Abstract
Amphibians in hot climates may be able to avoid high temperatures by controlling their rates of heating. In northern Australia, invasive cane toads (Rhinella marina) experience hot dry conditions in newly-colonized (western) sites but milder conditions in longer-occupied (eastern) sites. Under standardized conditions, toads from western sites heated less rapidly than did conspecifics from an eastern site. The availability of free water slowed heating rates of eastern but not western toads. Thus, the colonization of climatically extreme sites has been accompanied by a rapid shift in the toads’ ability to remain cool under hot conditions, even when free water is not available.
Highlights
Amphibians in hot climates may be able to avoid high temperatures by controlling their rates of heating
Body mass influenced the rate of heating [temperature at 20 min into the trials and heating rate declined with toad mass (r2 = 0.20, n = 32, P < 0.01)]
Toads from a population that experiences a relatively brief period of hot dry conditions each year (Townsville) heated faster than did conspecifics from locations that experienced hotter drier conditions for extended periods, and this disparity was greatest if the toads did not have access to free water (Figs. 2, 4)
Summary
Amphibians in hot climates may be able to avoid high temperatures by controlling their rates of heating. Most adult anuran amphibians are nocturnally active, avoiding diurnal thermal conditions by remaining within moist and shaded retreat-sites by day[2,3] If such sites are scarce, physiological control over the rate of heating may enable an anuran to keep its body temperature below lethal levels[4,5,6]. If the newly-invaded habitat is dry as well as hot, that physiological control over heating rate ideally should not depend upon access to free water. If toads are capable of physiological control over their rates of heating, we predict that individuals from cooler and moister eastern populations will heat up more rapidly than do conspecifics from the hotter and drier western populations. We predict that access to free water will allow toads from eastern populations to heat up less rapidly (because they utilize water for evaporative cooling) whereas the western toads will not depend on free water to curtail rates of heating
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