Has an invasive lizard lost its antipredator behaviours following 40 generations of isolation from snake predators?

Abstract

The introduction of species outside their native range is an insidious form of human-induced environmental change, with mounting evidence that behaviour, either through plastic behavioural responses or adaptive changes, can play a vital role in mediating invasion success. In particular, when species invade non-native habitats, they often leave behind native predators. Altered predator assemblages may then result in changes to antipredator responses overtime. Here, we capitalise on the well-characterised invasion history of an Australian reptile, the delicate skink, Lampropholis delicata, to investigate differences in antipredator responses between an invasive island population (Lord Howe Island) and its original mainland source (Coffs Harbour) following 40 generations of isolation. Specifically, we examined the responses of invasive and native skinks to scent cues taken from huntsman spiders, Heteropoda sp., a predator present in both populations, and red-bellied black snakes, Pseudechis porphyriacus, a predator absent from the invasive range. We measured the time skinks took to emerge from a shelter site and subsequent basking and foraging behaviours in the absence and presence of each predator scent. We did not detect any differences in responses between native and invasive skinks, although predator scent affected foraging behaviour. In a separate experiment, lizards were faced with a simulated bird strike and had the choice of retreating under a snake-scented or unscented shelter. When faced with such a threat, we found that skinks did not avoid snake-scented shelters. We also measured the activity and exploratory behaviour of each skink prior to exposure to predator cues, finding that increased activity and exploration appears to be linked to reduced antipredator behaviour for invasive but not native skinks. Contrary to our initial predictions, our results suggest that the relaxation of pressure from native predators may not necessarily translate to changes in key antipredator responses in invasive species, even after 40 generations of isolation.

Significance statement

Human movement introduce species into novel areas, where they are confronted with a suite of ecological challenges that must be navigated, including changes to predator assemblages, in order to successfully establish and become invasive. Altered predator assemblages encountered by invasive species may, in turn, result in changes to, or loss of, antipredator responses over time. We studied such a scenario in the delicate skink, an Australian lizard that has been repeatedly introduced to new areas. We compared the antipredator behaviour of skinks from an invasive island population to skinks from their original mainland source. We found that despite 40 generations of isolation, invasive skinks do not differ from native skinks in their antipredator behaviour. However, we found that greater activity and exploration levels had become linked to reduced antipredator behaviour in invasive but not native skinks.