FROM THE COVER ev –s LTE

ct en The genetic foundations of this divergence process are largely unknown and are here Introducti Speciation o populations ments despite the presence of initially high gene flow stood (Wu 2001; Via 2009; Nosil & Schluter 2011). One g effect of ter ‘QTLs’) how many across the genome, and how does their divergence influence selec-major effect can protect large genomic regions from Molecular Ecology (2012) 21, 2852–2862 doi: 10.1111/j.1365-294X.2012.05509.xfundamental unresolved question is how genetic differ-entiation that builds up between diverging populations is distributed across the genome. Adaptive divergence between populations certainly implies that selection is gene flow between selective environments (Turner et al. 2005; Via & West 2008; Via 2009). Within these regions, divergence between environments will be elevated rela-tive to the rest of the genome, and additional QTLs can become recruited for further adaptive divergence. At the other extreme, adaptive divergence might involve numerous QTLs of relatively small effect, in which cas