| dc.description.abstract | Sceloporus lizards are found all across the United States and Mexico. Males of this genus exhibit frequent sexual signaling, often via colorful abdomens but occasionally with sexual ornaments on other parts of the ventral surface of the body. These signals are energy expensive to maintain but convey important information to other males and to females about the health, strength, and fitness of the individual. It has been theorized that when women choose a mate based on a certain sexual ornament, the male offspring will inherit that same sexual ornament, while the female offspring will inherit the preference for the ornament. This sexual selection process allows certain signals that may not necessarily be beneficial for evolutionary fitness to remain in the gene pool because it plays such a large part in inter and intrasexual interactions. I wanted to determine to what degree visual opsins play a role in mate choice and perception of visual signals by identifying signatures of selection in opsins that may pertain to the colors of the sexual ornaments that different species exhibit. Identifying signatures of selection and tying those specific opsins to the colors that they perceive would lend evidence to the idea that visual perception has coevolved with sexual ornaments to allow species the best ability to interact with other individuals. I used preserved specimens of ten Sceloporus species and isolated and amplified the five visual opsin genes, as well as the 16S mitochondrial gene to vouch for the identity of the specimens. I followed QIAGEN DNeasy tissue extraction protocols and used custom primers for PCR, following thermocycles outlined in Zuniga-Vega et al. Clean PCR product was sequenced bidirectionally. The 16S sequences matched the sequences in GenBank and those were aligned to develop a phylogenetic tree, using Uta stansburiana, a close relative of Sceloporus, as the outgroup. Unfortunately, I ran into PCR optimization issues with the vast majority of visual opsin genes. I was able to salvage a few Rh1 sequences and supplement those with some GenBank sequences to generate a gene tree for Rh1. Upon qualitative inspection of the Rh1 gene tree, it appears relatively consistent with the evolutionary tree developed from the 16S gene sequences. Because Rh1 is responsible for light perception in areas of low lighting, it does not necessarily tell us much about the coevolution of the opsin with sexual signals. It does, however, tell us quite a bit about the habitat and how often these species rely on their rods for dim light perception. A distinct clade of S. merriami, S. marmoratus, and S. poinsettii was generated from the tree and is consistent with the habitats of these species. These three species are usually found in rocky areas such as arid mountains or canyons where they can bask in the sun and have little to no foliage for shade. The other species on the tree are found in woodland areas or semiarid environments with low foliage that provide some sort of shade and darkness. It would make sense that Rh1 evolved much longer ago in these species to allow them the ability to best interact with the low light environment around them. Unfortunately, I did not generate enough data for the color sensing visual opsins to draw any conclusions about the coevolution of the visual opsins with sexual ornamentation. Further PCR optimization and gel purification needs to be completed to generate visual opsin sequences and test for selection. | |
