Genetic Boundaries

The use of molecular genetic markers has now opened up an entirely new dimension in our ability to trace the migration and development of plant populations, especially during the post-glacial vegetation re-advance into marginal areas. We now know that Britain received oaks, shrews, hedgehogs and bears from Spain, and alder, beech, newts and grasshoppers from the Balkans (Hewitt, 1999).

In relation to marginal oceanic areas the postglacial history of oak is of particular interest. The distribution of some of the principal lineages of white deciduous oak is shown in Fig. 1.13. It is noteworthy that the post-glacial population that re-established itself in the west would have had a long period of residence in the more oceanic regions of Iberia (Brewer et al., 2005). Differentiation of the cpDNA haplotypes of this lineage as it now occurs within Britain and Ireland (Fig. 1.14) reveals a further differentiation between the oceanic regions of Ireland and western Britain as opposed to the more continental regions to the east, with one particular lineage being more predominant in the more oceanic regions (Lowe et al., 2005).

Further examples of the use of genetic markers in tracing plant migrations are discussed in Chapter 6 in relation to the long-term survival of the purple saxifrage (Saxifraga oppositifolia).

Snow patch Exposed ridge

Fig. 1.12 Ecotypic variation related to growing season length in arctic plants. Snow patch (left) and exposed ridge (right) forms of (a) Dryas octopetala and (b) Saxifraga oppositifolia. (The D. octopetala figure is reproduced with permission from McGraw & Antonovics, 1983, and S. oppositifolia from the drawing by Dagny Tande Lid, in Lid & Lid, 1994.)

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