Annals of Botany

Intraspecific floral scent variation in the context of evolutionary ecology

Floral scents attract pollinators, and a varied repertoire of floral scents has been documented among plant species. Delle-Vedove et al. survey the results of 81 studies investigating intraspecific variation of floral scents in 132 taxa.

Schematic representation of the various scales of floral scent variation and the main ecological and evolutionary processes associated.
Schematic representation of the various scales of floral scent variation and the main ecological and evolutionary processes associated. (A) Variation in floral scents among individuals can occur both within and among populations (solid circles). Within populations, variation can occur between groups of plants (e.g. sexual types, colour phenotypes, dashed circles) or among equivalent individuals. (B) Variation in floral scents within individuals occurs at several time scales: across flower ontogeny, between day and night and along a diel period. In the box are listed the main processes involved in variation of floral scents: (1) Pollinator-mediated selection can generate variation in floral scents (1a) if divergent selection occurs, either because the cost–benefit balance of the interaction with the same pollinator species varies (between plant genders ot between plant phenological stages) or because they interact with different pollinator species (that can vary both among populations and along with time); (1b) if pollination is achieved by deceit, since pollinators can cause variation through balanced selection. (2) If the identity, occurrence or effect of herbivores varies among populations or across time, herbivore-mediated selection can generate variation in floral scent. (3) The balance between the effects of genetic drift and gene flow impact variation among populations, particularly for biologically inactive volatile compounds. (4) The variation in some environmental components that affect the functioning of metabolic pathways or compound release (e.g. temperature, humidity or soil) should cause some variation in floral scents. (5) Finally, biochemical processes may explain some of the observed variations both within individuals (depending on the metabolic rhythms) and between individuals (of different colour).

Variation was classified according to identity, proportion or absolute quantities of Volatile Organic Compounds, as well as data with the potential to explain variation, such as methodology, plant origin or pollination biology. Variation was evident in almost all investigated species, both among individuals (among and sometimes within populations) and within individuals across different temporal scales. This review article suggests that floral scent variation can be mediated by temporal shifts in pollinator identity and behaviour among populations, deceit pollination and sex-specific selection, and also by natural enemies, genetic drift, gene migration and other constraints.

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