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

Abstract

Summary1. 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. 2. 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). 3. Critical thermal minima (CTmins) of field-collected toads (loss of the righting reflex) were lower for high-elevation than low-elevation toads (5Á5°C vs. 7Á5°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. 4. 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. 5. The toads' ability for rapid thermal acclimation suggests that current models underestimate the potential range of abiotic conditions accessible to this invading species.

The Acid Test: pH Tolerance of the Eggs and Larvae of the Invasive Cane Toad (Rhinella marina) in Southeastern Australia

“…As a consequence of escaping from competitors and predators, many invasive taxa can spread into areas outside the climatic envelope occupied within their native range (Sakai et al 2001;Broennimann et al 2007;Tingley et al 2014). To assess the probability of such extensive spread, we need to identify the abiotic challenges presented by these extralimital regions and the invader's ability to tolerate those conditions (e.g., McCann et al 2014).…”

“…Native to Central America and South America, this large bufonid anuran has been translocated to more than 40 countries worldwide in misguided attempts to control insect pests (Lever 2001). Despite its origins in well-watered tropical areas, the cane toad has spread successfully in many Australian habitats that superficially appear to be climatically unsuitable, including arid, semidesert regions (Florance et al 2011;Tingley and Shine 2011) and high mountains (Newell 2011;McCann et al 2014). That success reflects broad thermal tolerances (Floyd 1984) and a flexible adjustment of activity patterns to moisture availability in the landscape (Brown et al 2011).…”

Realized niche shift during a global biological invasion

“…Since its introduction to Australia in 1935 as a biological control agent, R. marina has expanded its range to include more than 1.2 million km 2 of the continent (20). This large-scale invasion has been facilitated by thermal acclimation (21,22), as well as evolutionary shifts in locomotor performance (23). Have the environmental tolerances of toads evolved as well?…”

Ecology, Impacts, and Management of Invasive Rodents in the United States

“…They are cold intolerant and therefore are unlikely to become widespread in most parts of the continental United States. However, recent research on cane toads in New South Wales, Australia, demonstrated that toads have the ability to acclimate rapidly to low temperatures (McCann et al 2014). It has been noted that while their populations expand and increase quickly, they also experience precipitous drops in population size (Simberloff 2004).…”