1) Not only mutualistic plant–pollinator interactions but also antagonistic plant–herbivore interactions can be a selective force on sex allocation in angiosperms. In this study, we investigate how predispersal seed predation affects the reproductive success and floral gender of andromonoecious herbs on a natural snowmelt gradient.

2) The developing fruits of an alpine herb (Peucedanum multivittatum: Apiaceae) were intensively predated by lepidopteran larvae (Phaulernis fulviguttella: Epermeniidae) in the early-snowmelt populations, where flowering occurred from mid to late July. In the late-snowmelt populations, where flowering occurred after early August, seed predation was negligible due to the oviposition of the predator moths being concentrated in early summer. The moths tended to oviposit on plants with more perfect flowers and taller inflorescences, whereas the number of male flowers was independent of their oviposition preference. 

3) Responding to the oviposition behavior, the proportion of male flowers was the largest and floral stems were the shortest in the early-snowmelt population suffering from intensive predation damage. The contribution of perfect flowers to intact seed production significantly decreased with earlier flowering along the snowmelt gradient. Fitness measurements using genetic markers revealed that the increase in flower number resulted in greater success as a pollen donor within a population. Thus, plants can ameliorate the risk of predation damage to sired seeds by wider pollen dispersal. 

4) Synthesis: Taken together, the greater production of male flowers at the expense of perfect flowers is advantageous under intensive predation pressure owing to the reduction of predation damage (female fitness) and the improvement of siring success (male fitness). These results revealed that predispersal seed predation acts as a selective force that promotes male-biased sex allocation in andromonoecious plants.