Thesis

Bilateral Asymmetry in Two Secondary Sexual Characters in the Western Fence Lizard (Sceloporus Occidentalis): Implications for a Correlation with Lateralized Aggression

ABSTRACT BILATERAL ASYMMETRY IN TWO SECONDARY SEXUAL CHARACTERS IN THE WESTERN FENCE LIZARD (SCELOPORUS OCCIDENTALIS): IMPLICATIONS FOR A CORRELATION WITH LATERALIZED AGGRESSION by Jackson D. Shedd Master of Science in Biological Sciences California State University, Chico Spring 2009 Three forms of bilateral asymmetry (antisymmetry, fluctuating asymmetry, and directional asymmetry) exhibited by animals have been recognized in the literature. A preference for the use of the left visual field during aggressive intraspecific interactions has been found in a variety of vertebrate taxa. However, correlations between the use of bilaterally asymmetric morphological characters and aggressive displays mediated by neurological asymmetry are not well studied. The western fence lizard (Sceloporus occidentalis) exhibits bilateral asymmetry in two secondary sexual characters used in territoriality; blue abdominal signal patches and femoral pores. Abdominal xiii patches are used in visual communication while femoral pores are used in chemical communication. Here I present data that supports implications for a correlation between visual signaling and left-eye aggression in male S. occidentalis. I measured abdominal patch length and femoral pore number for left and right sides of adult male and female lizards from five localities in northern California. The results from this study show that this species collectively exhibits left directional asymmetry (DA) in abdominal patch length across all field sites. Males also showed left DA in patch length separately from females, which were not found to do so. Further, females collectively expressed a significantly higher number of femoral pores on the left hind limb across all field sites, but males did not. However, both male and female voucher specimens examined from one population, the Sutter Buttes, expressed significant left DA in femoral pore number.

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