Host-shift effects on mating behavior and incipient pre-mating isolation in seed beetle

Mating behavior is based on communication among mates and includes both sexual signaling and mating preferences. In phytophagous insects, shift to a novel host will expose associated traits to novel selection regimes and eventually cause assortative mating and sexual isolation between populations inhabiting diverse host plants. We investigated the relationship between short- and long-term changes in mating systems on Acanthoscelides obtectus. Mating preferences were evaluated using measures of copulation frequency in mating trials within and among populations and by measuring time spent in sexual interactions prior to copulation. Sexual signaling was previously analyzed by chemical detection of contact pheromones (i.e., cuticular hydrocarbons [CHCs]), and these results were used in this study. Laboratory populations evolved for 50 generations either on the optimal host (common bean) or on the suboptimal host (chickpea). To determine short-term effects, subsets of individuals from each population were exposed to the alternative host for 1 generation. We revealed higher level of indiscriminate mating in populations, which evolved on the suboptimal host. Males from these populations spent less time in assessing mates although they had the ability to discriminate between signals. Short-term larval experience on the suboptimal host also decreased selectivity of mates. The results imply that plastically induced reduction in mate discrimination, after a shift to suboptimal host, may have been canalized through long-term genetic changes underlying behavioral development. Significant reproductive isolation between the 2 sets of populations was revealed regardless of the short-term host treatment.