Discrimination of family‐specific odours by juvenile coho salmon: roles of learning and odour concentration*

Free‐swimming coho salmon fry Oncorhynchus kisutch of some families showed preference (relative to the behaviour of naïve sibs) for the odours of similarly aged non‐sibs to whom they had been exposed during the post‐hatch (alevin) stage and the early free‐swimming (fry) stage, but not the embryo (egg) stage, indicating that odour‐learning had occurred during the later developmental periods. Recognition (i.e. preference) of sib‐ pecific odours was evident after a month, and in one case 5 months, of separation from those odours. Thus, young salmon incubating in their gravel nests in streams appear to have the capacity to learn the chemical characteristics of conspecifics and retain this memory for at least several months without reinforcement. However, in addition to the general attractiveness of sibs and familiar non‐sibs over unfamiliar non‐sibs, some non‐sibs were consistently more attractive than others. Preference between two different non‐sib odours could be reversed by changing their relative concentrations, indicating that relative attractiveness is a function of both familiarity and odour concentration. Therefore, although juvenile coho salmon learn, remember, and are subsequently attracted by sib‐specific odours in early life, familiar odours are not always preferred over unfamiliar conspecific odours. Preference in dyadic assays is therefore an insensitive measure of recognition.     

Could learning of pollen odours by honey bees (Apis mellifera) play a role in their foraging behaviour?

Abstract. The role of pollen odour cues in the foraging behaviour of honey bees (Apis mellifera L.) is poorly understood. Using classical conditioning of the proboscis extension response, in which bees learn to associate an odour with a sucrose reward, the present study tests whether odours of bee-collected pollen from the hive environment or odours of fresh pollen on the anthers of flowers could be used in pollen foraging. Honey bees efficiently learn odours from field-bean (Vicia faba) bee-collected pollen and oilseed-rape (Brassica napus) bee-collected pollen, hand-collected pollen, anthers and whole flowers, demonstrating that honey bees can learn pollen odours associatively in biologically realistic concentrations. Honey bees learn pollen odours of oilseed rape better than field bean and, although they generalize these two odours, they easily distinguish between them in discrimination tests, suggesting that pollen odours may be used in species recognition/discrimination. There is little evidence that honey bees can recognize whole flowers based on previous experience of bee-collected pollen odour. However, they generalize the odours of oilseed-rape anthers and whole flowers, suggesting that anther pollen in situ may play a more prominent role than bee-collected pollen in foraging behaviour.     

Local variation in helminth burdens of Egyptian spiny mice (Acomys cahirinus dimidiatus) from ecologically similar sites: relationships with hormone concentrations and social behaviour

Populations of Egyptian spiny mice (Acomys cahirinus dimidiatus) in a fragmented montane wadi system in the Sinai showed significant differences in the abundance of gut helminths. Differences in parasite load between populations were positively associated with measures of androgen activity but showed no significant relationship with glucocorticoid activity. Social discrimination tests with adult males from different wadis showed that those from sites with greater helminth abundance were less likely to investigate odours from other males and were less aggressive when subsequently interacting with the odour donors. Subjects showed markedly more investigation towards the odours of males from distant wadis compared with those from their own or immediately neighbouring wadi, but were less aggressive when confronted with odour donors from distant wadis. Despite this, there was a positive relationship between the amount of investigation towards distant male odour and subsequent aggression towards the male. While aggressiveness was positively associated with measures of androgen and glucocorticoid activity, no significant relationship emerged with individual helminth infection. Thus aggressiveness appeared to relate to overall local population levels of infection rather than individual challenge.     

棉铃虫成虫对两种关键花香气味的联系性学习

为了明确棉铃虫对苯乙醛和乙酸苯甲酯两种关键花香气味的联系性学习行为,在室内分别测定了不同学习训练的棉铃虫雌雄成虫对两种关键花香气味的选择偏好性反应和雄成虫的触角电位反应。偏好性测定结果表明,无花香气味接触经历的棉铃虫对苯乙醛和乙酸苯甲酯的选择频次均无显著差异,且单纯的花香气味接触经历也不能诱导棉铃虫气味偏好性的显著改变,唯有花香气味接触经历伴随蔗糖溶液进行强化训练时,才能诱导气味偏好性的显著性改变。从对两种花香气味的联系性学习看,棉铃虫更容易将苯乙醛与蔗糖溶液进行联系性学习,而不容易将乙酸苯甲酯与蔗糖溶液进行联系性学习。从性别差异看,雌虫比雄虫具有更强的将花香气味与蔗糖溶液进行联系性学习的能力。触角电位测定结果表明,不同学习训练的棉铃虫雄成虫对两种花香气味和绿叶气味顺-3-己烯-1-醇的EAG反应值之间不存在显著性差异。总之,花香气味伴随食物资源的联系性学习经历,能够明显提高棉铃虫成虫对花香气味的选择偏好,可以此为基础进一步优化花香引诱剂的配方设计和应用技术。     

Environmental diversity constrains learning in Drosophila melanogaster

1. Much is known about how enriched environmental diversity affects ability to learn across the months and years that are the developmental periods of large animals. 2. Less is known about how diversity impacts learning across the minutes and hours during which sensory environments of small foraging animals such as insects may vary dramatically. 3. This study shows that Drosophila melanogaster exposed to a diversity of odour–taste associations over a few minutes subsequently learn standard associative learning tasks poorly. 4. This effect is robust to variation in odours used in all parts of experiments. 5. Findings may have an impact on at least three major research areas in ecology: the relationship between biodiversity and ecosystem functioning; the evolution of floral constancy in pollinators; and the pest‐protective effects of mixed species crops.     

Brief exposure to the odour of a parasitized male alters the subsequent mate odour responses of female mice

Parasites can affect mate choice, with females preferentially selecting parasite-free males. Prior exposure to, or experience with, males has also been suggested to influence mate responses. Here, we examined the effects of an immediate, brief (1 or 15 min) pre-exposure to the urinary and associated odours of either an uninfected male house mouse,Mus domesticus , or a male infected with the natural murine nematode parasite, Heligomosomoides polygyrus, on the subsequent responses of female mice to the odours of infected and uninfected males. Using an odour preference test we found that females displayed a marked overall preference for the odours of uninfected males. Pre-exposure to the odours of a parasitized male decreased female preference for nonparasitized males and increased female preference for parasitized males. This ‘prior male’ effect was evident for both the total odour preference and initial odour choice. Females pre-exposed to the odour of a parasitized male displayed decreased choosiness and made no particular initial choice of a male, while still maintaining an overall preference for the odours of uninfected males. These shifts in initial choice and odour preference were not directly associated with either female stress responses or stress-related odour cues of the males. Our findings show that female mice can distinguish between parasitized and nonparasitized males on the basis of odour and suggest that a brief exposure to the odours of infected males influences females' immediate odour preferences, and their subsequent preference for and choice of males. This rapid, infection-associated ‘prior male’ effect may contribute to the reported variations in female mate preference and choice. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour      

Reliability of odour–genes covariance despite diet changes: a test in mound‐building mice

Odour–genes covariance (i.e. that individual odour similarities covary with genetic similarity) allows animals to assess their genetic relatedness to one another by comparing the similarities between their individual odours. The reliability of the odour–gene covariance phenomenon under environmental changes has not yet been explored. Using an innovative habituation‐generalization procedure, we tested whether the modifications of body odours induced by a change in diet interfered with the perceived similarity of individual odours of more genetically similar individuals. The effects of a change in diet, by adding aniseed flavour to the drinking water, was assessed in male mound‐building mice, a species in which odour–genes covariance has already been demonstrated. The results obtained indicate that mice perceive more similarities in the odours of sibling males than in those of nonrelatives, despite the effects of diet on body odours. We suggest that the reliability of signals arising from odour–genes covariance is likely a result of the independence between traits indicating genetic relatedness and indicator signals of biological states (e.g. diet) in body odours. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 682–688.     

Do house mice modify their foraging behaviour in response to predator odours and habitat?

Predator odours and habitat structure are thought to influence the behaviour of small mammalian prey, which use them as cues to reduce risks of predation. We tested this general hypothesis for house mice, Mus domesticus, by manipulating fox odour density via addition of fox scats and habitat via patchy mowing of vegetation, for populations in 15 × 15-m field enclosures. Using giving-up densities (GUDs), the density of food remaining when an animal quits harvesting a patch, we measured foraging behaviours in response to these treatments. Mice consistently avoided open areas, leaving GUDs two to four times greater in these areas than in densely vegetated patches. However, mouse GUDs did not change in response to the addition of fox scats, even immediately after fresh scats were added. There was no interaction between fox odour and habitat use. We then tested whether habituation to fox odours had occurred, by comparing the individual responses to scats of eight mice born into enclosures with fox scats to those of eight mice born into scat-free enclosures and five wild mice. In smaller enclosures, GUDs of trays with scats did not differ from GUDs of trays without scats for any treatment. We conclude that exposure to high levels of fox odours did not alter the foraging behaviour of mice, but that mice did reduce foraging in areas where habitat was removed, perceiving predation risk to be greater in these areas than controls. We suggest further that studies using the ‘scat-at-trap’ technique, which have shown avoidance of predator odours by mice and other small mammals, may overestimate the general avoidance of predator odours by free-living prey, which must forage with a constant background of predator odours.     

Interspecific odour discrimination by a lizard (Eumeces laticeps)

When presented with odours on cotton swabs, adult borad-headed skinks (Eumeces laticeps) of both sexes flicked their tongues at much higher rates to conspecific odour stimuli than to those of their most closely related congeners, E. fasciatus and E. inexpectatus, during 60-s exposures to cloacal odours from lizards of the opposite sex. A successive discrimination design was used in which each lizard responded to five different odour treatments in a random sequence. In addition to the three lizard odours, water was used as a measure of baseline tongue protrusion rates and a cologne was used as a pungency control. There were no significant differences among the four non-conspecific odour treatments in numbers of tongue flicks elicited, but the skinks emitted significantly greater numbers of tongue flicks to conspecific cloacal odours than to any of the other stimuli. It is hypothesized that E. laticeps produces a pheromone which may function for species identification. Although it is tempting to speculate that the pheromone may serve as a pre-mating mechanism for maintaining reproductive isolation from syntopic congeners, insufficient information is avialable to draw firm conclusions regarding such a function.     

Olfactory memory capacity of the cricket Gryllus bimaculatus

Olfactory learning in insects is a useful model for studying neural mechanisms underlying learning and memory, but memory storage capacity for olfactory learning in insects has not been studied. We investigate whether crickets are capable of simultaneously memorizing seven odour pairs. Fourteen odours were grouped into seven A/B pairs, and crickets in one group were trained to associate A odours with water reward and B odours with saline punishment for all the seven pairs. Crickets in another group were trained with the opposite stimulus arrangement. Crickets in all the groups exhibited significantly greater preference for the odours associated with water reward for all the seven odour pairs. We conclude that crickets are capable of memorizing seven odour pairs at the same time.     

Social learning of floral odours inside the honeybee hive

A honeybee hive serves as an information centre in which communication among bees allows the colony to exploit the most profitable resources in a continuously changing environment. The best-studied communication behaviour in this context is the waggle dance performed by returning foragers, which encodes information about the distance and direction to the food source. It has been suggested that another information cue, floral scents transferred within the hive, is also important for recruitment to food sources, as bee recruits are more strongly attracted to odours previously brought back by foragers in both honeybees and bumble-bees. These observations suggested that honeybees learn the odour from successful foragers before leaving the hive. However, this has never been shown directly and the mechanisms and properties of the learning process remain obscure. We tested the learning and memory of recruited bees in the laboratory using the proboscis extension response (PER) paradigm, and show that recruits indeed learn the nectar odours brought back by foragers by associative learning and retrieve this memory in the PER paradigm. The associative nature of this learning reveals that information was gained during mouth-to-mouth contacts among bees (trophallaxis). Results further suggest that the information is transferred to long-term memory. Associative learning of food odours in a social context may help recruits to find a particular food source faster.     

Speculating about pyrazines

Of the various types of alerting signals found in nature, odours are the least well understood. The worldwide distribution of pyrazines in plants, insects, terrestrial vertebrates, marine organisms, fungi and bacteria suggests that they are of special significance. We speculate that these molecules served as natural points of convergence in the evolution of widespread alerting signals, which are used for differing but related intraspecific purposes by various species. In aposematic, self-advertising toxic insects and their mimics, for example, pyrazines function as additional warning signals; preliminary data indicates that their odour can potentiate taste aversion learning in rats and the associative learning of immune suppression in mice. The latter suggests that in addition to their alerting properties, pyrazine odours may act as ectohormones which interact with predator physiology.     

Genetic relatedness assessment through individual odour similarities in mice

Previous research has demonstrated that closer genetic relatedness between individuals (from kin to across species) is associated with greater similarity in the qualities of their individual odours ('odour-genes covariance'). This predictable relationship between individual genotypes and individual odours could enable animals to assess their degree of genetic relatedness to other individuals by comparing the degree of similarity between another individual's odour and their own odour. In two-choice tests with odours of unfamiliar mice from different populations and species, subjects from two species of wild mice, Mus spicilegus and M. musculus , that had been raised in mixed litters of both species spent significantly more time investigating the ano-genital odour of the more genetically similar individual. This differential interest was not affected by common rearing with heterospecifics. These responses are consistent with a self-referencing mechanism enabling differential responses across a wide spectrum of genetic relatedness from kin through populations to heterospecifics. These assessments depend on the degree of similarity between the donor's and the subject's odours rather than on differences between them. Such a parsimonious mechanism may provide a basis for differential responses to conspecifics as opposed to heterospecifics that may function as a premating isolating mechanism.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78, 595–603.     

幼小鼠对种内几种化学信息的识别和反应

50年代以来,国际上相继开展了一些关于化学信息在小家鼠繁殖中作用的研究,并在实验室中揭示了一些反应:如集群雌鼠气味使雌鼠性周期延长的Lee-Boot效应,雌鼠气味能解除集群雌鼠对性周期的抑制、并促使它们同期发情的Whitten效应,以及陌生雄鼠气味中断妊娠的Bruce效应等等。但是,在成鼠间起作用的几种化学信息,是否能被幼鼠感受,对幼鼠的发育和性成熟是否产生影响,还是一个未知的问题。 影响小鼠发育的因素很多,除环境因子外,近来还出现了有关社群因素中外激素对小鼠性成熟影响的报道,发现雄鼠或给予雄激素的雌鼠有促进幼雌鼠性成熟的作用,范志勤发现父本气味和陌生雄鼠气味对幼雌鼠性成熟均有促进作用。但是,目前关于种内雌鼠气味、集群雌鼠气味、幼鼠气味影响性成熟的研究尚不多见。有关各种气味对性成熟效应的比较的报道亦少。本文的目的在于通过实验方法,阐明种内的几种化学信息,诸如父本、陌生雄性、雌性、集群雌性、幼雌等几种气味,对幼雌小鼠性成熟的影响,并据此了解幼鼠识别这几种信息的能力。     

The Sound and the Fury—Bees Hiss when Expecting Danger

Honey bees are important model systems for the investigation of learning and memory and for a better understanding of the neuronal basics of brain function. Honey bees also possess a rich repertoire of tones and sounds, from queen piping and quacking to worker hissing and buzzing. In this study, we tested whether the worker bees’ sounds can be used as a measure of learning. We therefore conditioned honey bees aversively to odours in a walking arena and recorded both their sound production and their movement. Bees were presented with two odours, one of which was paired with an electric shock. Initially, the bees did not produce any sound upon odour presentation, but responded to the electric shock with a strong hissing response. After learning, many bees hissed at the presentation of the learned odour, while fewer bees hissed upon presentation of another odour. We also found that hissing and movement away from the conditioned odour are independent behaviours that can co-occur but do not necessarily do so. Our data suggest that hissing can be used as a readout for learning after olfactory conditioning, but that there are large individual differences between bees concerning their hissing reaction. The basis for this variability and the possible ecological relevance of the bees’ hissing remain to be investigated.     

Responses of Snow Voles, Chionomys nivalis, Towards Conspecific Cues Reflect Social Organization during Overwintering Periods

Among microtine rodents, reaction to chemical cues from conspecifics is assumed to reflect social and spatial relationships. Generally, strong attraction of particular odours correlates with non‐aggressive behaviour and high spatial tolerance towards odour donors, whereas weak attraction correlates with greater levels of aggression and spatial segregation. In the present study, we examined whether winter odour preferences of the snow vole Chionomys nivalis, a rock‐dwelling microtine principally found at high‐mountainous regions, differ from that of other vole species, owing to their different social organization during overwintering periods. The social structure of C. nivalis over the winter period is relatively unusual among vole species in that they become nomadic and solitary. In odour choice trials under laboratory conditions, we found that both males and females avoided zones with conspecific odours of both sexes in comparison with unscented control zones or own odours. These results are consistent with the elevated levels of intraspecific aggression and spatial isolation of C. nivalis during overwintering periods. Furthermore, scent‐elicited self‐grooming increased when their own odour was offered against conspecific cues. This, in combination with an active avoidance of conspecific odours, might functionally contribute to minimize direct confrontations between solitary individuals, thereby reducing the risks of aggressive encounters during overwintering periods.     

Effects of experience on parasitoid movement in odour plumes

Abstract. Insects commonly improve the effectiveness with which they locate biotic resources through learning, but the mechanism by which experience exerts its effects has rarely been studied in detail. The effect of oviposition experience on upwind movement of the eucoilid parasitoid, Leptopilina heterotoma (Thomson) (Hym.: Eucoilidae), in odour plumes of host microhabitats, was quantified with the use of a Kramer-type locomotion compensator. A 2h exposure to host Drosophila melanogaster larvae in either fermenting apple-yeast or decaying mushroom substrate (known to affect their preference for these odours in glasshouse and field choice experiments) had a number of effects on movement in plumes of each substrate. Females experienced with a particular substrate walked faster and straighter, made narrower turns and spent more time in upwind movement (i.e. toward the source) in a plume of odour from that substrate than in odour from an alternative substrate. Inexperienced females, by contrast, generally showed little or no significant difference in responses to alternative odours. In addition to affecting the mean values of movement parameters, experience also affected variability around those means. When walking speed or path straightness in an odour plume was increased by experience, variability among individuals was correspondingly decreased. The consequences of odour learning for microhabitat choice is discussed briefly.     

Recognition of interspecific familiar versus unfamiliar odours among bank voles and yellow-necked mice

Two experiments (laboratory and field-laboratory) were designed to determine whether individual bank volesClethrionomys glareolus (Schreber, 1780) and yellow--necked miceApodemus flavicollis (Melchior, 1834) could distinguish heterospecific odour cues from familiar and unfamiliar individuals. In the laboratory experiment each male bank vole was familiarized for 24 h with odour (cotton wool impregnated with urine and faeces) of male yellow-necked mice and yellow-necked mice were familiarized with odour of male bank voles. In the field-laboratory experiment the individual bank voles and yellow-necked mice captured at the same point were considered familiar and transfered to the laboratory. In laboratory, these individuals were tested in a box (for 5 h) affording them the choice between the odours of familiar and unfamiliar heterospecific males. Bank voles discriminated between familiar and unfamiliar yellow--necked mouse odours. Male yellow-necked mice seemed to have a similar ability to recognise odours of familiar bank voles. It is proposed that interactions between these two species occur not only on the species level, but also on the level of individual. This phenomenon (probably asymmetric) can play an important role in spatial orientation, and influence direct contacts between individuals of these species.