Floral plasticity: Herbivore‐species‐specific‐induced changes in flower traits with contrasting effects on pollinator visitation

Abstract

Plant phenotypic plasticity in response to antagonists can affect other community members such as mutualists, conferring potential ecological costs associated with inducible plant defence. For flowering plants, induction of defences to deal with herbivores can lead to disruption of plant–pollinator interactions. Current knowledge on the full extent of herbivore‐induced changes in flower traits is limited, and we know little about specificity of induction of flower traits and specificity of effect on flower visitors. We exposed flowering Brassica nigra plants to six insect herbivore species and recorded changes in flower traits (flower abundance, morphology, colour, volatile emission, nectar quantity, and pollen quantity and size) and the behaviour of two pollinating insects. Our results show that herbivory can affect multiple flower traits and pollinator behaviour. Most plastic floral traits were flower morphology, colour, the composition of the volatile blend, and nectar production. Herbivore‐induced changes in flower traits resulted in positive, negative, or neutral effects on pollinator behaviour. Effects on flower traits and pollinator behaviour were herbivore species‐specific. Flowers show extensive plasticity in response to antagonist herbivores, with contrasting effects on mutualist pollinators. Antagonists can potentially act as agents of selection on flower traits and plant reproduction via plant‐mediated interactions with mutualists.

Urbanization alters plastic responses in the common dandelion Taraxacum officinale

“…Urbanization affects insect species richness and size (Merckx et al, 2018; Piano et al, 2017) and consequently herbivore pressure, but its direction and strength varies among species and locations (Raupp, Shrewsbury, & Herms, 2010). Previous work has found that plants are known to react to herbivory through the induction of defenses (Agrawal & Karban, 1999; Karban, 2011; Poelman, Broekgaarden, Loon, & Dicke, 2008), increased seed dispersal (Bonte et al, 2012; de la Pena & Bonte, 2014), and shifting flowering phenology (Agrawal, Strauss, & Stout, 1999; Rusman, Poelman, Nowrin, Polder, & Lucas‐Barbosa, 2019). The induction of defenses by spines or toxins, or the developmental of tolerance is energetically costly and is expected to trade‐off with vital traits as seed production and/or seed mass (Agrawal et al, 1999; Stearns, 1989).…”

Ecology of Plastic Flowers

“…Flowering plants are therefore expected to respond to the environment, including visitation by antagonists and mutualists. Indeed, flower traits readily change in response to herbivory or pathogen attack, even when these antagonists attack plant organs other than flowers [8,9]. Flower traits also change in response to the activity of mutualists such as pollinators [10][11][12][13] and beneficial microbes [14][15][16].…”

Plant ontogeny determines strength and associated plant fitness consequences of plant‐mediated interactions between herbivores and flower visitors

“…These changes at the same time reduce the attraction of bumblebees that use floral volatiles during foraging (Schiestl, Kirk, Bigler, Cozzolino, & Desurmont, ). Indeed, herbivore‐induced changes in expression of flower traits affect the visitation of mutualistic and antagonistic flower visitors (McArt, Halitschke, Salminen, & Thaler, ; Rusman, Poelman, Nowrin, Polder, & Lucas‐Barbosa, ; Stam, Dicke, & Poelman, ). Because flower visitors directly interact with the reproductive organs of the plant, herbivore–flower visitor interactions may come with important plant fitness consequences (Chautá, Whitehead, Amaya‐Márquez, & Poveda, ; Moreira, Castagneyrol, Abdala‐Roberts, & Traveset, ; Rusman, Lucas‐Barbosa, & Poelman, ).…”

“…In addition to resource‐based mechanisms, flowering plants change flower traits as part of their defensive response induced by herbivory (Rusman, Lucas‐Barbosa, et al, ). Such changes are apparent in traits that function in both defence and reproduction, such as flower volatiles and colour (Desurmont, Laplanche, Schiestl, & Turlings, ; Rusman, Poelman, et al, ). For example, flowering turnip plants change floral volatile emission upon herbivore attack to increase the attraction of natural enemies of the herbivores, but these changes reduce pollinator attraction (Schiestl et al, ).…”