Daily Activity Patterns of Whiptail Lizards (Squamata: Teiidae: Aspidoscelis): A Proximate Response to Environmental Conditions or an Endogenous Rhythm?

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...

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Bibliographic Details
Published in:Functional ecology 2004-06, Vol.18 (3), p.314-321
Main Authors: Winne, C. T., Keck, M. B.
Format: Article
Language:English
Subjects:
Animal and plant ecology
Animal, plant and microbial ecology
Aspidoscelis
Autoecology
Biological and medical sciences
Biology
Body temperature
Circadian rhythm
Cnemidophorus
Deserts
Ecology
environmental constraints
Fundamental and applied biological sciences. Psychology
General aspects
Human ecology
Lizards
Photoperiod
reptile
Reptiles
Soil temperature
temperature
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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.
ISSN:0269-8463
1365-2435
DOI:10.1111/j.0269-8463.2004.00819.x