An Introduced Competitor Elevates Corticosterone Responses of a Native Lizard (Varanus varius)

Abstract

Glucocorticoid hormone profiles are increasingly used as physiological markers to infer the strength of species interactions that can influence fitness and ensuing population dynamics of animals. Here we investigated two aims. First, we measured the effect of a 90-min capture stress protocol on the plasma corticosterone responses of a large native Australian lizard, the lace monitor (Varanus varius). Second, we compared the basal and postcapture stress corticosterone responses of lace monitors in habitats where they were exposed to high or low densities of the European red fox (Vulpes vulpes), an introduced competitor. Lace monitors responded to the capture stress protocol by significantly increasing plasma levels of corticosterone above basal at 45- and 90-min-postcapture blood-sampling intervals. In habitats with high fox densities, lace monitors produced a significantly greater basal and capture-stress-induced corticosterone response compared to individuals in low-fox density habitat. A significant interaction among fox density, time postcapture, and body condition was also found to influence plasma corticosterone values. These results suggest competition with red fox, perhaps via nutritional stress and increased hypersensitivity of the adrenocortical axis in lizards. At present, without further research, we do not understand whether such responses mediate lizard fitness or whether they have adaptive or maladaptive consequences for lizard populations in response to red fox competition. Nevertheless, our results help broaden understanding of the physiological implications arising from species interactions and specifically how introduced competitors could mediate diverse impacts on native biodiversity.

Stress in biological invasions: Introduced invasive grey squirrels increase physiological stress in native Eurasian red squirrels

“…Similar results were found in a system of a native lizard (the lace monitor , Varanus varius ) and an introduced alien predator (red fox, Vulpes vulpes ) in Australia. In habitats with high fox densities, lizards produced a significantly greater basal and capture stress‐induced corticosterone response compared to individuals in low–fox density habitat, suggesting competition with red foxes, perhaps via nutritional stress and increased hypersensitivity of the adrenocortical axis in lizards (Jessop et al., ). So far, it is not clear whether such responses mediate lizard fitness.…”

“…Previous studies used an approach where they compared areas without predator manipulation to areas with predator manipulation (e.g. Anson et al., ; Jessop et al., ). We used a new approach: removal over time comparing the observed changes in faecal glucocorticoid metabolites within populations using sites as independent replicates.…”

“…Previous studies used an approach where they compared areas without predator manipulation to areas with predator manipulation (e.g. Anson et al, 2013;Jessop et al, 2015).…”

“…The two most important physiological responses are the stimulation of the sympathetic nervous system (resulting in the release of catecholamines) and the activation of the hypothalamic–pituitary–adrenal (HPA) axis, resulting in the secretion of glucocorticoids (GCs), lasting several minutes to hours, which helps to restore homeostasis (Sapolsky, Romero, & Munck, ). However, while the effects of short‐term elevated GC concentrations (acute stress) can help an individual to escape from life‐threatening situations (Wingfield et al., ), activation of the HPA axis and elevated GC concentrations over a longer period of time (several weeks–months) may have negative effects on body condition, survival or reproductive output (Blas, Bortolotti, Tella, Baos, & Marchant, ; Jessop, Anson, Narayan, & Lockwood, ; Narayan, Jessop, & Hero, ; Sheriff, Krebs, & Boonstra, ). If the stressor persists and GCs remain elevated, alterations of behaviour and/or energy balance, inhibition of growth and/or reproduction (Cabezas, Blas, Marchant, & Moreno, ; Sheriff et al., ), increase in blood glucose levels, suppression of digestion (Caso, Leza, & Menchen, ) and suppression of immunity and the inflammatory response (Romero, ; St. Juliana, Khokhlova, Wielebnowski, Kotler, & Krasnov, ) can be observed.…”

“…Although there are many studies on the impact of invasive species on native species, only a few have used glucocorticoid metabolites (before and after the stressor) to investigate the degree of physiological impact of invasive predators on native species (frogs, Platymantis vitiana , Narayan, Cockrem, & Hero, ; Narayan et al., ; iguanas or lizards, Amblyrhynchus cristatus , Berger et al., ; Urosausus ornatus , Graham, Freidenfelds, McCormick, & Langkilde, ; Varanus varius, Anson et al., ; Jessop et al., ).…”