A climatic relict or a long distance disperser: conservation genetics of an Arctic disjunct polyploid plant

Abstract

The Primula sibirica group is a set of approximately a dozen Arctic, taxonomically unrelated plant species that share a similar disjunct distribution on the shores of the Arctic Ocean and the northernmost part of the Baltic Sea. The origin of this phylogeographic pattern is not known. It has been suggested, first, that the species arrived after the last glaciation from the White Sea, second, that they are relicts of once larger populations or, third, that they arrived via jump dispersal. One of the species is the polyploid Creeping alkali grass, Puccinellia phryganodes, which is critically endangered in Finland. Here we used microsatellite markers to study seven extant and three extinct populations from coasts of the Bothnian Bay and the Arctic Sea (N = 297). We estimated the genetic diversity in the study populations and applied principal component analysis and Bayesian and coalescence methods to examine their population genetic structure and evolutionary history. We found that the endangered Bothnian Bay population still harbors a reasonably high amount of genetic diversity and is differentiated from the geographically closest populations. We show that Puccinellia phryganodes is more likely a climatic relict in the Bothnian Bay than a long-distance disperser and that the endangered southern population should be considered as an evolutionary significant unit rather than a mere representative of the main population.