On the road: postglacial history and recent expansion of the annual Atriplex tatarica in Europe.
Aim The Holocene history of annual plant species is at best shadowy because, for most, the palaeobotanical data are scarce or absent. Hence, there is limited information on their glacial refugia and postglacial colonization pathways. Also, little is known on how human activity has affected their expansion. Here, we outline the joint influences of postglacial colonization and recent expansions on the genetic diversity of the continental, sub-halophyte species Atriplex tatarica during the late Pleistocene and the Holocene. Location Europe. Taxon Atriplex tatarica (Amaranthaceae). Methods We analysed 780 individuals from 80 populations throughout the current European distribution range, employing chloroplast DNA sequences and microsatellite markers. Results Five haplotype lineages were recognized based on the results of the cpDNA phylogenetic analyses. These lineages originated 0.43-0.22 myr BP. Bayesian clustering analyses divided populations of A. tatarica into two clusters: (a) populations in the Pannonian Basin and the Bohemian Massif and (b) populations in the North European Plain, the Balkan Peninsula, the Carpathian Arc and the Pontic region. The ABC approach provided the strongest statistical support for a model proposing refugia in the Balkan Peninsula and the Pannonian Basin. Expansions from these refugia occurred around 7,000 yr BP. Main conclusion Atriplex tatarica represents a continental species growing exclusively in man-made habitats. It serves as a phylogeographic model for annual ruderal taxa currently spreading in central Europe along highways and representing a large group of alien plant species, the so-called archaeophytes. Atriplex tatarica survived the last glaciation in both a southerly located Balkan refugium and in a more northerly refugium in the Pannonian Basin. From these, the species has colonized Europe as a result of expansion of humans and the anthropogenic climate change. The massive colonization of central north Europe is very recent, with the expansion estimated to have occurred only hundreds of years ago.