One Hundred Twenty Years of Koala Retrovirus Evolution Determined from Museum Skins
María C. Ávila-Arcos†,1, Simon Y.W. Ho†,2, Yasuko Ishida†,3, Nikolas Nikolaidis†,4,5, Kyriakos Tsangaras6, Karin Hönig6, Rebeca Medina4,5, Morten Rasmussen1, Sarah L. Fordyce1, Sébastien Calvignac-Spencer7, Eske Willerslev1,M. Thomas P. Gilbert1, Kristofer M. Helgen8, Alfred L. Roca*,3, and Alex D. Greenwood*,6
1Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark
2School of Biological Sciences, University of Sydney, New South Wales, Australia
3Department of Animal Sciences, University of Illinois at Urbana-Champaign
4Department of Biological Science, California State University, Fullerton
5Center for Applied Biotechnology Studies, California State University, Fullerton
6Leibniz-Institute for Zoo and Wildlife Research, Berlin, Germany
7Robert-Koch-Institut, Emerging Zoonoses, Berlin, Germany
8National Museum of Natural History, Smithsonian Institution, Washington, DC
†These authors contributed equally to this work.
*Corresponding authors: E-mail: ; .
Associate editor: Beth Shapiro
Although endogenous retroviruses are common across vertebrate genomes, the koala retrovirus (KoRV) is the only retrovirus known to be currently invading the germ line of its host. KoRV is believed to have first infected koalas in northern Australia less than two centuries ago. We examined KoRV in 28 koala museum skins collected in the late 19th and 20th centuries and deep sequenced the complete proviral envelope region from five northern Australian specimens. Strikingly, KoRV env sequences were conserved among koalas collected over the span of a century, and two functional motifs that affect viral infectivity were fixed across the museum koala specimens. We detected only 20 env polymorphisms among the koalas, likely representing derived mutations subject to purifying selection. Among northern Australian koalas, KoRV was already ubiquitous by the late 19th century, suggesting that KoRV evolved and spread among koala populations more slowly than previously believed. Given that museum and modern koalas share nearly identical KoRV sequences, it is likely that koala populations, for more than a century, have experienced increased susceptibility to diseases caused by viral pathogenesis.