With the right tropical tree, a quick sniff can tell the boy flowers from the girls.
These Glochidion and Phyllanthus species separate their sex organs into male-only and female-only clusters of flowers. Even a human nose easily identifies the sex, says Tomoko Okamoto of the Forestry and Forest Products Research Institute in Tsukuba, Japan.
Many flowers of a single species smell similar, if not identical. After all, they need to lure the same pollinator. Among the double-odor trees, however, clarifying the sex of the flower might serve their pollinators’ unusual needs, Okamoto and her colleagues suggest October 22 in the Proceedings of the Royal Society B.
Those pollinators, female Epicephala moths, lay their eggs in female flowers and depend on developing seeds to nourish caterpillars. Okamoto, then at Kyoto University, and her colleagues found that of 38 female moths in a lab test making their first scent-seeking choice, 30 picked a male odor instead of a female one. Finding a male first lets a female moth snag pollen grains. When she moves on to a female flower, she deposits pollen, boosting chances that seeds will develop and feed her youngsters.
Analyzing the scents of 11 tree species, the team found that the seven pollinated by Epicephala moths emitted odors with quite different major ingredients for male and female flowers. The remaining species, with pollinators that don’t need seeds, didn’t have such disparate odors.
Okamoto enjoys most of the trees’ odors. “I wish I could use the scent extract of Glochidion flowers as perfume,” she says.
T. Okamoto et al. Active pollination favours sexual dimorphism in floral scent. Proceedings of the Royal Society B. Published online October 22, 2013. doi: 10.1098/rspb.2013.2280.
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M. Kato, A. Takimura and A. Kawakita. An obligate pollination mutualism and reciprocal diversification in the tree genus Glochidion (Euphorbiaceae). Proceedings of the National Academy of Sciences. Vol. 100, April 29, 2003, p. 5264. doi: 10.1073/pnas.0837153100
T.-L. Ashman et al. The scent of a male: the role of floral volatiles in pollination of a gender dimorphic plant. Ecology. Vol. 86, August 2005, p. 2099. doi: 10.1890/04-1161.
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