The Basis of Reproductive Isolation Between Ecologically Divergent Host Plant Races

Sammanfattning: Insects and their host plants constitute a considerable proportion of the diversity on earth, and host shifts hence provide excellent study systems to study the process that drive diversification. In this study, I address what the mechanism to achieve assortative mating is in two host races using different host plants to increase our understanding of how reproductive isolation can arise in the face of ecological specialization. The focal species Tephritis conura is a peacock fly that has recently diverged into two host races through a host plant shift from Cirsium heterophyllum to C. oleraceum. I performed behavioral trials on the two host races, in sympatric and allopatric populations, to test host plant preference and the importance of both visual and olfactory cues for identifying and choosing host plant. I found that the flies preferred the scent of their host plant and spent significantly longer time in the part of a Y-maze with the scent from their host plant. Conversely, flies did not spend significantly longer time in a compartment with visual contact with their host plants. T. conura is thus able to identify their host plant, indicating that host plant preference acts as a pre-mating isolating barrier between the two host plant races. If there would be stronger selection for a plant preference in sympatry to avoid maladaptive hybridization we would expect the preference to be stronger in sympatry than allopatry, but I did not detect any such difference in preference strength between the sympatric and allopatric population with C. oleraceum as host plant with the sample size used in this study. Studies identifying the genetic basis of host plant adaptation and preference would be interesting to further understand how mate preference is coupled to performance differences on host plants during host plant driven diversification.