Do female reproductive stage and phenotype influence thermal requirements in an oviparous lizard?

Abstract

Reproduction is an energetically costly activity that can alter thermal requirements in Squamata. This phenomenon has been largely studied in many viviparous species; however, little is known about the role of oviparous females in controlling temperature during vitellogenesis and embryo development before oviposition. Diversity of female phenotypes could be associated with diversity of thermoregulatory performance, since thermal requirements are frequently influenced by body shape. Furthermore, studying the thermoregulatory behaviour is fundamental to understand how females regulate their body temperature. Here, we aimed to determine whether reproduction alters thermal requirements in an oviparous model, Tropidurus spinulosus, and if the preferred body temperature and thermoregulatory behaviour vary among reproductive stages and in relation to the female phenotype. We characterized the female phenotypes according to multiple morphological traits (snout-vent length, inter-axillar length, abdominal perimeter, body condition and head width). Reproductive structures were diagnosed by portable ultrasound scanning. To determine body temperatures, the lizards were placed in an open-top terrarium, where a thermal gradient ranging from 18 to 50 °C was set up; we also recorded the permanence of individuals in cold, temperate and warm zones during each experiment. Reproductive females preferred higher temperatures and presented lower amplitude in thermal variability than non-reproductive females. Moreover, within reproductive females, females with wide abdominal perimeter and high body condition showed thermal stability. Females with oviductal eggs tended to select higher temperature and also show more thermal stability than females with vitellogenic follicles. The latter females used the temperate zone most frequently and to a lesser degree the warm one, whereas females with oviductal eggs used the temperate and warm zones with similarly high frequency. We conclude that reproductive stage and phenotypic traits influence the selection of preferred body temperatures and thermoregulatory behaviour in T. spinulosus females.