Natural selection drives chemical resistance of Datura stramonium.
Plant resistance to herbivores involves physical and chemical plant traits that prevent or diminish damage by herbivores, and hence may promote coevolutionary arm-races between interacting species. Although Datura stramonium's concentration of tropane alkaloids is under selection by leaf beetles, it is not known whether chemical defense reduces seed predation by the specialist weevil, Trichobaris soror, and if it is evolving by natural selection. We measured infestation by T. soror as well as the concentration of the plants' two main tropane alkaloids in 278 D. stramonium plants belonging to 31 populations in central Mexico. We assessed whether the seed predator exerted preferences on the levels of both alkaloids and whether they affect plant fitness. Results show great variation across populations in the concentration of scopolamine and atropine in both leaves and seeds of plants of D. stramonium, as well as in the intensity of infestation and the proportion of infested fruits by T. soror. The concentration of scopolamine in seeds and leaves are negatively associated across populations. We found that scopolamine concentration increases plant fitness. Our major finding was the detection of a positive relationship between the population average concentrations of scopolamine with the selection differentials of scopolamine. Such spatial variation in the direction and intensity of selection on scopolamine may represent a coevolutionary selective mosaic. Our results support the view that variation in the concentration of scopolamine among-populations of D. stramonium in central Mexico is being driven, in part, by selection exerted by T. soror, pointing an adaptive role of tropane alkaloids in this plant species.
Laboratory of Ecological Genetics and Evolution, Department of Evolutionary Ecology, Institute for Ecology, Universidad Nacional Autónoma de México , Mexico City , México.
Adán
A
Miranda-Pérez
Laboratory of Ecological Genetics and Evolution, Department of Evolutionary Ecology, Institute for Ecology, Universidad Nacional Autónoma de México, Mexico City, México; Laboratorio Nacional de Análisis y Síntesis Ecológica, Escuela Nacional de Estudios Superiores, Universidad Nacional Autónoma de México, Campus Morelia, Michoacán, México.
Guillermo
G
Castillo
Department of Entomology, Rutgers University, P.E. Marucci Center , Chatsworth, NJ , United States.
Johnattan
J
Hernández-Cumplido
Department of Biology, Universidad Autónoma Metropolitana , Mexico City , México.
Pedro L
PL
Valverde
Laboratory of Ecological Genetics and Evolution, Department of Evolutionary Ecology, Institute for Ecology, Universidad Nacional Autónoma de México , Mexico City , México.
María
M
Borbolla
Laboratory of Ecological Genetics and Evolution, Department of Evolutionary Ecology, Institute for Ecology, Universidad Nacional Autónoma de México , Mexico City , México.
Laura L
LL
Cruz
Laboratory of Ecological Genetics and Evolution, Department of Evolutionary Ecology, Institute for Ecology, Universidad Nacional Autónoma de México , Mexico City , México.
Rosalinda
R
Tapia-López
Laboratory of Ecological Genetics and Evolution, Department of Evolutionary Ecology, Institute for Ecology, Universidad Nacional Autónoma de México , Mexico City , México.
Juan
J
Fornoni
UBIPRO, Facultad de Estudios Superiores Iztacala Universidad, Nacional Autónoma de México , Tlalnepantla , México.
César M
CM
Flores-Ortiz
Laboratory of Ecological Genetics and Evolution, Department of Evolutionary Ecology, Institute for Ecology, Universidad Nacional Autónoma de México , Mexico City , México.
Juan
J
Núñez-Farfán
Atropine; Datura stramonium; Natural selection; Plant resistance; Scopolamine; Seed predation; Selection differential; Trichobaris soror; Tropane alkaloids