Loss-of-function mutations in ASIP and MC1R are associated with coat colour variation in marsupials

Pigmentation in mammalian hair follicles is governed in part by interactions between agouti signalling protein (ASIP) and the melanocortin 1 receptor (MC1R). The most common coat colours in mammals result from alternating bands of dark eumelanin and light phaeomelanin within individual hair shafts. However, coats dominated by a single melanin have arisen several times. Here, we examine the genetic basis of two instances in marsupials: a melanistic morph of the eastern quoll (Dasyurus viverrinus) found at high frequency in the wild, and a rare case of fixed xanthism in the marsupial moles. In eastern quolls, we identify a deletion encompassing the ASIP start codon which was found to be homozygous only in the melanistic animals examined. This mutation appears to be convergent with that recently discovered in its dark-coated relative, the Tasmanian devil (Sarcophilus harrisii). Conversely, we show that a non-sense mutation which severely truncates MC1R in the southern marsupial mole (Notoryctes typhlops) is a candidate driver of its pale-yellow coat. Together with other recent findings, our results suggest that loss-of-function mutations have occurred repeatedly within the marsupials, representing a mechanism underpinning coat colour variation.