Land ahead: using genome scans to identify molecular markers of adaptive relevance

Adaptation is back on the research schedules of evolutionists and ecologists. This renewed interest is driven by globalchange, to which species, in particular arctic and alpine ones, either react by migration or adaptation. In this overview, wegive a brief introduction to the use of genome scans along with environmental data to identify molecular markers of adap-tive relevance. This approach encompasses the sampling of many populations along ecological gradients or from differenthabitat types combined with genome scans using presumably neutral markers such as amplified fragment length polymor-phisms or microsatellites. To identify markers linked to genes under selection, two different methods (besides others) areparticularly relevant. (1) One searches for markers exhibiting higher genetic differentiation among populations thanexpected under neutrality. The frequencies of alleles at such outlier loci can then be related to ecological factors. (2) Theother method uses logistic regression between allele presence/absence and ecological factors (i.e. an allele distributionmodel). It thus directly links marker occurrence with environmental data. We illustrate these two methods with examplesfrom the literature. The strength of genome scans used in parallel with environmental data is that they provide distinct cluesfor selective forces acting on molecular markers of adaptive relevance in real landscapes. We further discuss limitations ofgenome scans (e.g. sensitivity to phylogeographic structure and bottlenecks) and of other genomic approaches to detectadaptive molecular markers such as candidate genes, quantitative trait loci or transcription profiling. We stress that theselective advantage of particular alleles has to be proven in selection experiments. We conclude that combining studies onadaptive and neutral molecular markers will largely contribute to our understanding of how species react to global changeand will allow us to investigate the ‘migration of adaptation’.