Magnus Popp

The proposed age of the striking biogeographic disjunction between the Arctic and southernmost South America varies from more than 65 million to a few thousand years, but no estimates based on explicit models and molecular data are available. Here we address the origin of bipolarity in crowberries ( Empetrum ), which are heath-forming dwarf shrubs with animal-dispersed fruits. We apply a fossil-calibrated relaxed molecular clock to model sequence evolution in two nuclear low-copy and two plastid DNA regions from 41 individual plants (420 clones for the nuclear regions) representing the entire geographic distribution of crowberries. The plastid region mat K and four fossil calibration points were used to infer the ages of the crowberry stem and crown groups. All analyses resolved three major crowberry clades (A–C). Clade A contained sequences from the eastern Canadian pink-fruited crowberry ( E. eamesii ) as sister to clades B and C, which both contained sequences from the black-fruited northern hemisphere crowberry ( E. nigrum ). Clade B also contained a subclade with all sequences from the red-fruited southern hemisphere crowberry, which is often referred to as a distinct species, E. rubrum . Its closest relatives were consistently identified as black-fruited plants from northwestern North America. The median time to the most recent common ancestor for northern and southern hemisphere crowberries was estimated to 0.56–0.93 Ma, and 0.26–0.59 Ma for the southern plants only. We conclude that a single dispersal by a bird from northwestern North America to southernmost South America, taking place in the Mid-Pleistocene, is sufficient to explain the disjunction in crowberries.

Aim  Many plants occurring on the isolated mountain peaks of Africa have their closest relatives in very remote areas, even in temperate Europe and Asia. Their biogeographical history is poorly understood. The Afro‐montane element of the primarily Eurasian genus Lychnis is a typical example of such a disjunction. Here, we aim to reconstruct the phylogeny of the Afro‐montane endemics of Lychnis and to infer the history of immigration into Africa and of the subsequent dispersal and speciation.Location  The Afro‐montane representatives of Lychnis occur in Ethiopia, Kenya, Tanzania, Uganda, Rwanda, Burundi, the Democratic Republic of Congo, Cameroon, and Nigeria.Methods  Silica‐dried plant materials collected in Ethiopia in 2004 as well as herbarium material were used for DNA extractions. We used parsimony analysis of nucleotide data from the rps16 intron and psbE‐petL region in plastids, and the internal transcribed spacer (ITS) and a region spanning exon 18–24 in the second largest subunit of RNA polymerase II (RPB2) from the nucleus. DAPI‐flow cytometry was used to determine relative genome size and to infer polyploidization events.Results  Monophyly of the Afro‐montane Lychnis with the Eurasian diploid L. flos‐cuculi resolved as sister was strongly supported by the phylogenetic analyses. The Afro‐montane group was further divided into two strongly supported groups correlated with DNA ploidy levels. The relative genome size was species‐specific except for L. abyssinica, which had two genome‐size variants.Main conclusions  Our results demonstrate that the biogeographical history of the Afro‐montane Lychnis has been highly dynamic, including polyploidization and both old and recent long‐distance dispersal events, even between Eastern and West Africa. The ancestor is inferred to have immigrated once from Eurasia via the Arabian Peninsula to the Ethiopian highlands. Divergence in the lineage containing diploid taxa was followed by several dispersals from Ethiopia to the Eastern and Western Rift Mountains, and recently to West Africa. Divergence of the lineage including the tetraploid L. crassifolia may have taken place in Ethiopia, from where it dispersed to the Eastern and Western Rift Mountains; alternatively, it may have taken place in the Eastern Rift Mountains, followed by dispersal from there to the Western Rift Mountains and then to Ethiopia.

Nuclear DNA sequences from introns of the low‐copy nuclear gene family encoding the second largest subunit of RNA polymerases and the ribosomal internal transcribed spacer (ITS) regions, combined with the psbE‐petL spacer and the rps16 intron from the chloroplast genome were used to infer origins and phylogenetic relationships of North American polyploid Silene species and their closest relatives. Although the vast majority of North American Silene species are polyploid, which contrasts to the diploid condition dominating in other parts of the world, the phylogenetic analyses rejected a single origin of the North American polyploids. One lineage consists of tetraploid Silene menziesii and its diploid allies. A second lineage, Physolychnis s.l., consists of Arctic, European, Asian, and South American taxa in addition to the majority of the North American polyploids. The hexaploid S. hookeri is derived from an allopolyploidization between these two lineages. The tetraploid S. nivea does not belong to any of these lineages, but is closely related to the European diploid S. baccifera. The poor resolution within Physolychnis s.l. may be attributed to rapid radiation, recombination among homoeologues, homoplasy, or any combination of these factors. No extant diploid donors could be identified in Physolychnis s.l.