Characterisation of chloroplast DNA haplotypes to reveal the provenance and genetic structure of oaks in Ireland

The first phylogeographical description of oak populations in Ireland is presented and discussed in an European context. Using chloroplast DNA PCR-RFLP, a geographical genetic structure was obtained for oak populations across the island of Ireland. Two chloroplast haplotypes, 10 and 12, predominated and most populations were fixed for a single haplotype. The distribution of haplotypes within the species was shown to be unequal in Quercus petraea and more equal in Quercus robur. Haplotype 12 predominated in Q. petraea and haplotype 10 was more evenly distributed between the two species. Haplotype diversity is lower than in Britain and much lower than in France or Spain. We ascribe this to Irelandʹs isolation and hence to limited ʹfounderʹ populations. The haplotype distribution was used to infer possible postglacial migration routes of oak into Ireland. The putative migration routes confirm those deduced from palaeoecological data and give further information on the dynamics of invasion. While the origin of the haplotypes is confirmed to be the Iberian Peninsula refugium, the proposed routes of migration into Ireland are still tentative.