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Natural selection on common milkweed (Asclepias syriaca) by a community of

Summary: Natural selection on common milkweed
(Asclepias syriaca) by a community of
specialized insect herbivores
Anurag A. Agrawal*
Department of Ecology and Evolutionary Biology,
Cornell University, Corson Hall, Ithaca, NY 14853, USA
Hypothesis: Genetic variation in plant defence structures a community of herbivores and
ultimately mediates co-evolution.
Organisms: Common milkweed (Asclepias syriaca) and five natural insect herbivores
(seed bug, leaf mining fly, monarch caterpillar and two beetles).
Methods: Quantitative genetic field experiment over 2 years, genetic selection analyses,
and measurement of five defensive traits (cardenolides, latex, trichomes, leaf toughness and
nitrogen content).
Results: All plant traits were genetically variable; directional selection favoured resistance
to herbivory, latex production and the nitrogen content of leaves. Trichomes and latex were each
negatively genetically correlated with abundances of herbivores, but not with herbivore damage;
cardenolides and induced plant resistance were negatively genetically correlated with growth of
Conclusion: Selection for plant defence was influenced by: (1) genetic correlations in plant


Source: Agrawal, Anurag - Department of Ecology and Evolutionary Biology & Entomollogy, Cornell University


Collections: Environmental Sciences and Ecology