Effect of floral organ sizes on female reproductive success inErythronium japonicum (Liliaceae)

Abstract

We examined the effects of floral organ size on female reproductive success in self-incompatible Erythronium japonicure. We measured tepal size and anther.stigma separation and investigated the relationship between these measurements and fruiting and seeding success. We found that tepal length was positively correlated with fruiting success and the number of seeds per fruit. This su~ests that pollinator attraction is affected by tepal length in E.japonicum and that the number of pollinator visits affects female reproductive success. Anther.stigma separatlon was the most variable floral trait measured and was not correlated with either fruiting or seeding success in this species, su~esting that the proportion of outcross pollen deposited on stigmas by pollinators does not increase with antherstigma separation. This is inconsistent with a previous report on E~/htonium. grandiflorum. Pollinator size might explain this interspecHic difference in the effect of anther-stigma separation on female reproductive success.Keywords: anther-stigma separation, Erythroniurn, femal reproductive success, pollinator attraction, tepal size Pollinator-mediated selection in angiosperms is thouDht to modify floral characteristics, such as shape, size, color, and scent (Darwin, 1859;Stebbins, 1970). Animal-pollinated flowers typically consist of attractionrelated organs, such as sepals and petals, and matingrelated organs, such as stamens and pistils. It has been su~ested that the sizes of these organs sometimes evolve under different selection pressures (Galen and Stanton, 1989;Conner, 1997;Ushimaru and Nakata, 2001). For example, floral attractiveness is often influenced by petal or sepal size, and larger petals or sepals increase pollinator visits per flower in several taxa of flowering plants (Bell, 1985;Galen, 1989; Galen and Stanton, 1989;Campbell et al., 1991; Eckhart, 1991;Conner and Rush, 1996). In such angiosperms, pollinator-mediated selection should favor larger attraction-related organs. On the other hand, the sizes of the stamens and pistils often affect pollen dispatch and receipt (Thomson and Stratton, 1985;Murcia, 1990;Motten and Stone, 2000;Ushimaru and Nakata, 2001). In some plant species, stigmas that are more prominent relative to the anthers receive more outcrosspollen (Thomson and Stratton, 1985;Murcia, 1990), and anther-stigma separation affects the outcrossing *Corresponding author; fax +81-75-229-6150 e-mail ushimaru@chikyu.ac.jp rate (Motten and Stone, 2000). Thus, the sizes of both attraction-related organs and mating-related organs would affect reproductive success in flowering plants.This paper briefly reports on how floral organ size affects female reproductive success in the spring ephemeral, E.japonicum. This species is self-incompatible and needs insect vectors for pollination. Substantial variation in anther-stigma separation was reported in closely related E. grandiflorum, in which flowers with more anther-stigma separation received more outcrosspollen (Thomson and Stratton, 1985). We measured the ...

Flowers adaptively face down‐slope in 10 forest‐floor herbs

“…This species is mainly pollinated by relatively large bees, such as Xylocopa , Tetralonia , Nomada and Bombus species (Utech & Kawano 1975). However, we have observed that E. japonicum flowers are most frequently visited by small bees in the OFR (Ushimaru et al . 2003).…”