Olfactory signal coding in an odor background

AbstractInsects communicating with pheromones are confronted with an olfactory environment featuring a diversity of volatile organic compounds from plant origin. These volatiles constitute a rich and fluctuant background from which the information carried by the pheromone signal must be extracted. Thus, the pheromone receptor neurons must encode into spike trains the quality, intensity and temporal characteristics of the signal that are determinant to the recognition and localization of a conspecific female. We recorded and analyzed the responses of the pheromone olfactory receptor neurons of male moths to sex pheromone in different odor background conditions. We show that in spite of the narrow chemical tuning of the pheromone receptor neurons, the sensory input can be altered by odorant background

Clonal variation in aggregation and defensive behavior in pea aphids

The presence of several clonal lineages within a single aphid colony raises the possibility for conflict between clones over safer positions within multiclonal colonies. To study the effect of relatedness on group dynamics, we manipulated the clonal composition of pea aphid groups (2 pure clonal groups and 1 mixed group) under laboratory conditions and allowed the individuals to cluster together freely on a leaf. We found variation between the clones in both the speed at which individuals joined the group and the aggregation level, where mixed colonies showed intermediates. Experimental and simulation results showed a nonrandom distribution of aphids in mixed colonies between the center and the periphery area, suggesting that one of the clones exhibits selfish herd behavior. In a second set of experiments, aphid groups were exposed to a single parasitoid female. Interestingly, we found that aphids from pure colonies were more likely to react by falling from the plant than individuals in mixed colonies. Our results revealed unexpected kin recognition abilities by nonsocial aphids, which make aphid colony dynamics more complex than previously thought. © 2014 The Author

Rôle des odeurs de plantes sur l'orientation à la phéromone sexuelle chez les noctuelles

La localisation d'une ressource telle que le partenaire sexuel, une source de nourriture ou un site de ponte est une étape essentielle dans la vie des insectes. Elle implique la capacité de détecter et de discriminer des signaux chimiques révélant sa présence. ainsi, chez les noctuelles la communication est essentiellement assurée par une phéromone émise par la femelle, et détectée par le mâle via son système olfactif. Mais le mâle doit s'orienter vers la femelle dans un environnement odorant bruité et complexe qui contient notamment un grand nombre de composés volatils émis par les plantes. Nous avons étudié chez deux espèces de noctuelles, Spodoptera littoralis et Agrotis ipsilon, l'effet de différents composés volatils de plantes (VPCs) sur la réponse à la phéromone. Nous avons analysé leurs effets sur les réponses à la phéromone des neurones récepteurs olfactifs (antennes) et des neurones centraux (lobes antennaires) du système olfactif par des approches électrophysiologiques ou des techniques d'imagerie calcique. De plus, nous avons étudié leur impact sur l'orientation des mâles grâce à des approches comportementales réalisées en compensateur à locomotion et tunnel de vol. Nous avons pu montrer que les composés volatils de plantes pouvaient, selon l'espèce, activer la voie du système olfactif spécifique à la phéromone sexuelle. Appliqué en bruit de fond, les VPCs altèrent le codage du signal phéromonal à différents niveaux du traitement de l'information olfactive. Les odeurs de plantes ont un effet suppresseur sur la réponse à la phéromone, mais améliorent le codage temporel du signal phéromonal. Ils peuvent également perturber le comportement d'orientation à la phéromone, mais leur interaction avec la phéromone est indépendante de l'état d'accouplement du mâle. Les odeurs généralistes présentes dans le milieu olfactif environnant peuvent donc moduler la perception et la réponse à un signal spécifique. Ceci indique que les mâles sont sensibles aux changements de leur environnement odorant et aux modifications qu'elles amènent dans la perception du signal.The localization of a resource such as a sexual partner, a food source or an oviposition site are essential steps in an insect's life. It involves the ability to detect and discriminate chemical signals revealing its presence. Thus, in moths communication is mainly provided by a sex pheromone emitted by the female and detected by the male via the olfactory system. But, the male should be directed to the female in a noisy and complex odorant environment which contains a large number of volatile compounds emitted by surrounding plants. We studied in two moth species, Agrotis ipsilon and Spodoptera littoralis, the effects of different volatile plant compounds (VPCs) on the sex pheromone response. We have analyzed their effects on the response of olfactory receptor neurons and antennal lobes neurons by electrophysiological approaches or calcium imaging techniques. In addition, we have studied their impact on the male orientation with behavioral approaches made in locomotion compensator and in wind tunnel. We showed that volatile plants compounds, according to species, may activate the pheromone specific sub-system. As background , VPCs alter the coding of pheromone signal at the different levels of its processing. The VPCs have a suppressive effect on the pheromone response, but also improve temporal coding of pheromone signal. They may also affect the orientation behavior toward pheromone, but their interaction with the sex pheromone is independent of the mate male state. General odorants present in the surrounding olfactory environment can modulate the perception and the response to a specific signal. This indicates that males are sensitive to changes in their odorant environment and to modulations of the signal perception.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Atypical plant odor responses in the pheromone system in a moth

International audienc

Olfaction and Taste II : No sex without food: atypical plant odor responses in the pheromone processing system of a male moth

International audienceMale noctuid moths rely on olfactory cues to find females for reproduction. They also use volatile plant compounds (VPCs) to find food sources and might use host odor cues to identify the habitat of calling females. Both the sex pheromone and VPCs trigger a well-described oriented flight behavior towards the odor source. Whereas detection and central processing of sex pheromones and VPCs were considered to be highly separated from each other, recent studies have shown interactions of both types of odors already early in the olfactory pathway. In addition to interactions, we show that even detection and early processing of pheromones and VPC can overlap. Using complementary methodological approaches, going from peripheral detection over central processing to behavior (single-sensillum recording of olfactory receptor neurons, intracellular recordings of macroglomerular complex neurons, in vivo calcium imaging in the antennal lobe, flight behavior in wind tunnel experiments), we show in the present study that a plant odorant alone, heptanal, activates the pheromone specific pathway in male Agrotis ipsilon. To our knowledge, this is the first report of a plant odorant with no chemical similarity with the molecular structure of the pheromone, acting as a partial agonist of a moth sex pheromone

A Background of a Volatile Plant Compound Alters Neural and Behavioral Responses to the Sex Pheromone Blend in a Moth

International audienceRecognition of intra-specific olfactory signals within a complex environment of plant-related volatiles is crucial for reproduction in male moths. Sex pheromone information is detected by specific olfactory receptor neurons (Phe-ORNs), highly abundant on the male antenna. The information is then transmitted to the pheromone processing macroglomerular complex (MGC) within the primary olfactory center, the antennal lobe, where it is processed by local interneurons and projection neurons. Ultimately a behavioral response, orientation toward the pheromone source, is elicited. Volatile plant compounds (VPCs) are detected by other functional types of olfactory receptor neurons (ORNs) projecting in another area of the antennal lobe. However, Phe-ORNs also respond to some VPCs. Female-produced sex pheromones are emitted within a rich environment of VPCs, some of which have been shown to interfere with the detection and processing of sex pheromone information. As interference between the different odor sources might depend on the spatial and temporal features of the two types of stimuli, we investigated here behavioral and neuronal responses to a brief sex pheromone blend pulse in a VPC background as compared to a control background in the male noctuid moth Agrotis ipsilon. We observed male orientation behavior in a wind tunnel and recorded responses of Phe-ORNs and MGC neurons to a brief sex pheromone pulse within a background of individual VPCs. We also recorded the global input signal to the MGC using in vivo calcium imaging with the same stimulation protocol. We found that VPCs eliciting a response in Phe-ORNs and MGC neurons masked responses to the pheromone and decreased the contrast between background odor and the sex pheromone at both levels, whereas α-pinene did not interfere with first order processing. The calcium signal produced in response to a VPC background was tonic, lasting longer than the VPC stimulus duration, and masked entirely the pheromone response. One percent heptanal and linalool, in addition to the masking effect, caused a clear delay in responses of MGC neurons to the sex pheromone. Upwind flight toward the pheromone in a wind tunnel was also delayed but otherwise not altered by different doses of heptanal