Metabolic Consequences of Viviparity in a Lizard,Sceloporus jarrovi

Abstract

Metabolic rates of gravid females of the viviparous lizard Sceloporus jarrovi are higher than those of nonreproductive lizards: the allometric relationship between oxygen consumption and body mass in gravid females (V̇o2 = 0.437 m.735) has a statistically equivalent slope but a significantly higher intercept than that for males (V̇o2 = 0.225 m.812). The elevated metabolism of females during pregnancy is greater than can be accounted for by the increased mass of the pregnant female, indicating that the mass-specific oxygen consumption of the embryos is not scaling to maternal body mass. In fact, metabolism of gravid females is even higher than predicted if embryo metabolism is scaling to embryo body mass. Mean oxygen consumption of newborn S. jarrovi (mean body mass = 0.75 g) was 0.245 cm³ O₂ · h⁻¹, which is 1.4 times higher than that predicted from the allometric relationship for nonpregnant adults, but it is not statistically different from estimates of metabolism of embryos just before birth. During parturition, oxygen consumption of the female is 57%–162% higher than resting levels. The elevated oxygen consumption of viviparous female lizards during gestation could constitute a significant component of reproductive effort in these species.