Ivan Mendez, Rebeiz Lab
Sarah Petrosky, Rebeiz Lab
Investigating the Genetic Background of Adaptive Pigmentation in African Drosophila melanogaster Populations
The relationship between an adaptive variant and its genetic background is often unclear. Heterogeneity and interactions between genes s increase the difficulty of linking genotype and phenotype in adaptive variants. The Drosophila melanogaster pigmentation system is one of few in which a clear molecular picture of an adaptive trait is possible, due to the substantial genetic tools available in D. melanogaster and the extensive previous knowledge of the Drosophila pigmentation network. African populations of D. melanogaster from Ethiopia and Zambia display a strong correlation between habitat altitude and cuticle melanization. The Ethiopian population was captured from a region of high altitude, while the Zambian population was captured from a region of lower altitude. These flies have noticeably different pigmentation, with a strong correlation between habitat altitude and cuticle melanization, resulting in Ethiopian flies that are dark relative to the Zambian flies. Although a similar phenotypic adaptation can be observed between multiple high elevation populations, bulk segregant analysis has indicated that there are different causative loci in each line, and that the phenotypes observed in the dark lines are heterogeneous. To understand the genetics underlying this trait, the validity of the candidate genes must be determined. I have begun investigating the candidate gene yellow by examining its expression using the reciprocal hemizygosity test, in situ hybridization, and transgenic reporter flies. After validation of candidate genes, the possibility of gene interactions such as epistasis will be examined by introducing causative loci from the dark population into the light population.
Investigating the evolution of a Hox-regulated pigmentation trait
Morphological diversity appears to evolve primarily from functional changes within cis-regulatory elements of developmental genes. In animals, the identity of each body segment is determined by the deeply conserved Hox genes. Due to their essential developmental role, changes in the regulation of Hox genes have been implicated in the evolution of animal diversity. Despite their central role in the evo-devo field, previous studies have not been able to precisely determine the causative regulatory changes at Hox loci. In fly species from the melanogaster group the abdominal pigmentation the A5 and A6 abdominal segments are covered with melanic pigmentation only in males. This trait represents a novelty that evolved within a monomorphically pigmented lineage ca. 40 MYA. The formation of adult pigments depends on the activity of enzymatic genes that are expressed during late pupal development under the control of the Hox transcription factor Abdominal-B. We aim to test whether regulatory changes in Abdominal-B were crucial for the origin of the male-specific pigmentation pattern within the melanogaster group. Specifically, we hypothesize that in non-pigmented species Abdominal-B expression is arrested during pupal development, whereas in pigmented species, regulatory changes resulted in an extended temporal expression of Abdominal-B followed by the activation of the downstream pigmentation genes. The extensive knowledge of the genes involved in abdominal pigmentation and the available molecular tools in Drosophila provide a great opportunity to investigate how a novel morphological trait can be originated by regulatory changes in a Hox gene.
Friday, September 28th
Langley Hall A219B