HOST-PLANT-INDUCED ASSORTATIVE MATING IN ENCHENOPA TREEHOPPERS.

The hypothesis tested here is whether extrinsic host-plant-induced life-history timing and mating biology promote assortative mating along host-plant lines. In the arboreal, univoltine Enchenopa treehopper system, host plants mediate the timing and synchronization of egg hatch. The result is a uniform age structure with a restricted mating window during which females mate once. Enchenopa on host plants that differ in phenology have asynchronous life histories and mating windows, suggesting that temporal differences may promote assortative mating. To test this hypothesis, egg hatch of Enchenopa from the same host-plant species was manipulated to produce continuous adult age-classes. Under experimental conditions with no spatial barriers, mating occurred between individuals similar in age. The mechanism promoting this assortative mating is differential mortality in males and females, such that few males are still alive when females in successive age-classes mate. Such host-plant-induced assortative mating is viewed as an effective mechanism to protect the integrity of gene pools from migrants, permitting selection for host-plant-adapted genotypes and speciation. © 1990 The Society for the Study of Evolution.