Phylogeography of Homalothecium sericeum (Hedw.) Br. Eur.;: toward a reconstruction of glacial survival and postglacial migration

Analyses of variation in ITS1 sequences among 75 populations ( 102 individuals) of the moss Homalothecium sericeum revealed the presence of 22 distinct haplotypes as well as nine recombinants. The recombinants, always found in areas of overlap between the putative parent haplotypes, show that establishment from spores is at least sometimes effective. Northern and central European populations possess only the two commonest and widespread haplotypes, while southern populations show much greater diversity and unique haplotypes. Two particularly distinct haplotype groups occur, respectively, in the eastern Mediterranean and in Iberia North Africa. These results, similar to those obtained in previous studies on a range of organisms, suggest glacial survival in, and recolonization from, the Mediterranean peninsulas. In the present case, the Balkan and Italian peninsulas are the most likely source of extant northern populations. The pattern shown by H. sericeum differs, however, from that exhibited by other organisms studied in showing high levels of unique haplotypic diversity in the British Isles and adjacent mainland, providing evidence that it survived in periglacial refugia in these areas. Nesting of H. lutescens sequences within those of H. sericeum indicates that it has been derived from within the latter. Molecular clock estimates of the timing of major divergences within the network are consistent with the Pleistocene glacial record.