Now for Something a Little Less Cute...

This example is slightly different to that of the bank vole as the research was carried out from a different angle. Pauls et al (2006) looked at the phylogeography of the montane caddisfly by examining the genetic make-up of individuals from present day populations rather than fossil records. This allowed them to gain an understanding of ‘the historical processes that may be responsible for the contemporary geographic distributions of individuals’. They are able to trace the ‘fragmentation’ and ‘recolonisation’ of caddisflies from once isolated refugia by detecting ‘secondary contact and/or hybridisation between previously isolated lineages’ (Pauls et al 2006: 2154). They use this evidence to suggest that the caddisfly species D. discolor survived the Pleistocene glaciations in more Northern refugia rather than retreating and recolonizing from refugia in Southern Europe like many other species. This study is also unique in the fact that it was the first study of its kind to focus on an aquatic insect species – exciting, huh?

D. discolor exists today in ‘island’ populations across the major mountain regions of Europe. Pauls et al (2006) analysed the ‘motochondrial sequence data’ of 254 individual caddisflies across their entire distribution and came up with some interesting results. The data they collected showed only a very small amount of genetic variability between the different populations but a significant amount of genetic divergence. Genetic variability is ‘a measure of the tendency of individual genotypes in a population to vary from one another’. Whilst genetic divergence is ‘the process in which two or more populations of an ancestral species accumulate independent genetic changes (mutations) through time, often after the populations have become reproductively isolated for some period of time’.

This basically shows that the populations have been isolated for long periods of time (i.e. when in refugia) which allowed for the populations to develop distinct mitochondrial lineages separately of one another. So, the make-up and structuring of modern day populations of D. discolor can be explained by the existence of past populations in multiple, isolated refugia – clever, isn’t it? What’s even more special about this piece of research is that the number of proposed refugia is much higher than usual (compared with similar studies focusing on different species), and that they have data that points to the existence of refugia over not just one but many glacial cycles. This highlights the need for more studies into the responses of aquatic organisms to climatic change.

I think it’s really interesting how scientists from different disciplines, for example geneticists, conservation ecologists and palaeoecologists, have all produced research findings that point to the existence of cryptic Northern refugia. This study clearly adds to our collection of evidence in favour of certain species surviving glacial periods in cryptic Northern refugia. If aquatic species like the caddisfly can exist in refugia in this way rather than drastically altering their ranges then surely this tells us something about the way in which they might possibly respond to climate change in the future? More importantly, if we want to preserve this species of caddisfly in the future then maybe we could identify and preserve suitable refugial areas or even create artificial ones? Just an idea, but something to think about!

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?