Wednesday, February 21, 2007

DNA Analysis Reveals Rapid Population Shift In Pleistocene Cave Bears

Sudden replacement of cave bear mitochondrial DNA in the late Pleistocene. 2007. M. Hofreiter et al. Current Biology 17, R122-R123.
Studying DNA obtained from teeth of ancient cave bears, researchers have been able to identify a shift in a particular population of the bears inhabiting a European valley in the late Pleistocene era.
From the press release:

To investigate the stability of ancient cave bear populations over time, the researchers studied mitochondrial DNA sequence from 29 cave bear teeth from three geographically close caves in the Ach Valley, near the Danube River in modern-day southern Germany.

The findings indicated that while four sequence types (known as haplotypes) corresponded to bears 28,000 to 38,000 years old, a fifth DNA haplotype was found only in bears that were 28,000 years old or younger. These data suggested that what had been a stable, long-established cave bear population became disrupted around 28,000 years ago and was replaced by a new, genetically distinct cave bear group.

The timing of the disruption appears to roughly coincide with the arrival of modern humans in the Ach Valley, thought to have occurred by 32,000 years ago. The researchers suggest that human influence in the form of hunting and competition for sheltering caves may represent a plausible explanation for the disruption in the cave bear population. image

Phylogenetic tree of 26 published cave bear haplotypes and temporal relationship of the two haplogroups in the Ach Valley.

(A) Phylogenetic positions of the sequences from two reproductively isolated cave bear populations from Austria (dotted arrows) and from the Ach Valley (normal arrows). Haplotypes from the older sequence group from the Ach Valley fall within the same clade as those from the higher elevation site (2,000 m) in Austria (blue arrows), while the younger haplotype from the Ach Valley clusters with haplotypes from the lower elevation site (1,300 m above sea level) in Austria (red arrows). (B) Radiocarbon dates for the fossil teeth from the Ach Valley. The different sequence groups are shown in the same colors as in (A).