The effect of stress and stress hormones on dynamic colour-change in a sexually dichromatic Australian frog

Abstract

Rapid colour changes in vertebrates have fascinated biologists for centuries, herein we demonstrate dynamic colour change in an anuran amphibian, the stony creek frog (Litoria wilcoxii), which turns from brown to bright (lemon) yellow during amplexus. We show this by comparing the colour of baseline (unpaired males) and amplecting (paired) males. We also investigate the possible role of stress and stress hormones on this colour change. Frogs were subjected to four different levels of stressors (handling, toe-clipping, saline injection and adrenocorticotropic hormone [ACTH] injection) and the colour change was measured using digital photography. A comparison of baseline colour and stress hormone (corticosterone) levels was also conducted to give further insight to this topic. From the images, the Red Blue Green (RGB) colour values were calculated, and a principal components analysis (PCA) was used to create a single colour metric (the major axis) as an index of colour in the visible spectrum. A moderate stressor (toe-clipping) led to a significant change in colour (within 10 min) similar to that of amplecting males. Surprisingly, neither a mild stressor (handling and saline injection) nor the maximum stressor (handling and ACTH injection) led to a lightening response. This study confirms that the dynamic male colour change in this species in response to medium stressors adds new knowledge to the understanding of the functional mechanisms of dynamic colour change in amphibians.

60 YEARS OF POMC: Melanocortin receptors: evolution of ligand selectivity for melanocortin peptides

“…In addition, chronic stressors will promote the release of ACTH from the anterior lobe of the pituitary that can also activate MC1R receptors on human melanocytes (Costin & Hearing 2007). This chronic stress response on integument color change by the anterior pituitary also appears to occur for an amphibian and a reptile (Greenberg 2002, Kindermann et al 2013.…”

Physiological Stress Responses in Amphibian Larvae to Multiple Stressors Reveal Marked Anthropogenic Effects even below Lethal Levels

“…The HPI axis modulates a hormonal cascade resulting in the activation of the interrenal gland and glucocorticoid (GC) production: corticosterone (CORT) in amphibians, reptiles, and birds and cortisol in most mammals and fish (Romero 2004). GCs elicit the mobilization of energetic metabolic substrates (e.g., lipids; Peckett et al 2011), which affect essential functions of the organism such as reproduction, behavior, and growth (Denver et al 2002;Schoech et al 2009;Kindermann et al 2013), thus conditioning the transition between life-history stages (Crespi et al 2013). Prolonged secretion of CORT has been associated with mobilization of energetic substrates and increased metabolic demands in multiple tissues (Peckett et al 2011;Lattin and Romero 2015) while resulting in reduced long-term survival (Bonier et al 2009).…”

Sight of a Predator Induces a Corticosterone Stress Response and Generates Fear in an Amphibian

“…The glucocorticoid hormone corticosterone, the major stress hormone in amphibians (also found in birds, reptiles and many rodents), is secreted by the HPI-axis when individuals respond to a stressor [1–5]. This short-term increase in corticosterone promotes key changes in behaviour and physiology that enable individuals to cope with stress [6–10]. Some of the key behaviours affected by corticosterone in amphibians and also in other vertebrates (small mammals and lizards) include initiation of hiding and defensive behaviours [11–13], increased locomotor activity [14,15], and increased thermoregulatory behaviour [16,17].…”