American Journal of Botany, Vol 84, 1383, Copyright © 1997 by Botanical Society of America, Inc.

REPRODUCTIVE BIOLOGY

Variation in pollinator abundance and selection on fragrance phenotypes in an epiphytic orchid

JD Ackerman, EJ Melendez-Ackerman and J Salguero-Faria

Extraordinary floral variation is common among some orchids that employ deception to attract pollinators. This variation may be maintained by frequency-dependent selection where rare phenotypes are preferred. Over a 2-yr period, 1993-1994, we monitored the reproductive success of Tolumnia variegata, an obligately outcrossing epiphytic orchid, at three localities in Puerto Rico that differed in pollinator service. Plants varied in floral morphology and fragrance characteristics. Artificial arrays of varying frequencies of scentless and fragrant phenotypes were established to test for frequency-dependent selection. Where pollinators were rare (Cambalache, range of census average = 0-0.2 bees/h), 0.9-1.2% of the flowers were effectively visited (pollinarium removals and pollinations). At Tortuguero where 0.4-1.1 bees/h were observed, 4-9.2% of the flowers were visited. At Pi;atnones where bees were the most abundant (1.4-5.2 bees/h), 20.9-25.0% of the flowers were visited. A significant portion of the variance in all measures of reproductive success (male, female, and combined) was explained by differences among populations, which we attribute mostly to variation in pollinator abundance. Neither the fragrance phenotype nor its frequency had a significant effect on success as revealed by a split-plot ANOVA. There was a significant interaction between population and phenotypic frequencies in all our measures of reproductive success, but only for the 1994 flowering season. Thus, variation in floral fragrance phenotypes is not likely maintained by frequency-dependent selection. High levels of variation remain unexplained.

This article has been cited by other articles:

				C. C. Salzmann, A. M. Nardella, S. Cozzolino, and F. P. Schiestl Variability in Floral Scent in Rewarding and Deceptive Orchids: The Signature of Pollinator-imposed Selection? Ann. Bot., October 1, 2007; 100(4): 757 - 765. [Abstract] [Full Text] [PDF]

				V. PARRA-TABLA and C. F. VARGAS Phenology and Phenotypic Natural Selection on the Flowering Time of a Deceit-pollinated Tropical Orchid, Myrmecophila christinae Ann. Bot., August 1, 2004; 94(2): 243 - 250. [Abstract] [Full Text] [PDF]

				E. Cayenne Engel and R. E. Irwin Linking pollinator visitation rate and pollen receipt Am. J. Botany, November 1, 2003; 90(11): 1612 - 1618. [Abstract] [Full Text] [PDF]

				T. Miyake and M. Yafuso Floral scents affect reproductive success in fly-pollinated Alocasia odora (Araceae) Am. J. Botany, March 1, 2003; 90(3): 370 - 376. [Abstract] [Full Text] [PDF]

				J. Kunze and A. Gumbert The combined effect of color and odor on flower choice behavior of bumble bees in flower mimicry systems Behav. Ecol., July 1, 2001; 12(4): 447 - 456. [Abstract] [Full Text] [PDF]

				M. R. M. Neiland and C. C. Wilcock Fruit set, nectar reward, and rarity in the Orchidaceae Am. J. Botany, December 1, 1998; 85(12): 1657 - 1657. [Abstract] [Full Text]