Meeting Abstract
Upon colonizing the cave environment, the blind Mexican cavefish, Astyanax mexicanus, has evolved a variety of extreme phenotypes that contrast starkly with the extant surface morphotype. Degenerative traits such as a visual system and pigmentation have been extensively documented in this system, based on direct comparisons between derived cave morphologies and the (surrogate) ancestral, surface forms. Little is known, however, of the complex gene network controlling melanophore patterning in this system. In this study, we focused on two genes, pmela and tyrp1b. These genes are jointly involved in variations of melanosome shape and number, and early melanoblast development in zebrafish. Using analysis of cross-developmental in-situ hybridization and gene knockdown by morpholino, we established clearer roles of pmela and tyrp1b in Astyanax pigmentation development. Based on in-situ hybridization quantification, we observed the greatest divergence between morphotypes at 21-24 hpf. The total number of tyrp1b or pmela positive cells was not significantly different between cave and surface fish; however, tyrp1b was expressed in a significantly different number of cells in the tail (p-value<0.05). Conversely, at the same developmental stage, pmela was expressed in a significantly different number of cells on the surface fish yolk sac (p-value<0.05) and tail (p-value<0.01). This quantitative analysis of the developmental changes in pigment cell gene expression through pmela and tyrp1b allows for a better understanding of the mechanisms driving degenerative trait evolution in the extreme cave environment. This work was supported by a grant from the National Science Foundation (DEB-1457630) to JBG.
