Olfactory recognition of individuals by male cavies (Cavia aperea)

The response of rodents to scent marks: four broad hypotheses

This article is part of a Special Issue "Chemosignals and Reproduction". Many terrestrial mammals must be able to distinguish between the myriad of scent marks they encounter in order for them to facilitate or deter direct interactions with their scent donors. I review studies that examine how rodents, mainly meadow voles (Microtus pennsylvanicus), respond when they encounter the scent marks of conspecifics and heterospecifics, and how context, as well as the age and condition of senders and receivers, affect their responses. The review uses four broad hypotheses to discuss the response of rodents to scent marks. The four hypotheses are as follows: 1) Scent marks convey accurate information to the receiver about the sender's state and phenotype and genotype. 2) Scent marks are individually distinct. 3) The response of receivers to scent marks is flexible and would be modulated by the cognitive abilities of receivers. 4) Receivers respond to the information contained or conveyed by the scent mark in a manner that will increase their survival and fitness. The studies cited in this review show that scent marks signal accurate information about the sender's phenotype, genotype, and condition, which receivers use to distinguish among the scent marks of different conspecifics and heterospecifics, and by doing so, receivers tailor their response accordingly to increase their survival and fitness. Thus, the four broad hypotheses may serve as guide to increase our understanding of the response of receivers to scent marks and provide a conceptual framework for future research and the development of additional hypotheses.

Sex differences in scent-marking in sifaka: Mating conflict or male services?

Male and female interests can either be in conflict or serve as a basis for exchange. Communication is thus an important aspect of intersexual relationships. Verreaux's sifaka (Propithecus verreauxi verreauxi), like many prosimians, uses chemical signals as one form of communication. The goals of this study were to determine 1) if males and females exhibit sex differences in their scent-marking behavior, and 2) if scent-marking is an example of mating conflict or cooperation. All occurrences of scent-marks, scent-mark context, and scent-mark style were collected on 23 sifaka in the Kirindy Forest of western Madagascar for 7 months (September 2001-March 2002). Scent-mark rates were collected using continuous focal animal sampling from November 2000-March 2002. Home-range data were collected using monthly censuses and instantaneous focal sampling throughout those 17 months. The pressures of behavioral ecology seem to have shaped scent-marking in sifaka: the sexes exhibited significantly different scent-marking behavior. Results from this study are consistent with the hypotheses that 1) females scent-mark to advertise their presence and mark their resources, 2) clean-chested males use scent-marks as between-group communication to advertise their presence, and 3) stained-chested males use scent-marks as a form of olfactory mate-guarding. Scent-marking does not appear to be a "service" that males provide to females, because overmarking limits female communication rather than adding to the overall number of scent-marks. Scent-marking behavior is a crucial aspect of the mating conflict and for understanding intersexual relationships in sifaka.

Recognition of competitors by male golden hamsters

Golden hamsters, like many animals, form dominant/subordinate relationships after aggressive encounters. We examined whether behavioral responses by males that won or lost fights would differ toward familiar and unfamiliar male stimulus animals. In Experiment 1, male winners or losers of fights explored an arena containing a confined stimulus animal that was either familiar or novel and had either won or lost a fight. Compared to dominant males, losers spent less time in proximity to stimulus males and investigated them less. Losers also displayed higher levels of stretch-attend postures (indicative of risk assessment) than winners, and they showed more escape and locomotion in response to familiar winners than to unfamiliar winners, indicating recognition of the male that they had lost to. In Experiment 2, losers scent marked less to the odors of a familiar winner than to those of an unfamiliar winner. Thus, male hamsters appear to use familiarity with a former opponent's odors to adaptively regulate their responses to variations in social threat.

Odorant source used in Eurasian beaver territory marking

Mammals use urine, feces, or the secretion of specialized skin glands to mark their territories. These sources can carry different information and, thus, have different functions. Presently it is not known if beavers (Castor spp.) deposit castoreum (primarily a mixture of secondary metabolites from urine) from the castor sacs and secretion from the anal glands (AGS) together or alone when scent marking their territories. We hypothesized that castoreum would be the main scent signal used in the defense of beaver territories during winter and predicted that castoreum would be deposited more often than AGS. A total of 96 scent marks on snow were collected from January 1 to March 31, 1997-1999 in the Bø River, Telemark County, Norway. In order to obtain control material, we chemically analyzed AGS and castoreum from 60 dead beavers collected during January-May 1997-1999. We compared the compounds found in the dead beavers with compounds found in the scent marks on snow. Samples were analyzed by using gas chromatography-mass spectrometry (GC-MS). All 96 scent marks contained compounds from castoreum, whereas compounds from AGS were found in only four scent marks. This suggests that beavers do not specifically deposit AGS on scent mounds as they do with castoreum and that the AGS compounds we found probably were remnants of AGS from the feet or fur following pelt lubrication or coprophagy behavior. We conclude that castoreum is the main scent signal used in the defense of beaver territories during winter.

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. Copyright 1998 The Association for the Study of Animal Behaviour.

Nuzzling in the gray short-tailed opossum. II: Familiarity and individual recognition

Nuzzling is a chemosensory exploratory behavior that enables South American gray short-tailed opossums to dissolved dry conspecific odor deposits in naso-oral secretions and incorporate them into their vomeronasal organs. This report documents that male opossums nuzzle novel (unfamiliar conspecific) male odors significantly longer than familiar (own of familiar conspecific) male odors or clean substrates. Such findings suggest that an important ethological function of nuzzling behavior involves individual recognition of conspecifics. The first experiment demonstrates that a very short (3-min) exposure to a conspecific odor is sufficient to establish familiarity. The second experiment reveals that a brief exposure results in prolonged (at least 2 h) odor retention. Both experiments establish that nuzzling by males is normally followed by scent marking; thus, novel male odors also elicit increased scent marking. We have identified four novel forms of scent marking by male Monodelphis domestica (ventral, chin, anal/cloacal, and neck) and our data suggest that marking style may be at least partially dependent on the physical properties of the substrata.

Individual odors of rats are discriminable independently of changes in gonadal hormone levels

Male Long-Evans hooded rats were tested for their ability to discriminate between the urine odors from individual outbred Long-Evans rats using the habituation-dishabituation method. There were discriminable differences between the urine odors of two individual intact males, castrated males, estrous/proestrous females, diestrous/metestrous females and ovariectomized females. Thus, individual outbred rats of both sexes can be discriminated on the basis of their urine odors using this technique and discrimination between individuals occurs despite changes in gonadal hormone levels. This suggests that individual recognition is independent of reproductive state and social status although these may influence the production of body odors used for individual discrimination in rats. Individual odors most likely reflect genetic differences between individuals within the outbred strain.

Habituation to individual odors occurs following brief, widely-spaced presentations

The possibility that male guinea pigs (Cavia porcellus) habituate to individual female conspecific urine odors following very brief, widely-spaced presentations was tested. On day 1 of test week 1, each male was exposed for 2 min to urine of one female, on day 3 to urine of a second female and on day 5 to urine of a third female. The number of seconds investigating the samples was recorded. This same procedure was repeated for 3 more weeks. On weeks 5 through 8, three novel females provided urine samples for testing which was conducted in an identical manner. On week 9, urine samples of the original 3 donors was tested. Results indicated that male guinea pigs habituated to urine odors presented for only 2 min 7 days apart and that dishabituation occurred following presentation of samples from novel donors. These data demonstrate an exquisite sensitivity to female urine odors, a long memory for individual differences in these odors, and a consistency over time in the composition of an individual's urine.

Perineal scent gland of wild and domestic cavies: bacterial activity and urine as sources of biologically significant odors

Several studies were conducted to evaluate the source of biologically relevant odorous substances in male wild cavy (Cavia aperea ) perineal gland secretions. In the first study, using a habituation procedure, male wild cavies distinguished between the urine of two individuals after exposure to the perineal secretions of one of the individuals. However, these animals did not distinguish between the perineal secretions of two individuals after exposure to the urine of one of the individuals. These results suggest that urine is a component of cavy perineal gland secretions as normally found in the perineal sac. Other studies were designed to evaluate the possible role of bacteria in producing biologically relevant odors from cavy perineal gland secretions. Microbiological analyses of secretion that had accumulated in the perineal sacs ("dirty") or been squeezed directly from the glands ("clean") of wild and domestic (C. porcellus) cavies indicated large numbers of bacteria inhabited these secretions. In behavioral studies using two-choice preference tests, male wild cavies spent more time investigating conspecific dirty perineal gland secretions than clean secretions. Clean secretions, however, which had been incubated for 48 hr at 37 degrees C were preferred by these cavies over clean secretions which had been frozen at -60 degrees C during the same time period. In a final experiment it was found that wild cavies preferred conspecific clean secretion that had been sterilized and incubated with bacteria over uninoculated sterilized secretion. Together, these results indicate that urine and bacteria are responsible for components of biologically significant odors of cavy perineal scent marks.