Floral scents: their roles in nursery pollination mutualisms

Abstract

Mutualisms are interspecies interactions in which each participant gains net benefits from interacting with its partner. In nursery pollination mutualisms, pollinators reproduce within the inflorescence they pollinate. In these systems, each partner depends directly on the other for its reproduction. Therefore, the signal responsible for partner encounter is crucial in these horizontally transmitted mutualisms, in which the association between specific partners must be renewed at each generation. As in many other interspecies interactions, chemical signals are suspected to be important in the functioning of these mutualisms. We synthesized and compared the published data available on the role of floral scents in the functioning of the 16 known independently evolved nursery pollination mutualisms. So far, attraction of pollinators to their specific hosts has been investigated in only seven of these systems, and the majority of the studies have been conducted on one of them, fig/fig wasp interactions. While such unevenness of the information limits the potential for meta-analysis, some patterns emerge from this review concerning the role of flower volatiles in maintaining the specificity of pollinator attraction, in signaling the appropriate phenological stage for pollinator visit, in attracting the pollinator toward the rewardless sex in dioecious plant species and in aiding the location and exploitation of resources by parasites and predators associated with these mutualisms. Finally, we highlight new perspectives on the evolution of signals in these diversified systems depending on the age and the degree of specificity of the interaction, and on the effect of phylogenetic inertia on the evolutionary dynamics of plant signals.

Pollinator sharing and gene flow among closely related sympatric dioecious fig taxa

“…Our experimental evidence suggests that the relationship between the chemical composition of the floral volatiles and pollinator choice is more complicated than has been generally proposed [10][11] . These results indicate that pollinator specificity, even among this most strict case of dioecious obligate mutualists [28], is not completely fixed, and that pollinator sharing among closely related sympatric figs could be rather common.…”

“…The floral volatile signature, which often consists of a mixture of volatile organic compounds, is believed to be the main mechanism for maintaining pollinator specificity in many obligate pollination systems [10,15]. Intraspecific variations in floral volatiles may allow multiple pollinator species to coexist on one host [16], while their similarity among different plant species may facilitate pollinator sharing or shifts [17,18].…”

Floral Scent Contributes to Interaction Specificity in Coevolving Plants and Their Insect Pollinators

“…Chemical cues have the potential to augment or even be the major factor shaping interactions between some plants and pollinating floral parasites (Hossaert-McKey et al 2010;Raguso 2008;Schaefer et al 2004). Some pollinating floral parasites are known to respond more strongly to the floral scent signal of their specific hosts in areas where several potential host plant species occur in sympatry and attract different but closely related insect pollinators (Chen and Song 2008;HossaertMcKey et al 2010;Okamoto et al 2007;Proffit et al 2007;Svensson et al 2010).…”

Floral volatiles, pollinator sharing and diversification in the fig–wasp mutualism: insights from Ficus natalensis , and its two wasp pollinators (South Africa)

“…The chemical message generally comprises several compounds and is differentiated among species [24,25]. The wasps are assumed to recognize a mixture of volatile organic compounds constituting the host species'-specific signature [23,[25][26][27]. Data on two Ficus species have evidenced significant among-population variation of receptive fig floral odour within species [28].…”