The tundra muskox, one of the few large northern mammals to have survived to the present day, saw its genetic diversity decrease greatly at the end of the Pleistocene period, around 10,000 years ago. A study published in the open access journal BMC Evolutionary Biology reveals that the muskox (Ovibus moschatus) was genetically much more diverse before the Pleistocene/Holocene transition, the period that witnessed the extinction of other great mammals such as the mammoth.
Ross MacPhee and Alex Greenwood, from the American Museum of Natural History in New York, USA, collaborated with colleagues from Russia and the Netherlands to sequence samples of muskox ancient mitochondrial DNA (hypervariable region and cytochrome b sequences) and compared the data with DNA sequences from modern muskoxen. The ancient DNA samples dated from the late Pleistocene to the late Holocene and were collected in the Arctic Archipelago of North America, Yukon, and the Arctic periphery of Siberia in northeastern Asia. Modern samples came from northern North America and Greenland - the only regions where muskoxen can be found today.
The authors identified two groups of haplotypes (haploid genotypes, or gene sets associated on single chromosomes) within the analysed sequences. 'Extinct haplotypes' (EHs), or haplotypes which no longer occur in modern muskoxen, were recovered only in northern Asia where the muskox is now extinct. Such haplotypes were found in a number of specimens dated from ~44,000 to ~18,000 years ago.
'Surviving haplotypes' (SHs) include all other known haplotypes, which are closely related, or identical, to modern haplotypes. Some northern Asian fossil specimens, dating from up to ~22,000 years ago, yielded sequences conforming to known SHs. So did the last known Asian muskoxen, which died out on the Taimyr Peninsula of Siberia about 2000 years ago. This evidence shows that SHs and EHs coexisted for at least several thousand years and probably much longer.
In accordance with previous research, their results show that SH samples from both continents show little to no genetic variation. By contrast, EHs in Pleistocene samples were found to diverge by several substitutions from one another as well as from modern muskoxen, for both cytochrome b and the hypervariable region.
The authors write, "Ovibos, one of the few high-latitude megafaunal mammals to have survived into recent times, has clearly done so with reduced genetic variability [...] at what point before the present this variability was lost cannot be satisfactorily established with existing data".
Late Quaternary Loss of Genetic Diversity in Muskox (Ovibos)
Ross D. E. MacPhee, Alexei N. Tikhonov, Dick Mol and Alex D. Greenwood
BMC Evolutionary Biology 2005, 5:49 (6 October 2005)