Ogburn, R. Matthew , Edwards, Erika .
A quantitative, ecophysiologically-relevant measure of succulence as a basis for comparative evolutionary studies.
Understanding the evolution of succulent water storage tissues in a phylogenetic comparative context requires a metric that captures quantitative variation among taxa. To date, evolutionary studies of succulence have commonly relied on discrete morphological categorizations of growth form, comparisons of cell size, or measurements of parenchyma tissue in two-dimensional sections. A rapidly obtainable, ecophysiologically-meaningful metric that captures the relevant aspects of tissue succulence is therefore desirable to facilitate collection for large numbers of taxa as well as encourage general use. We collected data on succulence index (SI = mass of water at full hydration divided by tissue dry mass) for a range of taxa from the clade Portulacineae, which present an array of growth forms and degrees of succulence. To verify the ecophysiological utility of this trait, we correlated SI values with ecophysiological data derived from pressure-volume curves from a smaller number of taxa. Phylogenetically independent contrasts indicated SI values were well correlated with tissue saturated water content, relative capacitance, and relative water content at turgor loss point, supporting their utility as a meaningful proxy for succulence to be used in comparative studies. They also accorded well with intuitive, gestalt-based notions of the degree of succulence between different taxa. Mapping SI values on the Portulacineae phylogenetic tree will form the basis for comparisons of correlations of succulence with traits such as degree of CAM photosynthesis, ecological niche parameters, and for analyzing directional patterns of trait evolution.
Graduate student training in ecophysiology field techniques, strengthened connections between our home institution and herbaria and universities in Chile, Argentina, and South Africa, where data were collected. Some of this research will also form the basis for future podcasts on the creaturecast.org website as part of a larger scientific outreach project.
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1 - Brown University, Department of Ecology and Evolutionary Biology, 80 Waterman St., Providence, RI, 02912, USA
Presentation Type: Oral Paper:Papers for Topics
Location: 551B/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 1:30 PM