Does side matter? The evolution of asymmetric genitalia in livebearing fish

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Morphological asymmetries are ubiquitous among otherwise bilaterally symmetric organisms. The simple left-right nature of asymmetry facilitates comparisons across organisms, thus holding great potential to increase our understanding of evolutionary processes. Particularly promising is the evolution of asymmetric polymorphisms in animal genitalia, because of its strong correlation with fitness. It is now clear that sexual selection plays a fundamental role in the evolution of animal genitalia; however, the specific mechanisms are still unclear. Currently, the most plausible explanations are cryptic female choice, male-male sperm competition, and sexually antagonistic coevolution. Distinguishing among them is challenging because these are not mutually exclusive. Another limitation has been the focus on a single or few species. I propose to study the evolution of genital asymmetry in a group of livebearing fishes using phylogenetically controlled comparative methods. Most species in Anablepidae show internal fertilization, and many species exhibit genital asymmetry. Yet, the evolutionary implications of this asymmetry remain largely unstudied. I propose to conduct a series of experiments aimed to further our understanding of the causes and consequences of genital asymmetry in Anablepidae. First, I will produce a well-resolved phylogeny based on genome-wide markers, and map asymmetry into this phylogeny to make inference on the evolutionary history of genital asymmetry in Anablepidae. Then, I will conduct population genetic analyses in natural populations to determine the consequences of asymmetry for random mating and population differentiation. Finally, I will conduct specific crosses and pedigree analyses to determine the fitness consequences and genetic bases of genital asymmetry in Anablepidae.