Reproductive Influences on the Thermoregulatory Behavior of a Live-Bearing Lizard

Both male and female Sceloporus jarrovi thermoregulate on every day during the summer when weather is suitable for lizard activity. Pregnant females, however, regulate a lower body temperature (: = 32.0 C) than do males or postparturient females (9 = 34.5 C) and, using the standard deviation about the mean as a measure of precision, also thermoregulate more carefully (FSD: females = 0.9 C, males and post-parturient females = 1.4 C). The variability in mean body temperature both within and between pregnant and non-pregnant lizards is related to shifts in the maximum and minimum body temperatures voluntarily tolerated in the field. Demographic and climatic considerations that make early birth advantageous at both high and low altitudes result in the prediction that lizards should regulate the highest body temperature possible during pregnancy. The shift to a lower preferred body temperature by female S. jarrovi during pregnancy could thus reflect a compromise by the female between two conflicting thermal optima, her own preferred body temperature and a lower optimum temperature for development of her embryos.