Variation in female reproduction between populations of the arboreal lizard Urosaurus bicarinatus (Squamata: Phrynosomatidae) from two different environments in Mexico

Local and geographic variation in several life history characteristics (body size at sexual maturity, clutch size, clutch frequency, egg volume, offspring size) were analysed in the arboreal lizard Urosaurus bicarinatus in three populations (Chamela, Jalisco; Jojutla, Morelos; and Paso del Chivo, Michoacan) from two different environments (tropical dry forest and thorn bush) in Mexico. Variations in these life history traits were found to exist between populations. Adult females from Chamela exhibited smaller snout-vent length (SVL) than females from Jojutla and Paso del Chivo. A similar pattern was found in others reproductive characteristics, including clutch size, relative clutch mass, egg volume, and hatchling SVL. These differences could be interpreted in terms of trade-offs, where some populations or species under conditions of low resource availability and high mortality tend to expend higher costs on reproduction; such could be the case in the population of Chamela. However, more studies are needed in many species with a broad geographic distribution to better understand the effects of the environment and genetics on variation in life histories.