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We examined whether western fence lizards Sceloporus occidentalis

occurring in thermally divergent environments display differential

responses to high temperature in locomotor performance

and heat-shock protein (Hsp) expression. We measured

maximum sprint speed in S. occidentalis from four populations

at paired latitudes and elevations before and after exposure to

an experimental heat treatment and then quantified hind-limb

muscle Hsp70 expression. Lizards collected from northern or

high-elevation collection sites suffered a greater reduction in

sprint speed after heat exposure than lizards collected from

southern or low-elevation sites. In addition, lizards from northern

collection sites also exhibited an increase in Hsp70 expression

after heat exposure, whereas there was no effect of

heat exposure on Hsp70 expression in lizards from southern

collection sites. Across all groups, there was a negative relationship

between Hsp70 expression and sprint speed after thermal

stress. This result is significant because (a) it suggests that

an increase in Hsp70 alone cannot compensate for the immediate

negative effects of high-temperature exposure on sprint

speed and (b) it demonstrates a novel correlation between an

emergent property at the intersection of several physiological

systems (locomotion) and a cellular response (Hsp70 expression).

Ultimately, geographic variation in the effects of heat on

sprint speed may translate into differential fitness and population

viability during future increases in global air temperatures.

Journal Name

Physiological and Biochemical Zoology

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