Tropical Biology Section
Gonsiska, P. A. , Givnish, Thomas J. .
A Tale of Two Catopsis: Trichomes in two epiphytic bromeliads of contrasting light environment and trophic ecology.
The epiphytic genus Catopsis (Bromeliaceae: Tillandsioideae) spans a wide range of light regimes and includes carnivorous and non-carnivorous species, as well as tank-forming and non-tank-forming taxa. These characteristics make Catopsis an excellent model for studies of epiphyte ecology and evolution. Like other epiphytic bromeliads, Catopsis absorbs water and nutrients through peltate trichomes. Potential tradeoffs exist between energy and nutrient absorption in this group. Trichomes could shade the leaf and reduce photosynthetic rate, especially in the shade, whereas greater absorptive surface is needed in nutrient-poor microenvironments. Therefore, we compared trichome size, density, and leaf surface coverage of C. sessiliflora and C. berteroniana. These two species differ in evolutionary history, light environment, and nutrient acquisition strategy. A molecular phylogenetic analysis of 6527 aligned bases from the plastid genome shows that Catopsis contains two major lineages, with C. sessiliflora in the “dark-green” clade, and C. berteroniana in the “light-green” clade. While both form tanks, C. sessiliflora is a low-light, non-carnivorous species, and C. berteroniana is a purportedly carnivorous species from high-light environments. We sampled trichomes using SEM at proximal, medial, and distal positions on adaxial and abaxial leaf surfaces of both species. Catopsis berteroniana had significantly higher trichome coverage on both the abaxial and adaxial surface of its leaf bases than C. sessiliflora. These differences resulted from differences in trichome size rather than density. No significant differences were found in trichome area or density on the medial and distal adaxial surfaces, suggesting that light environment does not affect trichome cover in Catopsis. Ongoing studies examine the C:N ratio and δ15N of each species to determine what fraction of nitrogen each derives from insects vs. lower trophic levels, and how these relate to their differences in light regime, leaf orientation, and absorptive trichome area.
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1 - University of Wisconsin-Madison, Botany, 430 Lincoln Dr., Birge Hall, Madison, WI, 53706, U.S.A.
2 - University of Wisconsin-Madison, Department of Botany, Birge Hall, 430 Lincoln Dr., Madison, WI, 53706, U.S.A.
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Alpine A/Snowbird Center
Date: Monday, July 27th, 2009
Time: 10:30 AM