Theory suggests sexual dimorphism arises from selection operating differently on males and females. The degree of sexual dimorphism can be a direct result of the intensity of intrasexual competition. Mate competition is a key element of fitness as reproductive success increases with the number of mates. The operational sex ratio (OSR), or the ratio of sexually-active males to sexually-receptive females, is directly related to variation in mating competition. Theory predicts that biases in the OSR reduce mating competition within the less abundant sex, and thus influence the evolutionary of the primary sex ratio. Biases in the OSR also select for parental ability to facultatively adjust the offspring sex ratio. Squamates have played an important role in advancing sex ratio theory because species studied to date exhibit a broad range of sex allocation responses to the OSR that are both consistent and contradictory to traditional predictions. Despite availability of data for a considerable number of species, information about sex allocation in response to perturbations of the OSR is lacking for many squamates, particularly those with unique reproductive biologies. The brown anole, Anolis sagrei, is one of these species. This species can facultatively adjust sex allocation, but responses to OSR have not yet been evaluated. Females produce a single egg once a week, so mothers are able to differentially invest into each offspring across its extended reproductive season. Also, A. sagrei reaches sexual maturity at about six months and most individuals live about one year. Thus, the OSR is likely to predict the intensity of future intra-sexual competition for early-produced offspring. But the juvenile sex ratio (JSR) is likely to better predict future intra-sexual competition for late produced progeny. This proposal aims to evaluate facultative sex allocation in response to OSR and JSR in the brown anole, Anolis sagrei.
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