Artificial selection of plants promotes temporal reproductive isolation in insect population: A test case using highbush blueberry and the blueberry stem gall wasp

Abstract. Humans have artificially manipulated the genomes of agriculturally important plants for centuries, selecting for traits to increase their suitability to human requirements during crop domestication. However, few studies have investigated the consequences of artificial selection and domestication of plant species on the evolution of reproductive isolation and population divergence of herbivorous insects that use these plants. Here, we test the hypothesis that artificial selection for different cultivars of highbush blueberries (Vaccinium corymbosum) that have different growth phenologies, results in temporal reproductive isolation of a host-specific pest insect, the blueberry stem gall wasp, Hemadas nubilpennis (Hymenoptera: Pteromalidae). Using a series of field- and laboratory-based studies we found that differences in the emergence timing of adult stem gall wasps at commercial farms in the blueberry growing region of western and eastern Michigan, USA are associated with differences in the growth phenology of six different cultivars. These differences in the timing of adult emergence, when coupled with a short reproductive stage, can result in strong pre-zygotic temporal isolation between specific sympatric wasp populations using these different cultivars. Incidentally, artificially-induced changes in plant phenology of cultivars during domestication may have “cascading” effects that reduce gene flow between host-associated populations of H. nubilipennis. Given that populations of blueberry stem gall wasp on these different cultivars share a diverse community of natural enemies that attack the wasp at different life stages, our results set the stage for testing for parallelism in the role of cascading reproductive isolation across multiple trophic levels.