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(American Journal of Botany. 2007;94:249-258.)
© 2007 Botanical Society of America, Inc.

Article

Colored floral organs influence pollinator behavior and pollen transfer in Commelina communis (Commelinaceae)1

Atushi Ushimaru5, Takeshi Watanabe and Kensuke Nakata

2Research Institute for Humanity and Nature, 335 Takashima-cho, Kyoto 602-0878, Japan; 3Department of Zoology, Faculty of Science, Kyoto University, Kitashirakawa Oiwake-cho, Kyoto 606-8502, Japan; and 4Faculty of Human Environment, Nagasaki Institute of Applied Science, Abamachi 536, Nagasaki 851-0193, Japan

ABSTRACT

Visual floral guides such as colored anthers, lines, dots, and UV-absorption patterns on petals are commonly observed in insect-pollinated angiosperms. Floral guides that are known to enhance foraging efficiency of visitors on flowers thus promote return visits (foraging facilitation hypothesis, which predicts that visitors will discriminate against flowers with inferior floral guides). In this study, we experimentally examined the hypothesis that floral guides also prevent pollen-theft behavior by floral visitors (theft prevention hypothesis), which has rarely been tested. Nectarless flowers of Commelina communis have three types of brightly colored floral organs: large blue petals, rewarding yellow anthers, and nonrewarding yellow anthers. Colored floral organs were removed artificially from plants in two natural populations of C. communis. Removal of the nonrewarding yellow anthers diminished hoverings in front of flowers and tended to reduce the number of total floral visitor landings, supporting the foraging facilitation hypothesis. Additionally, removal of the rewarding yellow anther decreased the frequency of legitimate landings on flowers and the legitimate landing-to-total landing ratio, which is consistent with the theft prevention hypothesis. The nonrewarding anthers and the rewarding yellow anthers were shown to play an important role in increasing visitor landings and orienting floral visitors toward a landing point appropriate for pollination, respectively. We also showed that the absence of yellow anthers decreased both pollen dispatch from brown anthers and receipt by stigmas in C. communis. These findings support both the foraging facilitation hypothesis and the theft prevention hypothesis.

Key Words: anther differentiation • Commelina • floral guide • pollen theft • zygomorphic flower






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