TRANSCRIPTOME ANALYSIS OF SUBTERRANEAN AND SURFACE AMPHIPOD SPECIES STYGOBROMUS TENUIS AND CRANGONYX SHOEMAKERI

The development of troglomorphism in a variety of subterranean lineages has led to many questions involving the mechanisms driving the convergent evolution of these phenotypes. The complex nature of these traits, such as eye regression and increased extra-optic systems, make understanding the role of adaptation, neutral mutations and pleiotropy in the development of these phenotypes even more challenging. A key factor in understanding these mechanisms is to identify possible genes of interest through comparison of organisms with different degrees of troglomorphism. This study analyzes gene expression of two populations of two Amphipods, Stygobromus tenuis and Crangonyx shoemaker in the Washington, DC and Great Falls, MD area. These species, although collected from the same hypotelminorheic habitat, show a varying degree of troglomorphism, with S. tenuis believed to have adapted strictly to the subterranean habitat due to loss of functional eyes and pigment. Cross-species differential gene expression showed significant downregulation of 8 genes involved in eye development along with significant upregulation of 2 genes with an eye function, one being involved in programmed retinal cell death. Furthermore, this study identifies many other possible genes of interest in the development of troglomorphic traits that should be considered in future studies involving subterranean organisms.