title: Interplay among nocturnal activity, melatonin, corticosterone and performance in the invasive cane toad (Rhinella marinus).
abstract: Most animals conduct daily activities exclusively either during the day or at night. Here, hormones such as melatonin and corticosterone, greatly influence the synchronization or regulation of physiological and behavioral cycles needed for daily activity. How then do species that exhibit more flexible daily activity patterns, responses to ecological, environmental or life-history processes, regulate daily hormone profiles important to daily performance? This study examined the consequences of (1) nocturnal activity on diel profiles of melatonin and corticosterone and (2) the effects of experimentally increased acute melatonin levels on physiological and metabolic performance in the cane toad (Rhinella marinus). Unlike inactive captive toads that had a distinct nocturnal melatonin profile, nocturnally active toads sampled under field and captive conditions, exhibited decreased nocturnal melatonin profiles with no evidence for any phase shift. Nocturnal corticosterone levels were significantly higher in field active toads than captive toads. In toads with experimentally increased melatonin levels, plasma lactate and glucose responses following recovery post exercise were significantly different from control toads. However, exogenously increased melatonin did not affect resting metabolism in toads. These results suggest that toads could adjust daily hormone profiles to match nocturnal activity requirements, thereby avoiding performance costs induced by high nocturnal melatonin levels. The ability of toads to exhibit plasticity in daily hormone cycles, could have broad implications for how they and other animals utilize behavioral flexibility to optimize daily activities in response to natural and increasingly human mediated environmental variation.
authors: Department of Zoology, University of Melbourne, Victoria 3010, Australia. Electronic address: tjessop@unimelb.edu.au.
authors: Tim S
authors: TS
authors: Jessop
authors: Department of Zoology, University of Melbourne, Victoria 3010, Australia.
authors: Tim
authors: T
authors: Dempster
authors: School of Biological, Earth and Environmental Sciences, The University of New South Wales, NSW 2052, Australia.
authors: Mike
authors: M
authors: Letnic
authors: School of the Environment, University of Technology, Broadway, NSW 2007, Australia.
authors: Jonathan K
authors: JK
authors: Webb
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents / Q000097:blood / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology; D002024:Bufo marinus / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D003345:Corticosterone / Q000097:blood / Q000494:pharmacology*; D058865:Introduced Species; D008550:Melatonin / Q000097:blood / Q000494:pharmacology*; D016192:Resting Phase, Cell Cycle / Q000187:drug effects*; D013312:Stress, Physiological / Q000187:drug effects
chemical_list: D000893:Anti-Inflammatory Agents; D000975:Antioxidants; D008550:Melatonin; D003345:Corticosterone
keywords: Behavioral flexibility; Ecology; Environmental variation; Hormonal plasticity; Organismal performance; Sleep–wake cycles