David Laloi

Olfactory conditioning of the proboscis extension in bumble bees

The foraging behaviour of bumble bees is well documented for nectar and/or pollen gathering, but little is known about the learning processes underlying such behaviour. We report olfactory conditioning in worker bumble bees Bombus terrestris L. (Hymenoptera: Apidae) obtained under laboratory conditions on restrained individuals. The protocol was adapted from the proboscis extension conditioning previously described in the honey bee Apis mellifera L. Bumble bees were found to be able to learn a pure odorant when it was presented in paired association with a sugar reward, but not when odour and reward were presented in an explicitly unpaired procedure. This suggests an associative basis for this olfactory learning. Bumble bees showed similar conditioning abilities when stimulated with two different floral odours. An effect of the sugar reward concentration on the learning performances was found.

Multiple paternity in clutches of common lizard Lacerta vivipara: data from microsatellite markers

The common lizard (Lacerta vivipara) is a small live‐bearing lacertid that reproduces once a year. In order to document the poorly known mating system of this species, we present here an assessment of multiple paternity using microsatellite markers. Paternities were established within 122 clutches belonging to two wild populations from contrasted areas and to four seminatural enclosed populations. The proportion of multiply sired clutches was found to be very high (between 50.0% and 68.2%) and similar among populations, which suggests that the mating system of this species may be insensitive to environmental and population conditions.

RECOGNITION OF COMPLEX ODORS BY RESTRAINED AND FREE-FLYING HONEYBEES, Apis mellifera

Complex odor recognition in the honeybee was investigated using two behavioral assays: (1) the conditioning of the proboscis extension (CPE) with restrained individuals, and (2) the observation of foragers visiting an artificial feeder in a flight room. Nine compounds, previously identified as oilseed rape flower volatiles, were tested either individually or in mixtures. Different sets of experiments were done to determine: (1) the acquisition rate of the nine compounds in the CPE assay, and (2) the discrimination of the individual compounds after conditioning to a mixture, using the CPE assay and free-flying foragers. After conditioning to a complex mixture, honeybees established a hierarchy among the components, with some of them accounting for a major part of the behavioral activity of the mixture. Both behavioral assays led to the same classification of compounds, indicating good agreement between discriminating abilities of restrained individuals and of a population of foragers. The key compounds for recognition of these mixtures were those that were well learned when presented individually. However, the recognition of some compounds was affected by the other components of the mixture, with the activity of some compounds being either enhanced or reduced.

Evolution of female choosiness and mating frequency: effects of mating cost, density and sex ratio

Choice for mate quality and number of mates are key components of female mating strategies. We investigated how selection on female choosiness also influences number of matings in various ecological conditions. In our individual-based model, females choose their first mate according to an evolving acceptance threshold and then mate with males of increasing quality (trade-up choice). We simulated evolution of this threshold under various conditions of density, sex ratio and mating cost. Thresholds rapidly evolve towards a small set of values that depend on the tested parameters. Consistent with intuitive predictions, choosier females are selected when either number of encounters with males or mating cost is high. Selection results in most females sharing the same threshold. Variation in female mating patterns remains because some variation in thresholds is maintained, at least by mutations, and because of random events affecting number of matings. Our model indicates that mating cost strongly affects evolution of female choosiness and mating frequency. Moreover, it influences the relative importance of other factors: when mating cost is low, selection on acceptance thresholds is weak and relatively more females use thresholds that differ from the norm. In that context, mate quality is therefore the most important factor affecting female reproductive success. When mating cost is high, females evolve thresholds such that both the cost of multiple mating and the risk of remaining unmated become as important as mate quality. High mating cost, by selecting for high choosiness, also leads to females mating with fewer males.

Bumble Bees Show Asymmetrical Discrimination Between Two Odors in a Classical Conditioning Procedure

Olfactory processing of two odorants and their mixture was investigated in bumble bees Bombus terrestris using classical conditioning of the proboscis extension. In a standard procedure, workers were able to learn linalool, phenylacetaldehyde, and the mixture of these two components, with a similar level of response to these three stimuli. Thereafter, when we applied a differential conditioning procedure where one rewarded odorant was presented alternately against an unrewarded one, an asymmetrical discrimination between the two pure odors was found. Bumble bees performed well in the discriminative task when linalool was the rewarded stimulus and phenylacetaldehyde the unrewarded one, but they had difficulty learning phenylacetaldehyde if it was the rewarded odor in the symmetrical procedure. Indeed, unrewarded stimulations with linalool appeared to disrupt the learning of the alternative odor, possibly due to an innate biological meaning of linalool.

Condition dependence of reproductive strategy and the benefits of polyandry in a viviparous lizard

Species in which males do not contribute to reproduction beyond the provision of sperm offer good opportunities to study the potential genetic benefits that females can obtain from polyandry. Here, we report the results of a study examining the relationships between polyandry and components of female fitness in the common lizard (Lacerta vivipara). We found that polyandrous females produce larger clutches than monandrous females. Polyandrous females also lose fewer offspring during the later stages of gestation and at birth, but we did not find any relationship between polyandry and physical characteristics of viable neonates. Our results were consistent with the predictions of the intrinsic male quality hypothesis, while inbreeding avoidance and genetic incompatibility avoidance might also explain some part of the variation observed in clutch size. Moreover, the benefits of polyandry appeared to depend on female characteristics, as revealed by an interaction between reproductive strategy and female length on reproductive success. Thus, all females did not benefit equally from mating with multiple males, which could explain why polyandry and monandry coexist.

Prior classical olfactory conditioning improves odour-cued flight orientation of honey bees in a wind tunnel

SUMMARY Odours are key cues used by the honey bee in various situations. They play an important role in sexual attraction, social behaviour and location of profitable food sources. Here, we were interested in the role of odours in orientation at short distance, for instance the approach flight to a floral patch or in close proximity to the hive entrance. Using a newly designed wind tunnel, we investigated the orientation behaviour of the bee towards two different odours: a social odour and a floral component, linalool. We then tested the effect of prior olfactory conditioning (conditioning of the proboscis extension reflex) on subsequent flight orientation. We showed that both stimuli induced orientated behaviour (orientated flights, circling around the odour source) in up to 70% of the worker bees, social odour being slightly more attractive than the linalool. We found thereafter that orientation performance towards the floral compound can be significantly enhanced by prior classical olfactory learning. This type of information transfer, from a Pavlovian associative context to an orientation task, might allow future foragers to acquire, within the hive, relevant information about the odours and food they will encounter during their later foraging bouts.

Individual learning ability and complex odor recognition in the honey bee, Apis mellifera L.

Individually restrained worker bees were trained to recognize complex odors in a conditioned proboscis extension assay. Three groups of bees were considered, based on the responses recorded during the experimental procedure: selective learners, nonselective learners, and nonlearners. For conditioning, three concentrations of two synthetic mixtures were used. The distribution of bees between groups was not significantly affected by the nature or by the concentration of the conditioning mixture. After conditioning, bees were tested with the individual compounds, and the responses were analyzed with respect to the three groups. Selective learners showed discriminative responses to a few key compounds, while nonselective learners responded to all the compounds, and nonlearners to none. These results showed that complex odor recognition is based on the recognition of key components and relies on the ability of bees to learn.

Kin competition drives the evolution of sex-biased dispersal under monandry and polyandry, not under monogamy

The relation between mating system and sex-biased dispersal has been debated for three decades. However, the relative importance of the processes involved in this relation remains poorly known. In this study, we paid special attention to kin competition. We built an adaptive individual-based model fixing three mating systems (monandry, polyandry, monogamy) in a metapopulation, and allowing dispersal across patches to evolve independently for males and females. Our simulations showed that a difference in the number of mates can determine the evolution of sex-biased dispersal. Dispersal appears male biased under monandry and polyandry, but balanced under monogamy. By contrast, we showed that inbreeding can influence but does not promote sex-biased dispersal, and that the primary sex ratio does not qualitatively affect the evolution of sex-biased dispersal under monandry and polyandry. These results are driven by the interaction of two factors: the variation in reproductive success between patches in the metapopulation and kin competition. These two factors are influenced by the mating system, which modifies both the competition for access to partners and the mean relatedness between individuals. To ascertain that kin competition actually drives sex-biased dispersal, we made simulations with destruction of any genetic structure in the metapopulation, and we found that in this case dispersal was not sex biased.

Patriline-level variability in olfactory learning in the honey bee

Genetically determined differences among honeybee workers are known to contribute to task specialisation. To investigate the genetic component of olfactory learning we used proboscis extension conditioning to record individual performance, and a patriline-level analysis to separate the variance in learning performance into its different components. We found that the among-patriline within-colony component (solely genetic) explained 11.2% of the variance in acquisition performance and 6.5% of the variance in resistance to extinction. While environmental effects appeared to be the main source of variation, our results confirm that olfactory learning has a significant genetic basis. If colonies benefit from genetic differences among workers in task expression thresholds, colonies might also benefit from genetic differences in cognitive performance among workers by influencing task performance.ZusammenfassungGenetisch betimmte Unterschiede zwischen Arbeiterinnen der Honigbiene tragen zur Aufgabenteilung und somit zur Anpassung des Volkes an die Umwelt bei. In der vorliegenden Studie untersuchten wir, ob sich genetisch unterschiedliche Arbeiterinnen (Arbeiterinnen verschiedener Patrilinien) in ihrem Duftlernverhalten unterscheiden. Wir untersuchten dies mit Hilfe des Rüsselreflexes, um individuelle Verhaltensäußerungen aufzuzeichnen. Hierbei untersuchten wir zwei verschiedene Verhaltenstypen: Akquisition während der Konditionierungsphase und resistance to extinction der konditionierten Reaktion während einer Extinktionsphase. Anschließend führten wir Patrilinienanalysen durch, um die verschiedenen Komponenten der Varianzen des Lernverhaltens aufzuschlüsseln: Varianzen zwischen verschiedenen Völkern, zwischen verschiedenen Patrilinien innerhalb eines Volkes und zwischen Arbeiterinnen innerhalb einer Patrilinie. Wir fanden, dass 11,2 % der Varianz der Akquisition und 6,5 % der Varianz der resistance to extinction durch Unterschiede zwischen verschiedenen Patrilinien innerhalb eines Volkes erklärt werden können. Die Erblichkeiten liegen bei 0,22, bzw. 0,13. Umwelteinflüsse scheinen die Hauptquelle der Varianzen zu sein. Doch unsere Ergebnisse bestätigen, dass auch das olfaktorische Lernen eine signifikante genetische Grundlage hat. Gleichermaßen nimmt das Schwellenmodell an, daß Völker von genetischen Unterschieden zwischen den Arbeiterinnen profitieren, die ihre Schwellen bestimmen, bestimmte Aufgaben im Volk zu übernehmen. Die Völker könnten ebenso von genetischen Unterschieden in den kognitiven Leistungen zwischen Arbeiterinnen profitieren: durch den Einfluss von Lernen und Gedächtnis auf die Aufgabenwahrnehmung.