Glacial survival may matter after all: nunatak signatures in the rare European populations of two west-arctic species

Abstract

Biogeographers claimed for more than a century that arctic plants survived glaciations in ice-free refugia within the limits of the North European ice sheets. Molecular studies have, however, provided overwhelming support for postglacial immigration into northern Europe, even from the west across the Atlantic. For the first time we can here present molecular evidence strongly favouring in situ glacial persistence of two species, the rare arctic-alpine pioneer species Sagina caespitosa and Arenaria humifusa. Both belong to the 'west-arctic element' of amphi-Atlantic disjuncts, having their few and only European occurrences well within the limits of the last glaciation. Sequencing of non-coding regions of chloroplast DNA revealed only limited variation. However, two very distinct and partly diverse genetic groups, one East and one West Atlantic, were detected in each species based on amplified fragment length polymorphisms (AFLPs), excluding postglacial dispersal from North America as explanation for their European occurrences. Patterns of genetic diversity and distinctiveness indicate that glacial populations existed in East Greenland and/or Svalbard (A. humifusa) and in southern Scandinavia (S. caespitosa). Despite their presumed lack of long-distance dispersal adaptations, intermixed populations in several regions indicate postglacial contact zones. Both species are declining in Nordic countries, probably due to climate change-induced habitat loss. Little or no current connectivity between their highly fragmented and partly distinct populations call for conservation of several populations in each geographic region.

Glacial refugia and post-glacial colonization patterns in European bryophytes

“…Even though extreme environmental conditions in glaciated areas make this seem unlikely, species able to survive in small populations may have existed in favourable microrefugia within the ice sheet (Holderegger andThiel-Egenter 2009, Rull 2009). Recent studies support glacial survival of both arctic angiosperms (Westergaard et al 2011) and conifers (Parducci et al 2012) in Scandiand conifers (Parducci et al 2012) in Scandi- (Parducci et al 2012) in Scandiin Scandinavia during the LGM. Moreover, based on radiocarbon dating, Kullman (2008) concluded that Betula trees grew on Andøya in northern Norway approximately 17 000 year BP.…”

“…If vascular plants survived in northern areas during the LGM (Westergaard et al 2011, Parducci et al 2012, Vorren et al 2013, other plants should also have been able to survive the extreme environments in the north (cf. Stenøien et al 2011a, b, Kyrkjeeide et al 2012, Vorren et al 2013.…”

Trans-Atlantic genetic uniformity in the rare snowbed sedge Carex rufina

“…The DNA extraction and AFLP analyses followed Westergaard et al (2011). Because we did not observe any variation in initial tests, we included as many as 48 primer combinations with two or three selective bases for MseI in an extended test, including 4-8 individuals from different geographic regions.…”

Phylogeography of Alpine populations of Rhytidium rugosum (Bryophyta) in a European context

“…Compared with Scandinavian regions, Hedenäs (2014) found a high haplotype diversity in a Rhytidium population in Val Poschiavo in SE Switzerland. It was suggested that the more complicated patterns of glacial refugia in and close to the Alps (Schönswetter et al 2005) than in the almost completely ice-covered Scandinavia (Lambeck et al 2010;Westergaard et al 2011;Vorren et al 2013) during the Late Glacial Maximum (LGM, c. 30-16 kA BP) could explain this high diversity. Some European Rhytidium haplotypes that are unique to the Alps were found by Hedenäs (2015).…”