Preimaginal learning as a basis of colony-brood recognition in the ant Cataglyphis cursor

Social environment affects sensory gene expression in ant larvae

Social insects depend on communication to regulate social behaviour. This also applies to their larvae, which are commonly exposed to social interactions and can react to social stimulation. However, how social insect larvae sense their environment is not known. Using RNAseq, we characterized expression of sensory-related genes in larvae of the ant Formica fusca, upon exposure to two social environments: isolation without contact to other individuals, and stimulation via the presence of other developing individuals. Expression of key sensory-related genes was higher following social stimulation, and larvae expressed many of the same sensory-related genes as adult ants and larvae of other insects, including genes belonging to the major insect chemosensory gene families. Our study provides first insights into the molecular changes associated with social information perception in social insect larvae.

Colony-age-dependent variation in cuticular hydrocarbon profiles in subterranean termite colonies

Cuticular hydrocarbons (CHCs) have, in insects, important physiological and ecological functions, such as protection against desiccation and as semiochemicals in social taxa, including termites. CHCs are, in termites, known to vary qualitatively and/or quantitatively among species, populations, castes, or seasons. Changes to hydrocarbon profile composition have been linked to varying degrees of aggression between termite colonies, although the variability of results among studies suggests that additional factors might have been involved. One source of such variability may be colony age, as termite colony demographics significantly change over time, with different caste and instar compositions throughout the life of the colony. We here hypothesize that the intracolonial chemical profile heterogeneity would be high in incipient termite colonies but would homogenize over time as a colony ages and accumulates older workers in improved homeostatic conditions. We studied caste-specific patterns of CHC profiles in Coptotermes gestroi colonies of four different age classes (6, 18, 30, and 42 months). The CHC profiles were variable among castes in the youngest colonies, but progressively converged toward a colony-wide homogenized chemical profile. Young colonies had a less-defined CHC identity, which implies a potentially high acceptance threshold for non-nestmates conspecifics in young colonies. Our results also suggest that there was no selective pressure for an early-defined colony CHC profile to evolve in termites, potentially allowing an incipient colony to merge nonagonistically with another conspecific incipient colony, with both colonies indirectly and passively avoiding mutual destruction as a result.

Chemically induced plasticity in early life history of Palaemon argentinus: are chemical alarm cues conserved within palaemonid shrimps?

Most aquatic animals use infochemicals from both conspecifics and heterospecifics to assess local predation risks and enhance predator detection. Released substances from injured conspecifics and other species (chemical alarm cues) are reliable cues to indicate an imminent danger in a specific habitat and often mediate the development of inducible defenses. Amphibian and fish embryos have been shown to acquire this information while at the embryonic stage of development, in relation to the developing nervous system and sensory development. With the exception of Daphnia, there is no information on chemically mediated responses to alarm cues in embryos of any crustacean groups. Therefore, we tested whether embryo exposure to chemical cues simulating predation on conspecifics or heterospecifics (closely related, non-coexisting species), or a mixture of both, alters embryonic developmental time, size and morphology of the first larval instar in Palaemon argentinus (Crustacea: Decapoda). Embryonic exposure to chemical alarm cues from conspecifics shortened the embryonic developmental time and elicited larger larvae with a longer rostrum. Rostrum length of the first larval instar changed independently of their size, thus elongated rostra can be considered a defensive feature. Embryonic developmental time was not altered by chemical alarm cues from either heterospecifics or the mixed cues treatment; however, exposure to these cues resulted in larger larvae compared with the control group. Chemically induced morphological plasticity in larvae in response to alarm cues from con- and heterospecifics suggests that such cues are conserved in palaemonids shrimps, providing embryos with an innate recognition of heterospecific alarm cues as predicted by the phylogenetic relatedness hypothesis.

Pre-birth sense of smell in the wild boar: the ontogeny of the olfactory mucosa

Animals recognize their surrounding environments through the sense of smell by detecting thousands of chemical odorants. Wild boars (Sus scrofa) completely depend on their ability to recognize chemical odorants: to detect food, during scavenging and searching partners, during breeding periods and to avoid potential predators. Wild piglets must be prepared for the chemical universe that they will enter after birth, and they show intense neuronal activity in the olfactory mucosa. With this in mind, we investigated the morpho-functional embryonic development of the olfactory mucosa in the wild boar (in five stages before birth). Using mRNA expression analysis of olfactory marker protein and neuropeptide Y, involved in the function of olfactory sensory neurons, we show early activation of the appropriate genes in the wild boar. We hypothesize olfactory pre-birth development in wild boar is highly adaptive.

Odor Experiences during Preimaginal Stages Cause Behavioral and Neural Plasticity in Adult Honeybees

In eusocial insects, experiences acquired during the development have long-term consequences on mature behavior. In the honeybee that suffers profound changes associated with metamorphosis, the effect of odor experiences at larval instars on the subsequent physiological and behavioral response is still unclear. To address the impact of preimaginal experiences on the adult honeybee, colonies containing larvae were fed scented food. The effect of the preimaginal experiences with the food odor was assessed in learning performance, memory retention and generalization in 3–5- and 17–19 day-old bees, in the regulation of their expression of synaptic-related genes and in the perception and morphology of their antennae. Three-five day old bees that experienced 1-hexanol (1-HEX) as food scent responded more to the presentation of the odor during the 1-HEX conditioning than control bees (i.e., bees reared in colonies fed unscented food). Higher levels of proboscis extension response (PER) to 1-HEX in this group also extended to HEXA, the most perceptually similar odor to the experienced one that we tested. These results were not observed for the group tested at older ages. In the brain of young adults, larval experiences triggered similar levels of neurexins (NRXs) and neuroligins (Nlgs) expression, two proteins that have been involved in synaptic formation after associative learning. At the sensory periphery, the experience did not alter the number of the olfactory sensilla placoidea, but did reduce the electrical response of the antennae to the experienced and novel odor. Our study provides a new insight into the effects of preimaginal experiences in the honeybee and the mechanisms underlying olfactory plasticity at larval stage of holometabolous insects.

Innate attraction supplants experience during host plant selection in an obligate plant-ant

In order to assess the relative contributions of innate attraction and environmentally-induced preference to nest plant selection by the obligate plant-ant Tetraponera aethiops, we submitted both mature and callow workers to paired choice tests using the leaves of four plant species, including their natural host plant Barteria fistulosa. Mature workers taken from nature as well as mature workers after 25 days of laboratory breeding (with or without contact with B. fifstulosa leaves) always showed a great preference for shelters made with the leaves of B. fistulosa. Similar results were obtained with callow workers isolated from any plant material during the first 25 days of imaginal (=adult) life or during pre-imaginal development. But those reared in contact with test-plant leaves for the same two periods showed significantly less preference for B. fistulosa than did the controls. As a result, experience gained during the larval and nymphal stages as well as during the first part of adult life (i.e. pre-imaginal as well as early learning) was demonstrated in T. aethiops, but in this situation of species-specific interaction it reinforces innate attraction as both larvae and adults live in contact with B. fistulosa in nature. These results are discussed in comparison with previous data collected on arboreal ants not specifically paired with a plant, for which an environmentally-induced preference can supplant innate attraction.

Larval memory affects adult nest-mate recognition in the ant Aphaenogaster senilis

Prenatal olfactory learning has been demonstrated in a wide variety of animals, where it affects development and behaviour. Young ants learn the chemical signature of their colony. This cue-learning process allows the formation of a template used for nest-mate recognition in order to distinguish alien individuals from nest-mates, thus ensuring that cooperation is directed towards group members and aliens are kept outside the colony. To date, no study has investigated the possible effect of cue learning during early developmental stages on adult nest-mate recognition. Here, we show that odour familiarization during preimaginal life affects recognition abilities of adult Aphaenogaster senilis ants, particularly when the familiarization process occurs during the first larval stages. Ants eclosed from larvae exposed to the odour of an adoptive colony showed reduced aggression towards familiar, adoptive individuals belonging to this colony compared with alien individuals (true unfamiliar), but they remained non-aggressive towards adult individuals of their natal colony. Moreover, we found that the chemical similarity between the colony of origin and the adoptive colony does not influence the degree of aggression, meaning that the observed effect is likely to be due only to preimaginal learning experience. These results help understanding the developmental processes underlying efficient recognition systems.

Interindividual variability in social insects - proximate causes and ultimate consequences

Individuals within social groups often show consistent differences in behaviour across time and context. Such interindividual differences and the evolutionary challenge they present have recently generated considerable interest. Social insects provide some of the most familiar and spectacular examples of social groups with large interindividual differences. Investigating these within-group differences has a long research tradition, and behavioural variability among the workers of a colony is increasingly regarded as fundamental for a key feature of social insects: division of labour. The goal of this review is to illustrate what we know about both the proximate mechanisms underlying behavioural variability among the workers of a colony and its ultimate consequences; and to highlight the many open questions in this research field. We begin by reviewing the literature on mechanisms that potentially introduce, maintain, and adjust the behavioural differentiation among workers. We highlight the fact that so far, most studies have focused on behavioural variability based on genetic variability, provided by e.g. multiple mating of the queen, while other mechanisms that may be responsible for the behavioural differentiation among workers have been largely neglected. These include maturational, nutritional and environmental influences. We further discuss how feedback provided by the social environment and learning and experience of adult workers provides potent and little-explored sources of differentiation. In a second part, we address what is known about the potential benefits and costs of increased behavioural variability within the workers of a colony. We argue that all studies documenting a benefit of variability so far have done so by manipulating genetic variability, and that a direct test of the effect of behavioural variability on colony productivity has yet to be provided. We emphasize that the costs associated with interindividual variability have been largely overlooked, and that a better knowledge of the cost/benefit balance of behavioural variability is crucial for our understanding of the evolution of the mechanisms underlying the social organization of insect societies. We conclude by highlighting what we believe to be promising but little-explored avenues for future research on how within-colony variability has evolved and is maintained. We emphasize the need for comparative studies and point out that, so far, most studies on interindividual variability have focused on variability in individual response thresholds, while the significance of variability in other parameters of individual response, such as probability and intensity of the response, has been largely overlooked. We propose that these parameters have important consequences for the colony response. Much more research is needed to understand if and how interindividual variability is modulated in order to benefit division of labour, homeostasis and ultimately colony fitness in social insects.

Temporal changes in colony cuticular hydrocarbon patterns ofSolenopsis invicta : Implications for nestmate recognition

Heritable cuticular hydrocarbon patterns ofSolenopsis invicta workers are consistent within colonies for a given sampling time but vary sufficiently from colony to colony to distinguish the colonies from each other. In addition, cuticular hydrocarbon patterns change within colonies over time. Nestmate recognition cues found on the individual's cuticle, can be from heritable or environmental sources, and are a subset of colony odor. The cuticular hydrocarbons can be used as a model for heritable nestmate recognition cues. We propose that because potential nestmate recognition cues, both environmental and genetic, are dynamic in nature rather than static, during its lifetime a worker must continually update its perception (template) of colony odor and nestmate recognition cues.

Maternal diet influences offspring feeding behavior and fearfulness in the precocial chicken

Background

In chicken, oils in the maternal diet confer a specific scent to the yolk. Embryos are known to perceive and memorize chemosensory signals of the surrounding environment; however, the potential impact of the maternal diet has not previously been investigated. In the present study, we hypothesized that chicken embryos memorize the chemical signals of the maternal diet and that this perceptual learning may orient subsequent feeding behavior of the hatchlings.

Methodology/Principal Findings

Laying hens were fed standard food enriched with 2% menhaden oil (MH group) or 2% soybean oil (controls). The scent of menhaden was significantly more detected in MH egg yolks than in control yolks by a human panel. We analyzed the development and behavior of offspring towards different types of food, bearing or not bearing the menhaden scent. When chicks were exposed to a 3-min choice test between the familiar food bearing the menhaden scent and the familiar food without menhaden, no effect of treatment was observed. In a 3-min choice test with unfamiliar food (mashed cereals) MH chicks showed a clear positive orientation toward the unfamiliar food bearing the menhaden scent. By contrast, control chicks showed a preference for the non-odorized unfamiliar food. MH chicks expressed higher emotional reactivity level than control chicks as expressed by food neophobia and longer immobility in a restraint test.

Conclusion/Significance

Chicks exposed in ovo to menhaden oil via the maternal diet preferentially oriented their feeding behavior towards food containing menhaden oil, but only when the food was unfamiliar. We propose that oil in the maternal diet engenders maternal effects and contributes to the development of behavioral phenotype in the offspring. In ovo chemosensory learning may have evolved to prepare precocial offspring for their environment. This suggests a common principle of embryonic chemosensory learning across vertebrate taxa.

Changes in the hydrocarbon proportions of colony odor and their consequences on nestmate recognition in social wasps

In social insects, colonies have exclusive memberships and residents promptly detect and reject non-nestmates. Blends of epicuticular hydrocarbons communicate colony affiliation, but the question remains how social insects use the complex information in the blends to discriminate between nestmates and non-nestmates. To test this we altered colony odor by simulating interspecific nest usurpation. We split Polistes dominulus paper-wasp nests into two halves and assigned a half to the original foundress and the other half to a P. nimphus usurper for 4 days. We then removed foundresses and usurpers from nests and investigated whether emerging P. dominulus workers recognized their never-before-encountered mothers, usurpers and non-nestmates of the two species. Behavioral and chemical analyses of wasps and nests indicated that 1) foundresses marked their nests with their cuticular hydrocarbons; 2) usurpers overmarked foundress marks and 3) emerging workers learned colony odor from nests as the odor of the female that was last on nest. However, notwithstanding colony odor was usurper-biased in usurped nests, workers from these nests recognized their mothers, suggesting that there were pre-imaginal and/or genetically encoded components in colony-odor learning. Surprisingly, workers from usurped nests also erroneously tolerated P. nimphus non-nestmates, suggesting they could not tell odor differences between their P. nimphus usurpers and P. nimphus non-nestmates. Usurpers changed the odors of their nests quantitatively, because the two species had cuticular hydrocarbon profiles that differed only quantitatively. Possibly, P. dominulus workers were unable to detect differences between nestmate and non-nestmate P. nimphus because the concentration of some peaks in these wasps was beyond the range of workers' discriminatory abilities (as stated by Weber's law). Indeed, workers displayed the least discrimination abilities in the usurped nests where the relative odor changes due to usurpation were the largest, suggesting that hydrocarbon variations beyond species-specific ranges can alter discrimination abilities.

Feel, smell and see in an egg: emergence of perception and learning in an immature invertebrate, the cuttlefish embryo

It is now well established that prenatal sensory experience affects development itself and has long-term consequences in terms of postnatal behavior. This study focused on the functionality of the sensory system in cuttlefish in ovo. Embryos of stage 23, 25 and 30 received a tactile, chemical or visual stimulus. An increase of mantle contraction rhythm was taken to indicate a behavioral response to the stimulus. We clearly demonstrated that tactile and chemical systems are functional from stage 23, whereas the visual system is functional only from stage 25. At stage 25 and 30, embryos were also exposed to a repeated light stimulus. Stage 30 embryos were capable of habituation, showing a progressive decrease in contractions across stimulations. This process was not due to fatigue as we observed response recovery after a dishabituation tactile stimulus. This study is the first to show that cuttlefish embryos behaviorally respond to stimuli of different modalities and that the visual system is the last to become functional during embryonic development, as in vertebrate embryos. It also provides new evidence that the memory system develops in ovo in cuttlefish.

Prenatal and early sucking influences on dietary preference in newborn, weaning, and young adult cats

Early experiences are of potential importance in shaping long-term behavior. This study examined the relative influence of prenatal and/or early postnatal experience of chemosensory stimuli on subsequent olfactory and dietary preferences of cats as newborns, at 9-10 weeks, and at 6 months. Cats were exposed to vanillin or 4-ethylguaiacol via their mother's diet either prenatally, postnatally, perinatally (prenatal and postnatal), or experienced no exposure to the stimuli (control). Newborns were given a two-choice olfactory test between the familiar "odor" and no odor; 9-10 week olds were tested for their preference between two food treats, one flavored with the familiar stimulus and the other unflavored; at 6 months, cats were given a choice of two bowls of food, one flavored with the familiar stimulus and the other unflavored. At all ages, cats preferred the familiar, and avoided the unfamiliar, stimulus. Perinatal exposure exerted the strongest influence on preference. Prenatal exposure influenced preference at all ages and postnatal exposure exerted a stronger effect as the cat aged. We conclude that long-term chemosensory and dietary preferences of cats are influenced by prenatal and early (nursing) postnatal experience, supporting a natural and biologically relevant mechanism for the safe transmission of diet from mother to young.

Recognition of social identity in ants

Recognizing the identity of others, from the individual to the group level, is a hallmark of society. Ants, and other social insects, have evolved advanced societies characterized by efficient social recognition systems. Colony identity is mediated by colony specific signature mixtures, a blend of hydrocarbons present on the cuticle of every individual (the "label"). Recognition occurs when an ant encounters another individual, and compares the label it perceives to an internal representation of its own colony odor (the "template"). A mismatch between label and template leads to rejection of the encountered individual. Although advances have been made in our understanding of how the label is produced and acquired, contradictory evidence exists about information processing of recognition cues. Here, we review the literature on template acquisition in ants and address how and when the template is formed, where in the nervous system it is localized, and the possible role of learning. We combine seemingly contradictory evidence in to a novel, parsimonious theory for the information processing of nestmate recognition cues.

Cattle discriminate between familiar and unfamiliar conspecifics by using only head visual cues

Faces have features characteristic of the identity, age and sex of an individual. In the context of social communication and social recognition in various animal species, facial information is relevant for discriminating between familiar and unfamiliar individuals. Here, we present two experiments aimed at testing the ability of cattle (Bos taurus) to visually discriminate between heads (including face views) of familiar and unfamiliar conspecifics represented as 2D images. In the first experiment, we observed the spontaneous behaviour of heifers when images of familiar and unfamiliar conspecifics were simultaneously presented. Our results show that heifers were more attracted towards the image of a familiar conspecific (i.e., it was chosen first, explored more, and given more attention) than towards the image of an unfamiliar one. In the second experiment, the ability to discriminate between images of familiar and unfamiliar conspecifics was tested using a food-rewarded instrumental conditioning procedure. Eight out of the nine heifers succeeded in discriminating between images of familiar and unfamiliar conspecifics and in generalizing on the first trial to a new pair of images of familiar and unfamiliar conspecifics, suggesting a categorization process of familiar versus unfamiliar conspecifics in cattle. Results of the first experiment and the observation of ear postures during the learning process, which was used as an index of the emotional state, provided information on picture processing in cattle and lead us to conclude that images of conspecifics were treated as representations of real individuals.

Are you my mother? Kin recognition in the ant Formica fusca

In social insects, workers trade personal reproduction for indirect fitness returns from helping their mother rear collateral kin. Colony membership is generally used as a proxy for kin discrimination, but the question remains whether recognition allows workers to discriminate between kin and nonkin regardless of colony affiliation. We investigated whether workers of the ant Formica fusca can identify their mother when fostered with their mother, their sisters, a hetero-colonial queen or hetero-colonial workers. We found that workers always displayed less aggression towards both their mother and their foster queen, as compared to an unfamiliar hetero-colonial queen. In support of this finding, workers maintain their colony hydrocarbon profile regardless of foster regime, yet show modifications when exposed to different environments. This indicates that recognition entails environmental and genetic components, which allow both discrimination of kin in the absence of prior contact and learning of recognition cues based on group membership.

Preimaginal and adult experience modulates the thermal response behavior of ants

Colonies of social insects display an amazing degree of flexibility in dealing with long-term and short-term perturbations in their environment. The key organizational element of insect societies is division of labor. Recent literature suggests that interindividual variability in response thresholds plays an important role in the emergence of division of labor among workers (reviewed in [1, 2]). Genetic variation can only partly explain the variability among workers. Here we document the effects of both preimaginal and adult thermal experience on the behavioral differentiation of Camponotus rufipes ant workers. We show that preimaginal temperature (22 degrees C or 32 degrees C during pupal stage) affects temperature-response thresholds and temperature preferences of adult brood-tending workers. We further show that brood-carrying experience gathered as adult during several repeated temperature increases modifies thermal behavior. Experienced workers showed a faster transition from first sensing the temperature stimulus to responding with brood translocation. Developmental plasticity of workers provides a colony with flexibility in dealing with thermal variations and constitutes an important mechanism underlying interindividual variability. Adult thermal experience further fine tunes the behavioral response thresholds and reinforces behavioral differentiation among workers.

Retention of memory through metamorphosis: can a moth remember what it learned as a caterpillar?

Insects that undergo complete metamorphosis experience enormous changes in both morphology and lifestyle. The current study examines whether larval experience can persist through pupation into adulthood in Lepidoptera, and assesses two possible mechanisms that could underlie such behavior: exposure of emerging adults to chemicals from the larval environment, or associative learning transferred to adulthood via maintenance of intact synaptic connections. Fifth instar Manduca sexta caterpillars received an electrical shock associatively paired with a specific odor in order to create a conditioned odor aversion, and were assayed for learning in a Y choice apparatus as larvae and again as adult moths. We show that larvae learned to avoid the training odor, and that this aversion was still present in the adults. The adult aversion did not result from carryover of chemicals from the larval environment, as neither applying odorants to naïve pupae nor washing the pupae of trained caterpillars resulted in a change in behavior. In addition, we report that larvae trained at third instar still showed odor aversion after two molts, as fifth instars, but did not avoid the odor as adults, consistent with the idea that post-metamorphic recall involves regions of the brain that are not produced until later in larval development. The present study, the first to demonstrate conclusively that associative memory survives metamorphosis in Lepidoptera, provokes intriguing new questions about the organization and persistence of the central nervous system during metamorphosis. Our results have both ecological and evolutionary implications, as retention of memory through metamorphosis could influence host choice by polyphagous insects, shape habitat selection, and lead to eventual sympatric speciation.

Larval host plant origin modifies the adult oviposition preference of the female European grapevine moth Lobesia botrana

According to the 'natal habitat preference induction' (NHPI) hypothesis, phytophagous insect females should prefer to lay their eggs on the host species on which they developed as larvae. We tested whether this hypothesis applies to the breeding behaviour of polyphagous European grapevine moth, Lobesia botrana, an important pest in European vineyards. We previously found that different grape cultivars affect several life history traits of the moth. Because the different cultivars of grapes are suspected to provide different plant quality, we tested the NHPI hypothesis by examining oviposition choice of L. botrana among three Vitis vinifera cultivars (Pinot, Chasselas and Chardonnay). In a choice situation, females of L. botrana that had never experienced grapes were able to discriminate between different grape cultivars and preferentially selected Pinot as an oviposition substrate. This 'naive' preference of oviposition could be modified by larval environment: Females raised on grapes as larvae preferred to lay eggs on the cultivar that they had experienced. Furthermore, experience of the host plant during adult emergence could be excluded because when pupae originating from our synthetic diet were exposed to grapes, the emerging adults did not show preference for the cultivar from which they emerged. The NHPI hypothesis that includes the two sub-hypothesis "Hopkins host selection principle" and "chemical legacy" may thus be relevant in this system.

Learning of colonial odor in the ant Cataglyphis niger (Hymenoptera; Formicidae)

Ants learn the odors of members of their colony early in postnatal life, but their ability to learn to recognize noncolony conspecifics and heterospecifics has never been explored. We used a habituation-discrimination paradigm to assess individual recognition in adult Formicine ants, Cataglyphis niger. Pairs of workers from different colonies were placed together for repeated trials, and their ability to discriminate the ant that they encountered from another familiar or unfamiliar ant was observed. Some ants were isolated between encounters, and others were returned to their home colonies. Our results suggest for the first time in ants that C. niger adults learn about individual ants that they have encountered and recognize them in subsequent encounters. Ants are less aggressive toward non-nestmates after they are familiar with one another, but they are aggressive again when they encounter an unfamiliar individual. Learning about non-nestmates does not interfere with an ant's memory of members from its own colony.

Pre-pupation behaviour of the aphid parasitoid Aphidius ervi (Haliday) and its consequences for pre-imaginal learning

Olfactory learning may occur at different stages of insect ontogeny. In parasitoid wasps, it has been mostly shown at adult emergence, whilst it remains controversial at pre-imaginal stages. We followed larval growth of the parasitoid wasp, Aphidius ervi Haliday, inside the host aphid, Acyrthosiphom pisum Harris, and characterised in detail the behaviour of third instar larvae. We found that just before cocoon spinning begins, the third instar larva bites a hole through the ventral side of the mummified aphid exoskeleton. We then evaluated whether this period of exposure to the external environment represented a sensitive stage for olfactory learning. In our first experiment, the third instar larvae were allowed to spin their cocoon on the host plant (Vicia faba L.) surface or on a plastic plate covering the portion of the host plant exposed to the ventral opening. Recently emerged adults of the first group showed a preference for plant volatiles in a glass Y-olfactometer, whereas no preference was found in adults of the second group. In a second experiment, during the period in which the aphid carcass remains open or is being sealed by cocoon spinning, third instar larvae were exposed for 24 h to either vanilla odours or water vapours as control. In this experiment, half of the parasitoid larvae were later excised from the mummy to avoid further exposure to vanilla. Adult parasitoids exposed to vanilla during the larval ventral opening of the mummy showed a significant preference for vanilla odours in the olfactometer, regardless of excision from the mummy. The larval behaviour described and the results of the manipulations performed are discussed as evidences for the acquisition of olfactory memory during the larval stage and its persistence through metamorphosis.

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

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.

Perinatal Olfactory Learning in the Domestic Dog

The ability of individuals to learn about chemosensory stimuli in the prenatal, or immediate postnatal, period may be advantageous in acquiring information about "safe" foods after weaning. In this study, we examined the influence of perinatal exposure to aniseed via the mother's diet on a two-choice food test in the domestic dog. Pups were tested at 10 weeks of age following "prenatal" exposure to aniseed (the last 20 days of gestation), "postnatal" exposure to aniseed (the first 20 days after birth), "perinatal" exposure to aniseed (pre- and postnatal exposure combined), or no exposure to aniseed prenatally or postnatally (control). Perinatal exposure resulted in a significantly greater preference for the aniseed food than the other types of exposure. At 10 weeks, there was no evidence for the retention of any prenatal learning of the aniseed. It is suggested that exposure to a chemosensory stimulus across the perinatal period results in a greater effect than simply the sum of pre- and postnatal exposure due to priming of the chemosensory system via prenatal chemosensory experience. Such a system may confer survival advantages by promoting the acquisition of information about safe foods.

Pituitary adenylate cyclase activating polypeptide plays a role in olfactory memory formation in chicken

PACAP plays an important role during development of the nervous system and is also involved in memory processing. The aim of the present study was to investigate the function of PACAP in chicken embryonic olfactory memory formation by blocking PACAP at a sensitive period in ovo. Chicken were exposed daily to strawberry scent in ovo from embryonic day 15. Control eggs were treated only with saline, while other eggs received a single injection of the PACAP antagonist PACAP6-38 at day 15. The consumption of scented and unscented water was measured daily after hatching. Animals exposed to strawberry scent in ovo showed no preference. However, chickens exposed to PACAP6-38, showed a clear preference for plain water, similarly to unexposed chicken. Our present study points to PACAP's possible importance in embryonic olfactory memory formation.

Social Learning in Noncolonial Insects?

Social-information use has generated great interest lately and has been shown to have important implications for the ecology and evolution of species. Learning about predators or predation risk from others may provide low-cost life-saving information and would be expected to have adaptive payoffs in any species where conspecifics are observable and behave differently under predation risk. Yet, social learning and social-information use in general have been largely restricted to vertebrates. Here, we show that crickets adapt their predator-avoidance behavior after having observed the behavior of knowledgeable others and maintain these behavioral changes lastingly after demonstrators are gone. These results point toward social learning, a contingency never shown before in noncolonial insects. We show that these long-lasting changes cannot instead be attributed to long re-emergence times, long-lasting effects of alarm pheromones, or residual odor cues. Our findings imply that social learning is likely much more phylogenetically widespread than currently acknowledged and that reliance on social information is determined by ecological rather than taxonomic constrains, and they question the generally held assumption that social learning is restricted to large-brained animals assumed to possess superior cognitive abilities.

Role of early experience in ant enslavement: a comparative analysis of a host and a non-host species

BACKGROUND

Ants use the odour of the colony to discriminate nestmates. In some species, this odour is learned during the first days following emergence, and thus early experience has a strong influence on nestmate discrimination. Slave-making ants are social parasites that capture brood of other ant species to increase the worker force of their colony. After emerging in the slave-maker nest, slave workers work as if they were in their own colony. We tested the hypothesis that early experience allows the deception of commonly enslaved species, while non-host species use a different mechanism, which does not involve learning.

RESULTS

Pupae of a host species, Temnothorax unifasciatus, and a non-host species, T. parvulus, were allowed to emerge in the presence of workers of one of two slave-maker species, Chalepoxenus muellerianus or Myrmoxenus ravouxi. When T. unifasciatus was exposed to slave-makers for 10 days following emergence, they were more aggressive towards their own sisters and groomed the slave-maker more. T. parvulus gave a less clear result: while workers behaved more aggressively towards their sisters when exposed early to C. muellerianus workers, this was not the case when exposed early to M. ravouxi workers. Moreover, T. parvulus workers allogroomed conspecific nestmates less than T. unifasciatus. Allogrooming activity might be very important for the slave-makers because they are tended by their slaves.

CONCLUSION

Our findings show that early experience influences nestmate discrimination in the ant T. unifasciatus and can account for the successful enslavement of this species. However, the non-host species T. parvulus is less influenced by the early environment. This might help to explain why this species is never used by social parasites.

Exploratory studies of classical conditioning of the preoral cavity in harnessed carpenter ants (Camponotus pennsylvanicus)

An attempt was made to classically condition the mouthparts of harnessed worker ants (Camponotus pennsylvanicus) in anticipation of feeding. Experiments were designed to investigate classical conditioning with one CS, discrimination between two CSs, and pseudoconditioning. Analysis indicated a small acquisition effect that could be accounted for by pseudoconditioning. The preparation can be used to study nonassociative learning and some instrumental conditioning situations.

An olfactory sensory map in the fly brain

We have isolated the "complete" repertoire of genes encoding the odorant receptors in Drosophila and employ these genes to provide a molecular description of the organization of the peripheral olfactory system. The repertoire of Drosophila odorant receptors is encoded by 57 genes. Individual sensory neurons are likely to express only a single receptor gene. Neurons expressing a given gene project axons to one or two spatially invariant glomeruli in the antennal lobe. The insect brain therefore retains a two-dimensional map of receptor activation such that the quality of an odor may be encoded by different spatial patterns of activity in the antennal lobe.

Olfactory information transfer in the honeybee: compared efficiency of classical conditioning and early exposure

We investigated the ability of honeybees, Apis mellifera, to use olfactory information gained in a given experimental context, in other contexts. First, restrained bees were subjected to a Pavlovian associative learning procedure, based on the conditioning of the proboscis extension response (PER), where a floral odour was paired with a sugar reward. We observed the orientation behaviour of conditioned and naïve bees in a four-armed olfactometer with four contiguous fields either scented with the conditioning odour or unscented. Information transfer was clearly shown, conditioned bees orienting towards the conditioning odour, whilst naïve bees shunned it. Second, the effect of passive olfactory exposures during the bees' development was assessed in two behavioural contexts: either orientation in the olfactometer or a PER conditioning procedure. Two exposure periods were applied: (1) the pupal stage (9 days before emergence); (2) the early adult stage (8 days after emergence). No effect of preimaginal exposure was recorded, but exposure during the early adult stage induced a higher choice frequency of the odour field in the olfactometer, and lower learning performance in the PER conditioning assay. These observations show that olfactory information gained during development can modify bees' later behaviour in different contexts: this is another instance of olfactory information transfer in bees. These results also suggest that nonassociative learning phenomena, taking place at a critical period during development, might be involved in the maturation of the bees' olfactory system, and in the organization of odour-mediated behaviours. Copyright 2000 The Association for the Study of Animal Behaviour.

Chemosensory learning in the chicken embryo

Prenatal chemosensory learning has been demonstrated in mammals, fish, amphibians, and insects, but not birds, although there is evidence of the avian's ability to learn auditory stimuli before hatching. This paper examines how exposure to a chemosensory stimulus (strawberry) prior to hatching affects subsequent chemosensory preferences of newly hatched chicks. The chicks' preferences were assessed at 2 days after hatching using an "olfactory" preference test (strawberry-smelling shavings versus water-coated shavings) and at 4 days after hatching using a "gustatory" preference test (strawberry-flavoured water versus unflavoured water). Chicken embryos were exposed to strawberry from Day 15 to Day 20 of incubation by either presenting the odour in the air around the egg, rubbing it onto the shell, or injecting it into the air space. With no exposure to strawberry before hatching, strawberry was highly aversive to chicks after hatching. However, following exposure to strawberry before hatching, chicks expressed a greater preference for (or weaker aversion to) the strawberry stimulus. Chicks exposed to strawberry before hatching drank more strawberry-flavoured water and spent more time in a strawberry-scented area than chicks having no exposure before hatching. This change in preference was specific to the stimulus experienced before hatching and was present in the absence of any posthatching exposure to the stimulus. The results demonstrate that a chick's chemosensory preferences are changed as a result of experience with a stimulus before hatching and are suggestive of learning. The results, similar to those obtained in other animal groups, indicate the universality of "prenatal" chemosensory learning in the animal kingdom. A possible role of embryonic chemosensory learning for recognition is discussed.