Metabolic Rates of Female Viviparous Lizards (Sceloporus jarrovi) throughout the Reproductive Cycle: Do Pregnant Lizards Adhere to Standard Allometry?

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Abstract
The standard metabolic rate (SMR) of viviparous female lizards (Sceloporus jarrovi) was measured at different times during the reproductive cycle at 30°C. The pattern of change in rate of O₂ consumption ( ) during pregnancy is sigmoidal. Oxygen consumption increases slowly during the first two-thirds of pregnancy and rapidly during the last trimester, with a slight plateau before parturition. Immediately following parturition, decreases sharply and is not different from of nonreproductive females. The SMRs of early, middle, and late pregnant lizards is 80%, 98%, 140%, respectively, of that expected of nonreproductive lizards, after adjusting SMR for body mass. Deviations from standard allometry are due mostly to changes in litter metabolism. Litter metabolism is low during early pregnancy because litter mass consists mostly of metabolically inert yolk. At the end of gestation most of the mass of a litter consists of metabolically active embryos, which have nearly twice the mass-specific metabolic rate of the female's somatic mass. It can no longer be assumed that gravid or pregnant lizards conform to inter-or intraspecific allometric equations relating to body mass. When constructing energy budgets for female squamates, investigators should take into account changes in maternal during pregnancy, as well as the litter's contribution to that change.