February 24, 2010

Ancient caribou DNA suggests replacement triggered by climate change and/or volcanic eruption


ResearchBlogging.orgI’ve become increasingly interested in the practice of paleoecology of late, trying to find and gather bits and pieces when I have time. This study from Molecular Ecology came to me, which, based on the probability that you can assign probabilities to cosmic events, I’m going to carefully and tentatively (and gentlemanly) attribute to Providence, or Wiley Interscience press releases.

In the Yukon, there are several distinct caribou herds that inhabit and move within certain, definable regions. The authors wanted to use DNA sampled from living caribou in the different regions and compare it to that of ancient caribou, using well-preserved soft tissues and bones excavated from scattered ice patches, in order to determine the historic ranges of these animals and the level of gene flow between herds. Establishing these genetic/ecological reference points and comparing modern data to them can provide administrators with more accurate data which can be used to create more effective management plans.

When Kuhn et al. compared the modern caribou DNA from the Southern Lakes region to that of caribou living in that area over 1,000 years ago, they found that the historic residents were more closely related to herds in the northwest than the existing population of caribou in the region. In other words, the caribou currently living in the Southern Lakes region did not descend from the animals that lived there over a millennium ago.

So what happened to the ancient caribou? How were they displaced completely by these genetically dissimilar animals? There are two suspects that might have worked together in purging these animals from the area.

The first is climate change (Clade 1 is the clade accounting for the Southern Lakes herds):

The appearance of Clade 1 in the Southern Lakes region at ~1000 BP follows a 400 year period during which no remains were preserved within the sample ice patches (1440–1030 BP, Farnell et al. 2004).

Coincidently, this was concurrent with the Medieval Warming Period, where temperatures increased globally. This would produce negative ecological circumstances for the caribou like frequent thaws and loss of snow patches that could have cut their numbers.

But there was another, much more sudden event that could have affected these animals. Mt. Churchill in the Wrangell Mountains erupted twice between ~1200 and 1900 years ago; the second time created the so called “eastern lobe” of the White River Ash (noted as "2" in the illustration), covering an area of over 300,000 square kilometers with tephra, which has been shown in studies to be deadly to both livestock and caribou.

When the dangers began to disappear and the cold temperatures returned, the area was re-colonized, but not by the herds in the surrounding regions. Most likely the modern Southern Lakes caribou are descended from herds farther to the south riding the sweep of the Little Ice Age that returned optimal temperatures to the area.

KUHN, T., MCFARLANE, K., GROVES, P., MOOERS, A., & SHAPIRO, B. (2010). Modern and ancient DNA reveal recent partial replacement of caribou in the southwest Yukon Molecular Ecology DOI: 10.1111/j.1365-294X.2010.04565.x

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