Temporal changes in calyx tube length of Clematis stans (Ranunculaceae): a strategy for pollination by two bumble bee species with different proboscis lengths

Abstract

We examined the adaptive significance of a temporal decrease in the calyx tube length of Clematis stans, a dioecious species pollinated by Bombus diversus (long proboscis) and B. honshuensis (short proboscis). We compared visitation frequency, pollen removal, pollen deposition, and fruit set after a single visit among three flower stages, differentiated by calyx tube length. Bombus diversus frequently visited and removed significantly more pollen from long flowers. Bombus honshuensis visited and tended to remove more pollen from short flowers. Both pollinators deposited more pollen in short flowers, resulting in higher fruit set. These results indicate that size correspondence between the proboscis and the calyx tube enhances visitation frequency and pollen removal, but not pollen deposition. Because a single visit does not fertilize all ovules of a flower, multiple visits by two bumble bee species may increase seed production and genetic diversity of offspring. By temporally changing calyx tube length, C. stans can use two bumble bee pollinators and maintain specialized relationships with each. This strategy may be adaptive when the pollinator fauna fluctuates, and is economical because it eliminates costs required to produce different types of flowers. This constitutes a novel pattern of temporal specialization in flower-pollinator relationships.

Floral development in Anemoneae (Ranunculaceae)

“…In some species of Clematis , nectar is produced on the ventral side of the lower part of the stamen filaments or lower part of the staminodes (Schaffnit, 1904; Daumann & Slavíková, 1968). For Clematis stans Siebold & Zucc., an origin from the ‘base of the calyx tube’ has been mentioned, but without a precise indication of the site of the secretory tissue (Dohzono & Suzuki, 2002; Dohzono, Suzuki & Murata, 2004).…”

Geographic Variation in Flower Size and Flower-Visitor Composition of Two Bumblebee-Pollinated, Spring-Flowering Herbs, <i>Lamium album</i> L. var. <i>barbatum</i> (Lamiaceae) and <i>Meehania urticifolia</i> (Lamiaceae)

“…Moreover, bumblebees have been reported to visit these flowers (L. album [17] [27]; M. urticifolia [28] [29]). Many studies have shown that in long-tubed flower species, flower dimensions such as corolla length and corolla tube length are correlated with pollinator size [22] [30] [31]. However, nectar robbers sometimes seriously decrease the fitness of long-tubed flower species [32], and adaptive changes in flower traits to prevent nectar robbing have been reported in some plants [9] [11].…”

Alien Bumble Bee Affects Native Plant Reproduction Through Interactions With Native Bumble Bees

“…Spur or floral tube lengths in many groups of flowering plants are positively correlated with the lengths of the mouthparts (proboscis) of certain pollinators, implying specialized relationships between the species (Grant and Grant 1965, Inouye 1980, Nilsson 1988, Suzuki 1992, Dohzono et al 2004). Such specialist mutualisms may be more vulnerable to invasive alien pollinators than generalist plants that are visited by a variety of native pollinators.…”