Sporck, Margaret, J. , Sack, Lawren .
Adaptive radiation of leaf venation and the meaning of disjunct veins in the C4 Hawaiian Euphorbia.
The diversity of leaf venation architecture within and across lineages is gaining increasing interest as a source of functional adaptation to contrasting environments. The Hawaiian Euphorbia (Euphorbiaceae) are a group of C4 eudicots that radiated from one colonizing species into nearly 30 taxa. This group includes a variety of life forms, exceptional for a C4 lineage, from woody sub-shrubs to trees over six meters tall, with taxa adapted to diverse habitats, from rain forest to dry forest to the coasts and bogs. The group also includes eight endangered taxa, and understanding their biology and their unique value can further motivate their conservation. Taxa in the Hawaiian Euphorbia radiation vary strongly in leaf morphology, ranging 80-fold in leaf size and eight-fold in leaf mass per area. Theory would predict strong variation in venation across taxa linked with their striking environmental range. Additionally, D. Herbst (Science, 1971) described a unique trait in this group-"disjunct minor veins," which are unattached to the vein network, but their variation across taxa and their significance had not been quantified. For 27 native Euphorbia taxa, we cleared leaves chemically and quantified traits relating to venation architecture, including densities (= length/area) and widths of all vein orders, and of disjunct veins. We tested for correlation of venation traits with climate and habitat and with other aspects of leaf structure and composition. We hypothesized that taxa occupying sites of higher temperatures and establishing under higher irradiance would have higher vein density, and that disjunct veins would be associated with moist rainforest habitats, as these shade adapted C4 species might not suffer from the loss of connecting vein length and could benefit from reduced vein and bundle sheath construction cost. We found support for these hypotheses, suggesting that Hawaii's isolated location and strong climatic gradients have led to relatively rapid adaptive diversification in venation characteristics, and we explore hypotheses for the evolution and physiological significance of this diversity.
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1 - University of Hawaii, Manoa, Department of Botany, Ecology, Evolution and Conservation Biology, 3190 Maile Way, St. John 101, Honolulu, HI, 96822
2 - University of California, Los Angeles, Ecology and Evolutionary Biology, 621 Charles E. Young Drive, Los Angeles, CA, 90095, USA
Presentation Type: Oral Paper:Papers for Topics
Location: 551B/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 10:15 AM