Abstract
Variation in morphological, genetic, or behavioural traits within and among native species can modify vulnerability to impacts from an invasive species. If an individual’s vulnerability depends upon its cognitive performance, we may see adaptive shifts in cognitive traits post-invasion. Commonly, animals with enhanced cognitive abilities perform better in novel tasks, often by prioritising decision accuracy over decision speed. In eastern Australia, giant monitor lizards (Varanus varius) are fatally poisoned if they ingest invasive cane toads (Rhinella marina), but vulnerability is lower for individuals that carefully evaluate the novel prey type before swallowing it. To test if toad-imposed selection for neophobia and caution affected cognitive performance, we tested free-ranging monitors with a device that required lizards to manipulate the apparatus in order to obtain food. Success at accomplishing that task, and the speed of that success, was lower and slower in lizards from long-colonised sites than from uninvaded sites. Our results suggest that toad invasion has modified cognitive phenotypes within populations of this apex predator, a change that might have substantial effects on other species.
Significance statement
Many studies of the impacts of biological invasions focus on the numerical effect of an invader on the abundances of native taxa, neglecting other types of impacts. Colonising taxa can also impose selection on behavioural traits of native species, generating shifts in behaviour as native taxa adapt to intruders. Such shifts in behaviour are interesting not only in their own right but also because such shifts (especially in apex predators) may influence other taxa within food webs. Importantly, the nature and magnitude of such shifts may change over time post-invasion.
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Data availability
Data are available from the Figshare repository: 10.6084/m9.figshare.12863993.
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Acknowledgements
We thank two anonymous reviewers for their suggestions to improve the manuscript.
Funding
The work was funded by the Australian Research Council (FL120100074), and LP was supported by funding from the Holsworth Wildlife Research Endowment, the Ethel Mary Read Research Grant and the Australian Wildlife Society University Grant.
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LP designed the study, performed all fieldwork, conducted the statistical analyses, and drafted the manuscript. GWF designed the study and critically revised the manuscript. RS conceived and designed the study, and critically revised the manuscript. All authors gave final approval for publication.
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All procedures were approved by the University of Sydney ethics committee (approval 2017/1202) and were carried out in accordance with relevant guidelines and regulations under licence from state and federal wildlife agencies.
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Pettit, L., Ward-Fear, G. & Shine, R. Invasion of cane toads (Rhinella marina) affects the problem-solving performance of vulnerable predators (monitor lizards, Varanus varius). Behav Ecol Sociobiol 75, 39 (2021). https://doi.org/10.1007/s00265-021-02978-6
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DOI: https://doi.org/10.1007/s00265-021-02978-6