Sauria

Abstract: Thermal constraint on energy assimilation is an important source of life history variation in geographically widespread ectotherms such as the eastern fence lizard (Sceloporus undulatus). Fence lizards in southern populations grow faster and produce more offspring per year than do those in northern populations. Biophysical models indicate that this difference in production is the result of thermal constraints on energy assimilation, but they do not exclude intraspecific variation in behavior or physiology. I quantified both thermoregulatory behavior and the thermal sensitivity of metabolizable energy intake (MEI) in lizards from New Jersey (NJ) and South Carolina (SC) populations of Sceloporus undulatus. In the laboratory, I conducted feeding trials to estimate MEI at body temperatures experienced by field-active lizards (20°, 30°, 33°, and 36°C). I also measured preferred body temperature (T p ) of lizards in a thermal gradient. In the field, I estimated the accuracy of thermoregulation by lizards. Both NJ and SC lizards exhibited a maximal MEI at their T p (33°C), but lizards from SC had a significantly higher MEI at this temperature than lizards from NJ. Although lizards in both populations thermoregulated within 2°C of T p , lizards in SC could maintain T p for a longer duration on a daily and annual basis. Therefore, lizards in SC could assimilate more energy because they had a higher maximal MEI during activity and were active for longer durations than lizards in NJ. Geographic variation in the life history of S. undulatus may be caused by differentiation of physiology between populations, as well as by differences in the thermal environments of populations.

Abstract: Reproductive mode data were extracted piecemeal from the literature and superimposed over currently accepted phylogenies to permit estimation of the minimum frequencies with which viviparity (live-bearing) has evolved in lizards, aswell as to facilitateanalysisoffactors hypothesizedto inlluencethis evolution. Viviparity has arisen on at least 45 separate occasions in the Sauria. Each ofthese origins is pinpointed phylogeneticallyas far as is now possible. Ofthese origins, 22 have occurred in the Scincidae, ten in the Iguanidae, five in the Anguidae, two each in the Lacertidae and Gekkonidae, and one each in the Chamaeleontidae, Xantusiidae, Agamidae, and Cordylidae. Further origins may be detected in the Scincidae, Iguanidae, and Diploglossa as phylogenetic relationships are elucidated. Over 19 % of the saurian species are live-bearing, and about 2/3 of the viviparous species are skinks. Most of the sub-generic saurian origins ofviviparity have occurred in cold climates, possibly as an adaptation to facilitate maternal thermoregulation of the developing embryos. Phylogenetic distributions of these origins are consistent with hypotheses that genetic sex-determination of the male-heterogametic type as weil as a tendency towards egg'retention preadapt a lineage for viviparity. Evolution of the live-bearing mode may be constrained by temperature-dependent sex determination, female heterogamety, and formation of highly calcified eggshells.