Is the behavioural divergence between range-core and range-edge populations of cane toads (Rhinella marina) due to evolutionary change or developmental plasticity?

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.

Keywords: Bufo marinus; adaptation; evolution; spatial sorting.

Figure 1.

Behavioural traits of cane toads from wild-caught and captive-raised populations of Western Australian (range-edge) and Queensland (range-core) origin. Graphs show mean values and associated standard errors (where relevant) for traits measured during trials of exploratory behaviour (time spent moving, rate of movement), risk-taking (emerged from shelter, latency to emerge) and neophilia (approached novel object, time with novel object).