Evolutionary Responses to Invasion: Cane Toad Sympatric Fish Show Enhanced Avoidance Learning

Georgina Caller,Culum Brown,Michael Somers

doi:10.1371/journal.pone.0054909

Abstract

The introduced cane toad (Bufo marinus) poses a major threat to biodiversity due to its lifelong toxicity. Several terrestrial native Australian vertebrates are adapting to the cane toad’s presence and lab trials have demonstrated that repeated exposure to B. marinus can result in learnt avoidance behaviour. Here we investigated whether aversion learning is occurring in aquatic ecosystems by comparing cane toad naïve and sympatric populations of crimson spotted rainbow fish (Melanotaenia duboulayi). The first experiment indicated that fish from the sympatric population had pre-existing aversion to attacking cane toad tadpoles but also showed reduced attacks on native tadpoles. The second experiment revealed that fish from both naïve and sympatric populations learned to avoid cane toad tadpoles following repeated, direct exposure. Allopatric fish also developed a general aversion to tadpoles. The aversion learning abilities of both groups was examined using an experiment involving novel distasteful prey items. While both populations developed a general avoidance of edible pellets in the presence of distasteful pellets, only the sympatric population significantly reduced the number of attacks on the novel distasteful prey item. These results indicate that experience with toxic prey items over multiple generations can enhance avoidance leaning capabilities via natural selection.

Highlights

The human facilitated introduction of novel organisms into new ecosystems has been occurring, both intentionally and accidentally, for thousands of years [1], [2]
In the Native Only treatment, the proportion of sympatric fish attacks on the native tadpoles did not differ significantly from the proportion of naıve allopatric fish attacks on the native tadpoles (ANOVA: F1,26 = 2.79, P = 0.107) and both groups showed a clear preference for the vial containing native tadpoles over the empty vial (Fig. 1)
Cane toad sympatric fish were less inclined to attack any kind of tadpole but were less likely to attack cane toad tadpoles than were the cane toad naıve fish

Summary

Introduction

The human facilitated introduction of novel organisms into new ecosystems has been occurring, both intentionally and accidentally, for thousands of years [1], [2]. On the other hand phenotypic plasticity is relatively rapid, allowing animals to adapt to environmental change with little loss of genetic variation [11], [12]. While some of this plasticity is morphological, it most often occurs through the learning process as a result of interactions with the invasive species [13], [14]. In this way the learning ability of animals is a key aspect to overcoming the threat posed by invasive species and other rapid ecosystem shifts [15]

Methods

Results

Conclusion