A Final Vole-Related Note…

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I realise quite a few of my blog posts have (unintentionally!) focused on voles, but here’s just one more. This article by Herman and Searle (2011) was only published online a few weeks ago (so it’s literally hot off the palaeoecological press!) and it challenges the view that only refugia that existed during the LGM are important in terms of recolonisation and the origin of modern temperate species populations - something which could mean a complete reconsideration of the phylogeographic data on post-glacial recolonisation is necessary.

Herman and Searle (2011) used genetic analysis to date the post-glacial expansion of the Eurasian field vole. Their findings show that the correct calibration is essential to inferring the absolute timing and scale of demographic changes (in the case of the field vole and other species). Their data shows that the field voles went through a bottleneck – ‘an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing’ – during the Younger Dryas and not the Last Glacial Maximum (which is generally referred to as the time when present-day patterns were determined). So, instead of recolonizing from refugia after the LGM as expected, they found that the field vole populations expanded from this bottleneck (/recolonised from refugia) following the Younger Dryas instead. They conclude that the wide-ranging genetic structure of the field vole was shaped by the climatic events of the Younger Dryas rather than it being the result of post-glacial expansion from LGM refugia. They suggest that the source of error in some studies that highlight the importance of LGM refugia might be ‘calibration with inappropriate external substitution rates’. Based on this evidence from the field vole they propose that the Younger Dryas may have been more significant in shaping the current ‘phylogeographic structure’ of temperate taxa than the LGM.

This recent study proves that scientists are constantly making new discoveries and presenting evidence that challenges the findings of earlier studies. I’m sure that if I was writing this blog in a few years time then there would be a lot of new stuff to include and the articles reviewed over the past few weeks may have been proven outdated or their findings incomplete (much like the Southern refugia hypothesis). This is one of the reasons why I have tried focus mainly on the most recent studies in my posts, especially as the cryptic Northern refugia hypothesis only really emerged and developed over the past 10 years or so.