Abstract
Individuals at the leading edge of expanding biological invasions often show distinctive phenotypic traits, in ways that enhance their ability to disperse rapidly and to function effectively in novel environments. Cane toads (Rhinella marina) at the invasion front in Australia exhibit shifts in morphology, physiology and behaviour (directionality of dispersal, boldness, risk-taking). We took a common-garden approach, raising toads from range-core and range-edge populations in captivity, to see if the behavioural divergences observed in wild-caught toads are also evident in common-garden offspring. Captive-raised toads from the invasion vanguard population were more exploratory and bolder (more prone to ‘risky’ behaviours) than toads from the range core, which suggests that these are evolved, genetic traits. Our study highlights the importance of behaviour as being potentially adaptive in invasive populations and adds these behavioural traits to the increasing list of phenotypic traits that have evolved rapidly during the toads' 80-year spread through tropical Australia.
Highlights
Individuals at the leading edge of expanding biological invasions often show distinctive phenotypic traits, in ways that enhance their ability to disperse rapidly and to function effectively in novel environments
The two broad categories of explanation involve (i) behavioural plasticity, induced by the novel environments experienced at the range edge and (ii) the rapid elaboration of heritable traits driven by the unique evolutionary pressures imposed by an invasion
The distinctive behavioural traits seen at expanding range edges may result from both adaptive and non-adaptive processes
Summary
Individuals at the leading edge of expanding biological invasions often show distinctive phenotypic traits, in ways that enhance their ability to disperse rapidly and to function effectively in novel environments. A propensity to explore, take risks and engage with novel environments (neophilia) is likely to promote range expansion by stimulating dispersal [12,13], and these traits enhance an individual’s ability to find water, food, shelter and mates in novel environments [11,14,15] In keeping with these predictions, behavioural traits have been linked to range expansion and invasion success in several species. The two broad categories of explanation involve (i) behavioural plasticity, induced by the novel environments experienced at the range edge and (ii) the rapid elaboration of heritable traits driven by the unique evolutionary pressures imposed by an invasion
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