Differential Evolutionary History in Visual and Olfactory Floral Cues of the Bee-Pollinated Genus Campanula (Campanulaceae).

Paulo Milet-Pinheiro,Manfred Ayasse,Samuel Prieto-Benítez,Stefan Dötterl,Pablo Sandro Carvalho Santos

doi:10.3390/plants10071356

Abstract

Visual and olfactory floral signals play key roles in plant-pollinator interactions. In recent decades, studies investigating the evolution of either of these signals have increased considerably. However, there are large gaps in our understanding of whether or not these two cue modalities evolve in a concerted manner. Here, we characterized the visual (i.e., color) and olfactory (scent) floral cues in bee-pollinated Campanula species by spectrophotometric and chemical methods, respectively, with the aim of tracing their evolutionary paths. We found a species-specific pattern in color reflectance and scent chemistry. Multivariate phylogenetic statistics revealed no influence of phylogeny on floral color and scent bouquet. However, univariate phylogenetic statistics revealed a phylogenetic signal in some of the constituents of the scent bouquet. Our results suggest unequal evolutionary pathways of visual and olfactory floral cues in the genus Campanula. While the lack of phylogenetic signal on both color and scent bouquet points to external agents (e.g., pollinators, herbivores) as evolutionary drivers, the presence of phylogenetic signal in at least some floral scent constituents point to an influence of phylogeny on trait evolution. We discuss why external agents and phylogeny differently shape the evolutionary paths in floral color and scent of closely related angiosperms.

Highlights

Pollination is a critical step for successful sexual reproduction in flowering plants [1].It is sometimes performed by abiotic agents, such as wind and water [2,3], but mostly by biotic agents, i.e., animals [4]
We found evidence of a phylogenetic signal for some floral scent constituents (Abouheif’s C mean and Pagel’s λ indices showed signal in phylogenetic PCA (pPCA) global structures), but not for others and for the overall scent bouquet
While the detection of phylogenetic signals in some constituents of the scent bouquet of Campanula species suggests that the evolution of scents in this genus is constrained in part by phylogenetic relatedness, the lack of phylogenetic signals in other scent constituents and in the whole scent bouquet, as well as in color reflectance, all point to external agents shaping the evolution of those traits

Summary

Introduction

Pollination is a critical step for successful sexual reproduction in flowering plants [1].It is sometimes performed by abiotic agents, such as wind and water [2,3], but mostly by biotic agents, i.e., animals [4]. Angiosperms typically offer floral resources (mainly pollen and nectar) as a reward for pollination services [1] Flowers advertise these rewards through floral signals, such as color and scent, which, as a consequence, are the subjects of selective pressures by their pollinators [5,6,7]. Floral traits of bee-pollinated flowers vary considerably, making the delineation of a single signature of this syndrome somewhat inappropriate [12]. In spite of this great variability, some traits are more attributed to bee-pollinated flowers than others [13], suggesting that distinct floral traits experience unequal selective pressures by pollinating bees. Evidence is lacking for converging patterns on floral scent chemistry in this pollination syndrome [14]

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Conclusion