Explore the vast range of titles available.

All plants synthesize a suite of several hundred terpenoid compounds with roles that include phytohormones, protein modification reagents, anti-oxidants, and more. Different plant lineages also synthesize hundreds of distinct terpenoids, with the total number of such specialized plant terpenoids estimated in the scores of thousands. Phylogenetically restricted terpenoids are implicated in defense or in the attraction of beneficial organisms. A popular hypothesis is that the ability of plants to synthesize new compounds arose incrementally by selection when, as a result of gradual changes in their biotic partners and enemies, the ‘old’ plant compounds were no longer effective, a process dubbed the ‘coevolutionary arms race’. Another hypothesis posits that often the sheer diversity of such compounds provides benefits that a single compound cannot. In this article, we review the unique features of the biosynthetic apparatus of terpenes in plants that facilitate the production of large numbers of distinct terpenoids in each species and how facile genetic and biochemical changes can lead to the further diversification of terpenoids. We then discuss evidence relating to the hypotheses that given ecological functions may be enhanced by the presence of mixtures of terpenes and that the acquisition of new functions by terpenoids may favor their retention once the original functions are lost.

Floral scent constitutes an ancient and important channel of communication between flowering plants, their pollinators, and enemies. Fragrance is a highly complex component of floral phenotype, with dynamic patterns of emission and chemical composition. The information content of specific volatile compounds is highly context dependent, and scent can function in direct and indirect ways from landscape to intrafloral scales. Floral scent promotes specialization in plant-pollinator relationships through private channels of unusual compounds, unique ratios of more widespread compounds, or through multicomponent floral filters. Floral scent also promotes outcrossing and reproductive isolation through floral constancy, via appetitive conditioning and discrimination on the basis of diverse mechanisms, including pheromone mimicry, odor intensity, complexity, composition, and synergy with visual stimuli. Finally, floral scent is a sexual signal and should be subject to the same selective pressures and modes of signal evolution as animal display, including signal honesty, sensory drive, and sensory exploitation.

Unrelated organisms that share similar niches often exhibit patterns of convergent evolution in functional traits. Based on bimodal distributions of hawkmoth tongue lengths and tubular white flowers in Africa, this study hypothesized that long-tongued hawkmoths comprise a pollination niche (ecological opportunity) that is distinct from that of shorter-tongued hawkmoths. Field observations, light trapping, camera surveillance and pollen load analysis were used to identify pollinators of plant species with very long-tubed (>8 cm) flowers. The nectar properties and spectral reflectance of these flowers were also measured. The frequency distributions of proboscis length for all captured hawkmoths and floral tube length for a representative sample of night-blooming plant species were determined. The geographical distributions of both native and introduced plant species with very long floral tubes were mapped. The convolvulus hawkmoth Agrius convolvuli is identified as the most important pollinator of African plants with very long-tubed flowers. Plants pollinated by this hawkmoth species tend to have a very long (approx. 10 cm) and narrow flower tube or spur, white flowers and large volumes of dilute nectar. It is estimated that >70 grassland and savanna plant species in Africa belong to the Agrius pollination guild. In South Africa, at least 23 native species have very long floral tubes, and pollination by A. convolvuli or, rarely, by the closely related hawkmoth Coelonia fulvinotata, has been confirmed for 11 of these species. The guild is strikingly absent from the species-rich Cape floral region and now includes at least four non-native invasive species with long-tubed flowers that are pre-adapted for pollination by A. convolvuli. This study highlights the value of a niche perspective on pollination, which provides a framework for making predictions about the ecological importance of keystone pollinators, and for understanding patterns of convergent evolution and the role of floral traits in plant colonization.

Despite progress in understanding pollination network structure, the functional roles of floral sensory stimuli (visual, olfactory) have never been addressed comprehensively in a community context, even though such traits are known to mediate plant–pollinator interactions. Here, we use a comprehensive dataset of floral traits and a novel dynamic data-pooling methodology to explore the impacts of floral sensory diversity on the structure of a pollination network in a Mediterranean scrubland. Our approach tracks transitions in the network behaviour of each plant species throughout its flowering period and, despite dynamism in visitor composition, reveals significant links to floral scent, and/or colour as perceived by pollinators. Having accounted for floral phenology, abundance and phylogeny, the persistent association between floral sensory traits and visitor guilds supports a deeper role for sensory bias and diffuse coevolution in structuring plant–pollinator networks. This knowledge of floral sensory diversity, by identifying the most influential phenotypes, could help prioritize efforts for plant–pollinator community restoration. Can floral phenotype predict the most influential species for maintaining plant–pollinator communities? Here, Kantsa et al. develop a methodology for trait-based analysis, revealing the critical role of floral scent, and floral colour as perceived by insects, in shaping visitation networks.

Previous studies have considered floral humidity to be an inadvertent consequence of nectar evaporation, which could be exploited as a cue by nectar-seeking pollinators. By contrast, our interdisciplinary study of a night-blooming flower, Datura wrightii , and its hawkmoth pollinator, Manduca sexta , reveals that floral relative humidity acts as a mutually beneficial signal in this system. The distinction between cue- and signal-based functions is illustrated by three experimental findings. First, floral humidity gradients in Datura are nearly ten-fold greater than those reported for other species, and result from active (stomatal conductance) rather than passive (nectar evaporation) processes. These humidity gradients are sustained in the face of wind and are reconstituted within seconds of moth visitation, implying substantial physiological costs to these desert plants. Second, the water balance costs in Datura are compensated through increased visitation by Manduca moths, with concomitant increases in pollen export. We show that moths are innately attracted to humid flowers, even when floral humidity and nectar rewards are experimentally decoupled. Moreover, moths can track minute changes in humidity via antennal hygrosensory sensilla but fail to do so when these sensilla are experimentally occluded. Third, their preference for humid flowers benefits hawkmoths by reducing the energetic costs of flower handling during nectar foraging. Taken together, these findings suggest that floral humidity may function as a signal mediating the final stages of floral choice by hawkmoths, complementing the attractive functions of visual and olfactory signals beyond the floral threshold in this nocturnal plant-pollinator system. Flowers are well known for attracting pollinators with visual and olfactory displays. Here, the authors show that in a nocturnal, desert pollination system, flower choice by pollinators is also mediated by floral humidity.

• Fragrance is a putatively important character in the evolution of flowering plants, but natural selection on scent is rarely studied and thus poorly understood. We characterized floral scent composition and emission in a common garden of Penstemon digitalis from three nearby source populations. • We measured phenotypic selection on scent as well as floral traits more frequently examined, such as floral phenology, display size, corolla pigment, and inflorescence height. • Scent differed among populations in a common garden, underscoring the potential for scent to be shaped by differential selection pressures. Phenotypic selection on flower number and display size was strong. However, selection favoured scent rather than flower size or colour, suggesting that smelling stronger benefits reproductive success in P. digitalis. Linalool was a direct target of selection and its high frequency in floral‐scent bouquets suggests that further studies of both pollinator‐ and antagonist‐mediated selection on this compound would further our understanding of scent evolution. • Our results indicate that chemical dimensions of floral display are just as likely as other components to experience selective pressure in a nonspecialized flowering herb. Therefore, studies that integrate visual and chemical floral traits should better reflect the true nature of floral evolutionary ecology.

Most research on plant–pollinator communication has focused on sensory and behavioral responses to relatively static cues. Floral rewards such as nectar, however, are dynamic, and foraging animals will increase their energetic profit if they can make use of floral cues that more accurately indicate nectar availability. Here we document such a cue—transient humidity gradients—using the night blooming flowers of Oenothera cespitosa (Onagraceae). The headspace of newly opened flowers reaches levels of about 4% above ambient relative humidity due to additive evapotranspirational water loss through petals and water-saturated air from the nectar tube. Floral humidity plumes differ from ambient levels only during the first 30 min after anthesis (before nectar is depleted in wild populations), whereas other floral traits (scent, shape, and color) persist for 12–24 h. Manipulative experiments indicated that floral humidity gradients are mechanistically linked to nectar volume and therefore contain information about energy rewards to floral visitors. Behavioral assays with Hyles lineata (Sphingidae) and artificial flowers with appropriate humidity gradients suggest that these hawkmoth pollinators distinguish between subtle differences in relative humidity when other floral cues are held constant. Moths consistently approached and probed flowers with elevated humidity over those with ambient humidity levels. Because floral humidity gradients are largely produced by the evaporation of nectar itself, they represent condition-informative cues that facilitate remote sensing of floral profitability by discriminating foragers. In a xeric environment, this level of honest communication should be adaptive when plant reproductive success is pollinator limited, due to intense competition for the attention of a specialized pollinator.

Chemical communication is ubiquitous. The identification of conserved structural elements in visual and acoustic communication is well established, but comparable information on chemical communication displays (CCDs) is lacking. We assessed the phenotypic integration of CCDs in a meta-analysis to characterize patterns of covariation in CCDs and identified functional or biosynthetically constrained modules. Poorly integrated plant CCDs (i.e. low covariation between scent compounds) support the notion that plants often utilize one or few key compounds to repel antagonists or to attract pollinators and enemies of herbivores. Animal CCDs (mostly insect pheromones) were usually more integrated than those of plants (i.e. stronger covariation), suggesting that animals communicate via fixed proportions among compounds. Both plant and animal CCDs were composed of modules, which are groups of strongly covarying compounds. Biosynthetic similarity of compounds revealed biosynthetic constraints in the covariation patterns of plant CCDs. We provide a novel perspective on chemical communication and a basis for future investigations on structural properties of CCDs. This will facilitate identifying modules and biosynthetic constraints that may affect the outcome of selection and thus provide a predictive framework for evolutionary trajectories of CCDs in plants and animals.

Flowering plants use volatiles to attract pollinators while deterring herbivores. Vegetative and floral traits may interact to affect insect behavior. Pollinator behavior is most likely influenced by leaf traits when larval stages interact with plants in different ways than adult stages, such as when larvae are leaf herbivores but adult moths visit flowers as pollinators. Here, we determine how leaf induction and corresponding volatile differences in induced plants influence behavior in adult moths and whether these preferences align with larval performance. We manipulated vegetative induction in four Nicotiana species. Using paired induced and control plants of the same species with standardized artificial flowers, we measured foraging and oviposition choices by their ecologically and economically important herbivore/pollinator, Manduca sexta . In parallel, we measured growth rates of M. sexta larvae fed leaves from control or induced plants to determine if this was consistent with female oviposition preference. Lastly, we used plant headspace collections and gas chromatography to quantify volatile compounds from both induced and control leaves to link changes in plant chemistry with moth behavior. In the absence of floral chemical cues, vegetative defensive status influenced adult moth foraging preference from artificial flowers in one species ( N. excelsior ), where females nectared from induced plants more often than control plants. Plant vegetative resistance consistently influenced oviposition choice such that moths deposited more eggs on control plants than on induced plants of all four species. This oviposition preference for control plants aligned with higher larval growth rates on control leaves compared with induced leaves. Control and induced plants of each species had similar leaf volatile profiles, but induced plants had higher emission levels. Leaves of N. excelsior produced the most volatile compounds, including some inducible compounds typically associated with floral scent. We demonstrate that vegetative plant defensive volatiles play a role in host plant selection and that insects assess information from leaves differently when choosing between nectaring and oviposition locations. These results underscore the complex interactions between plants, their pollinators, and herbivores.

Flowers use olfactory and visual signals to communicate with pollinators. Disentangling the relative contributions and potential synergies between signals remains a challenge. Understanding the perceptual biases exploited by floral mimicry illuminates the evolution of these signals. Here, we disentangle the olfactory and visual components of Dracula lafleurii, which mimics mushrooms in size, shape, color and scent, and is pollinated by mushroom-associated flies. To decouple signals, we used three-dimensional printing to produce realistic artificial flower molds that were color matched and cast using scent-free surgical silicone, to which we could add scent. We used GC-MS to measure scents in co-occurring mushrooms, and related orchids, and used these scents in field experiments. By combining silicone flower parts with real floral organs, we created chimeras that identified the mushroom-like labellum as a source of volatile attraction. In addition, we showed remarkable overlap in the volatile chemistry between D. lafleurii and co-occurring mushrooms. The characters defining the genus Dracula– a mushroom-like, ‘gilled’ labellum and a showy, patterned calyx – enhance pollinator attraction by exploiting the visual and chemosensory perceptual biases of drosophilid flies. Our techniques for the manipulation of complex traits in a nonmodel system not conducive to gene silencing or selective breeding are useful for other systems.