Behavioural flexibility allows an invasive vertebrate to survive in a semi-arid environment

Abstract

Plasticity or evolution in behavioural responses are key attributes of successful animal invasions. In northern Australia, the invasive cane toad (Rhinella marina) recently invaded semi-arid regions. Here, cane toads endure repeated daily bouts of severe desiccation and thermal stress during the long dry season (April-October). We investigated whether cane toads have shifted their ancestral nocturnal rehydration behaviour to one that exploits water resources during the day. Such a shift in hydration behaviour could increase the fitness of individual toads by reducing exposure to desiccation and thermal stress suffered during the day even within terrestrial shelters. We used a novel method (acoustic tags) to monitor the daily hydration behaviour of 20 toads at two artificial reservoirs on Camfield station, Northern Territory. Remarkably, cane toads visited reservoirs to rehydrate during daylight hours, with peaks in activity between 9.00 and 17.00. This diurnal pattern of rehydration activity contrasts with nocturnal rehydration behaviour exhibited by adult toads in their native geographical range and more mesic parts of Australia. Our results demonstrate that cane toads phase shift a key behaviour to survive in a harsh semi-arid landscape. Behavioural phase shifts have rarely been reported in invasive species but could facilitate ongoing invasion success.

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

“…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). For example, cane toads have colonized arid sites by modifying their times and places of activity and their desiccation thresholds for movement (Tingley and Shine 2011;Tingley et al 2012;Webb et al 2014). They have colonized high, cold montane areas by rapidly adjusting their critical thermal minima (McCann et al 2014).…”

Restricting access to invasion hubs enables sustained control of an invasive vertebrate

“…; Webb et al . ). During periods of dry and hot climatic conditions, typical of semi‐arid regions, high desiccation rates, thermal stress and limited moisture availability restrict cane toads to moist microhabitats such as sites with standing water or underground shelter sites (Reynolds & Christian ; Brown, Kelehear & Shine ; Doody et al .…”

“…; Webb et al . ), but unlike most native Australian desert‐dwelling frogs, which possess physiological adaptations (cocoon formation, aestivation, reduced metabolic rate) to survive long dry periods (Withers ), cane toads cannot physiologically control evaporative water loss through their skin and must use behavioural means to maintain homeostasis (Seebacher & Alford ; Letnic et al . ; Webb et al .…”

“…The cane toad has spread through more than 1 million km 2 of Australia since its introduction to Queensland in 1935 (Shine 2010). Cane toads are now invading semi-arid and arid regions of the continent (Kearney et al 2008;Webb et al 2014), but unlike most native Australian desert-dwelling frogs, which possess physiological adaptations (cocoon formation, aestivation, reduced metabolic rate) to survive long dry periods (Withers 1998), cane toads cannot physiologically control evaporative water loss through their skin and must use behavioural means to maintain homeostasis (Seebacher & Alford 2002;Letnic et al 2014b;Webb et al 2014). During periods of dry and hot climatic conditions, typical of semi-arid regions, high desiccation rates, thermal stress and limited moisture availability restrict cane toads to moist microhabitats such as sites with standing water or underground shelter sites (Reynolds & Christian 2009;Brown, Kelehear & Shine 2011;Doody et al 2014).…”

“…During periods of dry and hot conditions, cane toads only occupy and hence select habitats with permanent water such as natural water holes and bore-fed dams ( Fig. 1b: which supply water to livestock) (Letnic et al 2014a,b;Webb et al 2014).…”