Repeatedly out of Beringia:Cassiope tetragonaembraces the Arctic

Abstract

Aim Eric Hultén hypothesized that most arctic plants initially radiated from Beringia in the Late Tertiary and persisted in this unglaciated area during the Pleistocene glaciations, while their distribution ranges were repeatedly fragmented and reformed elsewhere. Whereas taxonomic and fossil evidence suggest that Cassiope tetragona originated in Beringia and expanded into the circumarctic area before the onset of the glaciations, lack of chloroplast DNA (cpDNA) variation may suggest that colonization was more recent. We address these contradictory scenarios using high-resolution nuclear markers.Location Circumpolar Arctic.Methods The main analysis was by amplified fragment-length polymorphism (AFLP), while sequences of chloroplast DNA verified the use of Cassiope mertensiana as an outgroup for C. tetragona. Data were analysed using Bayesian clustering, principal coordinates analyses, parsimony and neighbour-joining, and measures of diversity and differentiation were calculated.Results The circumpolar C. tetragona ssp. tetragona was well separated from the North American C. tetragona ssp. saximontana. The genetic structure in ssp. tetragona showed a strong east-west trend, with the Beringian populations in an intermediate position. The highest level of diversity was in Beringia, while the strongest differentiation in the data set was found between the populations from the Siberian Arctic west of Beringia and the remainder. Main conclusionsThe results are consistent with a Beringian origin of the species, but the levels and geographical patterns of differentiation and gene diversity suggest that the latest expansion from Beringia into the circumarctic was recent, possibly during the current interglacial. The results are in accordance with a recent leading-edge mode of colonization, particularly towards the east throughout Canada/Greenland and across the North Atlantic into Scandinavia and Svalbard. As fossils demonstrate the presence of the species in North Greenland 2.5-2.0 Ma, as well as in the previous interglacial, we conclude that C. tetragona expanded eastwards from Beringia several times and that the earlier emigrants of this woody species became extinct. The last major westward expansion from Beringia seems older, and the data suggest a separate Siberian refugium during at least one glaciation.

The Arctic – an evolutionary freezer?

“…Ploidy levels are indicated (* denote unknown ploidy level). correspond to previously described subspecies, for example in Saxifraga oppositifolia (Abbott et al 2000) and Cassiope tetragona (Eidesen et al 2007b). In Cassiope tetragona ssp.…”

“…tetragona; Eidesen et al 2007b) and Rubus chamaemorus (Ehrich et al 2008), gave surprisingly different results. Also these species have been found as early macrofossils in northern Greenland (2.5-2.0 million years old; Bennike and Böcher 1990).…”

“…In Cassiope tetragona ssp. tetragona, which follows a leading edge model of expansion from Beringia, there is high diversity in Beringia and eastern Siberia (Eidesen et al 2007b; see also below). Dryas octopetala, which consists of two distinct genetic groups in Eurasia (one of them with three subgroups), has high diversity not only in northern Siberia and the Urals, but also in secondary contact zones such as in northern Scandinavia, Svalbard and East Greenland (Skrede et al 2006).…”

Yukon Taiga – Past, Present and Future

“…Genetic investigations into possible refugia supporting post-Wisconsinan reinstatement of subarctic populations of plants, animals and fungi from East Beringia, although increasing in number, remain small, and the findings are also controversial (Senjo et al, 1999;Goetcheus & Birks, 2001;Abbott and Brochmann, 2003;Brochmann et al, 2003;Cook et al, 2005;Edwards et al, 2005;Lydolph et al, 2005;Geml et al, 2006Geml et al, , 2010Loehr et al 2006;Politov et al, 2006;Zazula et al, 2006;Eidesen et al, 2007;Shilo et al, 2007Shilo et al, , 2008Waltari et al 2007;Barnosky, 2008;Stewart and Dalén, 2008;Ickert-Bond et al, 2009;Levsen and Mort, 2009;Tsutsui et al 2009;Carlsen et al, 2010;Gérardi et al, 2010;Nakonechnaya et al, 2010;Shafer et al, 2010;Stewart et al, 2010;Westergaard et al 2010). …”

High mountain origin, phylogenetics, evolution, and niche conservatism of arctic lineages in the hemiparasitic genus Pedicularis (Orobanchaceae)

“…Phylogeographic studies provided information on postglacial plant migration and re-colonization, northern refugia during the last glacial maximum, and genetic diversity in arctic species (e.g., Abbott and Brochmann, 2003;Allen et al, 2012;Alsos et al, 2005Alsos et al, , 2007Alsos et al, , 2009Brochmann and Brysting, 2008;Brochmann et al, 2003;Ehrich et al, 2007;Eidesen et al, 2007aEidesen et al, , 2007bHoffmann, 2012;Koch et al, 2006;Skrede et al, 2006Skrede et al, , 2009Westergaard et al, 2010Westergaard et al, , 2011. Particularly, species with disjunct arcticalpine distributions have been studied in phylogeographic (reviewed by Abbott and Brochmann (2003)) and biogeographic contexts (Tkach et al, 2008c;Tolmachev, 1960;Yurtsev, 1962).…”