Use of olfaction for sexual recognition in the subterranean rodent<Emphasis Type="Italic">Ctenomys talarum</Emphasis>

The ability of the tuco-tucoCtenomys talarum Thomas, 1898 to recognize sex by olfactory cues contained in urine, faeces and soiled shavings was tested by using preference tests. Nonbreeding tuco-tucos selected odours from opposite-sex rather than same-sex conspecifics. This pattern differed between sexes: females spent more time sniffing male than female odours for all scent sources whereas males did not show any difference in the time they spent investigating odours of each sex for each tested odour sources. Dissimilarities in odour selections between sexes may be attributed to a different combination of factors involved in olfactory interest for each sex. The function of gender cues recognition is discussed.     

Discrimination of individuals by odor in male Mongolian gerbils, Meriones unguiculatus

The ability to discriminate among individuals plays a fundamental role in the establishment of social relationships in animals. We examined how Mongolian gerbils (Meriones unguiculatus) discriminate among individuals using odor. In the first experiment, the ability of male gerbils to discriminate among five odor sources from different individuals was investigated using a habituation-dishabituation paradigm. After male gerbils had been habituated to a scent from one individual, they were exposed to familiar and unfamiliar scents from different donors simultaneously. Where urine and ventral gland secretions were used, the subjects spent more time investigating novel odors than familiar ones, suggesting that they were able to discriminate individual differences in these odor sources. However, with the scents of feces and saliva, they could detect, but could not discriminate individual differences; with scent from inside the pinnae, they could not even detect. In the second experiment, we tested whether cross-habituation occurred between the scents of urine and ventral gland secretions. A male was exposed repeatedly to urine from one of two familiar donor males during four habituation trials, and was then exposed to the ventral gland secretions from two donors simultaneously. The subject males spent more time investigating scents of ventral gland secretions, but there was no difference in the investigation time between ventral gland scents from the two donors. These results suggest that male gerbils discriminate among individuals using odors from urine and ventral gland secretions and that cross-habituation may not occur between these scents during social-memory formation.     

Discrimination of individual odours by hamsters (Mesocricetus auratus) varies with the location of those odours

When animals perceive social signals, information about the identity and the location of the signaller can be important determinants of a response by the perceiver. An unfamiliar individual often elicits a greater response than does a familiar individual. Similarly, a signal from an unexpected location may elicit a greater response than if it came from an expected location. For example, in field experiments on vocal communication in birds, an unexpected location has been many metres away from the expected one. Laboratory experiments on the responses of voles and hamsters to scent overmarks and on the habituation of hamsters to social scents suggest that much smaller differences in the location of odours may be salient. To explore this further, we examined the influence of changes in spatial location of familiar and novel male scents on responses of female golden hamsters,M. auratus . The spatial changes were about 9 cm, less than three-fourths of the body length of our subjects. The decline in females' investigation of the same male's flank odour across four habituation trials was not affected by changing the location of the odour. During test trials, however, changes in location did influence the results. The expected higher level of investigation of a novel scent versus that of a familiar one was observed primarily when the novel scent occupied a novel location. Such increases in investigation were usually not seen when only one of these variables was changed (individual or location). Thus, small changes in spatial location influence the salience of conspecific odours in this species. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Effects of vomeronasal organ removal on olfactory sex discrimination and odor preferences of female ferrets

Previous research suggests that body odorants, including anal scents and urinary odors, contribute to sex discrimination and mate identification in European ferrets of both sexes. We assessed the possible role of the vomeronasal organ (VNO) in these functions by surgically removing the organ bilaterally in sexually experienced female ferrets. Lesioned (VNOx) and sham-operated control (VNOi) females reliably discriminated between male- and female-derived anal scent gland as well as fresh urinary odors in habituation/dishabituation tests. However, VNOi females spent significantly more time than VNOx subjects investigating male urinary odors in these tests. Also, VNOi females, but not VNOx subjects, preferred to investigate day-old male versus female urine spots as well as wooden blocks that had previously been soiled by male versus female ferrets. Both groups of female ferrets preferred to approach volatile odors from a breeding male instead of an estrous female in Y-maze tests and both groups showed similar levels of receptive sexual behavior in response to a male's neck grip. The VNO is apparently not required for olfactory sex discrimination or mate recognition in this carnivore, but instead may play a role in promoting continued contact with nonvolatile body odors previously deposited by opposite-sex conspecifics during territorial scent marking.     

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.     

鳄蜥对熟悉和陌生个体气味的辨别

个体辨别对于减少同种争斗以及配偶选择具有重要意义。我们用棉棒粘取鳄蜥(Shinisaurus crocodilurus)尿液作为气味源,以香水作为对照,测定鳄蜥对熟悉个体气味、陌生个体气味以及香水的舔舌次数和舔舌潜伏期,来探讨鳄蜥通过化学信息辨别熟悉和陌生个体的能力。结果显示,不论是雌性还是雄性,对不同个体尿液的舔舌次数均显著高于对香水的,舔舌潜伏期显著短于香水的;尽管雄性对陌生同性个体气味与熟悉同性个体气味的舔舌次数无显著差异,但对前者的舔舌潜伏期显著短于后者;雄性对陌生雌性气味的舔舌次数显著多于熟悉雌性气味的,对前者的舔舌潜伏期显著短于后者;雌性对陌生雄性气味的舔舌潜伏期显著短于对熟悉雄性气味的;雄鳄蜥对陌生雌性气味的舔舌次数显著多于雌鳄蜥对陌生雄性的。结果表明,鳄蜥能辨别同种个体的化学信息,并能通过化学信息来辨别熟悉和陌生个体,推测鳄蜥的这种辨别能力对其领域分配以及繁殖交配有重要作用。     

Cross-species Discrimination of Individual Odors by Hamsters (Muridae: Mesocricetus auratus,Phodopus campbelli)

Golden hamsters, Mesocricetus auratus, and Djungarian hamsters, Phodopus campbelli, Muridae, were tested for the ability to discriminate between individual odors from both their own species and the other species. Hamsters were tested using an habituation technique, in which differences in time spent investigating familiar and novel scents indicate discrimination of individual differences. Both species showed similar patterns of results when tested with flank gland scents from golden hamsters and ventral gland scents from Djungarian hamsters: The duration of investigation of samples from the same indivídual scent donor declined over trials, indicating recognition of this scent, but then increased when a scent from a novel individual was presented, indicating discrimination of individual differences. Thus, the capacity and tendency to respond differentially to signals from different individuals is not confined to a single species, suggesting the lack of species-specificity in the signals and perceptual mechanisms involved in individual recognition by scent. This capacity may be common in mammals, and if so suggests the possibility for considerable knowledge of heterospecific individuals.     

Behavioural development of conspecific odour preferences in Brandt’s voleMicrotus brandti

The behavioural development of conspecific odour preferences in Brandt’s voleMicrotus brandti (Radde, 1861) was evaluated in laboratory tests. During the weaning period (15th-30th day after the birth), the preference of pups to individual odours of their parents, novel adult males and females were examined. Pups investigated odours of unfamiliar adults significantly more than those of their parents and they displayed significantly more jumping and upward visual investigating behaviours on the bedding soiled by unfamiliar adults than they did on the bedding of their parents. However, the frequency of crossing the parent’s bedding was significantly higher than the frequency of crossing the bedding of alien adults. It is suggested that odour discrimination ability was associated with the age of pups. The Brandt’s vole pups might keep themselves away from unfamiliar environments by keeping away from the novel conspecific odours.     

Individual odour similarities across species parallel phylogenetic relationships in the S. ehrenbergi superspecies of mole-rats

Research using habituation techniques has shown that rodents from the same kin group, population, or species share similarities in their individual odours that covary with shared genetic similarities between them, that is, the closer their genetic relatedness, the more similar their odours. We assessed similarities in individual odours across four sibling species of subterranean mole-rats from the Spalax ehrenbergi superspecies in Israel. Mole-rats were habituated to the urine odour of a same-sex individual from one species then tested with urine odours of individuals from two different species of the superspecies. Subjects treated urine odours of individuals from more closely genetically related species as similar compared with the odours of individuals from a less closely related species, showing that the covariance between odours and genes extends across species. These similarities in odour also paralleled genetic similarities determined by molecular analysis: odours of descendent species were perceived as similar to those of their closest ancestral species, suggesting that some qualities of the odour of the ancestral species persist in the descendent species. It is generally assumed that during speciation incipient species develop species-specific markers, including, for example, odour markers, to facilitate discrimination of conspecifics from close ancestral heterospecifics. Our findings indicate that similarities in odours across species are more salient than species-specific odour markers. Such findings may also have important implications for mechanisms of species recognition. Copyright 2000 The Association for the Study of Animal Behaviour.     

Young female pigs can discriminate individual differences in odours from conspecific urine

The ability to discriminate odour cues from different conspecifics has been demonstrated in a variety of small mammalian species. We used a habituation-dishabituation procedure to investigate whether 10-week-old female pigs,Sus scrofa , are able to discriminate between urinary odours from similar-aged conspecifics that were unfamiliar (not encountered for at least 7 weeks). We also examined whether environmental factors can affect the ease with which urine from different individuals is discriminated. Subjects receiving urine samples from the same unfamiliar individual in two successive 2-min exposures separated by a 15-min interval showed habituation in their investigation response to the urine in the second exposure. This habituation was maintained in a third 2-min exposure, 15 min later, if the urine sample was again from the same individual. However, if the urine sample was from a different unfamiliar individual, there was a dishabituation of the investigation response. This was taken to indicate an ability to discriminate the two samples. These data indicate that young pigs could use urinary cues to discriminate other individuals. Effective individual discrimination should facilitate the formation and maintenance of stable social groupings but could be disrupted if, for example, animals from the same group share common odour cues that mask individually distinctive scents. However, urine samples from individuals living in the same group appeared to be no more difficult to discriminate than those from individuals living in different groups. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Individual Odours in Two Chromosomal Species of Blind,Subterranean Mole Rat (Spalax ehrenbergi): Conspecific and Cross-species Discrimination

Mole rats from two chromosomal species (2n = 58 and 2n = 60) of the Spalax ehrenbergi superspecies of Israel were tested to determine whether they were able to discriminate differences in the odour of urine from same-sex individuals of their own and of the other chromosomal species. An habituation-discrimination apparatus was designed for use with these solitary and blind subterranean rodents. Animals habituated to the odour of urine from one individual presented for 10 min at a centre sniffing area in the roof of a 50 cm long Perspex tunnel. The odour of urine from the original donor and from a second individual were presented at two other sniffing areas in the tunnel roof during a 5 min discrimination phase. Significant differences in the time spent investigating the two odours demonstrated successful discrimination between them. The results indicate that male and female mole rats of both species can discriminate between the individual-specific odour cues in urine from pairs of conspecifics and pairs of heterospecific mole rats.     

Odour-genes eovariance and differential investigation of individual odours in the Mus species complex

Previous research using habituation techniques has demonstrated that greater genetic similarity between two individuals is associated with more similarity in the qualities of their individual odours ('odour-genes eovariance'). We assessed odour similarities across species in two pairs of genetically close species within the Mus species complex (M. musculus and M. domesticus; M. spicilegus and M. macedonicus). Subjects treated odours within each species pair as similar compared with an odour from the other species pair. Subjects also treated odours of M. spicilegus males from the same population as similar compared with the odour of M. spicilegus males from a different population. This confirms odour-genes eovariance across species and within populations and also supports previous findings that odour similarities are more salient than specific odour markers. When adult males were presented with odours of females from two different heterospecific species, subjects spent more time investigating the odour from his own species pair than the other species pair, indicating greater interest in the odour of the closer heterospecific and demonstrating that odour-genes eovariance is reflected in behavioural responses to odours. Implications of odour-genes eovariance as a basis for identifying degrees of genetic relatedness of unfamiliar individuals through similarities in individual odours are discussed.     

The effects of sex, reproductive condition and context on discrimination of conspecific odours by giant pandas

To elucidate some of the functions of chemical communication in giant pandas, Ailuropoda melanoleuca, we systematically exposed captive males, oestrous and nonoestrous females to each others' odours by providing access to one another's temporarily unoccupied enclosures. In comparison with control observations, pandas from all reproductive categories displayed a dramatic increase in several measures of chemosensory responsiveness, both when visiting another panda's enclosure and when encountering scent deposited in their home enclosure. Evidence for discrimination between odours encountered as a resident versus a visitor was minimal, but male pandas' response patterns were suggestive of a territorial function. We also found evidence for discrimination of sex and reproductive condition via chemical cues. Males showed a marked preference for female odours, investigating, licking, scent marking and vocalizing more in response to female than male odours. Males also vocalized more in response to oestrous than nonoestrous female odours. Nonoestrous females licked more and oestrous females vocalized more when encountering male than female odours. Our data on vocalizations suggest a potential role for odours in the activation of sexual motivation. We argue that the low reproductive success observed in captivity may be attributed in part to failure to provide sufficient opportunities for chemical communication, and encourage the judicious management of social odours to promote natural mating (e.g. using intersexual odour exposure to increase libido and decrease aggressiveness prior to mating introductions). Copyright 2000 The Association for the Study of Animal Behaviour.     

Olfactory Experience Affects the Response of Meadow Voles to the Opposite‐Sex Scent Donor of Mixed‐Sex Over‐Marks

Scent marking and over‐marking are important forms of communication between the sexes for many terrestrial mammals. Over the course of three experiments, we determined whether the amount of time individuals investigate the scent marks of opposite‐sex conspecifics is affected by 4 d of olfactory experience with those conspecifics. In Experiment 1, female meadow voles, Microtus pennsylvanicus, spent more time investigating the scent mark of the novel male conspecific than that of the familiar male donor, whereas male voles spent similar amounts of time investigating the scent mark of the familiar female and a novel female conspecific. In Experiment 2, voles were exposed to a mixed‐sex over‐mark in which subjects did not have 4 d of olfactory experience with either the top‐scent donor or the bottom‐scent donor. During the test phase, male and female voles spent more time investigating the scent mark of the opposite‐sex conspecific that provided the top‐scent mark than that of a novel, opposite‐sex conspecific. Male and female voles spent similar amounts of time investigating the scent mark of the bottom‐scent donor and that of a novel opposite‐sex conspecific. In Experiment 3, voles were exposed to a mixed‐sex over‐mark that contained the scent mark of an opposite‐sex conspecific with which they had 4 d of olfactory experience. During the test phase, male voles spent more time investigating the mark of the familiar, top‐scent female than the scent mark of a novel female donor but spent similar amounts of time investigating the mark of the familiar, bottom‐scent female and that of a novel female donor. In contrast, female voles spent more time investigating the mark of a novel male donor than that of either the familiar, top‐scent male or that of the familiar, bottom‐scent male. The sex differences in the responses of voles to scent marks and mixed‐sex over‐marks are discussed in relation to the natural history and non‐monogamous mating system of meadow voles.     

Individual odours and mate recognition in the prairie vole,Microtus ochrogaster

A habituation-discrimination technique was used to demonstrate that male and female prairie voles can discriminate individual differences in the odours of soiled shavings and urine from male and female conspecifics. A second experiment, employing a Y-maze, showed that females significantly preferred the odours of their mate over those of either another mated male or an unmated male. Males preferred their mate's odours to those of other mated females but showed no significant preference between the odours of their mate and those of a virgin female. A third experiment demonstrated that, over a 10-h period, females built nests and/or stayed preferentially on the side of a Y-maze containing their mate's odours. Likewise, males preferentially built nests in their mate's side compared to the side containing odours from a virgin female. However, although the same trend was present when mate odours were paired with odours from another mated female, the preference was not statistically significant. Taken as a whole, these results indicate that mate recognition may be an important of individually distinctive odours in this species.     

Kin recognition in golden hamsters: evidence for kinship odours

Differential treatment of kin and non-kin has been well documented, but much remains unclear about how kin are recognized. If kin are recognized by a phenotype-matching mechanism, there must be a correlation between genetic relatedness and the similarity of cues used for recognition. A habituation technique was used with golden hamsters,Mesocricetus auratus, to investigate the relative similarity of the odour quality of flank gland secretions from siblings and unrelated individuals. Hamsters discriminated between the odours of their own, same-sex siblings but also treated these odours as similar compared to odours of non-siblings (experiment 1). They did not discriminate between the flank gland odours of unfamiliar siblings from another family (experiment 2). They also did not discriminate between the flank gland odours of unfamiliar, paternal half-siblings from another family (experiment 3). These results indicate that subjects perceived odours from genetically similar individuals as similar and provide evidence for kinship odour cues. The discrimination between the flank gland odours of subjects’ own siblings, however, indicates that hamsters learn the subtle differences between the odours of their close kin, probably through experience with siblings in the nest. When only volatile components from flank gland secretions were available to subjects (experiment 4), they again discriminated between the odours of their own siblings, suggesting that the volatile components from the flank gland secretion were sufficient for recognition of individual litter-mates.     

Odour–genes covariance within a natural population of subterranean Spalax galili blind mole rats

Previous research, using habituation techniques with multiple rodent species as subjects, has demonstrated (from kin to across species) the greater perceptual similarity in the qualities of individual odours of more closely genetically related individuals ('odour–genes covariance', abbreviated 'OGC'). This predictable relationship between individual genotypes and individual odours has only been assessed in rodents in which the genetic similarities and dissimilarities are known either through laboratory breeding or by selecting odour donors from different populations or species. To study OGC within a natural population of rodents, we genotyped Spalax galili blind mole rats using ten microsatellite markers, and conducted pairwise genetic distance comparisons to estimate genetic similarity and to calculate the relatedness coefficient between pairs of individuals. We then used habituation-generalization techniques to assess whether perceived odour similarities covaried with the genetic similarities we had identified. Indeed, animals treated odours from genetically closer donors as more similar than odours from less genetically similar donors. The results suggest an accurate and subtle ability to resolve genetically determined odour distinctions among familially unrelated animals within a population. Graded differential responses to conspecific odours based on degrees of similarity between other individuals' odours and one's own have been demonstrated in kinship and species discriminations and preferences. The evidence presented here provides the basis for hypothesizing a similar process that could promote optimal outbreeding and inclusive fitness within populations of conspecifics. The evolutionary implications of these findings are discussed.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 483–490.     

Meadow voles,Microtus pennsylvanicus,can discriminate between scents of individual house cats,Felis catus

Individual discrimination provides animals the opportunity to adjust their exposure and behavior when interacting with other animals, both conspecifics and heterospecifics. Meadow voles, Microtus pennsylvanicus, were exposed to scents of house cats, Felis catus. Our first experiment tested whether meadow voles could discriminate between caudal, interdigital, and facial scents produced by a cat with a habituation–dishabituation paradigm. Upon exposure to the familiar scent and a novel one, meadow voles did not investigate either scent more than the other. Our second experiment tested whether meadow voles discriminate between the facial scents of different cats. When exposed to a familiar scent of one cat and the unfamiliar scent of another cat, the meadow voles did discriminate and investigated the unfamiliar scent more than the familiar scent. The results suggest that meadow voles will discriminate between cats using any scent that the cat may inadvertently leave within the environment, thereby reducing the vole's risk of predation by that individual.     

Individual Odors in Djungarian Hamsters (Phodopus campbelli)

The sources of scent in Djungarian hamsters (Phodopus campbelli) that may be individually discriminated were investigated using an habituation paradigm. Male Djungarian hamsters were exposed to five presentations of a particular scent from one individual, and then to the same scent from a novel individual. Increased investigation of the scent from the novel individual indicated discrimination of scents from different individuals. Male hamsters distinguished individual differences in scents of other males from the midventral gland, urine, feces, mouth, and the corner of the mouth, which includes the sacculi; they did not discriminate among odors of different individuals when the scents were from the genital region, hindfeet, fur from behind ears or fur from the back. The results indicate that Djungarian hamsters have a repertoire of individually distinctive scents that are located in specific places on the body; these scents are not actively distributed to, nor passively picked up on, other parts of the body. The fact that scents from some areas do not contain individually distinctive information suggests that some sources may be specialized for producing individually distinctive scents.     

Individual Odour Similarity and Discrimination in the Coruro (Spalacopus cyanus, Octodontidae)

Previous studies of subterranean, fossorial and above‐ground rodents have demonstrated that similarities in individual odours covary with genetic similarities thus supporting the theory of odour‐genes covariance (i.e. the closer the individuals are genetically, the greater the similarities between their odours). We used the habituation‐generalization paradigm, where the subject is exposed to the same odour stimulus in three consecutive habituation trials followed by two test trials in which the odour from two other individuals are presented successively. Using this test design, we showed that the socially living coruros (Spalacopus cyanus) discriminate individuals on the basis of their ano‐genital odours and also respond to odour similarities between individuals. Male and female subjects treated ano‐genital odours of two same‐sex family members and also the odours of two sibling strangers as different to each other. At the same time, they treated the odours of siblings as similar compared with the odour of an unrelated individual. No gender differences were detected. Our results contrast with those from other rodent species that did not spontaneously discriminate between individual odours of siblings from a different family than their own. The polygyneous lifestyle may provide the selective background for that difference. Additional research will be necessary to explore this hypothesis and to rule out differences due to dietary preferences and due to the type of paradigm chosen for the tests.