Size-dependent sex allocation in a monocarpic perennial herb, Cardiocrinum cordatum (Liliaceae)

The size-dependent sex allocation model predicts that the relative resource allocation to female function often increases with plant size in animal-pollinated plants. If size effects on reproductive success vary depending on the environmental conditions, however, the size dependency may differ among populations. We tried to detect site-specific variation in size-dependent sex allocation of a monocarpic hermaphrodite with reference to light availability. Multiple flowers and fruits were sampled from the individuals of Cardiocrinum cordatum, a monocarpic understory herb, and pollen, ovule and seed production were measured with reference to the plant size in two populations. Furthermore, frequency and foraging behavior of pollinator visitation was observed. Ovule production per flower increased with plant size in both populations, while pollen production per flower increased with size only in the population under sparse canopy. Therefore, proportional allocation to male function decreased with plant size in the population under closed canopy, but did not change in the population under sparse canopy. Pollinators usually visited only one flower per plant, indicating the negligible geitonogamous pollination in this species. Although seed production under closed canopy was lower than that under sparse canopy, seed-set rate per flower and seed mass per fruit were independent of plant size in either of the populations. Size-dependent sex allocation in this species was site-specific, suggesting that not only resource storage before reproduction (i.e., plant size) but also resource availability of environment throughout the reproductive process (i.e., light availability) affect reproductive performance in this species.