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First published online May 8, 2007
Journal of Experimental Biology 210, 1762-1767 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.003426
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Fight versus flight: physiological basis for temperature-dependent behavioral shifts in lizards

A. Herrel1,*, R. S. James2 and R. Van Damme1

1 Laboratory for Functional Morphology, Department of Biology, University of Antwerp, Universiteitsplein 1, B-2610 Antwerpen, Belgium
2 Department of Biomolecular and Sport Sciences, Coventry University, James Starley Building, Priory Street, Coventry, CV1 5FB, UK


Figure 1
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  		Fig. 1. (A) Lateral view of the head of a Trapelus pallida specimen with the skin, the jugal, the postorbital and the squamosal bones removed, thus exposing the m. adductor mandibulae externus superficialis posterior. The muscle originates tendinously at the dorsal aspect of the quadrate and inserts broadly along the lateral aspect of the dentary. (B) Ventral view of the right hindlimb and tail of Trapelus illustrating the insertion of the m. caudofemoralis onto the femur.

 

Figure 2
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  		Fig. 2. Temperature dependence of in vivo whole organism performance traits in Trapelus pallida. Values are means ± s.e.m. (N=10). Note that bite force (filled circles) remains at almost 80% of its maximal capacity for nearly the entire range of temperatures tested. Sprint speed (open circles) on the other hand is strongly dependent on temperature and drops below 80% of its maximal capacity at a temperature of about 30°C.

 

Figure 3
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  		Fig. 3. The effect of temperature is different for the two muscles tested in vitro. Values are means ± s.e.m. (N=6). (A) Time (ms) needed to reach peak force in a tetanic stimulation increases significantly (over sixfold) as temperature decreased from 40°C to 20°C. Note also how the jaw closer muscle (m. adductor mandibulae externus superficialis posterior) is markedly faster than the femur retractor (m. caudofemoralis) at all temperatures. (B) Relative tetanic force as a function of temperature. Note how the peak force delivered by the jaw muscle is nearly independent of temperature (filled circles) whereas a notable optimum in force production appears to be present for the femur retractor (35°C; open circles).

 

Figure 4
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  		Fig. 4. The effect of temperature on peak active power of the m. caudofemoralis in Trapelus pallida. Values are means ± s.e.m. (N=6). (A) A clear decrease in muscle power output is notable between 35°C and 20°C. (B) Examples of work loops at 40°C and 20°C, respectively. Note how the shape and size of the work loops differ markedly at the two temperatures.

 




© The Company of Biologists Ltd 2007