Genetic linkage of ecological specialization and reproductive isolation inpea aphids

The evolution of ecological specialization generates biological diversity a nd may lead to speciation(1-3). Genetic architecture can either speed or re tard this process. If resource use and mate choice have a common genetic ba sis through pleiotropy or close linkage, the resulting genetic correlations can promote the joint evolution of specialization and reproductive isolati on, facilitating speciation(4-6). Here we present a model of the role of ge netic correlations in specialization and speciation, and test it by analysi ng the genetic architecture of key traits in two highly specialized host ra ces of the pea aphid (Acyrthosiphon pisum pisum; Hemiptera : Aphididae). We found several complexes of pleiotropic or closely linked quantitative trai t loci (QTL) that affect key traits in ways that would promote speciation: QTL with antagonistic effects on performance on the two hosts are linked to QTL that produce asortative mating (through habitat choice). This type of genetic architecture may be common in taxa that have speciated under diverg ent natural selection.