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In geographically widespread ectotherms, variation in life history phenotypes may be caused by differences in maintenance metabolism of individuals. I estimated daily and annual maintenance metabolism of eastern fence lizards, Sceloporus undulatus, from two populations with markedly different life histories; lizards in South Carolina grow faster, mature earlier, and have greater annual reproductive output than lizards in New Jersey. I measured diel cycles of resting metabolic rate (RMR) at four temperatures (20°, 30°, 33°, and 36°C) during spring, summer, and fall. In all seasons, RMR increased significantly from 20° to 33°C but did not differ significantly between 33° and 36°C. Adults from New Jersey had a higher RMR than adults from South Carolina in summer and fall but not in spring. Juveniles from South Carolina had a higher RMR than juveniles from New Jersey in summer but not in spring or fall. Annual maintenance metabolism of New Jersey lizards (53.7 kJ) was greater than that of South Carolina lizards (45.8 kJ), despite the shorter duration of activity in New Jersey. I conclude that the difference in maintenance metabolism between populations contributes to the greater production by S. undulatus in South Carolina.
Michael J. Angilletta (Mon,) studied this question.