Seasonal Specificity of Hormonal, Behavioral, and Coloration Responses to Within- and Between-Sex Encounters in Male Lizards (Sceloporus undulatus)

This study reports the gender and seasonal specificity of hormonal, behavioral, and coloration responses displayed by "resident" male lizards (Sceloporus undulatus) exposed to male or female "intruders" during staged encounters in outdoor enclosures. Resident males were engaged in staged encounters with males or females for 1 h per day on 9 consecutive days during the breeding and postbreeding seasons. Male-specific responses occurred during the breeding but not the postbreeding season. These included (1) a transient increase in plasma testosterone (T) that was evident on Day 4 and had subsided by Day 10, (2) behavioral displays of aggression (full shows and chases), and (3) a lightening of dorsal integumental color. Female-specific behavioral responses (nod sets) were displayed in both seasons. Season-specific responses consisted only of a transient increase in plasma corticosterone (B) during the breeding season that was evident on Day 4 and had subsided by Day 10. Pushups were displayed in response to both genders during both seasons, although the frequency of pushups was significantly higher in response to females than to males during the postbreeding season. The coloration of residents did not change in response to male intruders during the postbreeding season or to females during either season. These results define the gender and seasonal specificity of hormonal, behavioral, and coloration responses of resident male S. undulatus in social interactions with conspecifics. Thus, our results clarify the biological significance of these responses in terms of potentially aggressive versus courtship interactions and breeding versus postbreeding contexts.