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!