Chemical Ecology of Male Sceloporus Lizards: An Integrative Approach to the Study of Multimodal Signals, Hormones, and Behavior

Chemical cues mediate both social and predator-prey interactions that are critical for reproduction and survival, and hormones are involved in the production of chemical cues and in prey responses to predator odors. Males of many lizard species use chemicals produced from femoral glands (FGs) to display territory ownership, and some lizard species use chemicals to identify and avoid predators. The following chapters present a series of studies on the interactions of chemical cues, hormones, and behavior in male spiny (Sceloporus) lizards. First, evolutionary interactions between male chemical and visual signals were examined in four species of Sceloporus. Male Sceloporus have active FGs in the breeding season and also use visual signals (color and motion) during aggressive encounters with male conspecifics, but a key visual signal (colorful abdominal patches) has been evolutionarily lost in multiple species. Evolutionary loss of abdominal color patches was associated with increased responsiveness in male conspecifics, but there was no apparent interaction between loss of abdominal patches and composition of FG secretions. Changes in responsiveness to FG secretions may be the result of changes intrinsic to receivers but not signalers in male Sceloporus.;In the second study, associations between chemical and visual signals, as well as other phenotypic traits, were examined in male S. parvus that differed in throat color. Throat color has been linked to differences in hormone status and territorial behavior in other lizard species, but differences in throat color have not been thoroughly described in S. parvus. Throat color was associated with circulating plasma testosterone (T) levels and composition of FG secretions in male S. parvus. Throat color was not associated with body size, mite loads, or abdominal patch size or color, but males from different populations did differ in body condition, mite loads, and abdominal patch size and color. These results suggests that hormonally mediated multimodal signals (FG secretions and throat color) may be linked, but that the environment also influences signaling traits (abdominal color patches) in male S. parvus.;In the third study, male S. occidentalis were implanted with either T, empty implants (blank), or the T receptor blocker flutamide to test for effects of hormone status on production of FG secretions. Seasonal activation of FG glands is thought to be mediated by increased circulating T levels, but the relationship between T levels and variation in composition of FG secretions is poorly understood. Male lizards implanted with T had higher levels of circulating plasma T and produced greater quantities of FG secretions than blank- and flutamide-implanted males. There was no statistically significant difference among the three treatment groups in abundance of volatile organic compounds (VOCs) in FG secretions, but males implanted with T tended to produce lower quantities of compounds with low molecular weights.;Finally, male S. undulatus were presented with odors from three snake species to examine the potential for threat-sensitive behavioral and stress hormone (corticosterone, CORT) responses. Threat-sensitive responses of lizards to snake odors occur in some taxa, but no study has examined CORT responses to snake odors. Chemical cues from snake species that differ in body size and diet, two primary determinants of risk level, were presented to free-ranging male lizards. Odors of snakes posing higher risk elicited more head turns and chemosensory behavior than odors of the low risk snake and control stimuli, however, plasma CORT levels were elevated in lizards exposed to all three snake species relative to control. These results indicate that behavioral but not CORT responses are threat-sensitive in male S. undulatus.