SREL Reprint #2843

 

 

 

Daily activity patterns of Whiptail Lizards (Squamata: Teiidae: Aspidoscelis): a proximate response to environmental conditions or an endogenous rhythm?

C. T. Winne1 and M. B. Keck2

1Savannah River Ecology Laboratory, Drawer E Aiken SC 29802, USA
2Grayson County College, 6101 Grayson Dr, Denison TX 75020, USA

Summary:
1. The hypothesis that high soil temperatures are required to induce both initiation and cessation of daily activity in Whiptail Lizards (Aspidoscelis; formerly Cnemidophorus), as well as the hypotheses that hunger thresholds and high rates of evaporative water loss influence daily activity patterns, were experimentally tested in A. inornata and A. gularis.
2. Although a critical soil temperature was required to elicit the initiation of morning activity, high temperature was not a necessary stimulus for the cessation of activity.
3. Access to prey did not influence the pattern of daily activity; moreover, evaporative water loss did not appear to explain the cessation of afternoon activity.
4. Reversing the photoperiod 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.
5. These results provide strong evidence that circadian cycles can play a critical role in not only the initiation but also the cessation of activity.
6. While the ultimate cause (i.e. selective advantage, if any) of this unusual circadian rhythm may be related to extreme temperature, limited water supplies or some other exogenous factor, clearly, the rhythm persists in the absence of limiting environmental conditions.

Keywords: Circadian rhythm, Cnemidophorus, environmental constraints, reptile, temperature

SREL Reprint #2843

Winne, C. T. and M. B. Keck. 2004. Daily activity patterns of Whiptail Lizards (Squamata: Teiidae: Aspidoscelis): a proximate response to environmental conditions or an endogenous rhythm? Functional Ecology 18:314-321.

To request a reprint

 

 
http://srel.uga.edu www.uga.edu