North American Origin and Recent European Establishments of the Amphi-Atlantic Peat Moss Sphagnum Angermanicum

Abstract

Genetic and morphological similarity between populations separated by large distances may be caused by frequent long-distance dispersal or retained ancestral polymorphism. The frequent lack of differentiation between disjunct conspecific moss populations on different continents has traditionally been explained by the latter model, and has been cited as evidence that many or most moss species are extremely ancient and slowly diverging. We have studied intercontinental differentiation in the amphi-Atlantic peat moss Sphagnum angermanicum using 23 microsatellite markers. Two major genetic clusters are found, both of which occur throughout the distributional range. Patterns of genetic structuring and overall migration patterns suggest that the species probably originated in North America, and seems to have been established twice in Northern Europe during the past 40,000 years.We conclude that similarity between S. angermanicum populations on different continents is not the result of ancient vicariance and subsequent stasis. Rather, the observed pattern can be explained by multiple long-distance dispersal over limited evolutionary time. The genetic similarity can also partly be explained by incomplete lineage sorting, but this appears to be caused by the short time since separation. Our study adds to a growing body of evidence suggesting that Sphagnum, constituting a significant part of northern hemisphere biodiversity, may be more evolutionary dynamic than previously assumed.

Glacial refugia and post-glacial colonization patterns in European bryophytes

“…A similar scenario has been suggested for another amphi-Atlantic peat moss, Sphagnum angermanicum Melin, with European populations only found in Norway, Sweden and Iceland. Two genetic clusters have been recognized in this species in European and North American populations, both occurring on the two continents (Stenøien et al 2011a). One linage may have colonized Europe from North America before the LGM (~40 000 year BP) and the other after the LGM, and S. angermanicum may have survived the LGM in a southern cryptic refugium where it later went extinct after colonizing Scandinavia (Stenøien et al 2011a).…”

“…Two genetic clusters have been recognized in this species in European and North American populations, both occurring on the two continents (Stenøien et al 2011a). One linage may have colonized Europe from North America before the LGM (~40 000 year BP) and the other after the LGM, and S. angermanicum may have survived the LGM in a southern cryptic refugium where it later went extinct after colonizing Scandinavia (Stenøien et al 2011a). North American origin could also be suggested for S. affine Renauld & Cardot, as higher genetic variation is found along the eastern coast of North America than in Scandinavia (Thingsgaard 2001).…”

“…Low divergence between populations within and outside the ice sheet areas does not necessarily imply recent divergence, though, since this could also be caused by large ancestral sizes or recent gene flow (Nielsen and Beaumont 2009). Alternatively, high F ST could instead of long-time survival result from little genetic variation within versus among populations (Stenøien et al 2011a, Kyrkjeeide et al 2012.…”

“…Stenøien et al 2011a, b, Kyrkjeeide et al 2012, Vorren et al 2013. Bryophytes exhibit traits that might make them better suited than vascular plants for survival in small, northern refugia, including their poikilohydric nature, enabling survival through unfavourable periods (Proctor et al 2007; see also Segreto et al 2010).…”

“…Sundberg (2012) trapped peat moss spores across a large spatial scale and concluded that a major fraction of spores are dispersed regionally in boreal areas, but as much as 1% of the spore rain may have intercontinental origin. Wide distribution ranges in bryophytes suggest that they in general are exceptional dispersers (Szövenyi et al 2008, Stenøien et al 2011a). For instance, about 70% of moss species occurring in Europe are also present in North America (Frahm and Vitt 1993), while less than 7% of European vascular plant species are shared with North America (Qian 1999).…”