Learning magnifies individual variation in heterospecific mating propensity

Recent research indicating learning in the context of sexual behaviour in fruit flies suggests that learning could increase levels of assortative mating between partially diverged populations. We present a graphic model examining the role of learning and a series of experiments evaluating assumptions and predictions of the model. We found that male Drosophila persimilis that previously succeeded in mating with females of the sibling species, D. pseudoobscura, did not have a higher heterospecific mating success than males that were either virgin or previously mated with conspecific females. On the other hand, female D. pseudoobscura with apparently strict mating criteria, which rejected heterospecific males, were also more likely to reject conspecific males than were females inexperienced with males. Finally, D. persimilis males previously rejected by heterospecific females courted significantly less and had half as much heterospecific mating success as males previously accepted by heterospecific females. These results, combined with previous evidence demonstrating that males rejected by heterospecific females learn to avoid courting such females, indicate that learning can increase phenotypic divergence between populations with partial pre-mating isolation.