Postmating Sexual Selection and its Role in Population Divergence in Beetles

Speciation is the procedure explaining the development of new species and is at the heart of evolutionary biology. In accordance with the biological species concept only reproductively isolated types are considered good species. This dissertation is designed at identifying evolutionary processes which trigger population divergence and, ultimately, speciation. Natural and sexual selection are a couple of significant candidates driving changes in traits which could render populations reproductively incompatible. Recently, biologists have acknowledged that most animal species are polygamous. Therefore, sexual selection doesn’t end at mating but carries on to include connections between individuals after mating has took place but before zygote formation. Male-male sperm competition and mysterious female choice are 2 primary types of postmating sexual selection shaping reproductive traits like behaviour. The research offered in this dissertation concentrate on laboratory experiments trying to identify the role of postmating sexual selection in causing reproductive divergence across populations in beetles. Nearly all studies were performed utilizing a Bruchid beetle, Callosobruchus maculatus, a standard, worldwide pest on stored leguminose seeds. I employed 2 key methodological approaches. One technique attempts to find the traces left by past selection among extant conspecific populations, by evaluating the pattern of female reproductive responses to mating with males of decreasing relatedness. Next, I employed a variety experiment to disentangle the joint effect of natural and sexual selection acting simultaneously on diverging replicated selection lines. On the whole, these experiments exposed that postmating sexual selection can be an effective engine of incipient divergence between allopatric populations. Adjustments to traits underlying variables like female reproductive output, female mating rate or male success in sperm competition evolved rapidly and could in a few instances effectively minimize gene flow between conspecific populations. While postmating sexual selection per se can drive divergence, I discovered that interactions with natural selection can restrict divergence in reproductive characters. Sexual choice tended to reinforce natural selection under strong directional selection. In contrast, sexual choice caused a reproductive strain on populations under weak natural selection. Therefore, the joint effects of natural and sexual selection on allopatric populations are non-trivial and should be looked at in depth in future research of early divergence.


Natural selection
Sexual selection
Divergence patterns
Postmating prezygotic isolation
Aims of the thesis
Model species and Methods
Results and Discussion

Source: Uppsala University Library

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