Cryptic Color Change in a Crab Spider (Misumena vatia): Identification and Quantification of Precursors and Ommochrome Pigments by HPLC

International audienceMimicry is used widely by arthropods to survive in a hostile environment. Often mimicry is associated with the production of chemical compounds such as pigments. In crab spiders, the change of color is based on a complex physiological process that still is not understood. The aim of this study was to identify and quantify the ommochrome pigments and precursors responsible for the color change in the mimetic crab spider Misumena vatia (Thomisidae). A modified high performance reverse phase ion-pair chromatography technique enabled us to separate and quantify the ommochrome pigments, their precursors, and related metabolites in individual spiders. Compounds such as tryptophan, kynurenine, and kynurenic acid occurred only or mainly in white crab spiders. In contrast, compounds such as 3-hydroxy-kynurenine, xanthommatin, and ommatin D occurred only or mainly in yellow crab spiders. Factor analysis ranked the different color forms in accordance with their metabolites. The biochemical results enabled us to associate the different phases of formation of pigment granules with specific metabolites. Yellow crab spiders contain many unknown ommochrome-like compounds not present in white crab spiders. We also found large quantities of decarboxylated xanthommatin, whose role as precursor of new pathways in ommochrome synthesis needs to be assessed. The catabolism of ommochromes, a process occurring when spiders revert from yellow to white, warrants further study

Synchronized evolution of the chemical signature of Reticulitermes Endogenous synchronization of the chemical signature of Reticulitermes (Isoptera, Rhinotermitidae) worker termites

National audienceTermites of the genus Reticulitermes are characteristic of temperate regions. Their colonies comprise various castes, the most numerous being that of workers which can develop into soldiers or secondary reproductives (neotenics). Each caste has a mixture of hydrocarbons (HCs) on the cuticle forming a chemical signature. The primary aim of this study was to compare the changes in the chemical signature of a population of worker termites fed on paper with juvenile hormone to differentiate them into soldiers with a control population of termites fed only on paper or wood for one month. Gas chromatography was used to analyze the cuticular profi les of Reticulitermes fl avipestermites to determine whether they changed, and, if so, when and how. The data collected over one month showed that the workers fed with JH did not differentiate into soldiers but that there were progressive changes in the hydrocarbon profi le independent of the treatment. These results indicate that the differentiation of the chemical signature of the worker caste is a dynamic process, depending only on time and not on colony membership, confi rming that, for these termites, this signature has a lesser role in colony membership than caste membership, unlike the chemical signatures of other social insects. The temporal process of this cuticular change is also associated with a change in the alkene / methyl-branched alkane rati

Variations in Worker Cuticular Hydrocarbons and Soldier Isoprenoid Defensive Secretions Within and Among Introduced and Native Populations of the Subterranean Termite, Reticulitermes flavipes

International audienceIn social insects, cuticular hydrocarbons (CHCs) play a central role in nestmate recognition. CHCs have proved to be useful for identifying species and differentiating populations. In combination with CHCs, isoprenoid soldier defensive secretions (SDSs) have been previously used in some termite species for chemotaxonomic analyses. This study compared the levels of chemical variation within and among introduced (French) and native (U.S.) populations of the subterranean termite, Reticulitermes flavipes. Worker CHCs and soldier SDSs from termites collected from colonies in nine populations in Florida, Louisiana, and France were analyzed. Discriminant analyses revealed that both localities and populations can be distinguished by using the variation in CHC profiles. Principal component analyses of CHC profiles as well as the calculation of two distance parameters (Nei and Euclidean) revealed remarkable chemical homogeneity within and among French populations. These analyses also showed that the CHC profiles of French populations were closer to termite populations from Louisiana than to those from Florida. Of the six distinct SDS chemotypes, one was common to populations in France and Louisiana. The possibility that populations in France originated from Louisiana, and the potential causes and consequences of chemical homogeneity within introduced populations are discussed

Modifications of the Chemical Profile of Hosts after Parasitism Allow Parasitoid Females to Assess the Time Elapsed Since the First Attack

International audienceIn solitary parasitoids, only one adult can emerge from a given host. In some of these species, when several eggs are laid on the same host, supernumerary individuals are eliminated by lethal larval fights. In the solitary parasitoid Anisopteromalus calandrae, the probability of a second larva winning the fight depends on the time elapsed since the first oviposition. The older the first egg is at the moment a second egg is laid, the less chance the second egg has of winning the competition. As a consequence, females of this species lay their eggs preferentially on recently parasitized hosts rather than on hosts parasitized by an egg about to hatch. Anisopteromalus calandrae females parasitize bruchid larvae located in cowpea seeds. In a series of choice test experiments using an artificial seed system, we demonstrated that the cue that allows parasitoid females to differentiate between hosts parasitized for different lengths of time comes from the host and not from the artificial seed or the previously laid egg. This cue is perceived at short range, indicating that the chemicals involved are probably partly volatile. Interestingly, although parasitism stops host development, cuticular profiles continue to evolve, but in a different way from those of unparasitized hosts. This difference in the host's cuticular profile after parasitism, therefore, probably underlies the parasitoid female's discrimination

Cleptoparasites, social parasites and a common host: Chemical insignificance for visiting host nests, chemical mimicry for living in

International audienceSocial insect colonies contain attractive resources for many organisms. Cleptoparasites sneak into their nests and steal food resources. Social parasites sneak into their social organisations and exploit them for reproduction. Both cleptoparasites and social parasites overcome the ability of social insects to detect intruders, which is mainly based on chemoreception. Here we compared the chemical strategies of social parasites and cleptoparasites that target the same host and analyse the implication of the results for the understanding of nestmate recognition mechanisms. The social parasitic wasp Polistes atrimandibularis (Hymenoptera: Vespidae), and the cleptoparasitic velvet ant Mutilla europaea (Hymenoptera: Mutillidae), both target the colonies of the paper wasp Polistes biglumis (Hymenoptera: Vespidae). There is no chemical mimicry with hosts in the cuticular chemical profiles of velvet ants and pre-invasion social parasites, but both have lower concentrations of recognition cues (chemical insignificance) and lower proportions of branched alkanes than their hosts. Additionally, they both have larger proportions of alkenes than their hosts. In contrast, post-invasion obligate social parasites have proportions of branched hydrocarbons as large as those of their hosts and their overall cuticular profiles resemble those of their hosts. These results suggest that the chemical strategies for evading host detection vary according to the lifestyles of the parasites. Cleptoparasites and pre-invasion social parasites that sneak into host colonies limit host overaggression by having few recognition cues, whereas post-invasion social parasites that sneak into their host social structure facilitate social integration by chemical mimicry with colony members

Endogenous synchronization of the chemical signature of Reticulitermes (Isoptera: Rhinotermitidae) worker termites

International audienceTermites of the genus Reticulitermes are characteristic of temperate regions. Their colonies comprise various castes, the most numerous being that of workers which can develop into soldiers or secondary reproductives (neotenics). Each caste has a mixture of hydrocarbons (HCs) on the cuticle forming a chemical signature. The primary aim of this study was to compare the changes in the chemical signature of a population of worker termites fed on paper with juvenile hormone to differentiate them into soldiers with a control population of termites fed only on paper or wood for one month. Gas chromatography was used to analyze the cuticular profi les of Reticulitermes fl avipes termites to determine whether they changed, and, if so, when and how. The data collected over one month showed that the workers fed with JH did not differentiate into soldiers but that there were progressive changes in the hydrocarbon profi le independent of the treatment. These results indicate that the differentiation of the chemical signature of the worker caste is a dynamic process, depending only on time and not on colony membership, confi rming that, for these termites, this signature has a lesser role in colony membership than caste membership, unlike the chemical signatures of other social insects. The temporal process of this cuticular change is also associated with a change in the alkene / methyl-branched alkane ratio

Population diversity in cuticular hydrocarbons and mtDNA in a mountain social wasp

International audienceNestmate recognition is a common phenomenon insocial insects that typically is mediated by cuticular hydrocarbons.Geographical variation in cuticular hydrocarbons hasbeen observed, although the pattern of variation is not consistentacross species and is usually related to the biology andecology of the different species. Polistes biglumis(Hymenoptera: Vespidae) is a social wasp that lives in highmountains where populations are separated by significantgeographical barriers. Here we investigated the level of chemicalvariation among populations of P. biglumis in the Alps,and shed light on the phylogeography of this species.Populations could be discriminated bymeans of their cuticularhydrocarbon profiles, which showed a pattern consistent withthe isolation-by-distance hypothesis. Molecular datahighlighted two areas with different levels of haplotype diversity,although all wasps belonged to the same species. Theseresults suggest that the populations of P. biglumis in the Alpsare geographically isolated from one another, favoring theirgenetic and chemical differentiation

Environmental and hormonal factors controlling reversible colour change in crab spiders

National audienceHabitat heterogeneity that occurs within an individual's lifetime may favour the evolution of reversible plasticity. Colour reversibility has many different functions in animals, such as thermoregulation, crypsis through background matching and social interactions. However, the mechanisms underlying reversible colour changes are yet to be thoroughly investigated. This study aims to determine the environmental and hormonal factors underlying morphological colour changes in Thomisus onustus crab spiders and the biochemical metabolites produced during these changes. We quantified the dynamics of colour changes over time: spiders were kept in yellow and white containers under natural light conditions and their colour was measured over 15 days using a spectrophotometer. We also characterised the chemical metabolites of spiders changing to a yellow colour using HPLC. Hormonal control of colour change was investigated by injecting 20-hydroxyecdysone (20E) into spiders. We found that background colouration was a major environmental factor responsible for colour change in crab spiders: individuals presented with white and yellow backgrounds changed to white and yellow colours, respectively. An ommochrome precursor, 3-OH-kynurenine, was the main pigment responsible for yellow colour. Spiders injected with 20E displayed a similar rate of change towards yellow colouration as spiders kept in yellow containers and exposed to natural sunlight. This study demonstrates novel hormonal manipulations that are capable of inducing reversible colour change