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The Signaling Function of an Extra-floral Display: What Selects for Signal Development?

Listed author(s):
  • Tamar Keasar


  • Adi Sadeh
  • Avi Shmida
Registered author(s):

    The vertical inflorescences of the Mediterranean annual Salvia viridis carry many small, colorful flowers, and are frequently terminated by a conspicuous tuft of colorful leaves ("flags") that attracts insect pollinators. Insects may use the flags as indicators of the food reward in the inflorescences, as long-distance cues for locating and choosing flowering patches, or both. Clipping of flags from patches of inflorescences in the field significantly reduced the number of pollinators that arrived at the patches, but not the total number of inflorescences and flowers visited by them. The number of flowers visited per inflorescence significantly increased with inflorescence size, however. Inflorescence and flower visits rates signific antly increased with patch size when flags were present, but not after flag removal. 6% of the plants in the study population did not develop any flag during blooming, yet suffered no reduction in seed set as compared to flag-bearing neighboring individuals. These results suggest that flags signal long-distance information to pollinators (perhaps indicating patch location or size), while flower-related cues may indicate inflorescence quality. Plants that do not develop flags probably benefit from the flag signals displayed by their neighbors, without bearing the costs of flag production. Thus, flagproducing plants can be viewed as altruists that enhance their neighbors' fitness. Greenhouse-grown S. viridis plants allocated = 0.5% of their biomass to flag production, and plants grown under water stress did not reduce their biomass allocation to flags as compared to irrigated controls. These findings suggest that the expenses of flag production are modest, perhaps reducing the cost of altruism. We discuss additional potential evolutionary mechanisms that may select for the maintenance of flag production.

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    Paper provided by The Federmann Center for the Study of Rationality, the Hebrew University, Jerusalem in its series Discussion Paper Series with number dp468.

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    Length: 26 pages
    Date of creation: Nov 2007
    Handle: RePEc:huj:dispap:dp468
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    1. Tamar Keasar & Gad Pollak & Rachel Arnon & Dan Cohen & Avi Shmida, 2006. "Honesty of Signaling and Pollinator Attraction: The Case of Flag-Like Bracts," Levine's Bibliography 321307000000000599, UCLA Department of Economics.
    2. Tamar Keasar & Gad Pollak & Rachel Arnon & Dan Cohen & Avi Shmida, 2006. "Honesty of Signaling and Pollinator Attraction: The Case of Flag-Like Bracts," Discussion Paper Series dp438, The Federmann Center for the Study of Rationality, the Hebrew University, Jerusalem.
    3. Janne S. Kotiaho, 2002. "Sexual selection and condition dependence of courtship display in three species of horned dung beetles," Behavioral Ecology, International Society for Behavioral Ecology, vol. 13(6), pages 791-799, November.
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