Developing and Testing Evolutionary Models of Non-reproductive Sex including Homosexuality

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Homosexual behaviour has often been considered a 'Darwinian paradox' because a focus on non-reproductive sexual behaviour to the detriment of reproductive sex should result in fewer offspring. Yet, sexual behaviour between members of the same sex (homosexuality) is commonly observed in nature, and is particularly frequent in humans and other primates. A number of models have been proposed to explain the evolution of homosexuality, ranging from kin selection to intralocus sexual conflict. While many of these models have often been framed as alternatives to each other, there is actually a large degree of compatibility between them and extensive overlap in predictions. This is due, at least in part, to the conflation of both ultimate and proximate hypotheses, and equivalating incommensurate parameters such as mode of selection, fitness effects of traits, and types of genetic architecture, which track different parts of the evolutionary process. The present PhD projects aims are twofold; (1) To resolve current inconsistencies in the theoretical literature to produce a general framework for the evolution of homosexuality, underpinned by theoretical population genetics models. (2) To test predictions arising from this framework on empirical datasets.This will include:Extending single loci genetic and epigenetic models for the stability of polymorphism underpinning homosexuality, such as overdominance models, to multilocus models appropriate for complex trait architecture. This will be part of the process of formalising the Bisexuality Advantage Model proposed by Savolainen & Hodgson.Incorporating kin selection in to theoretical evolutionary genetic models of homosexuality in order to provide robust predictions for when sexuality could be promoted as a form of kin altruism. The aim is to incorporate ecological parameters in to all models to refine predictions across different social contexts such as mating systems.Testing predictions from the theoretical framework in cross-taxa distributions of homosexuality, and more specifically in behavioural datasets from studies on the Cayo Santiago research site in collaboration with other members of the Savolainen group.