Late Pleistocene Musk Ox Populations Contracted and Expanded Naturally Without Going Extinct

While some cold-adapted mammals of the Northern Hemisphere went extinct during the cold-to-warm and warm-to-cold oscillations of climate that have occurred between the present and 60 thousand years ago (kya), other species survived. Musk ox (Ovibos moschatus) are one of those survivors, despite their clear preference for extreme cold and dry conditions. Although musk ox were relatively abundant and widespread during the Pleistocene, they still thrive within a restricted range across the Canadian Arctic and Greenland (with a few transplanted populations living in other Arctic regions, such as Svalbard and Alaska). According to the IUCN Red List of Threatening Species, the musk ox is of "least concern" (Gunn and Forchhammer, 2008).

Campos and her co-authors (Campos et al., 2010) used analyzed mitochondrial DNA (mtDNA, 682 bp of the control region) from 149 radio-carbon dated samples of musk ox that ranged in age from approximately 56,900 ¹⁴C years BP to the present. Known genetic sequences from modern animals (compiled previously by other researchers) were pooled with the ancient data. A "combined temporal and spatial analysis" of all dated ancient samples was employed, generating a "Bayesian skyride" reconstruction of changes in genetic diversity over time.

The authors state: "Our results reveal that musk ox genetic diversity was much higher during the Pleistocene than at present, and has undergone several expansions and contractions over the past 60,000 years." Diversity was high between 80-60kya (during Marine Isotope Stage 4, MIS 4), when it was relatively cold, and then declined during MIS 3, 50-33kya, when it had warmed up. When it got cold again during the Last Glacial Maximum (LGM)-the last Ice Age-musk ox genetic diversity increased rapidly, only to decline steeply during the warm period leading into the Holocene (starting about 18kya). Surprisingly, genetic diversity increased again somewhat during the mid-Holocene (about 4.5kya), after the musk ox moved into Greenland. The size of the Greenland musk ox population increased rapidly after arrival, even though humans arrived there at about the same time.

Musk ox appear to have been more affected by climate change over the last 60ky than by human hunting, in contrast to some other large-bodied, cold-adapted Pleistocene mammals (Lorenzen et al., 2011). Thus, despite a very large decrease in geographic range over time and two pronounced declines in genetic diversity, musk ox currently maintain thriving populations across the Arctic. Recovery from dramatic declines in population size and genetic diversity is clearly not only possible but has occurred more often than previously assumed (Lorenzen et al., 2011). Such results have implications for the resilience of other Arctic-adapted species that are suggested to be at future risk from the effects of anthropogenic global warming.

Additional References
Gunn, A. and Forchhammer, M. 2008. Ovibos moschatus. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. www.iucnredlist.org. accessed 19 November 2011.

Lorenzen, E. D., Nogués-Bravo, D., Orlando, L., Weinstock, J., Binladen, J., Marske, K.A. and 49 additional co-authors. 2011. Species-specific responses of Late-Quaternary megafauna to climate and humans. Nature 479: 359-364.