Evol Ecol Res 5: 615-622 (2003)     Full PDF if your library subscribes.

Variation in floral organ size depends on function:

a test with Commelina communis, an andromonoecious species

Atushi Ushimaru,1* Tomoyuki Itagaki2 and Hiroshi S. Ishii3

1Center for Ecological Research, Kyoto University, Kamitanokami, Otsu 520-2113, 2Department of Ecology and Evolutionary Biology, Graduate School of Life Science, Tohoku University, Sendai 980-8578 and  3Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan

Address all correspondence to Atushi Ushimaru, Research Institute for Humanity and Nature, 335 Takashima-cho, Kyoto 602-0878, Japan.
e-mail: ushimaru@chikyu.ac.jp


We measured the size of floral organs in andromonoecious Commelina communis to test the hypothesis that pollinator-mediated selection might regulate variation in the size of floral organs. We compared variation in floral organ size between C. communis perfect flowers, with fertile pistils, and C. communis staminate flowers, with sterile pistils. We hypothesized that variation in size of the sexually functionless pistil would be large. We found supporting evidence from eight C. communis populations. These results suggest that pollinator-mediated selection may have stabilized variation in the style length of perfect flowers. We also found differences in variation in length among three different types of anthers in both perfect and staminate flowers, only two of which produce fertile pollen. This is consistent with our prediction that mating-related organs should vary less in size than attraction-related organs.

Keywords: andromonoecy, Commelina, phenotypic size variation, pollinator-mediated stabilizing selection.

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