When should fig fruit produce volatiles? Pattern in a ripening process

Structural variation underlies functional diversity at methyl salicylate loci in tomato

Methyl salicylate is an important inter- and intra-plant signaling molecule, but is deemed undesirable by humans when it accumulates to high levels in ripe fruits. Balancing the tradeoff between consumer satisfaction and overall plant health is challenging as the mechanisms regulating volatile levels have not yet been fully elucidated. In this study, we investigated the accumulation of methyl salicylate in ripe fruits of tomatoes that belong to the red-fruited clade. We determine the genetic diversity and the interaction of four known loci controlling methyl salicylate levels in ripe fruits. In addition to Non-Smoky Glucosyl Transferase 1 (NSGT1), we uncovered extensive genome structural variation (SV) at the Methylesterase (MES) locus. This locus contains four tandemly duplicated Methylesterase genes and genome sequence investigations at the locus identified nine distinct haplotypes. Based on gene expression and results from biparental crosses, functional and non-functional haplotypes for MES were identified. The combination of the non-functional MES haplotype 2 and the non-functional NSGT1 haplotype IV or V in a GWAS panel showed high methyl salicylate levels in ripe fruits, particularly in accessions from Ecuador, demonstrating a strong interaction between these two loci and suggesting an ecological advantage. The genetic variation at the other two known loci, Salicylic Acid Methyl Transferase 1 (SAMT1) and tomato UDP Glycosyl Transferase 5 (SlUGT5), did not explain volatile variation in the red-fruited tomato germplasm, suggesting a minor role in methyl salicylate production in red-fruited tomato. Lastly, we found that most heirloom and modern tomato accessions carried a functional MES and a non-functional NSGT1 haplotype, ensuring acceptable levels of methyl salicylate in fruits. Yet, future selection of the functional NSGT1 allele could potentially improve flavor in the modern germplasm.

Influence of elongation and desaturation on chemosensory properties in acrylates and their corresponding 1-alken-3-ones

Acrylates as well as 1-alken-3-ones are both known to be odour active substances but are generally identified in different materials. Nonetheless, butyl acrylate and 1-octen-3-one were both found to elicit a similar mushroom-like odour in previous studies. This led to the question of whether acrylates and enones with the same overall chain length generally elicited similar odours and whether they had similar odour thresholds. Overall, most of the investigated substances showed a mushroom-like, geranium-like or fruity odour. In contrast, short chained substances elicited garlic-like, lighter gas-like or glue-like, odour qualities, suggesting a correlation between the odour quality and the overall chain length. The results showed that only between the analogue structures butyl acrylate and 1-octen-3-one as well as hexyl acrylate and 1-decen-3-one could similar odour qualities be observed. All investigated substances showed low odour threshold values in air between 0.0032 ng/l_air (1-hexen-3-one) and 55 ng/l_air (1-dodecen-3-one). Overall, 1-alken-3-ones revealed a higher dependency on the chain length when compared to their respective acrylates. The introduction of a second terminal double bond led to a decrease of OT values in case of the acrylates and to an increase in case of the ketones that neither contained a second terminal double bond nor a double bond located close to the carbonyl group. Despite their structural similarities, the results suggest that both substance classes are perceived in a different manner and are therefore likely to be recognized by different types of receptors or are related to different activation patterns in multi-receptor stimulation processes.

Aeroscapes and the Sensory Ecology of Olfaction in a Tropical Dry Forest

Aeroscapes—dynamic patterns of air speed and direction—form a critical component of landscape ecology by shaping numerous animal behaviors, including movement, foraging, and social and/or reproductive interactions. Aeroecology is particularly critical for sensory ecology: air is the medium through which many sensory signals and cues propagate, inherently linking sensory perception to variables such as air speed and turbulence. Yet, aeroscapes are seldom explicitly considered in studies of sensory ecology and evolution. A key first step towards this goal is to describe the aeroscapes of habitats. Here, we quantify the variation in air movement in two successional stages (early and late) of a tropical dry forest in Costa Rica. We recorded air speeds every 10 seconds at five different heights simultaneously. Average air speeds and turbulence increased with height above the ground, generally peaked midday, and were higher overall at the early successional forest site. These patterns of lower air speed and turbulence at ground level and overnight have important implications for olfactory foraging niches, as chemotaxis is most reliable when air movement is low and steady. We discuss our results in the context of possible selective pressures and observed variation in the foraging ecology, behaviors, and associated morphologies of resident vertebrates, with a focus on mammals. However, these data also have relevance to researchers studying socioecology, invertebrate biology, plant evolution, community ecology and more. Further investigation into how animals use different forest types, canopy heights and partition activities across different times of day will further inform our understanding of how landscape and sensory ecology are interrelated. Finally, we emphasize the timeliness of monitoring aeroecology as global wind patterns shift with climate change and human disturbance alters forest structure, which may have important downstream consequences for biological conservation.

Interactions Between Figs and Gall-Inducing Fig Wasps: Adaptations, Constraints, and Unanswered Questions

The ancient interaction between figs (Ficus, Moraceae) and their pollinating fig wasps is an unusual example of a mutualism between plants and gall-inducing insects. This review intends to offer fresh perspectives into the relationship between figs and the diversity of gall-inducing sycophiles which inhabit their enclosed globular inflorescences that function as microcosms. Besides gall-inducing pollinators, fig inflorescences are also inhabited by other gall-inducing wasps. This review evaluates the state of current knowledge on gall-induction by fig wasps and exposes the many lacunae in this area. This review makes connections between fig and gall-inducing wasp traits, and suggests relatively unexplored research avenues. This manuscript calls for an integrated approach that incorporates such diverse fields as life-history theory, plant mate choice, wasp sexual selection and local mate competition, plant embryology as well as seed and fruit dispersal. It calls for collaboration between researchers such as plant developmental biologists, insect physiologists, chemical ecologists and sensory biologists to jointly solve the many valuable questions that can be addressed in community ecology, co-evolution and species interaction biology using the fig inflorescence microcosm, that is inhabited by gall-inducing mutualistic and parasitic wasps, as a model system.

Frugivory and seed dispersal by chelonians: a review and synthesis

In recent years, it has become clear that frugivory and seed dispersal (FSD) by turtles and tortoises is much more common than previously thought. We here review published and unpublished records of chelonian FSD, and assess the role of chelonians as seed dispersers, from individual species to the community level. We first discuss the distribution of chelonian FSD and the characteristics of the fruit and/or seed species eaten and dispersed by chelonians. We then use the seed dispersal efficiency framework to explore the quantitative and qualitative components of seed dispersal by tortoises and turtles, embarking on a journey from when the fruits and/or seeds are consumed, to when and where they are deposited, and assess how efficient chelonians are as seed dispersers. We finally discuss chelonian FSD in the context of communities and of chelonians as megafauna. A substantial proportion of the world's aquatic and terrestrial turtles and a major part of testudinid tortoises (71 species in 12 families) include fruits and/or seeds in their diet; fruits of at least 588 plant species in 121 families are ingested and/or dispersed by chelonians. For some chelonians, overall or in certain seasons, fruit may even form the largest part of their diet. Contrary to seed dispersal by lizards, the other major reptilian frugivores, chelonian FSD is not an island phenomenon in terms of geographic distribution. Nevertheless, on islands tortoises are often among the largest native terrestrial vertebrates - or were until humans arrived. We synthesise our knowledge of chelonian FSD, and discuss the relevance of our findings for conservation and restoration, especially in relation to rewilding with large and giant tortoises.

Frugivory and seed dispersal by chelonians: a review and synthesis

In recent years, it has become clear that frugivory and seed dispersal (FSD) by turtles and tortoises is much more common than previously thought. We here review published and unpublished records of chelonian FSD, and assess the role of chelonians as seed dispersers, from individual species to the community level. We first discuss the distribution of chelonian FSD and the characteristics of the fruit and/or seed species eaten and dispersed by chelonians. We then use the seed dispersal efficiency framework to explore the quantitative and qualitative components of seed dispersal by tortoises and turtles, embarking on a journey from when the fruits and/or seeds are consumed, to when and where they are deposited, and assess how efficient chelonians are as seed dispersers. We finally discuss chelonian FSD in the context of communities and of chelonians as megafauna. A substantial proportion of the world's aquatic and terrestrial turtles and a major part of testudinid tortoises (71 species in 12 families) include fruits and/or seeds in their diet; fruits of at least 588 plant species in 121 families are ingested and/or dispersed by chelonians. For some chelonians, overall or in certain seasons, fruit may even form the largest part of their diet. Contrary to seed dispersal by lizards, the other major reptilian frugivores, chelonian FSD is not an island phenomenon in terms of geographic distribution. Nevertheless, on islands tortoises are often among the largest native terrestrial vertebrates - or were until humans arrived. We synthesise our knowledge of chelonian FSD, and discuss the relevance of our findings for conservation and restoration, especially in relation to rewilding with large and giant tortoises.

Placenta, Pericarp, and Seeds of Tabasco Chili Pepper Fruits Show a Contrasting Diversity of Bioactive Metabolites

Chili pepper (Capsicum spp.) is one of the most important horticultural crops worldwide, and its unique organoleptic properties and health benefits have been established for centuries. However, there is little knowledge about how metabolites are distributed throughout fruit parts. This work focuses on the use of liquid chromatography coupled with high resolution mass spectrometry (UHPLC-ESI-HRMS) to estimate the global metabolite profiles of the pericarp, placenta, and seeds of Tabasco pepper fruits (Capsicum frutescens L.) at the red mature stage of ripening. Our main results putatively identified 60 differential compounds between these tissues and seeds. Firstly, we found that pericarp has a higher content of glycosides, showing on average a fold change of 5 and a fold change of 14 for terpenoids when compared with other parts of the fruit. While placenta was the richest tissue in capsaicinoid-related compounds, alkaloids, and tocopherols, with a 35, 3, and 7 fold change, respectively. However, the seeds were richer in fatty acids and saponins with fold changes of 86 and 224, respectively. Therefore, our study demonstrates that a non-targeted metabolomic approach may help to improve our understanding of unexplored areas of plant metabolism and also may be the starting point for a detailed analysis in complex plant parts, such as fruits.

Nocturnal scent in a 'bird-fig': A cue to attract bats as additional dispersers?

The plant genus Ficus is a keystone resource in tropical ecoystems. One of the unique features of figs is the diversity of fruit traits, which in many cases match their various dispersers, the so-called fruit syndromes. The classic example of this is the strong phenotypic differences found between figs with bat and bird dispersers (color, size, presentation, and scent). The 'bird-fig' Ficus colubrinae represents an exception to this trend since it attracts the small frugivorous bat species Ectophylla alba at night, but during the day it attracts bird visitors. Here we investigate day to night changes in fruit scent as a possible mechanism by which this 'bird-fig' could attract bats despite its fruit traits, which should appeal solely to birds. Analyses of odor bouquets from the bat- and bird-dispersal phases (i.e. day and night) differed significantly in their composition of volatiles. We observed a significant increase in relative amounts of sesquiterpene and aromatic compounds at night while relative amounts of two compounds of the fatty acid pathway were significantly higher during day. This finding raises the question whether Ficus colubrinae, a phenotypically classic 'bird-fig', might be able to attract bat dispersers by an olfactory signal at night. Preliminary observations from feeding experiments which indicate that Ectophylla alba is capable of finding ripe figs by scent alone point in this direction. However, additional behavioral experiments on whether bats prefer the 'night-bouquet' over the 'day-bouquet' will be needed to unequivocally answer this question.

Fungal infestation boosts fruit aroma and fruit removal by mammals and birds

For four decades, an influential hypothesis has posited that competition for food resources between microbes and vertebrates selects for microbes to alter these resources in ways that make them unpalatable to vertebrates. We chose an understudied cross kingdom interaction to experimentally evaluate the effect of fruit infection by fungi on both vertebrate (mammals and birds) fruit preferences and on ecologically relevant fruit traits (volatile compounds, toughness, etc). Our well-replicated field experiments revealed that, in contrast to previous studies, frugivorous mammals and birds consistently preferred infested over intact fruits. This was concordant with the higher level of attractive volatiles (esters, ethanol) in infested fruits. This investigation suggests that vertebrate frugivores, fleshy-fruited plants, and microbes form a tripartite interaction in which each part could interact positively with the other two (e.g. both orange seeds and fungal spores are likely dispersed by mammals). Such a mutualistic view of these complex interactions is opposed to the generalized idea of competition between frugivorous vertebrates and microorganisms. Thus, this research provides a new perspective on the widely accepted plant evolutionary dilemma to make fruits attractive to mutualistic frugivores while unattractive to presumed antagonistic microbes that constrain seed dispersal.

Diel variation in fig volatiles across syconium development: making sense of scents

Plants produce volatile organic compounds (VOCs) in a variety of contexts that include response to abiotic and biotic stresses, attraction of pollinators and parasitoids, and repulsion of herbivores. Some of these VOCs may also exhibit diel variation in emission. In Ficus racemosa, we examined variation in VOCs released by fig syconia throughout syconium development and between day and night. Syconia are globular enclosed inflorescences that serve as developing nurseries for pollinating and parasitic fig wasps. Syconia are attacked by gallers early in their development, serviced by pollinators in mid phase, and are attractive to parasitoids in response to the development of gallers at later stages. VOC bouquets of the different development phases of the syconium were distinctive, as were their day and night VOC profiles. VOCs such as α-muurolene were characteristic of the pollen-receptive diurnal phase, and may serve to attract the diurnally-active pollinating wasps. Diel patterns of release of volatiles could not be correlated with their predicted volatility as determined by Henry's law constants at ambient temperatures. Therefore, factors other than Henry's law constant such as stomatal conductance or VOC synthesis must explain diel variation in VOC emission. A novel use of weighted gene co-expression network analysis (WGCNA) on the volatilome resulted in seven distinct modules of co-emitted VOCs that could be interpreted on the basis of syconium ecology. Some modules were characterized by the response of fig syconia to early galling by parasitic wasps and consisted largely of green leaf volatiles (GLVs). Other modules, that could be characterized by a combination of syconia response to oviposition and tissue feeding by larvae of herbivorous galler pollinators as well as of parasitized wasps, consisted largely of putative herbivore-induced plant volatiles (HIPVs). We demonstrated the usefulness of WGCNA analysis of the volatilome in making sense of the scents produced by the syconia at different stages and diel phases of their development.

Fruit aromas in mature fleshy fruits as signals of readiness for predation and seed dispersal

The dispersal of seeds away from parent plants seems to be the underlying selective force in the evolution of fleshy fruits attractive to animals. Secondary metabolites, which are not essential compounds for plant survival, are involved in the interaction of fleshy fruits with seed dispersers and antagonists. Plant volatile organic compounds (VOCs) are secondary metabolites that play important roles in biotic interactions and in abiotic stress responses. They are usually accumulated at high levels in specific plant tissues and organs, such as fleshy fruits. The study of VOCs emitted during fruit development and after different biotic challenges may help to determine the interactions of fleshy fruits not only with legitimate vertebrate dispersers, but also with insects and microorganisms. A knowledge of fruit VOCs could be used in agriculture to generate attraction or repellency to pests and resistance to pathogens in fruits. This review provides an examination of specific fruit VOC blends as signals for either seed dispersal or predation through simple or complex trophic chains, which may also have consequences for an understanding of the importance of biodiversity in wild areas.