title: Herbivory and floral signaling: phenotypic plasticity and tradeoffs between reproduction and indirect defense.
abstract: Plant defense against herbivores may compromise attraction of mutualists, yet information remains limited about the mechanisms underlying such signaling tradeoffs. Here, we investigated the effects of foliar herbivory by two herbivore species on defense compounds, floral signaling, pollinator and parasitoid attraction, and seed production. Herbivory generally reduced the quantity of many floral volatile organic compounds VOCs) in Brassica rapa. By contrast, floral color, flower diameter, and plant height remained unaffected. The decreased amounts of floral volatiles led to reduced attractiveness of flowers to pollinators, but increased the attractiveness of herbivore-infested plants to parasitoids. Plants infested with the native butterfly Pieris brassicae produced more flowers during early flowering, effectively compensating for the lower olfactory attractiveness. Herbivory by the invasive Spodoptera littoralis increased the amounts of glucobrassicanapin, and led to delayed flowering. These plants tended to attract fewer pollinators and to produce fewer seeds. Our study indicates a tradeoff between pollinator attraction and indirect defense (parasitoid attraction), which can be mitigated by reduced floral VOC emission and production of more early flowers. We suggest that this compensatory mechanism is specific to plant-herbivore associations with a coevolutionary history.
authors.affiliation: Institute of Systematic Botany, University of Zürich, Zollikerstrasse 107, 8008, Zürich, Switzerland.
authors.forename: Florian P
authors.initials: FP
authors.lastname: Schiestl
authors.forename: Heather
authors.initials: H
authors.lastname: Kirk
authors.forename: Laurent
authors.initials: L
authors.lastname: Bigler
authors.forename: Salvatore
authors.initials: S
authors.lastname: Cozzolino
authors.forename: Gaylord A
authors.initials: GA
authors.lastname: Desurmont
mesh_terms: D000818:Animals; D001516:Bees; D029741:Brassica rapa / Q000502:physiology; D002080:Butterflies; D003116:Color; D035264:Flowers / Q000033:anatomy & histology / Q000737:chemistry / Q000502:physiology*; D060434:Herbivory; D054817:Pollination; D018411:Spodoptera; D013559:Symbiosis; D055549:Volatile Organic Compounds / Q000737:chemistry*; D014863:Wasps
chemical_list: D055549:Volatile Organic Compounds
keywords: floral volatile organic compound (VOC); glucosinolates; indirect defense; induced volatiles; parasitoid; plant defense; pollination; scent