Document: JOH-3-46-11

Genetic constraints and diffuse selection on resistance to deer herbivory in the Ivyleaf morning glory, Ipomoea hederacea.

STINCHCOMBE, J.R.* and M.D.RAUSHER

Duke University, Durham, NC, 27708, USA ¹

Abstract:
Recent theory has suggested that coevolution between plants and their natural enemies will be diffuse when either of two conditions are met. First, coevolution is likely to be diffuse if there is a genetic correlation between defenses to different species of natural enemies. Second, coevolution is likely to be diffuse if the pattern of natural selection imposed by one natural enemy is altered by the presence or absence of other natural enemies. Under this view of diffuse coevolution, the evolution of plant defense traits in response to multiple natural enemies is characterized by either genetic or ecological constraints, or both. We have evaluated whether or not the conditions for diffuse coevolution are met for the Ivyleaf morning glory, Ipomoea hederacea, and its insect, fungal, and mammalian natural enemies. Specifically, we used a quantitative genetics field experiment to estimate genetic correlations between resistance traits and measure the pattern of selection on resistance to deer herbivory in the presence and absence of both insect herbivores and pathogenic fungi. We have found that coevolution is likely to be diffuse in this system because both conditions for diffuse coevolution are satisfied. For example, there is a significant negative genetic correlation between resistance to deer herbivory and resistance to generalist insect herbivory. Furthermore, while selection favors greater resistance to deer herbivory in the presence of both insects and fungi, we were unable to detect selection on resistance to deer herbivory in the absence of either insects or fungi, or both. Thus, the pattern of natural selection on resistance traits is dependent on the composition of the natural enemy community. These results indicate that the evolution of resistance traits in this species is likely to be constrained by both genetic and ecological factors.

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This abstract is being presented at: 1:15 PM in session:
Oral Session #63: Evolutionary Ecology.