population densities result in more intense male gamete competition and select for increased levels of production of these gametes. This hypothesis will be tested by examining spatial and temporal correlations between density and male gamete production levels in natural populations of a colonial ascidian. Two additional considerations which might modify the effect that male gamete competition has on levels of male gamete production will also be explored. First, natural selection can only act on the genetic portion of total phenotypic variance. Secondly, selection acts simultaneously on the entire phenotype, and so the effect of selection on male gamete production could be constrained by genetic correlations between this and other life history traits that are also subject to strong selection. Negative genetic correlations between male gamete production and allocation to other traits or structures would generate a trade off, with enhanced male gamete production offset by reductions in other traits. Alternatively, positive genetic correlations would constrain selection to operate on total allocation patterns as a single unit. These two potential constraints on evolution will be examined via a laboratory breeding experiment that will estimate the narrow sense heritability of male gamete production levels and explore possible genetic correlations between male gamete production and other life history traits. Overall, this study will contribute to our knowledge of the evolution of reproductive strategies in marine organisms by examining the selective pressures that fertilization processes can exert on gamete production patterns.