This project will investigate the genetic basis of dark body pigmentation (melanism) in high altitude African populations of the fruit fly Drosophila melanogaster. Pigmentation genes identified in Cameroonian and Ethiopian populations will be compared to one already identified in a Ugandan sample to test whether melanism has evolved via distinct genetic pathways. High-throughput DNA sequence data will be collected from fly "introgression lines" (where dark pigmentation has been crossed into lightly pigmented fly stocks) to identify genomic regions containing pigmentation loci. Similar data from wild-collected fly stocks will allow specific genes within these regions to be tested for associations with pigmentation and evidence for natural selection.
This research will significantly improve scientific understanding of how natural selection operates at the genetic level. It will also lay the groundwork for studies that utilize the genetic resources of this model species to pursue the precise mutations underlying melanic evolution. Broader impacts supported by this grant will include (1) the development of instructional materials for the college evolution curriculum, (2) the involvement of a diverse group of undergraduates in research, and (3) the creation of a Virtual Stock Center for Drosophila Population Samples to allow researchers to more efficiently manage living fly stocks.
This project investigates the genetic changes responsible for the evolution of dark pigmentation in three separate African populations of the common fruit fly or vinegar fly, Drosophila melanogaster. This species was targeted because of its well-understood genome and the unique experimental approaches available to expedite studies like this one. The trait studied for this project (melanism) is known from previous work to have been driven by natural selection as an adaptation to local environments. By pursuing the genes and ultimately the specific mutations that helped fly populations evolve dark pigmentation, this project will improve general scientific understanding of how evolution works at the genetic level. Results favor the hypothesis that each of the three melanic populations has evolved its dark pigmentation through changes at different genes. Hence, the evolution of similar phenotypes is not predictable in terms of genetic mechanisms. One notable result concerns a gene called pale. Based on patterns of genetic diversity of pale, it's clear that this gene has experienced recent natural selection in the high altitude, darkly pigmented Ethiopian population. Examination of specific genetic variants at pale supports the hypothesis that selection was likely acting to alter pigmentation. These results have motivated follow-up studies that use controlled genetic changes to formally test whether genetic changes at pale helped Ethiopian flies evolve melanism, and to test which specific mutations were causative. The development of new experimental and statistical methods was an important part of this project. A new method was developed to use controlled fly crosses to identify genomic regions associated with a trait difference between the parental strains. And a new method was developed to use patterns of linked genetic variants to identify genes where natural selection acted in one population specifically. An important component of this project's impact was the scientific training received by postdoctoral and undergraduate researches who contributed to the research. These young scientists were exposed to cutting edge cross-disciplinary research, and had the opportunity to gain conceptual, statistical, and computational research skills. This project also featured the developed of the Drosophila Virtual Stock Center. This online resource allows fly labs to share inventories of the fly strains they maintain, which allows them to find the best fly strains for each experiment, and to make informed decisions regarding the effort they devote to each strain's maintenance.
