The tundra muskox, one of the few large northern mammals tohave survived to the present day, saw its genetic diversity decreasegreatly at the end of the Pleistocene period, around 10,000 years ago.A study published in the open access journal BMC Evolutionary Biologyreveals that the muskox (Ovibus moschatus) was genetically much morediverse before the Pleistocene/Holocene transition, the period thatwitnessed the extinction of other great mammals such as the mammoth.
RossMacPhee and Alex Greenwood, from the American Museum of Natural Historyin New York, USA, collaborated with colleagues from Russia and theNetherlands to sequence samples of muskox ancient mitochondrial DNA(hypervariable region and cytochrome b sequences) and compared the datawith DNA sequences from modern muskoxen. The ancient DNA samples datedfrom the late Pleistocene to the late Holocene and were collected inthe Arctic Archipelago of North America, Yukon, and the Arcticperiphery of Siberia in northeastern Asia. Modern samples came fromnorthern North America and Greenland - the only regions where muskoxencan be found today.
The authors identified two groups ofhaplotypes (haploid genotypes, or gene sets associated on singlechromosomes) within the analysed sequences. 'Extinct haplotypes' (EHs),or haplotypes which no longer occur in modern muskoxen, were recoveredonly in northern Asia where the muskox is now extinct. Such haplotypeswere found in a number of specimens dated from ~44,000 to ~18,000 yearsago.
'Surviving haplotypes' (SHs) include all other knownhaplotypes, which are closely related, or identical, to modernhaplotypes. Some northern Asian fossil specimens, dating from up to~22,000 years ago, yielded sequences conforming to known SHs. So didthe last known Asian muskoxen, which died out on the Taimyr Peninsulaof Siberia about 2000 years ago. This evidence shows that SHs and EHscoexisted for at least several thousand years and probably much longer.
Inaccordance with previous research, their results show that SH samplesfrom both continents show little to no genetic variation. By contrast,EHs in Pleistocene samples were found to diverge by severalsubstitutions from one another as well as from modern muskoxen, forboth cytochrome b and the hypervariable region.
The authorswrite, "Ovibos, one of the few high-latitude megafaunal mammals to havesurvived into recent times, has clearly done so with reduced geneticvariability [...] at what point before the present this variability waslost 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)
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