ORIGINAL ARTICLE: Phylogeographical history of the widespread meadow fescue (Festuca pratensis Huds.) inferred from chloroplast DNA sequences

摘要

Aim: Here we explore the variation in chloroplast DNA (cpDNA) in a widespread Eurasian diploid forage grass, meadow fescue (Festuca pratensis Huds.), to address its phylogeographical history. In particular, we aim to answer whether the post-glacial migration routes of meadow fescue are associated with the spread of agriculture or concurrent with well-documented natural migration pathways from glacial refugia. Location: A total of 56 Eurasian accessions of F. pratensis were analysed, representing the entire native distribution area as well as non-native areas in northernmost Europe. Methods: Based on initial sequencing of 10 non-coding cpDNA regions, three regions were sequenced for all F. pratensis accessions. For reference, three closely related species [the diploid Lolium perenne L. and the polyploids Festuca arundinacea Schreb. and Festuca gigantea (L.) Vill.] were also sequenced, as well as the more distantly related Festuca ovina L. Divergence times were estimated assuming a simple molecular clock, calibrated using a previously published estimate of 9 Myr for the divergence between fine-leaved (F. ovina) and broad-leaved fescues (F. pratensis, F. arundinacea and F. gigantea). Results: Limited, but geographically structured, cpDNA variation was observed in F. pratensis. Three haplotypes, estimated to have diverged 0.16 Ma, were identified: one western European (A), one with a wide eastern distribution from central-eastern Europe into Asia (B) and one Caucasian (C). The haplotypes of the polyploids and L. perenne were estimated to have diverged from haplotype A in F. pratensis 0.8-1.3 Ma. Main conclusions: We found no definite evidence for migration of the diploid F. pratensis associated with the spread of agriculture from the Fertile Crescent after the last glaciation. The distinct geographical structuring of the present-day variation in cpDNA can rather be explained by northwards expansion of the western haplotype from an Iberian refugium, expansion of the eastern haplotype from an unlocated (south-)eastern refugium and glacial survival without subsequent expansion from a Caucasian refugium. The high level of cpDNA divergence observed between this diploid and the polyploids which have probably been derived from it may suggest that the very low level of cpDNA variation in the diploid is caused by a recent bottleneck. Today, F. pratensis is widespread in the open agricultural landscape but appears otherwise confined to naturally open habitats such as river banks, and its populations may have been decimated when dense forests dominated in the previous interglacial.