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AJB Advance Access Published online ahead of print November 10, 2009; doi:10.3732/ajb.0900124 American Journal of Botany © 2009 Botanical Society of America, Inc.

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Cryptic bracts facilitate herbivore avoidance in the mycoheterotrophic plant Monotropsis odorata (Ericaceae)¹

² Department of Biological Sciences University of Cincinnati Cincinnati, Ohio 45221-0006 USA ³ Department of Biology Alma College Alma, Michigan 48801 USA

ABSTRACT

Plant coloration, shown to play a dynamic role in animal attraction, has been proposed as a means of defense, although these reports lack experimental evidence. This study empirically assesses defensive coloration in the mycoheterotrophic plant, Monotropsis odorata, which produces stems and flowers covered by dried vegetative bracts. Field studies were conducted using an experimental group of plants with bracts removed and a control group to evaluate the frequency of and fitness impacts associated with herbivory. Additionally, we quantitatively assessed the reflectance spectra of bracts, stems, and flowers of M. odorata relative to an ambient leaf litter substrate. Across the 2-yr study, the experimental group experienced a 20–27% higher mean herbivory rate and 7–20% lower mean fruit production relative to the control group. Bracts were shown to strongly resemble ambient leaf litter in spectral analyses, with stems and flowers having more conspicuous coloration. Results show that the presence of dried bracts effectively camouflages conspicuous stem and floral tissues, significantly reducing the frequency of floral and stem herbivory, and thereby increasing fruit set, a component of plant fitness. This study supports the principal hypothesis that coloration can play a fundamental role in plant defense.

Key Words: bracts • crypsis • Ericaceae • herbivory • Monotropoideae • Monotropsis odorata • reflectance spectrophotometry • sweet pine sap

Received for publication 30 April 2009. Accepted for publication 18 August 2009.

FOOTNOTES

¹ We extend thanks to D. Boone, J. Decker, M. Dodson, J. Gibson, M. Pistrang, and V. Soukup for assistance with locating populations and field manipulations. We are also grateful to members of the Clark Laboratory for assistance with reflectance measurements and data analyses. M. Bidartondo, D. Conover, C. Davis, S. Dunford, J. Macedonia, E. Maurer, A. R. Olson, and V. Soukup offered critical advice toward the development of this manuscript. Permission to conduct this research was granted by Cherokee N. F. and Daniel Boone N. F. Funding used to conduct this research was made possible through the University Research Council Fellowship and the Weiman, Wendel, Benedict Award offered by the University of Cincinnati to M. Klooster

⁴ Author for correspondence (e-mail: mklooster{at}oeb.harvard.edu); present address: Harvard University Herbaria 22 Divinity Ave., Cambridge, MA 02138 USA

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