Behavioral Ontogeny in Free-Ranging Juvenile Male and Female Green Anoles, Anolis carolinensis, in Relation to Sexual Selection

Abstract

Anolis carolinensis is sexually dimorphic in behavior and morphology in adults, primarily due to intrasexual selection acting to produce large, conspicuous, and aggressive males. However, the extent to which selection pressures acting on adults might also produce sex differences during ontogeny, but before sexual maturity, has not been considered. During June-August 1995 and 1996, I recorded the behavior of 20 juvenile male and 17 juvenile female A. carolinensis for 30-60 min each at a field site near Augusta, Georgia, USA: (1) to determine if as groups, juvenile males and females behaviorally differ, thereby suggesting the presence of sex differences from hatching; and (2) to determine if juvenile males or females show sex- specific, size-related behavioral changes, in order to describe the ontogenetic schedule by which sex differ- ences in behavior arise. I examined potential indicators of sex differences in space use (perch height and diameter, home range volume), social behavior patterns (body color and shift rate, nearest neighbor distance, headbobbing display rate, and display context), and behavior patterns affecting growth (feeding rate and foraging mode, proportion of time spent moving). Based on potential tradeoffs between behavior relevant to the immediate life history of juveniles and behavior that will lead to future reproductive success, I hypothesized that juveniles would show no sex differences in space use or social behavior patterns, but would differ in behavior patterns affecting growth. As expected, juvenile males ate and foraged actively more often than juvenile females. Furthermore, overall comparisons between juvenile males and females revealed no sex differences in space use or social interaction. However, contrary to my hypotheses, juvenile males did not decrease amounts of time spent moving with respect to juvenile females, and larger males occupied larger home ranges and spent more time green while females showed no ontogenetic shifts in these variables. My results suggest that juvenile A. carolinensis show both sex differences present from hatching and arising through ontogeny leading up to the adult endpoints, and that these differences may arise through the effects of sexual selection on ontogeny.