Characterising the genetic architecture and fitness effects of rapid morphological diversification.

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Explaining the diversity of life on earth has long been a goal of biology. However we understand very little about the changes in the genome that underlie variation in the way cells read, interpret and execute the instructions coded in that genome, and how such changes interact in order to produce an organism with a modified shape or size. There is also a paucity of knowledge about whether the genetic changes that affect a given trait also cause in differences in other traits, and even less about their effect on reproductive success. Male sexual characters are often among the first traits to diverge between closely related species. Characterising the genes involved, their interactions, the evolutionary forces involved and fitness consequences of this rapid evolution offers a great opportunity to understand the processes of animal diversification, reproductive isolation and the evolution of new species.Among Drosophila species, males exhibit striking differences in genitalia morphology. The posterior lobes and claspers, in particular, differ in size, shape and bristle number between species. Moreover these structures are important for proper attachment of the male to the female during mating. Despite previous mapping studies, none of the genes involved have been identified, which is required to characterise how the underling genetic changes interact, if they also cause differences in other traits, and their effect on reproductive success. Therefore, in this proposal, we aim to identify the genes underlying variation in the morphology of the clasper and posterior lobe between D. mauritiana and D. simulans. Our preliminary results have already identified several small genomic regions responsible for a large proportion of the variation in posterior lobe and clasper. Here we propose to investigate the role of candidate genes found in those regions of the genome during clasper and posterior lobe development in the model D. melanogaster, and then verify their direct role in the evolution of variation in these structures between D. mauritiana and D. simulans.Once we have identified the genes responsible for the differences in genital morphology, we will survey natural variation by sequencing those genes in several strains of each species and test if these sequences have evolved under directional selection or just by chance.Interaction between genes can either facilitate or delay the evolution of a given trait, Therefore, we will test how the D. mauritiana and D. simulans alleles interact with other genomic regions underlying variation in the clasper and posterior lobe to evaluate the contribution of additive and/or non-additive (epistatic) genetic interactions to the divergence of these two traits. Furthermore we will test if the causative genes affect gene expression or morphology, at other stages of development and in other tissues (pleiotropic effects), to evaluate these changes in the wider context of animals development and how this evolves. Finally we will test if the changes in posterior lobe and clasper morphology affect reproductive success.Our work will serve as platform for further research to test the generality our findings on genital evolution and broaden our knowledge of how the genetic mechanisms underlying developmental programs integrate genotypic information to specify the phenotype and help explain how the vast organismal diversity in the natural world has evolved. Moreover, our study of male genitalia diversity may also help to address questions regarding the genetic architecture of quantitative traits including the role of epistasis and any pleiotropic effects. Given both the prominence of studies relating genes to appearance and behaviour and our general fascination with animal diversity, research such as ours offers an opportunity to not only appreciate this diversity, but explain the genetic nuts and bolts that have shaped it.