One of the most prominent manifestations of the ongoing climate warming is the retreat of glaciers and ice sheets around the world. Retreating glaciers result in the formation of new ponds and lakes, which are available for colonization. The gradual appearance of these new habitat patches allows us to determine to what extent the composition of asexual (Daphnia) (water flea) populations is affected by environmental drivers versus dispersal limitation. Here we used a landscape genetics approach to assess the processes structuring the clonal composition of species in the (D. pulex) species complex that have colonized periglacial habitats created by ice-sheet retreat in western Greenland. We analyzed 61 populations from a young (<50 y) and an old cluster (>150 y) of lakes and ponds. We identified 42 asexual clones that varied widely in spatial distribution. Beta diversity was higher among older than among younger systems. Lineage sorting by the environment explained 14% of the variation in clonal composition whereas the pure effect of geographic distance was very small and statistically insignificant (Radj2 = 0.010, p= 0.085). Dispersal limitation did not seem important, even among young habitat patches. The observation of several tens of clones colonizing the area combined with environmentally-driven clonal composition of populations illustrates that population assembly of asexual species in the arctic is structured by environmental gradients reflecting differences in the ecology of clones.
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