Boris the Bank Vole and Friends

Let me introduce you to a little friend:

This little guy is Boris the bank vole and he is probably completely unaware of the fact that over the past few years his friends and ancestors have played an important role in the development of the cryptic Northern refugia hypothesis.

During last glaciation (around 25,000-10,000 years ago), climatic conditions rendered large continental areas uninhabitable for the bank voles and they were forced to retreat to sheltered refugia. The bank vole has proven to be an excellent subject for investigations into the existence and relative contribution of the more Northern refugia as opposed to those further away, because it is currently found on all 3 Mediterranean peninsulas (Kotlíket al 2006). For example, Bilton et al (1998) and Deffontaine et al (2005) have used the bank vole to propose that the closer refugia (in central and Eastern Europe) made a much more significant contribution to modern day populations in Europe than the more distant Mediterranean refugia.

One of the main Northern refugia for the bank voles is located in the Carpathian Mountain range that stretches across Central and Eastern Europe, where bank vole fossils have been identified and dated back to the last glaciation. Kotlík et al (2006) use mitochondrial DNA sequences to present what they call ‘the clearest evidence yet’ that the little bank voles stuck out the cold in a central European refugium throughout the last glaciation (summary of their findings presented in Fig 1.).

From the mitochondrial DNA data, Kotlík et al (2006) identified a number of clades (essentially, groups made up of the species of bank vole and all its descendants), one of which they named the ‘Carpathian clade’. Their analysis showed that this Carpathian clade is a ‘geographically localised’ (only found in one place, the Carpathian Mountains) and monophyletic (made up of just the bank vole and their ancestors) lineage. In simpler terms, this showed that the ancestors of the bank vole in the Carpathian clade had been genetically isolated from the ancestors of other clades in the past. In even simpler terms, this shows that the bank voles of the Carpathian clade must have existed in a refugium in the Carpathian Mountains during which time they were unable to interact with other bank vole populations. Kotlík et al (2006) then used the ‘Bayesian coalescent method’ to estimate when the Carpathian clade split from the Western clade, concluding that they must have existed in 2 separate refugia during the last period of glaciation but the 2 populations may have existed together in the same refugium in a previous glaciation.

So what’s the significance of this?

This study, along with others, gives us some important information about the responses of temperate woodland species to climatic change. If it is true that postglacial re-colonisation occurred from these Northern refugia as the evidence suggests, then the idea that temperate woodland species respond to climatic changes by drastically altering their distributions may not provide us with the complete picture. Their response strategy, instead, may be to persist in small, isolated populations in refugia where conditions are bearable. Isn’t it funny how little creatures like Boris and his friends can provide us with all this information?