Laid-back invaders: cane toads (Rhinella marina) down-regulate their stress responses as they colonize a harsh climate

In response to encountering abiotic extremes, many organisms exhibit stress responses as measured by levels of corticosterone and heat-shock protein (e.g., HSP70) in the blood. Such responses can enhance organismal viability. How quickly can those responses shift if the organisms encounter novel challenges, as occurs with climate change, or a species’ invasion into a new area? We found elevated levels of corticosterone and HSP70 in the blood of cane toads (Rhinella marina) that were desiccated, especially at low temperatures, a response that might jeopardize survival by increasing rates of water loss. Importantly, toads from the climatically equable native range in Brazil showed twofold higher levels of these stress hormones than did toads from the climatically harsh invaded range in Australia. Thus, the toads’ invasion of abiotically extreme habitats has been accompanied by a substantial down-regulation of the acute stress response.