The Preservation of Favoured Morphs in the Struggle Between Sexes

Sammanfattning: Sexual selection is particularly likely to promote population divergence, because sexual traits are expected to be subject to rapid evolutionary change. Identifying the relative roles of particular barriers to the amount of total reproductive isolation between populations or closely related species can provide important clues to the mechanisms of population divergence and speciation Phenotypic trait differences among populations are thought to reflect the interaction between the intensity of gene flow versus the strength of local selection and drift. Low levels of gene flow between populations will facilitate adaptation to the local environment and increase the strength of genetic drift. Conversely, when there is extensive gene flow circulating between populations, the high “migration load” will potentially enhance the level of population maladaptation. I examine the evolutionary dynamics of interactions between the sexes, and the significance of these interactions in shaping patterns of temporal and spatial population divergence. In my studies I take advantage of a female polymorphism, as colour polymorphisms in natural populations provide a visual marker that greatly aids in studies of the maintenance of genetic variation, as well as the mechanisms driving spatial and temporal fluctuations in selection regimes. In this thesis I investigated population divergence, changes in local selection patterns, female variation in response to male harassment, and large scale biogeographic patterns. The main goal of these studies was to aid in the understanding the evolutionary processes involved in the maintenance of genetic variation as well as potential causes of reproductive isolation and speciation. I also developed a theoretical model to examine consequences of male sperm limitations on mutual mate choice and conflicts between the sexes. Variation in selection is caused by feedbacks between the interacting phenotypes, both between and within the sexes. The studies in this thesis show that these feedbacks arise from the interaction between frequency-dependent and density-dependent dynamics of the female morphs, which in turn influence the spatially varying sexual selection regimes on males. The combination of the studies in this thesis demonstrates that local intra-specific interactions can have an important influence on observed large-scale biogeographic differentiation within a species.