Orchid-mycorrhizal fungi interactions reveal a duality in their network structure in two European regions differing in climate.

Network analysis is an effective tool to describe and quantify the ecological interactions between plants and root-associated fungi. Mycoheterotrophic plants, such as orchids, critically rely on mycorrhizal fungi for nutrients to survive, so investigating the structure of those intimate interactions brings new insights into the plant community assembly and coexistence. So far, there is little consensus on the structure of those interactions, described either as nested (generalist interactions), modular (highly specific interactions) or of both topologies. Biotic factors (e.g., mycorrhizal specificity) were shown to influence the network structure, while there is less evidence of abiotic factor effects. By using next-generation sequencing of the orchid mycorrhizal fungal (OMF) community associated to with plant individuals belonging to 17 orchid species, we assessed the structure of four orchid-OMF networks in two European regions under contrasting climatic conditions (Mediterranean vs. Continental). Each network contained four to 12 co-occurring orchid species, including six species shared among the regions. All four networks were both nested and modular, and fungal communities were different between co-occurring orchid species, despite multiple sharing of fungi across some orchids. Co-occurring orchid species growing in Mediterranean climate were associated with more dissimilar fungal communities, consistent with a more modular network structure compared to the Continental ones. OMF diversity was comparable among orchid species since most orchids were associated with multiple rarer fungi and with only a few highly dominant ones in the roots. Our results provide useful highlights into potential factors involved in structuring plant-mycorrhizal fungus interactions in different climatic conditions.

Some bee-pollinated plants provide nutritionally incomplete pollen amino acid resources to their pollinators.

For pollinators such as bees, nectar mainly provides carbohydrates and pollen provides proteins, amino acids, and lipids to cover their nutritional needs. Here, to examine differences in pollinator resources, we compared the amino acid profiles and total amino acid contents of pollen from 32 common entomophilous plants in seven families. Our results showed that the amino acid profiles and contents in pollen samples differed according to the plant family and the chromatography method used, i.e., high-performance liquid chromatography (HPLC) versus ion exchange chromatography (IEX). Pollen from Boraginaceae species had the highest total amino acid contents (361.2-504 µg/mg) whereas pollen from the Malvaceae family had the lowest total amino acid contents (136-243.1 µg/mg). Calculating an amino acid score (AAS) that reflects pollen nutritional quality showed that slightly less than half of the species (19 out of 32) had the maximum nutritional score (AAS = 1) and offered high nutritional quality pollen amino acids for bee pollinators. Though they had high total amino acid contents, the amino acid composition of the studied Boraginaceae species and several members of the Fabaceae was not optimal, as their pollen was deficient in some essential amino acids, resulting in suboptimal amino acid scores (AAS < 0.7). Except for cysteine, the measured amino acid contents were higher using IEX chromatography than using HPLC. IEX chromatography is more robust and is to be preferred over HPLC in future amino acid analyses. Moreover, our observations show that some bee-pollinated species fail to provide complete amino acid resources for their pollinators. Although the implications for pollinator behavior remain to be studied, these deficiencies may force pollinators to forage from different species to obtain all nutritionial requirements.

Flora richness of a military area: discovery of a remarkable station of Serapiasneglecta in Corsica.

One of the central issues in conservation today is identifying areas rich in biodiversity for priority conservation. On a global scale, the Mediterranean area is a biodiversity hotspot and, locally, Corsica contains high biodiversity with interesting sites for conservation. An inventory of flora was undertaken on the Solenzara military airbase. Five hundred and fifty-two plant species were inventoried, which represent an important species richness. Amongst these species, certain are rare or endemic. A large population of Serapiasneglectasubsp.neglecta was found and the size of this population was estimated. This species is localised at a global scale and has a protection status. This is the largest population known, with more than 155,000 individuals on the 550 ha of the airbase. Nineteen plant species have national protection status and 15 are classified as invasive alien species. The Solenzara airbase has a role in conserving many species; a management plan would be appropriate.

Dataset of costs of the mitigation hierarchy and plant translocations in France.

These data are coming from the derogation requests for the destruction of protected species in the context of construction or development work in France. These derogation requests include, among other things, the contents of an environmental impact assessment and the costs of the measures suggested to reduce the impact on the environment. In the article connected to this dataset, we studied the quality of the plant translocation protocols proposed in 95 derogation files (see Julien et al., 2022). We additionally collected during the reading of the files data that we make available here about the costs of (i) the total project, (ii) the mitigation hierarchy and (iii) the plant translocation operations and monitoring. These data complement our aforementioned paper by documenting how much translocations cost and in what proportion of the other costs reported in the projects we evaluated for quality. These data can be helpful for environmental stakeholders but also to further studies to determine the extent to which the environment is considered in land planning.

Quality assessment of mitigation translocation protocols for protected plants in France.

Mitigation translocations are increasingly used worldwide in response to land planning pressures. The quality of translocation protocols and their adjustment to the ecological traits of the translocated populations are crucial to optimise translocation success. We studied the quality of translocation protocols presented in derogation requests, a mandatory step in France to translocate a protected plant species. We analysed 103 translocation proposals for 93 different species in 92 files examined between 2018 and 2020. After tracing the history of the place of translocations in legal procedures in France, we assessed each translocation proposal according to an evaluation grid, which involved the quantity and quality of information on plant species and translocation sites in the files and the quality of translocation protocols. We have shown that the translocation protocols are of low quality, with a lot of missing information. The biology and ecology of the species suggested for translocation are not sufficiently known, nor are the ecological characteristics of the host sites. Derogation requests that received a favourable opinion from the assessment body are more likely to propose a protected host site and post-translocation monitoring. We believe that, to optimise their outcome, mitigation translocations need to be improved upstream, with more detailed protocols and better species knowledge. We highly recommend following the same guidelines for mitigation translocations as for conservation translocations.

Microsatellites and petal morphology reveal new patterns of admixture in Orchis hybrid zones.

PREMISE: The genetic structure of hybrid zones provides insight into the potential for gene flow to occur between plant taxa. Four closely related European orchid species (Orchis anthropophora, O. militaris, O. purpurea, and O. simia) hybridize when they co-occur. We aimed to characterize patterns of hybridization in O. militaris-O. purpurea, O. purpurea-O. simia, and O. anthropophora-O. simia hybrid zones using molecular and morphological data. METHODS: We used 11 newly isolated nuclear microsatellites to genotype 695 individuals collected from seven hybrid zones and six allopatric parental populations in France. Geometric morphometric analysis was conducted using 15 labellum landmarks to capture the main aspects of petal shape. RESULTS: Backcrossing was asymmetric toward O. militaris in multiple O. militaris-O. purpurea hybrid zones. Hybrids in O. purpurea-O. simia and O. anthropophora-O. simia hybrid zones were largely limited to F1 and F2 generations, but further admixture had occurred. These patterns were reflected in labellum geometric morphometric data, which correlated strongly with nuclear microsatellite data in all three species combinations. CONCLUSIONS: The coexistence of parental and admixed individuals in these Orchis hybrid zones implies they are likely to be tension zones being maintained by a balance between gene flow into the hybrid zone and selection acting against admixed individuals. The pattern of admixture in the three species combinations suggests intrinsic selection acting on the hybrids is weaker in more closely related taxa.

Why are there so many bee-orchid species? Adaptive radiation by intra-specific competition for mnesic pollinators.

Adaptive radiations occur mostly in response to environmental variation through the evolution of key innovations that allow emerging species to occupy new ecological niches. Such biological innovations may play a major role in niche divergence when emerging species are engaged in reciprocal ecological interactions. To demonstrate coevolution is a difficult task; only a few studies have confirmed coevolution as driver of speciation and diversification. Herein we review current knowledge about bee orchid (Ophrys spp.) reproductive biology. We propose that the adaptive radiation of the Mediterranean orchid genus Ophrys, comprising several hundred species, is due to coevolutionary dynamics between these plants and their pollinators. We suggest that pollination by sexual swindling used by Ophrys orchids is the main driver of this coevolution. Flowers of each Ophrys species mimic a sexually receptive female of one particular insect species, mainly bees. Male bees are first attracted by pseudo-pheromones emitted by Ophrys flowers that are similar to the sexual pheromones of their females. Males then are lured by the flower shape, colour and hairiness, and attempt to copulate with the flower, which glues pollen onto their bodies. Pollen is later transferred to the stigma of another flower of the same Ophrys species during similar copulation attempts. In contrast to rewarding pollination strategies, Ophrys pollinators appear to be parasitized. Here we propose that this apparent parasitism is in fact a coevolutionary relationship between Ophrys and their pollinators. For plants, pollination by sexual swindling could ensure pollination efficiency and specificity, and gene flow among populations. For pollinators, pollination by sexual swindling could allow habitat matching and inbreeding avoidance. Pollinators might use the pseudo-pheromones emitted by Ophrys to locate suitable habitats from a distance within complex landscapes. In small populations, male pollinators would disperse once they have memorized the local diversity of sexual pseudo-pheromone bouquets or if all Ophrys flowers are fertilized and thus repel pollinators via production of repulsive pheromones that mimic those produced by fertilized female bees. We propose the following evolutionary scenario: Ophrys radiation is driven by strong intra-specific competition among Ophrys individuals for the attraction of species-specific pollinators, which is a consequence of the high cognitive abilities of pollinators. Male bees record the pheromone signatures of kin or of previously courted partners to avoid further copulation attempts, thereby inducing strong selection on Ophrys for variation in odour bouquets emitted by individual flowers. The resulting odour bouquets could by chance correspond to pseudo-pheromones of the females of another bee species, and thus attract a new pollinator. If such pollinator shifts occur simultaneously in several indivuals, pollen exchanges might occur and initiate speciation. To reinforce the attraction of the new pollinator and secure prezygotic isolation, the following step is directional selection on flower phenotypes (shape, colour and hairiness) towards a better match with the body of the pollinator's female. Pollinator shift and the resulting prezygotic isolation is adaptive for new Ophrys species because they may benefit from competitor-free space for limited pollinators. We end our review by proritizing several critical research avenues.

Floral trait differentiation in Anacamptis coriophora: Phenotypic selection on scents, but not on colour.

Current divergent selection may promote floral trait differentiation among conspecific populations in flowering plants. However, whether this applies to complex traits such as colour or scents has been little studied, even though these traits often vary within species. In this study, we compared floral colour and odour as well as selective pressures imposed upon these traits among seven populations belonging to three subspecies of the widespread, generalist orchid Anacamptis coriophora. Colour was characterized using calibrated photographs, and scents were sampled using dynamic headspace extraction and analysed using gas chromatography-mass spectrometry. We then quantified phenotypic selection exerted on these traits by regressing fruit set values on floral trait values. We showed that the three studied subspecies were characterized by different floral colour and odour, with one of the two predominant floral volatiles emitted by each subspecies being taxon-specific. Plant size was positively correlated with fruit set in most populations, whereas we found no apparent link between floral colour and female reproductive success. We detected positive selection on several taxon-specific compounds in A. coriophora subsp. fragrans, whereas no selection was found on floral volatiles of A. coriophora subsp. coriophora and A. coriophora subsp. martrinii. This study is one of the first to document variation in phenotypic selection exerted on floral scents among conspecific populations. Our results suggest that selection could contribute to ongoing chemical divergence among A. coriophora subspecies.

Understanding intraspecific variation of floral scent in light of evolutionary ecology.

Background and Aims: Among the various floral traits involved in pollinator attraction and potentially under selection mediated by pollinators, floral scent/fragrance has been less investigated than other components of floral phenotype. Whether or not pollinator-mediated selection impacts floral scents depends on the heritability of scent/fragrance and the occurrence of some variation within species. Although most studies have investigated how scent varies among species, growing amounts of data are available on variation at the intraspecific level. Methods: The results of 81 studies investigating intraspecific variation of floral scents in 132 taxa were reviewed. For each study, whether variation was found in either identity, proportion or absolute quantities of volatile organic compounds (VOCs) was recorded, as well as information with the potential to explain variation, such as methodology, plant origin or pollination biology. Key Results: Variation was found for almost all investigated species, both among individuals (among and sometimes within populations) and within individuals across different temporal scales. Cases in which such variation is a possible result of pollinator-mediated selection were analysed, by discussing separately selection related to variation in pollinator identity/behaviour among populations or across time, deceit pollination and sex-specific selection. Not surprisingly, in many cases, pollinator-mediated selection alone does not explain the observed variation in floral scent. This led us to review current knowledge on less investigated factors, such as selection mediated by natural enemies, genetic drift and gene flow, environmental constraints, phylogenetic inertia, or biochemical constraints that could be invoked to explain scent variation. Conclusions: This review highlights the great potential of analysing floral scent variation and including it in integrated studies of floral phenotypes. We also have identified the current gaps in our understanding of this complex signal and we propose several methodological and conceptual future directions in this research area.

Integrative taxonomy of the fly orchid group: insights from chemical ecology.

Several authors have recently stressed the need to develop an integrative approach in taxonomy, but studies applying such an approach to Mediterranean orchids are scarce. In sexually deceptive orchids from the taxonomically difficult genus Ophrys, pollination is specific and performed by male insects attracted to the flowers by sex pheromone-mimicking floral scents. Floral compounds are therefore of primary importance for reproductive isolation and species delimitations in this genus. In the fly orchid group, molecular, morphological, and ecological characters have been extensively studied, but a comprehensive survey of floral scents is still lacking. In the present study, the blends of floral compounds of its three members, Ophrys insectifera, Ophrys aymoninii, and Ophrys subinsectifera, were extracted and analyzed by gas chromatography-mass spectrometry. A total of 107 compounds were found, with a majority of saturated and unsaturated hydrocarbons. Significant differentiation, both qualitative and quantitative, was found among the three taxa. This result, pooled with those from the literature, forms a comprehensive and congruent dataset that allows us to elucidate the taxonomic rank of the three members of the fly orchid group.

Responses of orchids to habitat change in Corsica over 27 years.

BACKGROUND AND AIMS: Orchids are known to be particularly sensitive to environmental changes due to their narrow ranges of secondary successional habitats. Lack of data at the community level limits our ability to evaluate how traits of different species influence their responses to habitat change. Here, we used a diachronic survey of Mediterranean orchid communities in Corsica to examine this question. METHODS: Using data from two field surveys conducted 27 years apart (1982-84 and 2009-11) at the same 45 sites in Corsica, we evaluated the impact of increase in woody plant cover (WPC) on (i) the richness and composition and (ii) the local extinction/colonization dynamics of orchids. We applied a Bayesian multispecies site-occupancy model to each of the 36 orchid species recorded at these sites to estimate the detection probability of each species, enabling us to account for under-detection in estimating their dynamics. KEY RESULTS: Between 1982 and 2011, WPC changed at 82·3 % of sites (increasing at 75·6 %, decreasing at 6·7 %). Despite marked changes in composition of orchid communities at the local scale, no significant change was detected in species richness at the regional scale. Canopy closure affected the probability of new colonization of sites, but had no significant influence on the probability of local extinction. However, the abundance of shade-intolerant species declined more sharply than that of shade-requiring species. Among orchid species, the detection probability was significantly and positively correlated with population density and plant height. CONCLUSIONS: This study reveals contrasted dynamics of orchid communities between local and regional scales in Corsica. Although high turnover in communities was found at the local scale, regional species richness was maintained despite major land-use changes. Conserving landscape mosaics could provide locally suitable habitats for orchids of different ecologies to maintain diversity at larger spatial scales.

Flower color polymorphism in Iris lutescens (Iridaceae): biochemical analyses in light of plant-insect interactions.

We describe a flower color polymorphism in Iris lutescens, a species widespread in the Northern part of the Mediterranean basin. We studied the biochemical basis of the difference between purple and yellow flowers, and explored the ecological and evolutionary consequences of such difference, in particular visual discrimination by insects, a potential link with scent emitted and the association between color and scent. Anthocyanins were found to be present in much greater concentrations in purple flowers than in yellow ones, but the anthocyanin composition did not differ between color morphs. Likewise, no quantitative difference in anthocyanin content was found between vegetative tissues of the two morphs. Floral anthocyanins were dominated by delphinidin 3-O-(p-coumaroylrutinoside)-5-O-glucoside (also called delphanin) and its aliphatic derivatives. Small amounts of delphinidin 3-O-(p-caffeoylrutinoside)-5-O-glucoside and its aliphatic derivatives were also characterized. Based on a description of bumblebees' (one of the main pollinators of I. lutescens) color perception, purple and yellow flowers of I. lutescens could be visually discriminated as blue and blue-green, respectively, and likely by a wide variety of other insects. The overall chemical composition of the scent produced was not significantly different between morphs, being dominated by terpenoids, mainly myrcene, (E)-ß-ocimene and limonene. A slight color-scent correlation was nevertheless detected, consistent with the shared biosynthetic origin of both pigments and volatile compounds. Therefore in this species, the difference in the amounts of pigments responsible for flower color difference seems to be the major difference between the two morphs. Pollinators are probably the main selective agent driving the evolution of flower color polymorphism in I. lutescens, which represents a suitable species for investigating how such polymorphism is maintained.

Morphological, ecological and genetic aspects associated with endemism in the Fly Orchid group.

The European genus Ophrys (Orchidaceae) is famous for its insect-like floral morphology, an adaptation for a pseudocopulatory pollination strategy involving Hymenoptera males. A large number of endemic Ophrys species have recently been described, especially within the Mediterranean Basin, which is one of the major species diversity hotspots. Subtle morphological variation and specific pollinator dependence are the two main perceptible criteria for describing numerous endemic taxa. However, the degree to which endemics differ genetically remains a challenging question. Additionally, knowledge regarding the factors underlying the emergence of such endemic entities is limited. To achieve new insights regarding speciation processes in Ophrys, we have investigated species boundaries in the Fly Orchid group (Ophrys insectifera sensu lato) by examining morphological, ecological and genetic evidence. Classically, authors have recognized one widespread taxon (O. insectifera) and two endemics (O. aymoninii from France and O. subinsectifera from Spain). Our research has identified clear morphological and ecological factors segregating among these taxa; however, genetic differences were more ambiguous. Insights from cpDNA sequencing and amplified fragment length polymorphisms genotyping indicated a recent diversification in the three extant Fly Orchid species, which may have been further obscured by active migration and admixture across the European continent. Our genetic results still indicate weak but noticeable phylogeographic clustering that partially correlates with the described species. Particularly, we report several isolated haplotypes and genetic clusters in central and southeastern Europe. With regard to the morphological, ecological and genetic aspects, we discuss the endemism status within the Fly Orchid group from evolutionary, taxonomical and conservation perspectives.

Evidence for intersexual chemical mimicry in a dioecious plant.

The dioecious Mediterranean fig, Ficus carica, displays a unique phenology in which males sometimes bloom synchronously with females (in summer), and sometimes not (in spring). Ficus carica is engaged in an obligatory mutualism with a specific pollinating wasp, which reproduces only within figs, localising them by their specific scents. We show that scents emitted by male figs show seasonal variation within individual trees. Scents of summer male figs resemble those of the co-flowering females, and are different from those of the same male trees in spring, when female figs are absent. These differences hold even if only compounds electrophysiologically active for pollinators are considered. The similar scents of summer males and females may explain why the rewardless females are still pollinated. These results offer a tractable model for future studies of intersexual chemical mimicry in mutualistic pollination interactions.

Colour-scent associations in a tropical orchid: three colours but two odours.

Colour and scent are the major pollinator attractants to flowers, and their production may be linked by shared biosynthetic pathways. Species with polymorphic floral traits are particularly relevant to study the joint evolution of floral traits. We used in this study the tropical orchid Calanthe sylvatica from Réunion Island. Three distinct colour varieties are observed, presenting lilac, white or purple flowers, and named respectively C. sylvaticavar.lilacina (hereafter referred as var. lilacina), C. sylvaticavar. alba (var. alba) and C. sylvatica var. purpurea (var. purpurea). We investigated the composition of the floral scent produced by these colour varieties using the non-invasive SPME technique in the wild. Scent emissions are dominated by aromatic compounds. Nevertheless, the presence of the terpenoid (E)-4,8-dimethylnona-1,3,7-triène (DMNT) is diagnostic of var. purpurea, with the volatile organic compounds (VOC) produced by some individuals containing up to 60% of DMNT. We evidence specific colour-scent associations in C. sylvatica, with two distinct scent profiles in the three colour varieties: the lilacina-like profile containing no or very little DMNT (<2%) and the purpurea-like profile containing DMNT (>2%). Calanthe sylvatica var. alba individuals group with one or the other scent profile independently of their population of origin. We suggest that white-flowered individuals have evolved at least twice, once from var. lilacina and at least once from var. purpurea after the colonisation of la Réunion. White-flowered individuals may have been favoured by the particular pollinator fauna characterising the island. These flowering varieties of C. sylvatica, which display three colours but two scents profiles prove that colour is not always a good indicator of odour and that colour-scent associations may be complex, depending on pollination ecology of the populations concerned.

Geographic variation of floral scent in a highly specialized pollination mutualism.

Floral scents are important signals for communication between plants and pollinators. Several studies have focused on interspecific variation of these signals, but little is known about intraspecific variation in flower scent, particularly for species with wide geographic distributions. In the highly specific mutualism between Ficus species and their pollinating wasps, chemical mediation is crucial for partner encounter. Several studies show that scents, i.e. blends of volatiles, are species-specific, but no studies address interpopulation variation of scents in fig pollination mutualisms, which often have broad geographic distributions. In this study, using absorption/desorption headspace techniques, we analyzed variation in floral scent composition among three populations of each of two widely distributed Asian Ficus species. We identified more than 100 different volatile organic compounds, predominantly terpenes. In both species, significant differences were found between scent bouquets of East Asian and Indian populations. These differences are discussed in relation to geographical barriers that could disrupt gene exchange between these two areas, thereby isolating Indian populations from those of Eastern Asia.

Helping in food-deceptive orchids? A possible new mechanism maintaining polymorphism of floral signals.

Why different colour morphs have evolved in flowering plants, and how they are maintained in populations, have long intrigued ecologists. The impact of variation in floral colour and odour (the two are frequently associated) on reproductive success remains poorly understood. In European rewardless orchids, many species occasionally show rare white-flowered individuals within populations of the common-coloured morph. In a recent study, we found that in Orchis mascula the presence of rare white-flowered morphs significantly increased the reproductive success (from 6% to 27%) of purple-flowered plants, while success of the white morph remained low. This surprising result appears due solely to floral color polymorphism, which in this species is not associated with odour polymorphism. We hypothesize that colour variation plays the key role in pollinator attraction, and that white-flowered individuals may be regarded to function as "sensory traps". We also propose that the maintenance of white-flowered mutants in O. mascula may result through kin selection, in which they act as helpers increasing the reproductive success of related purple individuals.

A case study of modified interactions with symbionts in a hybrid mediterranean orchid.

PREMISE OF THE STUDY: Most studies on orchid hybrids examine separately the effects of hybridization on interactions with pollinators or with mycorrhizal fungi. Here, we simultaneously investigated both interactions in the mediterranean food-deceptive Orchis simia, O. anthropophora, and their hybrid (O. ×bergonii) and tested a possible breakdown of coevolution using a multidisciplinary approach. • METHODS: We compared leaf growth, seed viability, emitted scent, and mycorrhizal fungi (species and rate of infection) among these three taxa. • KEY RESULTS: We show that leaf surface is greater in adult hybrids than in the parental species, suggesting a heterosis effect for vegetative growth. We demonstrate that flowers of the two parental species emit well-differentiated bouquets of volatile organic compounds, while hybrids emit larger quantities, accumulating most compounds of the two parental species. However, hybrids fail to attract pollinators and have a 10 times lower fruit set. We determined that closely related Tulasnellales are mycorrhizal in the three taxa, suggesting that the mycorrhizal partner does not impair hybrid survival. We propose an interpretative model for O. ×bergonii compared with its parents. • CONCLUSIONS: In hybrids, carbon resources normally devoted to reproduction may be reallocated to the mycorrhizal symbiosis as a result of the disruption of the pollination interaction in hybrids. Higher mycorrhizal infection may in turn enhance vegetative growth and scent emission. Such interplay between the two obligate biotic interactions yields new insights into hybridization among orchids.

Chemical mediation and niche partitioning in non-pollinating fig-wasp communities.

1. The parasitic chalcidoid wasps associated with the species-specific and obligatory pollination mutualisms between Ficus spp. and their agaonid wasp pollinators provide a good model to study the functional organization of communities. 2. However, communities of non-pollinating fig wasps (NPFWs) remain little characterized, and their functioning and evolutionary dynamics are still poorly understood. 3. We studied the communities of NPFWs associated with the monoecious F. racemosa and the dioecious F. hispida. Associated with these two fig species are a total of seven wasp species belonging to three genera. These species present contrasts in life history traits and in timing of oviposition. The species studied are thus broadly representative of the communities of NPFWs associated specifically with fig-pollinator mutualisms. 4. In our study systems, there is temporal segregation of oviposition time among members of NPFW communities. 5. We tested the role of volatile chemicals in the attraction of NPFWs associated with these two fig species, and tried to determine if chemical mediation can explain the organization of the communities. 6. We conducted odour choice tests using a Y-tube olfactometer. All the NPFWs studied were shown to use volatile chemicals produced by the fig to locate their host. Furthermore, the signals used by each species depended on the phenological stage of the fig they exploit. 7. Results demonstrated that the pattern of oviposition results from the utilization of volatile signals produced by figs that vary in their composition at different stages of fig development. Thus, chemical mediation allows resource partitioning in the NPFW communities associated with fig-pollinator mutualisms, and suggests hypotheses to explain coexistence in other parasite communities.