| One of the central goals of evolutionary biology is to understand the processes that underlie the generation and diversification of phenotypes. Identifying the genetic changes underlying phenotypic differences between species is an essential component in understanding how diversity is generated. Species generally vary in form, and such variation often plays an essential role in adaptation to ecological conditions, sexual selection, and many other relevant evolutionary processes.;Little information exists about the molecular genetic basis of complex morphological traits as multiple genes, environmental conditions and interactions between these two factors typically influence their expression making their study particularly challenging. Yet to answer important standing theoretical questions about the genetic basis of such traits, it is essential to streamline current methods to study quantitative variation and expand the number of empirical studies identifying genes underlying their variation.;I studied the genetic basis of complex morphological differences between closely related species of Drosophila within the melanogaster species subgroup. I focused on variation in eye size/shape between D. simulans and D. mauritiana, and abdominal pigmentation between D. yakuba and D. santomea . In the case of eye size/shape I test several methods to accurately quantify the variation between species and generate a rough QTL map of the X-chromosome. In the case of abdominal pigmentation I generated for the first time a high-resolution map of most of the genes involved in the generation of differences in a quantitative trait between species. I show how through repeated backcrossing coupled with selection it is possible to isolate each of the four different QTLs affecting abdominal pigmentation in a common background. Three of these QTLs produce discrete, traceable phenotypes in isolation thus making the study of individual genes considerably simpler. I narrowed all four QTLs to a fraction of their original size, in one case to an interval 2 orders of magnitude smaller. Finally, I show how this method lead to identification of a gene of previously unknown function that affects abdominal pigmentation variation in Drosophila and is likely to be involved in the evolution of abdominal pigmentation differences between D. yakuba and D. santomea. |
