The occurrence of hypomelanism in a population of Irwin's turtles (Elseya irwini) was found to affect only adult turtles (approximately 10%), primarily females. Its complete absence in immature and hatchling turtles indicates that the condition develops ontogenetically through the progressive, localized loss of specific types of chromatophores. Hypomelanistic females were lacking in a variety of pigments affecting virtually all parts of the body and appeared to represent extreme forms of the natural depigmentation process that accompanies maturation in this species.

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