Is Basking Opportunity in the Viviparous Lizard, Eulamprus Tympanum, Compromised by the Presence of a Predator Scent?

Abstract

Chemoreception is a common mechanism used by many species to detect the presence of a potential predator and subsequently respond to it. The perceived risk of predation may force retreat to suboptimal conditions, forcing a trade-off between the risk of predation and the ability to acquire resources. Responses to chemical cues of predators vary as a result of past experience, ontogeny, or reproductive state. The basking regime maintained by gravid females of the viviparous skink, Eulamprus tympanum, may directly alter sex ratios of offspring produced through temperature-dependent sex determination. The avoidance of predator scents may restrict basking ability and, in turn, alter the sex of offspring produced. We measured responsiveness to chemical cues using tongue flicks as an indicator of chemical discrimination in adult females and neonates and in females of different reproductive condition. We then measured activity rates and basking behavior of females in experimental enclosures in the presence of various chemical stimuli to determine whether basking opportunity is compromised by the presence of a predator scent. Neonates respond significantly more than nonreproductive adult females to all chemical stimuli suggesting an age-specific shift in response, whereas adult females respond differently depending upon reproductive state. Under laboratory conditions, gravid females modify their behavior and forego the opportunity to bask when there is a perceived predation risk. However, further experimentation conducted under field conditions would be necessary to test fully the hypothesis that basking opportunity is compromised by the presence of a predator stimulus and, in turn, could alter offspring sex ratios.