Associate Professor University of Kentucky Lexington, Kentucky
Plant-feeding insects are unusually diverse, but the mechanisms that give rise to this pattern remain unclear. Here, we use a pair of hybridizing pine sawflies that are specialized on different host plants as a model to understand the mechanisms underlying host-shift speciation. Previous work demonstrates that Neodiprion lecontei and Neodiprion pinetum (Hymenoptera, Diprionidae) have diverged with gene flow and differ in many different host related traits. One explanation for how these species have remained distinct in the face of gene flow and continued hybridization is that the genes underlying host-use differences are tightly clustered in the genome, reducing recombination. To test this hypothesis, we used a QTL mapping approach to characterize the genetic architecture of several host-use traits. Contrary to our predictions, we found that host-use QTL occur in many different regions of the genome. We also found evidence of host-associated fitness trade-offs for several egg-laying traits. Together, these traits render hybrid females ecologically sterile. Taken together, our data suggest that the causal genes within identified QTL peaks can be considered “speciation genes” and that reduced recombination is not necessary for sympatric speciation via host shift.
