The flickering genes of the last mammoths

Abstract

Woolly mammoths, Mammuthus primigenius, are arguably the most iconic of the extinct Pleistocene megafauna, and an abundance of large permafrost‐embedded bone and ivory material (Fig. 1) means they were also among the first to yield credible DNA sequences (Hagelberg et al. 1994; Hoss et al. 1994). Despite mammoth remains being numerous throughout northern Eurasia and North America, both the earliest and most recent fossils are found in northeast Siberia, with the last known population being confined to Wrangel Island in the Arctic Ocean from around 10,000 years ago until their extinction around 4,000 years ago. The extent to which these Holocene mammoths were descended from the Pleistocene populations of Wrangel Island and the demographic nature of their terminal decline have, until now, remained something of a mystery. In this issue of Molecular Ecology, Nyström et al. (2012) report the first use of autosomal variation to track the decline of the last mammoths and, in doing so, take a significant step towards resolving these questions. The authors genotyped four microsatellite loci in 59 Pleistocene and Holocene mammoths from Wrangel Island and Chukotka in mainland northeastern Siberia and showed that while the Pleistocene‐to‐Holocene transition is associated with a significant reduction in genetic diversity, subsequent levels of variation remain constant until extinction. Such a pattern is somewhat surprising as it indicates that while the last mammoths were confined to only a few Arctic islands, their final extinction on Wrangel Island was not a gradual process resulting from loss of genetic diversity/inbreeding. Instead, it seems they maintained a viable effective population size of around 500 until near their presumably rapid extinction. While the ultimate agent of mammoth extinction remains unknown, the work of Nyström et al. (2012). suggests that we should be looking for something sudden, like a rapid change in climate/ecology or perhaps the arrival of humans. 1 Sergey Vartanyan during field collection, holding a woolly mammoth tusk found along a river embankment in northeast Siberia (photographer: Diana Solovyeva).

The Eurasian mammoth distribution during the second half of the Late Pleistocene and the Holocene: Regional aspects

“…The studies of the ancient DNA of the mammoths from Wrangel Island and Chukotka region (Nystr€ om et al, 2010(Nystr€ om et al, , 2012Thomas, 2012;Pe cnerov a et al, 2016) have shown significant decrease in genetic diversity before isolation, during the Pleistocene/Holocene transition. The further isolation on Wrangel Island during six thousand years led to a decline in genetic diversity by 20% in autosomal heterozygosity and about 37% in allelic richness as the result of inbreeding and genetic drift when an estimated mean effective population size was about 326 individuals (Nystr€ om et al, 2012;Palkopoulou et al, 2015;Pe cnerov a et al, 2016).…”

Functional architecture of deleterious genetic variants in the Wrangel Island mammoth genome

“…Woolly Mammoths (Mammuthus primigenius) were among the most abundant cold adapted megafaunal species during the Middle to Late Pleistocene (ca 116-12 Kyr BP), inhabiting a large swath of steppe-tundra that extended from Western Europe, through Asia and Beringia, into North America. Paleontological and genetic data indicate that their once large populations experienced at least two demographic declines, the first during the Middle-Early Pleistocene ~285 Kyr BP (Palkopoulou et al, 2015) or Eemian interglacial ~130-116 Kyr BP (Palkopoulou et al, 2013) after which populations rebounded, and a final decline around the Pleistocene-Holocene transition (Nyström et al, 2012;Palkopoulou et al, 2013;Thomas, 2012).…”

Evolution: The Island of Misfit Mammoths

“…Nonetheless, the Wrangel mammoths provide a unique resource frozen in time for the study of island evolution. Fossil specimens can be used to track the genomic diversity and genomic composition of the Wrangel mammoths from the time they became isolated until their final extinction [12,13]. Was there an initial drop in Wrangel mammoth genetic diversity, followed by a long period of relative stability, as some evidence suggests [12,13]?…”