Glacial Refugia - Are They Being too Cryptic?

As previously promised, todays post will be discussing glacial refugia. During the Last Glacial Maximum at around 23,000 to 18,000 BP most of the temperate biota existed in lower latitude refugia. Extensive analysis has revealed the existence of three main refugia in the Mediterranean peninsulas of Iberia, Italy and the Balkans. After the LGM, Europe was recolonized from these refugia by species migrating northwards. However using phylogeographical evidence, the possibility of cryptic altitudinal refugia has arisen (Provan & Bennett 2008). This may have led to gross overestimations of species dispersal capabilities, which could in turn cause problems for estimations of species migrations in the future.

Phylogeographic techniques involve exploring species diversity as an indicator for possible refugia. Species that have survived the glacial maxima in refugia will expect to have high levels of genetic diversity. Secondly long term isolation of populations will lead distinct genetic lineages and lead to possible recolonization routes which can then be used to locate refugia. Areas with high genetic diversity that have been recolonized by many separate refugia might lead to confusion and should therefore be taken into account. Figure 2 below shows phylogeographic evidence of red seaweed (Palmaria palmata) showing a refugia in the English channel. The different colours represent different genetic types, with the highest proportion being shown in the dotted area.

Figure 2. Distribution of Palmaria palmata in Northern Europe (Provan et al. 2005)

Although phylogeographic evidence has had success locating recolonization pathways, it does not explain population dynamics during phases of species contraction. It is unclear whether species migrate to refugia during changes in climate or simply species outside the refugia become extinct. Studies of the Artic fox (Alopex lagopus) using ancient DNA data techniques have established that during post glacial contraction species outside the refugia became extinct (Dalen et al. 2007). This might have a massive effect on cold-adapted species that contract during periods of warming.

Phylogeographic techniques has provided new insights into the locations of glacial refugia. They have challenged the theory that the southern refugia were the only source of recolonization for temperate species after the LGM. The identification of cyrptic refugia has important implications for future climate change due to estimations of species migration range.