Elucidating the Genetic Basis of Pigmentation Differences between Drosophila Species.

Abstract

Understanding how phenotypes change has been a long-standing question in evolutionary biology. The research presented here investigates the genetic basis of the pigmentation difference exhibited between the dark pigmented Drosophila americana and lightly pigmented Drosophila novamexicana. It shows that the pigmentation genes ebony and tan contribute to this pigmentation divergence between these species and that tan mRNA is more highly expressed in D. americana. Variation in pigmentation within D. americana is also documented and is shown to be due in part to the same genes: ebony and tan. The contribution of tan to the pigmentation differences between species is further examined, and the 3ʼ region of tan intron 1 is determined to likely contain some of the causative nucleotides through functional transgenic analyses. The differences exhibited among D. americana strains was quantified and found to vary longitudinally with the darkest flies found in the eastern U.S. and lighter variants found in western populations of the U.S. This variation appears to be a consequence of local adaptation among D. americana populations. Desiccation resistance was investigated as a potential ultimate cause for the observed pigmentation differences, but found not to be associated with pigmentation. Two populations of D. americana were identified to contain D. novamexicana-like alleles of either tan or ebony. A survey of 51 populations was conducted to examine the frequency of this phenomena. No additional populations were found to contain D. novamexicana-like alleles, although genetic heterogeneity is identified among D. americana strains. This research presents a case of how phenotypic evolution has occurred by identifying genetic contributors and specific DNA sequence associated with this change in pigmentation both between species and within species. Research on the effectiveness of a specific pedagogical technique, online quizzes, in a large genetics course is also included in this thesis that resulted from participation in the Post-Secondary Science Education Masterʼs degree program. Although quizzes were not found to be statistically associated with increased student performance, students and instructor expressed positive sentiments towards the quizzes. This illustrates how classroom techniques can improve student attitude even if student performance is not directly impacted.