| Abdominal pigmentation is a rapidly evolving character within the genus Drosophila, differing among species groups, among species, and among individuals or sexes within species. It has been postulated to play a role in such adaptive traits as thermoregulation, crypsis, and mate recognition. The cardini group of Drosophila is an especially interesting group for the study of abdominal pigmentation evolution. The group is separated into two subgroups. The first consists of seven species distributed across islands in the Caribbean. Each island supports an endemic species, each species exhibits a consistent abdominal pigmentation pattern, and the pigmentation patterns form a more or less regular cline across the islands, with lighter species in the north and darker species in the south. The second group consists of an additional nine species that have much more extensive distributions, mostly in Central and South America. The majority of the species in this subgroup are highly polymorphic for abdominal pigmentation, ranging from almost completely pigmented abdomens to ones almost completely lacking in pigmentation. Interestingly, the control of this phenotype seems to be genetic in some species and environmental in others.; The subject of this dissertation is the evolution and development of abdominal pigmentation in the cardini group. Chapter one uses mitochondrial DNA and nuclear genes to provide a phylogenetic framework for this group. This phylogenetic hypothesis is then used to test several hypotheses about the group, and to examine the evolution of abdominal pigmentation in the group. Chapter two delves into the phylogeography of D. polymorpha, and incorporates the population structure of the species as a baseline to examine the extensive geographic variation in abdominal pigmentation that this species exhibits throughout its range. The third chapter examines molecular evolution at a candidate gene for abdominal pigmentation, optomotor-blind (omb). Variation at this locus is used to look for signatures of selection and for correlations with the abdominal pigmentation phenotype. Chapter four describes multiple developmental approaches to studying the expression of omb within and between species of fruit flies that differ in abdominal pigmentation pattern, addresses several questions left unanswered by this research, and provides a guideline for future research. |
