Abstract:
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
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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.
