The Functional Significance of Variation in the Production of Extrafloral Nectaries by Aspen

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Extrafloral nectaries (EFNs) are nectar-secreting glands located on the leaves and stems of many plant species. They can serve as a form of plant defense, by attracting insects that feed on the nectar and prey on herbivores. The investigators will use field experiments to examine the defensive function of EFNs in a common North American tree species, quaking aspen. Aspen have natural variation in the occurrence of EFNs on leaves, and this may result in differing levels of defense for aspen trees. Using this variation in EFN expression, the study will examine the role of EFNs in attracting natural enemies of the serpentine aspen leaf miner, an herbivore that currently heavily infests aspen throughout much of Alaska. Both ants and parasitic wasps are likely to be important predators on the miner. However, these species may be less able to access high versus low foliage and this could reduce the benefit of EFNs as trees grow. The study will test whether the benefits of EFNs are height-dependent. In addition, the investigators will test the hypothesis that the aspen leaf miner avoids laying eggs on leaves with EFNs, where its offspring face a greater risk of mortality. Broader Impacts: The study will contribute to our understanding of the evolution of plant defense and insect-plant interactions. In addition, it will provide a better understanding of the ecological interactions and defensive traits of quaking aspen, a widespread, ecologically and economically important tree species. The project will provide educational opportunities for two graduate students and many undergraduates at the University of Alaska, including Native Alaskans recruited through the National Science Foundation-sponsored Alaska Native Science and Engineering Program. In addition, the investigators will produce an interactive website designed to involve K-12 students in aspen ecology.