Rhytidium rugosum(Bryophyta) colonized Scandinavia from at least two glacial refugial source populations

Abstract

The Scandinavian post-glacial history of the moss Rhytidium rugosum is traced on the basis of information from the nuclear markers ITS and gpd for 229 Scandinavian and 81 other specimens. Some haplotypes, groups or lineages identified in a NeighborNet split network are predominantly northern Scandinavian, whereas others are southern. With the distributions of individual haplotypes and the timing of the deglaciation in different parts of Scandinavia, this implies colonization from the south and from the north or north-east. High haplotype and nucleotide diversity and the occurrence of certain private haplotypes in the north suggest that the species may have survived the Last Glacial Maximum in local refugia. Slightly higher numbers of private haplotypes in Scandinavia than in central or north-eastern Europe also favour an explanation with at least some local glacial survival. Low diversity in the southernmost contiguous region of the Scandinavian mountain range is probably a result of recent land uplift and late colonization. The Scandinavian lowland regional populations probably represent remains of an earlier widespread population that became increasingly restricted to small and isolated areas when the vegetation closed during the post-glacial period. Some of the lowland populations require extensive management to survive.

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

“…in the Alps to see whether its intraspecific geographical variation is consistent with what was hypothesized above for spore-dispersed plants and to possibly trace its post-glacial origin. In Rhytidium, the variation in the nuclear internal transcribed spacers 1 and 2 (ITS) and a portion of the gene region for glyceraldehyde 3-phosphate dehydrogenase (gpd) are considerable and shows a geographic pattern largely consistent with what is known about the late-to post-glacial history of Scandinavia (Hedenäs 2014(Hedenäs , 2015. 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). However, such geographically restricted haplotypes were not more common in central Europe than in Scandinavia, as would have been expected if a larger proportion of the species' total diversity had survived in the southern refugia than in the north (cf., Koch et al 2006;Schönswetter et al 2003).…”

“…Brochmann et al 2003;Hedenäs 2015;Hewitt 2000;Jaarola et al 1999;Kyrkjeeide et al 2014;Parducci et al 2012;Taberlet et al 1998). Several recent studies concerned plants, especially flowering plants, in the European Alps (from here on called 'the Alps') (e.g.…”

“…However, such geographically restricted haplotypes were not more common in central Europe than in Scandinavia, as would have been expected if a larger proportion of the species' total diversity had survived in the southern refugia than in the north (cf., Koch et al 2006;Schönswetter et al 2003). However, if there are a large number of haplotypes that are unique to the Alps, many of these likely went undetected in the earlier sparse sampling of this particular area (Hedenäs 2015). Whether the species immigrated to an area on a broad front or not could explain diversity differences (Alsos et al 2009), but we should also expect a higher diversity in the Alps than in Scandinavia if more Rhytidium haplotypes survived the last glaciation in situ, in local glacial refugia, or if it immigrated from a larger number of lowland glacial refugia.…”

“…Whether the species immigrated to an area on a broad front or not could explain diversity differences (Alsos et al 2009), but we should also expect a higher diversity in the Alps than in Scandinavia if more Rhytidium haplotypes survived the last glaciation in situ, in local glacial refugia, or if it immigrated from a larger number of lowland glacial refugia. Based on subfossil macro-remains, it can be inferred that Rhytidium was widely distributed in the European lowlands north of the Alps during the glacial period, and it still survives in interglacial refugia in some such areas with relaxed competition from flowering plants (Hedenäs 2014(Hedenäs , 2015Meinunger and Schröder 2007). Finally, lowlands where source populations for the extant occurrences likely occurred are, relative to the glaciated areas, both larger and more closely situated for the Alps than for most of Scandinavia.…”