title: Natural selection on plant resistance to herbivores in the native and introduced range.
abstract: When plants are introduced into new regions, the absence of their co-evolved natural enemies can result in lower levels of attack. As a consequence of this reduction in enemy pressure, plant performance may increase and selection for resistance to enemies may decrease. In the present study, we compared leaf damage, plant size and leaf trichome density, as well as the direction and magnitude of selection on resistance and plant size between non-native (Spain) and native (Mexico) populations of Datura stramonium. This species was introduced to Spain about five centuries ago and constitutes an ideal system to test four predictions of the enemy release hypothesis. Compared with native populations, we expected Spanish populations of D. stramonium to have (i) lower levels of foliar damage; (ii) larger plant size; (iii) lower leaf trichome density that is unrelated to foliar damage by herbivores; and (iv) weak or no selection on resistance to herbivores but strong selection on plant size. Our results showed that, on average, plants from non-native populations were significantly less damaged by herbivores, were less pubescent and were larger than those from native populations. We also detected different selection regimes on resistance and plant size between the non-native and native ranges. Positive selection on plant size was detected in both ranges (though it was higher in the non-native area), but consistent positive selection on relative resistance was detected only in the native range. Overall, we suggest that changes in selection pressure on resistance and plant size in D. stramonium in Spain are a consequence of 'release from natural enemies'.
authors.affiliation: Departamento de Biología, Universidad Autónoma Metropolitana-Iztapalapa, Apartado Postal 55-535, Mexico 09340, Distrito Federal, Mexico Departamento de Biología Vegetal y Ecología, Universidad de Sevilla, Apartado 1095, Sevilla 41080, Spain plvp@xanum.uam.mx.
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Valverde
authors.affiliation: Departamento de Biología Vegetal y Ecología, Universidad de Sevilla, Apartado 1095, Sevilla 41080, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Arroyo
authors.affiliation: Laboratorio de Genética Ecológica y Evolución, Departamento de Ecología Evolutiva, Instituto de Ecología UNAM, México 04510, Distrito Federal, México.
authors.forename: Juan
authors.initials: J
authors.lastname: Núñez-Farfán
authors.affiliation: Laboratorio de Genética Ecológica y Evolución, Departamento de Ecología Evolutiva, Instituto de Ecología UNAM, México 04510, Distrito Federal, México.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Castillo
authors.affiliation: Laboratorio de Genética Ecológica y Evolución, Departamento de Ecología Evolutiva, Instituto de Ecología UNAM, México 04510, Distrito Federal, México.
authors.forename: Adriana
authors.initials: A
authors.lastname: Calahorra
authors.affiliation: Departamento de Biología Vegetal y Ecología, Universidad de Sevilla, Apartado 1095, Sevilla 41080, Spain.
authors.forename: Rocío
authors.initials: R
authors.lastname: Pérez-Barrales
authors.affiliation: Laboratorio de Genética Ecológica y Evolución, Departamento de Ecología Evolutiva, Instituto de Ecología UNAM, México 04510, Distrito Federal, México.
authors.forename: Rosalinda
authors.initials: R
authors.lastname: Tapia-López
keywords: Datura stramonium; Spain; enemy release hypothesis (ERH); invasive species; natural selection; plant defence; resistance to herbivores; specialist and generalist herbivores