Effect of Genetic and Environmental Variation on Diversification Due to Sexual Selection

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We are interested in determining the molecular genetic basis for variation in female mate choice in guppies, an important system for studies of sexual and natural selection. Guppy males are brightly colored, while females do not exhibit coloration, but do exhibit mate choice based on these male coloration patterns. One of the strengths of the guppy system is that females exhibit variation within and between populations for the strength and type of mate choice. For example, females from some populations are much more attracted to orange coloration when choosing mates than are females from other populations. This variation in female mate choice is one of the main reasons why the guppy is such an important system for the study of the evolution of female mate choice, because it is not possible to study the evolution of a trait unless that trait shows variation. We are focusing on opsin genes, because opsins help tune the color sensitivity of the retina. For example, humans have only red, green and blue opsins, and when one of these is disrupted the individual is at least partially "colour blind." Guppies have 10 different opsin types, the most for any vertebrate, and we hypothesize that differences in the sequences of these opsins among individuals, or differences in when and where these genes are turned on or off, might explain much of the difference among females for mate choice. We are collecting guppies from natural populations experiencing various light environments, and also raising guppies in the lab under varying light conditions, to test whether genetic differences or variation in opsin gene expression correlates with mate choice. It is also possible that females differ in mate choice because they process sensory input from the retina in different ways, and we are using modern genomic techniques to survey all of the genes expressed in the brains of female guppies when they are shown attractive or non-attractive males. Our determination of the genetic basis of mate choice for color will be a major advance in the study of evolution, but will also give insight into the evolution and development of the vertebrate visual system.