Pigment cell distribution in a rapid colour changing amphibian (Litoria wilcoxii)

Abstract

Rapid skin colour changes in amphibians and other colour changing animals are possible due to different distributions of pigment cells (chromatophores) and the movement of pigment within them. Amphibians possess three types of chromatophore: xanthophores, iridophores and melanophores which are collectively referred to as the dermal chromatophore unit. Male stony creek frogs (Litoria wilcoxii) are capable of undergoing rapid colour change from brown to yellow during amplexus. Based on previous studies, it is expected that this is achieved through a change in chromatophore distribution or pigment movement within chromatophores. We examined brown and yellow dorsal skin samples from male L. wilcoxii using light microscopy which allowed us to determine differences in chromatophore and pigment distribution between each colour phase. Additionally, we compared thigh skin sections, which are comprised of permanently yellow and black patches. We found that in dorsal skin sections of yellow frogs, melanophore pigment granules had aggregated to the centre of the melanophore underneath the yellow xanthophore, whilst pigment was dispersed throughout the melanophores, partially covering the xanthophores in brown frogs. Black thigh sections consisted of elongated melanophores, other cell types appeared to be absent. In contrast, yellow thigh sections contained only xanthophores. This study demonstrates that the process of colour change in L. wilcoxii is through pigment aggregation and dispersion within melanophores. In addition, we show that there is significant variation in pigment cell distribution between colour changing and non-colour changing integument.