Format: ORAL

Gaku Kudo, Akari Shibata

Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan

Not only mutualistic plantpollinator interactions but also antagonistic plantherbivore interactions can be a selective force on sex allocation in angiosperms. The present talk addresses how predispersal seed predation affects the reproductive success and floral gender of andromonoecious herbs on a natural snowmelt gradient. The developing fruits of an alpine herb (Peucedanum multivittatum: Apiaceae) were intensively predated by a specialist lepidopteran larvae (Phaulernis fulviguttella: Epermeniidae) in the early-snowmelt habitat, where flowering occurred from mid to late July. In the late-snowmelt habitat, where flowering occurred after early August, seed predation was negligible because the oviposition of the predator moths was concentrated in early summer. The moths tended to oviposit on umbels with more perfect flowers and taller stems, whereas the number of male flowers was independent of their oviposition preference. Plants having male-biased umbels and short floral stems were prevalent in the early-flowering population, where plants suffered from intensive predation damage. The proportion of perfect flowers increased in the later flowering populations. The contribution of perfect flowers to intact fruit production was small when flowering occurred early in the season, and it consistently increased with the lateness of flowering period along the snowmelt gradient. Fitness measurements in the early-flowering population revealed that the production of many perfect flowers resulted in lower female fitness due to intensive seed predation. In contrast, male fitness as a pollen donor increased with total flower production irrespective of the composition of perfect and male flowers. Taken together, the greater production of male flowers at the expense of perfect flowers is advantageous under intensive predation pressure owing to the mitigation of predation damage with keeping the siring success. These results revealed that predispersal seed predation acts as a selective force that promotes male-biased sex allocation in andromonoecious plants.