October 13 2011

5:00 pm 154 BSRB

EcoEvoPub Series

Graduate Student Presentations


Dept of Ecology and Evolutionary Biology, UCLA
"A New Hypothesis for Small Leaf Size in Dry Habitats such as Mediterranean Ecosystems"

One of the most well-known trends in plant biogeography is that smaller leaves are typical in drier areas. However, there have been no direct explanations. We present here a new direct hydraulic hypothesis for small leaf size in dry areas. Across plant species, leaves vary enormously in their size and their venation architecture, of which one major function is to replace water lost to transpiration. The leaf hydraulic conductance (Kleaf) represents the capacity of the transport system to deliver water, allowing stomata to remain open for photosynthesis. Previous studies showed that Kleaf relates to the vein density (= vein length per area). Additionally, venation architecture determines the sensitivity of Kleaf to damage; severing the midrib caused Kleaf and gas exchange to decline, with lesser impacts in leaves with higher major vein density that provided more numerous water flow pathways around the damaged vein. Because xylem embolism during dehydration also reduces Kleaf, we hypothesized that higher major vein density would also reduce hydraulic vulnerability. Smaller leaves, which generally have higher major vein density, would thus have lower hydraulic vulnerability. Tests using simulations with a spatially explicit model confirmed that smaller leaves with higher major vein density were more tolerant of major vein embolism. Additionally, for ten species ranging strongly in drought tolerance, hydraulic vulnerability determined as the leaf water potential at 50% and 80% loss of Kleaf was lower with greater major vein density and smaller leaf size (|r| = 0.80-0.86; P < 0.01). These relationships were independent of other aspects of physiological and morphological drought tolerance. These findings point to a new functional role of venation architecture and small leaf size in drought tolerance, potentially contributing to well-known biogeographic trends in leaf size.

Christine Scoffoni1, Michael Rawls1, Athena McKown1, Hervé Cochard2 and Lawren Sack1

1Department of Ecology and Evolutionary Biology, University of California, Los Angeles, 621 Charles E. Young Drive South, Los Angeles, CA, 90095-1606, USA
2INRA, UMR 547 PIAF, F-63100 Clermont-Ferrand, France
3Clermont Université, Université Blaise Pascal, UMR 547 PIAF, BP 10448, F-63000 Clermont-Ferrand

Dept of Ecology and Evolutionary Biology, UCLA

"Re-emergence of ancestral plasticity and loss of a rare phenotype in threespine sticklebackRefreshments will be available with donation."


Phenotypic plasticity is traditionally thought to increase variation within species and permit persistence in the early stages of colonization. Less often considered is the possibility that retained plasticity may facilitate the return to ancestral phenotypes when the environment changes, often due to anthropogenic causes, around a long-established population and promote a loss in variation among populations. In conjunction with increased water productivity due to nearby housing development, we document a shift in the behavior of stickleback in Lynne Lake, Alaska, from the rare, behavioral limnetic (planktivorous) ecotype to the common benthic (bottom-feeding) ecotype with the consequence that large bottom feeding groups that cannibalize nests have now formed. The diversionary display behavior, thought to be lost from limnetic populations, has re-emerged in response to these cannibalistic foraging groups. The plasticity exhibited in foraging behavior is not mirrored in courtship behavior, which shows little change since 1994 and appears to have lost ancestral plasticity. The disparity between the foraging and courtship behavior suggests that the population will be forced to re-evolve inconspicuous courtship typical of ancestral ecotypes, and the extreme behavioral limnetic form will be lost, reducing the overall diversity in the local adaptive radiation.











































































































































































































































































































































































































































































































































































































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