Ghost rodents: Albinism in Australian rodent species

While almost half of all mammal species are rodents, records of albinism in free-ranging rodents are very rare. Australia has a large and diverse assemblage of native rodent species, but there are no records of free-ranging albino rodents in the published literature. In this study, we aim to improve our understanding of the occurrence of albinism in Australian rodent species by collating contemporary and historic records of this condition and providing an estimate of its frequency. We found 23 records of albinism (i.e., a complete loss of pigmentation), representing eight species, in free-ranging rodents native to Australia, with the frequency of albinism being generally <0.1%. Our findings bring the total number of rodent species in which albinism has been recorded globally to 76. While native Australian species represent only 7.8% of the world's murid rodent diversity, they now account for 42.1% of murid rodent species known to exhibit albinism. We also identified multiple concurrent albino records from a small island population of rakali (Hydromys chrysogaster) and discuss the factors that may contribute to the relatively high frequency (2%) of the condition on this island. We suggest that the small number of native albino rodents recorded in mainland Australia over the last 100 years means that traits associated with the condition are likely deleterious within populations and are thus selected against.

Automated summary

While nearly half of mammal species are rodents, albinism in free-ranging rodents is rare. This study focuses on Australian rodent species and found 23 records of albinism, representing 8 species, with a frequency generally less than 0.1%. Australian rodents now account for 42.1% of known murid rodent species with albinism. Factors contributing to the relatively high frequency of albinism on a small island population of rakali are discussed.