Meeting Abstract
Regressive evolution involves the degradation of formerly useful traits as organisms invade novel ecological niches. Committing to a strict subterranean habit can lead to regression of the eye, likely, in large part, due to a limited exposure to light. Several lineages of subterranean mammals show evidence of such degeneration, which can include decreased organization of the retina, malformation of the lens and subcutaneous positioning of the eye, corresponding with a degradation of genomic loci encoding visual functions. However, animals with eyes that are not necessarily degenerate also demonstrate evidence of visual gene loss, such as those modified for enhanced dim light photoreception. Therefore, it is unclear whether there is any substantial difference in the protein-coding visual gene repertoire between subterranean mammals and other dim light-adapted vertebrates, or whether such differences are solely attributable to changes in non-coding regions. Also, the regression of eyes in subterranean mammals is incomplete, raising the question of whether they are trending towards total loss or are being retained for non-image-forming photoreceptive functions. Here I test two hypotheses pertaining to these questions: (1) vision gene loss in subterranean mammals differs in quantity and quality (i.e., functional distribution) from other dim light-adapted vertebrates, such as nocturnal and deep sea species; (2) subterranean mammals retain functional orthologs of some non-pleiotropic visual genes that are evolving at rates consistent with purifying selection. I discuss my findings in the context of eye loss in other animals and regressive evolution as a whole.
