Variation in floral sex allocation and reproductive success within inflorescences of Corydalis ambigua (Fumariaceae): pollination efficiency or resource limitation?

Abstract

Summary 1The variation of floral sex allocation with flower position within inflorescences was investigated in the spring ephemeral, Corydalis ambigua . Investment in female function ( pistil), attraction (corolla) and nectar production decreased from bottom to top flowers, whereas male investment (stamen) did not differ. 2 This self-incompatible species appears to set seeds as a result of visitation by nectar robbing bumblebee queens. The tendency of bees to visit lower flowers first and then move upwards within an inflorescence should result in directional pollen flow from bottom to top flowers. 3 Naturally pollinated upper flowers set fewer seeds than intermediate and lower flowers due to pollen limitation. The lack of differences in seed set and seed mass per pod following artificial outcrossing indicated that resource limitation did not explain the variation in seed production of flowers in different positions. Pollen viability also did not differ significantly between flower positions. 4 A model of pollination was developed that incorporated the visitation pattern of bumblebees and observed variations in nectar distribution between flower positions. This predicted that receipt of outcross pollen would decrease from bottom to top flowers, but that pollen export to other plants would not differ between flower positions provided that the pollen exchange rate of pollinators was either small or positively correlated with nectar content of each flower position. The observed pattern of floral sex allocation would then be parallel to relative success of pollen export and import between flower positions within inflorescences.

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“…Dohzono, unpublished data). All flowers open progressively from the bottom to the top of an inflorescence within two days on average (range 1-6 days) and the total flowering period of an inflorescence is approximately 18 days (Kudo et al 2001). Subsequently, the seeds mature and fall from the pods.…”

“…Corydalis ambigua is self-incompatible and is visited exclusively by bumble bee queens (Ohara and Higashi 1994). The effectiveness of bumble bee pollination differs among regions due to differences in bumble bee fauna (Ohara and Higashi 1994, Washitani et al 1997, Kudo et al 2001, Kudo and Kasagi 2004. Although it is not known which bumble bee species pollinate C. ambigua in Siberia, Kamchatka, and Sakhalin, C. ambigua may have never experienced pollination by B. terrestris because their distributions do not overlap.…”

“…Legitimate B. ardens always insert their proboscis into the spur from the flower entrance and suck the nectar. In contrast, B. hypocrita and B. terrestris have the large mandibles and thick proboscis, thereby they invariably bite holes at the spur of C. ambigua from the top or side of the flower, and rob nectar (Higashi et al 1988, Ito 1991, Kudo et al 2001, Kudo and Kasagi 2004, Matsumura et al 2004, Kenta et al 2007; J. Yokoyama and I. Dohzono, unpublished data). At our study sites, other bumble bee species (B. diversus, B. hypnorum, and B. schrencki), the bombylid fly (Bombylius sp.…”

“…Two weeks later, we collected the inflorescence. All pods were opened under a dissection microscope, and seeds and ovules were categorized as matured, undeveloped, eaten, or unfertilized (Kudo et al 2001). Undeveloped (immature) seeds were larger than the conspicuously small, unfertilized ovules but were smaller than mature seeds.…”

“…4). Previous studies indicated that although B. hypocrita and B. terrestris rob nectar by perforating spurs (Ohara and Higashi 1994, Kudo et al 2001, Kudo and Kasagi 2004, the former species sometimes accidentally opens petals and picks up pollen while robbing, which can contribute to fertilization (robberlike pollination; Higashi et al 1988). In some areas in Hokkaido, Japan, C. ambigua is pollinated primarily by B. hypocrita, and floral sex allocation has been altered to improve pollen flow (Kudo and Kasagi 2004).…”