EVOLUTIONARY IMPLICATIONS OF SESQUITERPENE LACTONES IN VERNONIA (COMPOSITAE) AND MAMMALIAN HERBIVORES

Abstract

Summary: Eastern cottontail rabbits, Syhilagus floridanus (Allen), were demonstrated to prefer feeding upon Vernonia flaccidifolia Small which lacks sesquiterpene lactones rather than V. gigantea (Walt.) Trel. ssp. gigantea which contains the bitter sesquiterpene lactone glaucolide‐A. The rabbits also essentially avoided V. flaccidifolia coated with a thin layer of glaucolide‐A. Whitetail deer, Odocoileus virginianus (Zimmermann), were shown to prefer V. flaccidifolia over V. gigantea as well as V. flaccidifolia coated with glaucolide‐A. These experimentally determined feeding preferences supported field observations. Sesquiterpene lactones, in addition to functioning as insect feeding deterrents, also appear to defend Vernonia against browsing mammals. The wide distribution of sesquiterpene lactones in Compositae may be related to coevolution not only with insects but also with mammalian herbivores.