Responses of Mainland and Island Wall Lizards to Rat Chemical Cues

Abstract

Rats have followed mankind into a wide diversity of habitats around the world. This includes many smaller islands, where they present a possible threat to local fauna that have often evolved in the absence of mammalian predators and therefore may not recognise them as dangerous. Many lizards can detect chemicals left behind by predators (mostly snakes) and will change their behaviour in response to them. However, whether lizards recognise mammal scents in general, and of rats in particular, remains unclear. Here we compared the responses towards rat chemical cues between Italian wall lizards (Podarcis siculus) originating from mainland and island habitats. In a first experiment, tongue flick rates (indicative of chemosensorial excitement) and behaviour of lizards were observed in two control situations (blank and pungent) and in the presence of rat scent. Lingual sampling increased dramatically in response to rat cues in both mainland and island lizards, but the animals' overall behaviour hardly changed. We found no evidence that the rat cues elicited stress or anti-predator behaviour. In a second experiment, we offered the lizards the choice between two basking sites, one of which we labelled with rat scent. We found no evidence that lizards systematically avoided the rat-scented perch. We conclude that both mainland and island Italian wall lizards can detect chemicals produced by rats, but these do not elicit noticeable changes in their behaviour (other than increased tongue flick rates). However, in both the control and experimental treatments, island and mainland lizards differed in tongue flick rates and in several aspects of their behaviour.