Ghost rodents: Albinism in Australian rodent species

Abstract

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.

Keywords: Muridae; albino; mammal; mouse; pelage; rat.

FIGURE 1

Map showing the locations of the camera traps deployed to survey rakali on Barrow Island, Western Australia.

FIGURE 2

Images of two preserved albino rodent bodies identified from our survey of Australian museums: (a) dorsal image of a canefield rat (Rattus sordidus), which was labeled as ‘semi‐albino’ from the Australian Museum (New South Wales) but appears to have no pigmentation in the skin or fur except a faint pale gray at the base of the dorsal hairs (pers. comm. Sandy Ingleby; image credit Sandy Ingleby); (b) ventral image of the same canefield rat (image credit Sandy Ingleby); (c) image of a captive‐born long‐haired rat (R. villosissimus) from the South Australian Museum. No data were available on the founder source location or generation of the captive‐born animals (image credit David Stemmer).

FIGURE 3

Photographs of free‐ranging albino rodents native to Australia; (a) a female albino rakali (Hydromys chrysogaster) on Barrow Island, Western Australia (image credit: Keith Morris); (b) an albino bush rat (Rattus fuscipes) captured on a camera trap in the Otway Ranges, Victoria (image credit: Michael Loughnan); (c) a female albino bush rat from the Otway Ranges, Victoria, exhibiting the off‐white/straw colored pelage not uncommon with albino mammals; this rat also had red, as opposed to pink, eyes (image credit: Darcy Watchorn); (d) a male albino heath mouse (Pseudomys shortridgei) from the Grampians National Park, Victoria (image credit: Susie Hale); (e) an albino rakali observed on Barrow Island (image credit: Pendoley Environmental); (f) an albino rakali observed on Barrow Island (image credit: Pendoley Environmental).

FIGURE 4

Photographs of free‐ranging rakali from the camera trap survey on Barrow Island, Western Australia, undertaken from October 2019–January 2021: (a) an image of a non‐albino rakali from site RA36, (b) an image of an albino rakali from site RA36, (c) an image of a non‐albino rakali from site RA02, and (d) an image of an albino rakali from site RA02.

FIGURE A1

Flow diagram outlining the screening of the albino rodent literature from the Trove digitized newspaper database, resulting in the final list of 24 articles/free‐ranging albino records.