Abstract
Physiological plasticity may facilitate invasion of novel habitats; but is such plasticity present in all populations of the invader or is it elicited only by specific climatic challenges? In cold-climate areas of Australia, invasive cane toads (Rhinella marina) can rapidly acclimate to cool conditions. To investigate whether this physiological plasticity is found in all invasive cane toads or is only seen in cool climates, we measured the acclimation ability of toads from across Australia and the island of Hawai'i. We collected toads from the field and placed them at either 12 or 24°C for 12 h before measuring their righting response as a proxy for critical thermal minimum (CTmin). Toads from the coolest Australian region (New South Wales) demonstrated plasticity (as previously reported), with exposure to 12°C (vs. 24°C) decreasing CTmin by 2°C. In toads from other Australian populations, CTmins were unaffected by our thermal treatments. Hawai'ian toads from a cool, wet site also rapidly acclimated to cool conditions, whereas those from warmer and drier Hawai'ian sites did not. Thermal plasticity has diverged among populations of invasive cane toads, with rapid acclimation manifested only in two cool-climate populations from widely separated sites. Predictions about the potential range of invasive species thus must consider the possibility of geographic (intraspecific) heterogeneity in thermal plasticity; data from other parts of the species' range may fail to predict levels of plasticity elicited by thermal challenges.
Highlights
Understanding how invasive species flourish in particular environments is essential for accurately predicting the invader’s impact and informing management
Toads from Tom’s Farm near Volcano (TV) showed a similar response to those from New South Wales (NSW), with individuals acclimated to 12°C exhibiting a critical thermal minimum (CTmin) 2°C lower than those acclimated to 24°C (F1,21 = 7.04, P = 0.01; Fig. 3a)
At Mauna Lani (ML) toads showed the opposite pattern to TV, with toads acclimated to 12°C displaying a CTmin 2°C higher than those acclimated to 24°C (F1,19 = 6.44, P = 0.02; Fig. 3d)
Summary
Understanding how invasive species flourish in particular environments is essential for accurately predicting the invader’s impact and informing management. May occur when an invader encounters novel environments (Phillips et al, 2007; Whitney and Gabler, 2008; Kolbe et al, 2010; Tingley et al, 2012) either via plasticity (direct modifications in response to environmental factors: Agrawal, 2001) or through the evolution of trait values over time (Prentis et al, 2008) or through space (spatial sorting: Shine et al, 2011). Changes can occur over many timescales, for example rapid ‘cold-hardening’ in plants in response to frost (Beck et al, 2004) or more gradual physiological adjustment (e.g. seasonal thermal acclimatization: Piersma and van Gils, 2010). Incorporating information on variation and flexibility of traits may improve the accuracy of predictions of invader spread
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