Chemosensory genes and the evolution of aphid host races

The process of speciation involves the progressive evolution of reproductive isolation between divergent populations. When this process happens in the face of gene flow, differentiation is expected to be variable across the genome reflecting the direct operation of natural selection and the barrier created for regions surrounding selected loci. Population genomics and QTL mapping approaches have recently contributed significantly to detecting regions under selection and associated islands of differentiation but further progress is difficult in many systems. We argue that a candidate gene approach can significantly advance this field. We propose to study sequence and expression divergence for the entire known repertoire of chemosensory genes in host races of the pea aphid. This study system is unique in having multiple races at different levels of divergence, excellent background information and a sequenced genome. This allows us to apply the latest approaches (Nimblegen capture arrays, 454 sequencing and Illumina Digitial Gene Expression) to this major problem in evolutionary genetics.