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Rally for the rakali

The rakali is an Australian native rodent first described in 1804. It's scientific name, Hydromys chrysogaster, translates to "golden-bellied water mouse”. Rakali is the name given to the species by the Aboriginal people from the Murray River area. The species is also known as rabe or water-rat. It is a distinctive Australian rodent specialised for an aquatic existence, with broad partially webbed hind-feet, water-repellent fur, and abundant whiskers. It is the largest rodent in Australia, often weighing more than 1 kilogram!

The Australian water rat (Hydromys chrysogaster). Photo Credits and acknowledgements - Lizette Salmon, via (CC BY-NC 4.0)

Among murid rodents, semiaquatic species have evolved at least three times, including (1) Hydromys and relatives on New Guinea, (2) Nilopegamys and relatives of Africa, and (3) Waiomys of Sulawesi, Indonesia. The rakali is one of four species in the genus Hydromys, and it is the only one with a range extending beyond Papua New Guinea and Indonesian West Papua.

Having adapted to a unique niche of a semiaquatic and nocturnal lifestyle, this species lives in burrows on the banks of rivers, lakes and estuaries. The rakali have a diverse diet of aquatic insects, fish, small vertebrates, birds' eggs and water birds. There is some sexual dimorphism present in the rakali, with females being generally smaller than males. However, the thick and muscular tails, which help serve as a rudder when swimming, remain the same size in both genders.

At the beginning of the century, the rakali was considered a pest and were widely hunted for their soft fur which caused the wild population to drastically decrease. Humans have been their greatest predator, with rakali requiring protection by legislation in 1938. Since this legislation, wild populations have recovered in all Australian states except for Western Australia where the rakali is still at a “near threatened” status.

To support ongoing conservation efforts, DNA Zoo teamed up with Museums Victoria Senior Curator of Mammals Kevin C. Rowe to release the chromosome-length assembly for the rakali, Hydromys chrysogaster. The genome draft was generated with short-insert size Illumina reads [481, 563, 388 PE reads] and scaffolded to chromosome length with Hi-C [770, 408, 993 PE reads]. See our Methods page for more assembly details. Browse the 24 chromosomes (2n=48) of the rakali in the interactive Juicebox.js session below:

This work was enabled by resources provided by DNA Zoo Australia, The University of Western Australia (UWA) and DNA Zoo, Aiden Lab at Baylor College of Medicine (BCM) with additional computational resources and support from the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia.

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