Colour Confusion: Reviewing Ambiguities in the Identification and Classification of Chromatophore Deficiencies Among Amphibians

The colour of amphibian skin and eyes (retina and iris) is the result of light interacting with cells called chromatophores, primarily xanthophores, iridophores and melanophores, that can be found in various combinations. Thus, identifying the chromatophores involved in colour abnormalities in this group is challenging, particularly if it is solely based on a visual comparison of atypical versus typical individuals, as light may be interacting with several types of chromatophores at once. As most records of colour aberrations will likely continue to be based on visual assessments without the procurement of tissue samples, given that these observations are generally opportunistic, there is a need for consistency in how they are classified and explained so that the potential chromatophores that are affected can be deduced. Yet, this is complex as the outcome of different chromatophore defects may differ between species, especially when there are spatial differences in where the defects occur between tissue regions or combinations of abnormalities, while in the presence of other chromatophore types that remain unaffected. In this review, I explore the ambiguity and confusion that currently exists within the literature with regard to terminology used to define colour aberrations among amphibians and the specific types of chromatophores that are assumed to be the basis of colour abnormalities based upon visual assessments. I subsequently establish standards for the terminology and description of colour abnormalities among amphibians, specifically those related to chromatophore deficiencies: hypo-melanism, hypo-xanthism and hypo-iridism. This is followed by guidelines for collecting data on the physical manifestation of chromatophore deficiencies to prevent future ambiguity or errors.