Thursday, February 6, 2014

Why the mammoth disappeared

So far the common image of much of the northern hemisphere during the latest Ice Age has been of a landscape dominated by grass steppe. However, it seems that this conception doesn't hold any longer. The landscape was far more diverse and stable than today, and large well-known mammels animals like woolly rhino and mammoth fed on grasses and particularly on protein-rich forbs. Forbs are plants that have leaves and stems but no persistent woody stem above ground, and that are not grasses. At the Last Glacial Maximum 25,000 -- 15,000 years ago, at a time when the climate was at its coldest and driest, a major loss of plant diversity took place. As a result the animals barely survived. After the Ice Age ended about 10,000 years ago it became warmer again. After the large reduction of plant diversity during the Last Glacial Maximum another kind of vegetation now appeared. One of the key food sources of the large mammals- the protein-rich forbs -- did not fully recover to their former abundance. This likely proved fatal for species like woolly rhino, mammoth, and horse in Asia and North America. Even though it became warmer again after the end of the Ice Age the old landscapes did not return.

This scenario is based on findings of a new study just published in Nature. 30 teams from 12 countries worked on this study and they present 50 thousand years (kyr) of Arctic vegetation history, derived from the first large-scale ancient DNA metabarcoding study of circumpolar plant diversity. For this interval we also explore nematode diversity as a proxy for modelling vegetation cover and soil quality, and diets of herbivorous megafaunal mammals, many of which became extinct around 10 kyr before present.

The researchers were using mostly permafrost samples that contain large amounts of frozen DNA. They sequenced the short P6 loop sequence of the trnL plastid  region and a part of the ITS1 spacer region through metabarcoding, generating a total of over 14 million trnL plant DNA sequence reads and 1,6 million ITS reads. Those sequences were identified by comparison with an Arctic trnL taxonomic reference library, extended with ITS sequences for three families, a new north boreal trnL taxonomic reference library constructed by sequencing some 1300 modern plant samples representing 835 species; and with GenBank

Impressive work and the results are quite fascinating.

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