The extreme Beringian/Atlantic disjunction in Saxifraga rivularis (Saxifragaceae) has formed at least twice

• Published in: Journal of Biogeography
• Main Authors: Westergaard, Kristine Bakke, Jørgensen, Marte Holten, Gabrielsen, Tove M., Alsos, Inger Greve, Brochmann, Christian
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2010
• Subjects: Ecology; Ecology, Evolution, Behavior and Systematics; Arctic; Svalbard; Bering Sea; Svalbard Archipelago; Saxifraga rivularis; Beringia
• Online Access: http://dx.doi.org/10.1111/j.1365-2699.2010.02278.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2699.2010.02278.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2699.2010.02278.x

Abstract Aim The oceanic Saxifraga rivularis L. presents one of the most extreme disjunctions known in the arctic flora: it has a small amphi‐Beringian range and a larger amphi‐Atlantic one. It was recently suggested to have had a single allopolyploid origin in Beringia at least one glacial cycle ago, followed by gradual expansion in a more humid period and differentiation into two allopatric subspecies (the Atlantic ssp. rivularis and the Beringian ssp. arctolitoralis ). Here we explore the history of its extreme disjunction. Location The amphi‐Beringian and northern amphi‐Atlantic regions. Methods We obtained amplified fragment length polymorphisms (AFLPs) and chloroplast DNA sequences from 36 populations (287 individuals) and 13 populations (15 individuals), respectively. The data were analysed using principal coordinates analyses, Bayesian clustering methods, and analyses of molecular variance. Results Two distinctly divergent AFLP groups were observed, corresponding to the two described subspecies, but, surprisingly, four of the West Atlantic populations belonged to the supposedly Beringian endemic ssp. arctolitoralis . This was confirmed by re‐examination of their morphological characteristics. The overall AFLP diversity in the species was low (26.4% polymorphic markers), and there was no variation in the five investigated chloroplast DNA (cpDNA) regions. There was little geographic structuring of the AFLP diversity within each subspecies, even across the extreme disjunction in ssp. arctolitoralis , across the Bering Sea, and across the Atlantic Ocean, except that most plants from the arctic Svalbard archipelago formed a separate genetic group with relatively high diversity. Main conclusions The extreme disjunction in S. rivularis has evidently formed at least twice. The first expansion from Beringia was followed by allopatric differentiation into one Beringian and one Atlantic subspecies, which are distinctly divergent at AFLP loci but still harbour identical cpDNA haplotypes, suggesting that the ...