The Dermal Chromatophore Unit

Abstract

Rapid color changes of amphibians are mediated by three types of dermal chromatophores, xanthophores, iridophores, and melanophores, which comprise a morphologically and physiologically distinct structure, the dermal chromatophore unit. Xanthophores, the outermost element, are located immediately below the basal lamella. Iridophores, containing light-reflecting organelles, are found just beneath the xanthophores. Under each iridophore is found a melanophore from which processes extend upward around the iridophore. Finger-like structures project from these processes and occupy fixed spaces between the xanthophores and iridophores. When a frog darkens, melanosomes move upward from the body of the melanophore to fill the fingers which then obscure the overlying iridophore. Rapid blanching is accomplished by the evacuation of melanosomes from these fingers. Pale coloration ranging from tan to green is provided by the overlying xanthophores and iridophores. Details of chromatophore structure are presented, and the nature of the intimate contact between the chromatophore types is discussed.

Individual colour patches as multicomponent signals

“…They distinguished among (1) multiple messages, in which different traits indicate different aspects of signaler quality ; (2) redundant signals, which together indicate overall signaler quality ; and (3) unreliable signals, which are arbitrary traits not correlated with signaler quality. The outcomes of these and other models of multiple trait evolution rely on the costs to receivers of assessing multiple traits (Iwasa & Pomiankowski, (Bagnara et al, 1968 ;Bagnara & Hadley, 1973) of a hypothetical green frog, showing how the xanthophore, iridophore, melanophore and underlying fascia layers interact to determine the overall colour of the animal. Wavy lines depict the paths of light of differing wavelengths through the cell layers.…”

“…The dermal chromatophore unit model (Bagnara et al, 1968 ;Bagnara & Hadley, 1973) describes how the xanthophore, iridophore and melanophore layers interact to determine the overall reflectance spectrum of a colour patch (see Fig. 1).…”

“…The multilayer colour patch model that we derive below is essentially a mathematical representation of the dermal chromatophore unit model of Bagnara et al (1968) and Bagnara & Hadley (1973), with some modifications to take into account our current understanding of how chromatophores work (reviewed in Fujii, 1993 ;Herring, 1994). Although the model is intended to apply to all species with dermal chromatophores, it was necessary to use specific parameter values, and to make assumptions about ambient lighting conditions and the visual system of the receiver, before the features of the model could be explored.…”

“…melanin, carotenoid and pteridine), in reality, colour patches are multilayered, three-dimensional structures that often contain multiple pigment types and structural features. The standard dermal chromatophore unit (Bagnara, Taylor & Hadley, 1968;Bagnara & Hadley, 1973) of poikilothermic vertebrates consists of three contiguous cell layers (Fig. 1).…”

The Cellular Expression and Genetics of Purple Body (Pb) inPoecilia reticulata, and its Interactions with Asian Blau (Ab) and Blond (bb) under Reflected and Transmitted Light

“…violet-blue iridophore, leucophore and crystalline platelets (Fig 53-54) were 636 found resident in low numbers in dissected deep tissue. Their presence at 637 these locations is well below the dermis (Bagnara 1968 …”