Geographical divergence of behavioural traits in the invasive cane toad (Rhinella Marina)

Abstract

Understanding which traits drive the success of invasive species is vital to mitigate their impacts. Ongoing invasions provide an opportunity to examine how different selection pressures across the invasion range lead to divergence in traits. Invasion-front cane toads in Australia exhibit rapid evolution of morphological and physiological dispersal-related traits. Behavioural traits may evolve in similar ways. High exploration, risk-taking, attraction to novelty (neophilia) and sociality may drive invasion success as these traits may enhance dispersal and adaptation to novel environments. My PhD tested this prediction using laboratory trials to examine divergence in behaviour in long-colonised versus invasion-front populations across the toads’ invaded range. I tested exploration, risk-taking, neophilia and sociality in wild-caught toads from the range-edge and range-core of their tropical Australian invasion. I ran the same trials using common-garden raised toads to tease apart genetic from environmental effects on behavioural divergence. I also investigated climate effects on behavioural divergence; conducting trials using invasive cane toads from wet and dry climates in Hawai’i. I found strong divergence in behaviours that enhance dispersal and adaptation to novel environments across the cane toads’ invasion range. Invasion-front toads were more exploratory, risk-taking, neophilic and social than were conspecifics from long-colonised populations from Australia and Hawai’i. Common-garden raised toads exhibited the same pattern of divergence seen in wild-caught Australian toads, suggesting a heritable component. My research reveals that differential selection on behavioural responses to novel environments in long-colonised versus invasion-front populations has led to a distinctive highly exploratory, risk-taking, neophilic and social phenotype at the invasion-front.