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Sex ratio theory in a splash pool : the sex ratio trait of Tigriopus californicus

Sex ratio theory makes predictions about how sexually reproducing organisms should allocate their reproductive efforts towards sons and daughters. Fisher predicted that the optimal strategy is one of equal investment (i.e. the 50:50 sex ratio). Subsequent analysis has shown that Fisher's equilibrium sex ratio is contingent on a number of assumptions such as autosomal inheritance of sex ratio alleles, large population size, additive offspring costs, etc. When any of these assumptions are violated the equilibrium sex ratio is not necessarily the one predicted by Fisher. To test sex ratio theory requires systems that exhibit variation for the primary sex ratio. The harpacticoid copepod, Tigriopus californicus is one such system. I have repeatedly detected a large, extra-binomial variance component in the primary sex ratio among full sib families in several natural populations on Vancouver Island. Environmental factors such as temperature and larval density have a mild effect on the primary sex ratio but are not likely to drive sex ratio variation at the population level. Cytoplasmic sex ratio distorters such as Wolbachia are known to cause sex ratio fluctuations in the populations of other crustaceans but were not detected in T. californicus. In the absence of sex-biased mortality, lineage analysis revealed that the sex ratio trait in a local population of T. calijornicus was paternally transmitted. Uniparentally transmitted sex ratio factors are generally under strong selection to increase the proportion of the transmitting sex in their host population. This observation may provide an explanation as to why the population-wide primary sex ratio in T. californicus and other harpacticoid copepods is often male-biased.

Date10 April 2008
CreatorsVoordouw, Maarten Jeroen.
ContributorsAnholt, Bradley Ralph
Source SetsUniversity of Victoria
Detected LanguageEnglish

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