Molecules and migration: Biogeographical studies in cruciferous plants

In the past two decades our understanding of plant biogeography has been improved substantially by the introduction of various molecular marker systems. Especially within the angiosperms, maternally inherited chloroplast DNA based data sets have elucidated not only genetic relatedness but also geographic structuring of genetic variation. These findings were based on the observation that DNA molecules might mutate during migration, which consequently found its manifestation in the term phylogeography introduced in the late 80s by John Avise. However, other markers such as codominantly inherited allozymes were used before the advent of DNA techniques and were used in theoretical population genetic studies. In actual phylogeographic studies, highly variable markers, such as AFLPs (amplified fragment length polymorphisms), were needed to unravel recent species histories (e.g. pleistocenic differentiation). The levels of molecular variation at such markers are closer to that of allelic variation measured with allozymes. Hence, an increasing number of studies have relied on highly polypmorphic markers, such as DNA microsatellite loci. Herein, we try to present an overview on the various biogeographic and phylogeographic studies using various molecular (including isozyme) markers and methodological approaches to analyse them, concentrating on studies done with representatives of the Brassicaceae family. © Springer-Verlag 2006.