title: Ode to Ehrlich and Raven or how herbivorous insects might drive plant speciation.
abstract: Fifty years ago, Ehrlich and Raven proposed that insect herbivores have driven much of plant speciation, particularly at tropical latitudes. There have been no explicit tests of their hypotheses. Indeed there were no proposed mechanisms either at the time or since by which herbivores might generate new plant species. Here we outline two main classes of mechanisms, prezygotic and postzygotic, with a number of scenarios in each by which herbivore-driven changes in host plant secondary chemistry might lead to new plant lineage production. The former apply mainly to a sympatric model of speciation while the latter apply to a parapatric or allopatric model. Our review suggests that the steps of each mechanism are known to occur individually in many different systems, but no scenario has been thoroughly investigated in any one system. Nevertheless, studies of Dalechampia and its herbivores and pollinators, and patterns of defense tradeoffs in trees on different soil types in the Peruvian Amazon provide evidence consistent with the original hypotheses of Ehrlich and Raven. For herbivores to drive sympatric speciation, our findings suggest that interactions with both their herbivores and their pollinators should be considered. In contrast, herbivores may drive speciation allopatrically without any influence by pollinators. Finally, there is evidence that these mechanisms are more likely to occur at low latitudes and thus more likely to produce new species in the tropics. The mechanisms we outline provide a predictive framework for further study of the general role that herbivores play in diversification of their host plants.
authors.affiliation: Department of Biology and Whitney R. Harris World Ecology Center, University of Missouri-St. Louis, One University Boulevard, St. Louis, Missouri, 63121, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Marquis
authors.affiliation: Department of Biology and Whitney R. Harris World Ecology Center, University of Missouri-St. Louis, One University Boulevard, St. Louis, Missouri, 63121, USA.|Department of Integrative Biology, University of California-Berkeley, 3040 Valley Life Sciences Bldg #3140, Berkeley, California, 94720, USA.
authors.forename: Diego
authors.initials: D
authors.lastname: Salazar
authors.affiliation: Department of Biology and Whitney R. Harris World Ecology Center, University of Missouri-St. Louis, One University Boulevard, St. Louis, Missouri, 63121, USA.
authors.forename: Christina
authors.initials: C
authors.lastname: Baer
authors.affiliation: Department of Biology and Whitney R. Harris World Ecology Center, University of Missouri-St. Louis, One University Boulevard, St. Louis, Missouri, 63121, USA.|Department of Forest Resources, University of Minnesota, 1530 Cleveland Ave. N., St. Paul, Minnesota, 55108, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Reinhardt
authors.affiliation: Department of Biology and Whitney R. Harris World Ecology Center, University of Missouri-St. Louis, One University Boulevard, St. Louis, Missouri, 63121, USA.
authors.forename: Galen
authors.initials: G
authors.lastname: Priest
authors.affiliation: Department of Biology and Whitney R. Harris World Ecology Center, University of Missouri-St. Louis, One University Boulevard, St. Louis, Missouri, 63121, USA.|Hawkesbury Institute for the Environment, Western Sydney University, Hawkesbury Campus, Penrith, New South Wales, 2751, Australia.
authors.forename: Kirk
authors.initials: K
authors.lastname: Barnett
mesh_terms: D000818:Animals; D049810:Genetic Speciation; D060434:Herbivory / Q000502:physiology*; D007313:Insecta / Q000502:physiology*; D008954:Models, Biological; D018521:Plant Physiological Phenomena; D010944:Plants / Q000235:genetics*; D054817:Pollination / Q000235:genetics / Q000502:physiology
keywords: coevolution; defense evolution; herbivorous insects; latitudinal gradients; plant speciation; pollination; soils; tropical forests