June 5 2014

5:00 pm BSRB 154

EcoEvoPub Series

Graduate Student Presentations


Christine Scoffoni
Department of Ecology and Evolutionary Biology

"Leaf hydraulics and evolution
There has been increasing worldwide recognition of the importance of hydraulic physiology—the transport of water through the plant—in explaining plant growth and drought tolerance. By combining physiology and anatomy within an evolutionary framework, we can discover the mechanisms underlying species differences in hydraulic function, especially those of the leaf, the central organ in plant metabolism. I refined and developed new methods to investigate leaf water transport and its decline during drought, focusing on a critical measure of the capacity for water movement (leaf hydraulic conductance, Kleaf). I found that species most tolerant of Kleaf decline had small leaves with dense major veins, providing pathways for the water to bypass embolized conduits during drought giving a new, direct explanation to the fact that species of dry areas have small leaves. I also developed a new method to investigate the role of leaf shrinkage on water movement. As leaves shrink with dehydration, mesophyll cells lose connectivity, physically impacting water movement outside the xylem. I found that species most sensitive to Kleaf decline were those with strongest shrinkage in thickness. I then developed a new method to measure xylem hydraulic decline in leaves to test for a possible artifact of cutting leaf petioles under tension while under water. Such artifact has been recently found to occur in stems, and has put into question measurements of Kleaf. Across four diverse species, I found no sign of such an artifact in leaves, likely due to the lesser mechanical stress imposed when cutting a petiole vs. stem. Finally, I took an evolutionary perspective. I quantified the anatomical and physiological plasticity in leaves of six species of endemic Hawaiian lobeliads grown under different light regimes and found a high degree of plasticity in Kleaf with light, relating to leaf anatomical changes. Across 30 species of Viburnum I have identified the evolutionary shifts of leaf anatomy, water transport and drought tolerance. This work provides new techniques, clarity and applications toward understanding leaf water transport and its role in plant performance and drought tolerance, with applications for ecology, paleobiology and the conservation of species and ecosystems.

Kathryn Peiman
Department of Ecology and Evolutionary Biology

"Interference and exploitative competition between a migrant and resident passerine during the non-breeding season

Interactions both within and between species can have profound effects on their ecology and evolution. Competition is one of the main types of interactions and occurs through defense of resources (interference) and/or acquisition of food (exploitation). The White-eyed Vireo (Vireo griseus) and Thick-billed Vireo (Vireo crassirostris) is an ideal sister-species pair to study competition as they only coexist during the non-breeding season; there is no selection for reducing hybridization. I used the evolutionary contrast of sympatry and allopatry to test for the effects of heterospecific competitor presence, and the ecological contrast of low- vs high-quality habitats combined with the seasonal contrast of reduced rainfall from fall to winter to test for the effects of resource abundance on competition. I found strong evidence of interference competition within species but weaker evidence between species, as intraspecific territories were exclusive but interspecific territories overlapped, despite very high levels of aggression by V. crassirostris towards V. griseus. Additionally, there was evidence of both adaptive and non-adaptive behavioral syndromes in multivariate behavior towards conspecifics and heterospecifics. To investigate exploitative competition, I used stable isotopes from claw tips. Preliminary analyses indicate seasonal effects: both species fed higher on the food chain in the winter than the fall, yet individuals maintained their rank order differences in diet, implying specialization. This seasonal switch did not match changes in resource abundance.















































































































































































































































































































































































































































































































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