Herbivory-induced changes in the olfactory and visual display of flowers and extrafloral nectaries affect pollinator behavior

Abstract

Plants communicate with animals by means of multimodal displays and reward mutualistic partners with resources such as nectar. Floral nectar is a key resource for pollinators, whereas extrafloral nectaries (EFNs) support indirect plant defense. Animalpollinated flowers advertise their rewards using modalities such as scent, color and morphology. In EFNs the role of olfactory and visual traits is less well understood. Herbivory has been shown to induce changes in the multimodal display and in resource related characteristics of flowers and EFNs. This may consequently affect the behavior of nectar consumers such as pollinators that occasionally feed on extrafloral nectar in addition to floral nectar. We tested the effect of herbivory (simulated by jasmonic acid treatment) on olfactory, visual and resource related floral and EFN traits in Vicia faba, tracked alterations in bumblebee (Bombus terrestris) preference and evaluated potential outcomes for plant reproduction. In control plants, flowers and EFNs differed in olfactory and visual cues and also in nectar quantity and quality and pollinators clearly preferred to forage on flowers. After jasmonic acid treatment (JA), linalool emissions of EFNs increased in a large proportion of plants, the visual display of EFNs became more salient and nectar volumes increased. In flowers of JA-treated plants we found lower emissions of cinnamic aldehyde and lower sugar concentration in nectar, however visual cues were unaffected. Potentially because of these phenotypic changes bumblebees no longer preferred flowers over EFNs in JA-treated plants. Consequently, this may negatively affect reproductive success in V. faba, which is highly dependent on floral visitation for fruit set. Our study adds another aspect to the complexity of plant-pollinator interactions and reveals how herbivory may interfere with plant-pollinator communication. Our findings emphasize that the foraging behavior of

Deciphering the Biotic and Climatic Factors That Influence Floral Scents: A Systematic Review of Floral Volatile Emissions

“…The responses of floral scents to different environmental climatic factors such as temperature or drought are highly plastic ( Farré-Armengol et al, 2013 ; Farré-Armengol et al, 2014 ; Glenny et al, 2018 ), as are the responses to biotic interactions ( Huber et al, 2005 ; Lucas-Barbosa et al, 2011 ; Schiestl et al, 2011 ; Schiestl et al, 2014 ; Junker, 2016 ; Hoffmeister and Junker, 2017 ). The high plasticity of floral-scent emissions within individual plants is usually not considered in sufficient detail ( Majetic et al, 2009 ).…”

Mosquito phytophagy – sources exploited, ecological function, and evolutionary transition to haematophagy

“…Findings that the same set of semiochemicals guides mosquitoes to different resources (Nikbakhtzadeh et al, ; Lahondère et al, ; Peach et al, ) is evolutionarily significant. The concept that pollinators forage primarily for resources, not flowers specifically, has found support (Hoffmeister & Junker, ) and may also be applicable to mosquitoes. Shared resource cues imply that mosquitoes forage for resources in general, whether vertebrates or plants, and that vertebrate hosts (e.g., humans) are simply more attractive resources than others.…”

“…Extrafloral/extrasoral nectaries semiochemicals guide parasitoid wasps (Röse et al, ; Géneau et al, ). Of six headspace volatiles (benzaldehyde, benzyl alcohol, linalool, 1‐octanol, two unknowns) originating from EFN nectar of fava bean, Vicia faba L., most were also found in leaves, but one of the two unknowns was specific to EFN nectar (Hoffmeister & Junker, ). Benzaldehyde, benzyl alcohol, and linalool are floral odorants attractive to mosquitoes (Jhumur et al, ; Yu et al, ), whereas 1‐octanol causes flight aversion (von Oppen et al, ).…”

“…Benzaldehyde, benzyl alcohol, and linalool are floral odorants attractive to mosquitoes (Jhumur et al, ; Yu et al, ), whereas 1‐octanol causes flight aversion (von Oppen et al, ). Visual cues associated with EFNs are speculated to add to the attractiveness of EFNs (Hoffmeister & Junker, ).…”

Dispensing a synthetic green leaf volatile to two plant species in a common garden differentially alters physiological responses and herbivory

“…Whereas increased flower production is a strategy assumed to ameliorate fitness losses in the presence of an environmental stress (Agrawal, 1999, 2000), decreased flower production may be related to costs of chemically mediated defense (Heath et al , 2014). Additionally, herbivory affects floral attractiveness (Halpern et al , 2010; Hoffmeister and Junker, 2016), which may ultimately influence fitness (Kessler et al , 2011). Our data indicate that a volatile cue alone is sufficient to trigger changes in floral biology, but the magnitude and direction of those changes are plant species-specific.…”