Variation in metabolic rate between populations of a geographically widespread lizard

In geographically widespread ectotherms, variation in life history phenotyp es 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 h istories; lizards in South Carolina grow faster, mature earlier, and have g reater annual reproductive output than lizards in New Jersey. I measured di el cycles of resting metabolic rate (RMR) at four temperatures (20 degrees, 30 degrees, 33 degrees, and 36 degreesC) during spring, summer, and fall. In all seasons, RMR increased significantly from 20 degrees to 33 degreesC but did not differ significantly between 33 degrees and 36 degreesC. 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 th at of South Carolina lizards (45.8 kJ), despite the shorter duration of act ivity in New Jersey. I conclude that the difference in maintenance metaboli sm between populations contributes to the greater production by S. undulatu s in South Carolina.