Characterization of thermal and hydric conditions of nesting sites of female Aspidoscelis costatus costatus (Squamata: Teiidae)

Abstract

Reproductive success in oviparous squamates requires the selection of an appropriate nest site for oviposition. The resulting environmental conditions directly influence different biological traits of offspring. We studied thermal and hydric conditions of nesting sites before, during, and after the egg-laying season of Aspidoscelis costatus costatus (Balsas Basin Whiptail) in central Mexico to assess their respective relationships with the female reproductive cycle. We placed electronic thermometers directly into nests and measured soil humidity using a modification of the McGehee method. We measured and classified 45 nests of this subspecies, all located under volcanic rocks, as either active (i.e., with developing turgid, white-shelled eggs or shell remnants) or inactive (i.e., those from previous reproductive seasons as indicated by brown eggshells). We located active nests between June and September, whereas the inactive nests were found throughout the year. The average temperature and humidity in nests were 24.6° C and 19.5%, respectively, during the nesting season; however, neither temperature or humidity was optimal for clutch development in the months before and after the observed nesting season. Our study suggests that gravid female A. c. costatus respond to environmental seasonal cues for oviposition (obtained from nesting sites) that coincidentally influence completion of embryonic development. This is the first study of nesting sites in Aspidoscelis that could be monitored without destruction of the nest. Knowledge of the location of nesting sites for this species has major implications for its conservation, especially in patches of suitable habitat in a crowded urban landscape.