GROWTH, SEASONALITY, AND LIZARD LIFE-HISTORIES - AGE AND SIZE AT MATURITY

Temperature influences the activity seasons, reproductive phenology, s urvival rates, and growth rates of lizards. We present a model of liza rd growth that predicts phenotypic patterns of;ige and size at reprodu ctive maturity in different thermal environments (i.e. different activ ity seasons). The model predicts a threshold in length of activity sea son: above this threshold (long season), lizards can mature one year e arlier, but at a smaller size, compared to populations with activity s easons below the threshold. This environmentally imposed pattern refle cts the proximate consequences of temperature, together with simple ru les about the timing of maturation. A key prediction of the model is t hat age and size at maturity can vary non-linearly with the length of the activity season, and with the timing and duration of egg laying an d hatching. We tested these predictions with published data from field studies of the phrynosomatid lizard Sceloporus undulatus, which is ge ographically widespread and occupies a range of thermal environments. We estimated activity seasons for each population by modeling the link s between climates, microclimates and lizard body temperatures using h eal-transfer principles. Female age at maturity showed the predicted t hreshold in length of activity season, whereas female size at maturity did not show the predicted threshold, but instead was negatively corr elated with length of activity season. Two prairie populations were ex ceptions to this pattern: females matured in one year despite their sh ort activity seasons, and consequently matured at an unusually small s ize. Prairie populations may have evolved differences in growth respon se and reproductive timing. The thermal environment appears to be an i mportant correlate of life history variation among populations of Scel oporus undulatus.