title: Induced defences alter the strength and direction of natural selection on reproductive traits in common milkweed.
abstract: Evolutionary biologists have long sought to understand the ecological processes that generate plant reproductive diversity. Recent evidence indicates that constitutive antiherbivore defences can alter natural selection on reproductive traits, but it is unclear whether induced defences will have the same effect and whether reduced foliar damage in defended plants is the cause of this pattern. In a factorial field experiment using common milkweed, Asclepias syriaca L., we induced plant defences using jasmonic acid (JA) and imposed foliar damage using scissors. We found that JA-induced plants experienced selection for more inflorescences that were smaller in size (fewer flowers), whereas control plants only experienced a trend towards selection for larger inflorescences (more flowers); all effects were independent of foliar damage. Our results demonstrate that induced defences can alter both the strength and direction of selection on reproductive traits, and suggest that antiherbivore defences may promote the evolution of plant reproductive diversity.
authors.affiliation: Department of Biology, University of Toronto Mississauga, Mississauga, ON, Canada.|Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada.
authors.forename: K A
authors.identifier: 0000-0002-1487-3254
authors.initials: KA
authors.lastname: Thompson
authors.affiliation: Department of Biology, University of Toronto Mississauga, Mississauga, ON, Canada.
authors.forename: K A
authors.initials: KA
authors.lastname: Cory
authors.affiliation: Department of Biology, University of Toronto Mississauga, Mississauga, ON, Canada.
authors.forename: M T J
authors.initials: MTJ
authors.lastname: Johnson
mesh_terms: D031108:Asclepias; D035264:Flowers; D060434:Herbivory; D012098:Reproduction; D012641:Selection, Genetic
keywords: display size; floral traits; herbivory; induced resistance; induced response; jasmonic acid; milkweed; phenotypic selection; quantitative genetics