Rapid acclimation to cold allows the cane toad to invade montane areas within its Australian range

Abstract

Summary The cane toad (Rhinella marina) invasion of Australia has now reached areas much colder than most of its native range in tropical America. Understanding the toad's ability to function in such conditions can clarify its potential for further spread. In northeastern New South Wales (NSW), cane toads have been recorded up to 1100 m above sea level (asl). Our monitoring over summer 2012–2013 confirmed that ground temperatures were lower at three high‐elevation (750–1010 m asl) sites than at two nearby lower (100–210 m asl) sites (by day, 18°C vs. 25°C; at night, 17–18°C vs. 20–25°C, respectively). Critical thermal minima (CTmins) of field‐collected toads (loss of the righting reflex) were lower for high‐elevation than low‐elevation toads (5·5°C vs. 7·5°C), but laboratory acclimation abolished this difference. A toad's CTmin was not affected by site of collection, nor by 1 month's exposure to warm (24°C) or cool (12°C) conditions; instead, a toad's CTmin was determined by its thermal exposure over the previous 12 h. Locomotor ability was affected by test temperature, by elevation and by acclimation. Toads from high elevations exhibited equal endurance at cold and warm test temperatures after month‐long acclimation to cold conditions, whereas toads from low elevations performed better at high temperatures regardless of previous temperature treatments. Cane toads at the southern edge of their expanding Australian range can function under cool conditions by adjusting their thermal tolerance within a few hours of encountering low temperatures. The toads' ability for rapid thermal acclimation suggests that current models underestimate the potential range of abiotic conditions accessible to this invading species.