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Selected Body Temperature and Thermoregulatory Behavior in the Sit-and-Wait Foraging Lizard Pseudocordylus melanotus melanotus

Selected Body Temperature and Thermoregulatory Behavior in the Sit-and-Wait Foraging Lizard... We investigated the thermoregulatory abilities and behavior of Pseudocordylus melanotus melanotus (Drakensberg crag lizard) in terms of the relationship between the operative temperature (T e ), selected temperature (T sel ), set-point range (T set ) and field active body temperature (field T sel ), exposure to low temperature, body posture and activity. The T e range for P. m. melanotus was about 58 C (−3.20 C in winter to 54.94 C in summer). In a laboratory thermal gradient, in a setting that is independent of ecological costs or thermal constraints, lizards maintained T set (defined as the interquartile range of T sel , after Hertz et al., 1993) between 29.00 ± 0.36 C and 31.78 ± 0.16 C in winter and 29.61 ± 0.28 C and 32.47 ± 0.18 C in summer. The mean T sel was 30.08 ± 0.14 C in winter and 30.99 ± 0.11 C in summer. In the field, however, lizards achieved significantly lower T b , which suggests that the thermal environment limited the T b that lizards were able to achieve. Lizards were active for significantly longer and selected significantly higher T b in summer than in winter. During winter, lizards spent a significant amount of time at T b below their lower critical limiting temperature (defined by loss of righting). The most frequently assumed body postures in summer were those where the head or body were raised, whereas, in winter, lizards usually lay with head and body flat on the rock substrate. We suggest that these differences reflect the physiological requirements of the lizards: Head-up postures in sit-and-wait foragers are consistent with scanning for prey while head-down postures are likely motivated by thermoregulatory needs. It is clear that P. m. melanotus can thermoregulate efficiently, but the T b maintained may be constrained by the range of T e available to the lizards in their natural environment. Pseudocordylus m. melanotus currently appears to be geographically constrained by low environmental temperatures at the edge of its range. Should global warming become a reality in southern Africa, this species could inadvertently benefit by occupying new habitat that was previously unavailable because of thermal constraints. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Herpetological Monographs Allen Press

Selected Body Temperature and Thermoregulatory Behavior in the Sit-and-Wait Foraging Lizard Pseudocordylus melanotus melanotus

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Publisher
Allen Press
Copyright
The Herpetologists' League, Inc.
Subject
Articles
ISSN
0733-1347
eISSN
1938-5137
DOI
10.1655/08-027.1
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Abstract

We investigated the thermoregulatory abilities and behavior of Pseudocordylus melanotus melanotus (Drakensberg crag lizard) in terms of the relationship between the operative temperature (T e ), selected temperature (T sel ), set-point range (T set ) and field active body temperature (field T sel ), exposure to low temperature, body posture and activity. The T e range for P. m. melanotus was about 58 C (−3.20 C in winter to 54.94 C in summer). In a laboratory thermal gradient, in a setting that is independent of ecological costs or thermal constraints, lizards maintained T set (defined as the interquartile range of T sel , after Hertz et al., 1993) between 29.00 ± 0.36 C and 31.78 ± 0.16 C in winter and 29.61 ± 0.28 C and 32.47 ± 0.18 C in summer. The mean T sel was 30.08 ± 0.14 C in winter and 30.99 ± 0.11 C in summer. In the field, however, lizards achieved significantly lower T b , which suggests that the thermal environment limited the T b that lizards were able to achieve. Lizards were active for significantly longer and selected significantly higher T b in summer than in winter. During winter, lizards spent a significant amount of time at T b below their lower critical limiting temperature (defined by loss of righting). The most frequently assumed body postures in summer were those where the head or body were raised, whereas, in winter, lizards usually lay with head and body flat on the rock substrate. We suggest that these differences reflect the physiological requirements of the lizards: Head-up postures in sit-and-wait foragers are consistent with scanning for prey while head-down postures are likely motivated by thermoregulatory needs. It is clear that P. m. melanotus can thermoregulate efficiently, but the T b maintained may be constrained by the range of T e available to the lizards in their natural environment. Pseudocordylus m. melanotus currently appears to be geographically constrained by low environmental temperatures at the edge of its range. Should global warming become a reality in southern Africa, this species could inadvertently benefit by occupying new habitat that was previously unavailable because of thermal constraints.

Journal

Herpetological Monographs – Allen Press

Published: Dec 1, 2009

Keywords: Lizard ; Operative temperature ; Pseudocordylus ; Selected temperature ; Set-point range ; Sit-and-wait forager ; Thermoregulation ; Thermoregulatory behavior

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