Abstract
The ability to change colour rapidly is widespread among ectotherms and has various functions including camouflage, communication and thermoregulation. The process of colour change can occur as an aperiodic event or be rhythmic, induced by cyclic environmental factors or regulated by internal oscillators. Despite the importance of colour change in reptile ecology, few studies have investigated the occurrence of a circadian rhythm in lizard pigmentation. Additionally, although colour change also entails changes in near-infrared reflectance, which may affect thermoregulation, little research has examined this part of the spectrum. We tested whether the bearded dragon lizard, Pogona vitticeps, displays an endogenous circadian rhythm in pigmentation changes that could be entrained by light/dark (LD) cycles and how light affected the relative change in reflectance in both ultraviolet-visible and near-infrared spectra. We subjected 11 lizards to four photoperiodic regimens: LD 12∶12; LD 6∶18; LD 18∶6 and DD; and measured their dorsal skin reflectance at 3-hour intervals for 72 hours after a habituation period. A proportion of lizards displayed a significant rhythm under constant darkness, with maximum reflectance occurring in the subjective night. This endogenous rhythm synchronised to the different artificial LD cycles, with maximum reflectance occurring during dark phases, but did not vary in amplitude. In addition, the total ultraviolet-visible reflectance in relation to the total near-infrared reflectance was significantly higher during dark phases than during light phases. We conclude that P. vitticeps exhibits a circadian pigmentation rhythm of constant amplitude, regulated by internal oscillators and that can be entrained by light/dark cycles.
Highlights
Colour change is widespread in the animal kingdom, especially in ectothermic animals [1], including crustaceans [2], cephalopods [3], insects [4], amphibians [5], reptiles [6] and fishes [7]
This study investigated the circadian pigmentation rhythm in the central bearded dragon lizard P. vitticeps
A proportion of lizards (45.5%) displayed an endogenous circadian rhythm in dorsal skin reflectance, oscillating between a maximum occurring in the subjective night and a minimum occurring in the subjective day
Summary
Colour change is widespread in the animal kingdom, especially in ectothermic animals [1], including crustaceans [2], cephalopods [3], insects [4], amphibians [5], reptiles [6] and fishes [7]. Colour change is mediated by chromatophores (pigment cells that originate from the neural crest and migrate to the integument) and can be classified as two types [1]. Physiological colour change is induced by the migration of pigment-containing organelles within chromatophores and is much more rapid, occurring in a matter of seconds to hours. Physiological colour change can occur either as a singular event or a cyclic event (i.e. display rhythmicity) which may be elicited by environmental stimuli or mediated by neural and/or endocrine systems [1]. Adaptive colour change that occurs in response to specific stimuli (e.g. predators, conspecifics) has been widely studied, the occurrence and regulation of rhythmic colour change has received much less attention
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