WINNE, C.T.*; KECK, M.B.: Daily Activity Patterns in Cnemidophorus inornatus and C. septemvittatus: A Programmed Behavior?
ABSTRACT- In field studies of activity and thermal biology of whiptail lizards (genus Cnemidophorus: Teiidae), a strong correlation has been noted between daily activity patterns and temperature: Cnemidophorus consistently emerge from underground retreats at particular soil temperatures, and they retreat for a period of inactivity in the latemorning or early afternoon when the soil reaches a particular high temperature. Past researchers have hypothesized that soil temperatures were the proximate cue that controlled daily activity. We experimentally tested this hypothesis, as well as hypotheses that hunger thresholds and high rates of evaporative water loss influence daily activity patterns in Cnemidophorus, to determine if a causal relationship exists. We found that although a critical soil temperature was required to elicit the initiation of morning activity in C. inornatus and C. septemvittatus, it was not a necessary stimulus for the cessation of activity. Access to prey, and thus hunger thresholds, did not influence the pattern of daily activity in these species; moreover, evaporative water loss did not appear to explain the cessation of afternoon activity in these species. Reversing the photoperiods during our experiments led only to a change in the time of initiation of daily activity (i.e., activity began 12 h later), not a significant change in the duration of daily activity. We hypothesize that daily surface activity in these lizards is a circadian rhythm controlled by a biological clock. The biological clock is entrained to the photoperiod and/or temperature cycle. Thus, daily activity in C. inornatus and C. septemvittatus ceases relatively early without the influence of changing environmental conditions.