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

A General Odorant Background Affects the Coding of Pheromone Stimulus Intermittency in Specialist Olfactory Receptor Neurones

In nature the aerial trace of pheromone used by male moths to find a female appears as a train of discontinuous pulses separated by gaps among a complex odorant background constituted of plant volatiles. We investigated the effect of such background odor on behavior and coding of temporal parameters of pheromone pulse trains in the pheromone olfactory receptor neurons of Spodoptera littoralis. Effects of linalool background were tested by measuring walking behavior towards a source of pheromone. While velocity and orientation index did drop when linalool was turned on, both parameters recovered back to pre-background values after 40 s with linalool still present. Photo-ionization detector was used to characterize pulse delivery by our stimulator. The photo-ionization detector signal reached 71% of maximum amplitude at 50 ms pulses and followed the stimulus period at repetition rates up to 10 pulses/s. However, at high pulse rates the concentration of the odorant did not return to base level during inter-pulse intervals. Linalool decreased the intensity and shortened the response of receptor neurons to pulses. High contrast (>10 dB) in firing rate between pulses and inter-pulse intervals was observed for 1 and 4 pulses/s, both with and without background. Significantly more neurons followed the 4 pulses/s pattern when delivered over linalool; at the same time the information content was preserved almost to the control values. Rapid recovery of behavior shows that change of perceived intensity is more important than absolute stimulus intensity. While decreasing the response intensity, background odor preserved the temporal parameters of the specific signal

Brief Exposure to Sensory Cues Elicits Stimulus-Nonspecific General Sensitization in an Insect

The effect of repeated exposure to sensory stimuli, with or without reward is well known to induce stimulus-specific modifications of behaviour, described as different forms of learning. In recent studies we showed that a brief single pre-exposure to the female-produced sex pheromone or even a predator sound can increase the behavioural and central nervous responses to this pheromone in males of the noctuid moth Spodoptera littoralis. To investigate if this increase in sensitivity might be restricted to the pheromone system or is a form of general sensitization, we studied here if a brief pre-exposure to stimuli of different modalities can reciprocally change behavioural and physiological responses to olfactory and gustatory stimuli. Olfactory and gustatory pre-exposure and subsequent behavioural tests were carried out to reveal possible intra- and cross-modal effects. Attraction to pheromone, monitored with a locomotion compensator, increased after exposure to olfactory and gustatory stimuli. Behavioural responses to sucrose, investigated using the proboscis extension reflex, increased equally after pre-exposure to olfactory and gustatory cues. Pheromone-specific neurons in the brain and antennal gustatory neurons did, however, not change their sensitivity after sucrose exposure. The observed intra- and reciprocal cross-modal effects of pre-exposure may represent a new form of stimulus-nonspecific general sensitization originating from modifications at higher sensory processing levels

Priority of precedence: receiver psychology, female preference forleading calls and sexual selection in insect choruses

International audienceIn species in which males display collectively, females may evaluate display features that arise specificallyin groups in addition to basic features of signal energy. For example, in acoustic insects and anuransthat chorus, males often adjust their song timing relative to neighbours, and females may pay attentionto these adjustments in timing. Many laboratory studies show how males may delay the phase of theirsong rhythm with respect to a song stimulus such that they call just prior to the stimulus; similarly,females may choose a male whose song rhythm leads a neighbour by a brief interval. However, theimportance of male phase adjustments and female attention to call order in actual choruses hasremained poorly understood. We studied female choice in laboratory choruses in the bushcricketEphippiger diurnus, a species with preferences for leading calls but also for longer calls and fasterrhythms, features representing broadcast energy. Although chorusing males varied in all features, wefound that females largely focused on call order. This overriding preference for call order may be reflectedby the prevalence of male phase adjustment throughout the population, a feature that wouldhave been subject to strong sexual selection.We found that the broadcast of leading calls within a choruswas not repeatable among males but rather shifted among the chorus participants. This observation toomay reflect the strong selection imposed by female choice for call order, and it may have implications forthe role of receiver psychology in the evolution of mate choice. 2013 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved

Evolution of synchronies in insect choruses

International audienc

Animal choruses emerge from receiver psychology OPEN

National audienceSynchrony and alternation in large animal choruses are often viewed as adaptations by which cooperating males increase their attractiveness to females or evade predators. Alternatively, these seemingly composed productions may simply emerge by default from the receiver psychology of mate choice. This second, emergent property hypothesis has been inferred from findings that females in various acoustic species ignore male calls that follow a neighbor's by a brief interval, that males often adjust the timing of their call rhythm and reduce the incidence of ineffective, following calls, and from simulations modeling the collective outcome of male adjustments. However, the purported connection between male song timing and female preference has never been tested experimentally, and the emergent property hypothesis has remained speculative. Studying a distinctive katydid species genetically structured as isolated populations, we conducted a comparative phylogenetic analysis of the correlation between male call timing and female preference. We report that across 17 sampled populations male adjustments match the interval over which females prefer leading calls; moreover, this correlation holds after correction for phylogenetic signal. Our study is the first demonstration that male adjustments coevolved with female preferences and thereby confirms the critical link in the emergent property model of chorus evolution

Group synchrony and alternation as an emergent property:elaborate chorus structure in a bushcricket is an incidentalby-product of female preference for leading calls: Group synchrony and alternation as an emergent property: elaborate chorus structure in a bushcricket is an incidental by-product of female preference for leading calls

International audienceMany acoustic animals exhibit temporally structuredchorusing, and in some cases, groups of calling malesdisplay elaborate forms of synchrony and/or alternation. Suchtemporal structure has traditionally been explained as an adaptationby which chorusing males preserve critical call features,maximize the attractiveness of their local group to females,or improve their ability to detect, evaluate, and/orevade rival males or predators. However, an alternative possibilityis that synchrony and alternation simply emerge as incidentalby-products of basic pairwise signal interactions betweenmale neighbors. Thus, females may not be influencedby synchrony and alternation, and males may not benefit perse from the very chorus that they collectively produce. Westudied chorusing in the bushcricket Ephippiger diurnus, aspecies that sings in both synchrony and alternation, by presentingnatural and modified chorus stimuli to females in aseries of playback tests. We found that females respondedreadily to the various stimuli, but we did not observe an elevatedresponse to the natural chorus stimuli in any experimentor in any of the several E. diurnus populations tested. Ourresults demonstrate for the first time how elaborate forms ofsynchrony and alternation can represent emergent propertiesof choruses as opposed to specialized group displays that affordparticular advantages to the individual singers

Phylogeographic structure without pre-mating barriers: Do habitat fragmentation and low mobility preserve song and chorus diversity in a European bushcricket?

International audienc

Characterization of 16 novel microsatellite loci for Ephippiger diurnus (Orthoptera: Tettigoniidae) using pyrosequencing technology and cross-species amplification

A novel panel of 16 microsatellite markers, obtained by pyrosequencing of enriched genomic libraries, is reported for the fl ightless European bushcricket Ephippiger diurnus (Dufour) (Orthoptera: Tettigoniidae). Five multiplex and one simplex PCR protocols were optimized, and the polymorphism at the 16 loci was assessed in two natural populations from southern France. The mean allele number and (expected mean heterozygosity) were 8.94 (0.71) and 6.57 (0.70), respectively, in each population. Several loci were at Hardy-Weinberg disequilibrium (HWD), possibly due to the incidence of null alleles. The occurrence of null alleles has been previously reported for this species, and it is a common feature of microsatellite loci in Orthoptera. Cross-amplifi cation tests demonstrated the transferability of some of these loci to other ephippigerine species. The microsatellite loci reported here substantially increase the number of available loci for this species and will afford an accurate picture of E. diurnus phylogeography, the genetic structure of its populations, and an improved understanding of the evolution of male song and other sexually-selected traits in this highly variable specie

What determines lek size? Cognitive constraints and per capita attraction of females limit male aggregation in an acoustic moth

International audienceIt has been proposed that leks arise because of increased mating benefits in aggregations of displaying males, and some evidence supports this hypothesis. But observations also indicate that lekking aggregations include only a small percentage of the males in a population, implying that certain factors limit lek size. Potential factors include increasing travel costs to find and form large but distant aggregations, greater attraction of predators and higher levels of aggression. Any one of these constraints may cause the number of females arriving at larger leks to decelerate such that per capita male attractiveness, and hence mating success, declines above an optimum lek size. None the less, relatively little empirical workhas examined what determines lek size. In particular the possibility that cognitive aspects might constrain lek size has rarely been considered. We studied this question in Achroia grisella, an acoustic moth in which singing males form small aggregations that attract females. We created artificial leks in the laboratory and tested their relative attractiveness to females; we also tested male preferences to form and join such aggregations. Females preferred male aggregations over solitary singers, but the marginal per capita attractiveness of an aggregation of n þ 2 males versus n males waned for n 5. Similarly we found that males were attracted to other males singing in the vicinity, but this effect disappeared for n 4. We infer that lek size is limited because the marginal per capita attractiveness of larger leks only occurs for small groups. This constraint probably arises because females distinguish leks by overall song rate but are neuroethologically incapable of discriminating rates above a threshold value corresponding to groups of four to six males. These findings emphasize the critical role that neural constraints may play in determining fundamental parameters of complex behaviours such as lekking