Attraction of male guinea pigs to conspecific urine

The Role of Urine in Semiochemical Communication between Females and Males of Domestic Dog (Canis familiaris) during Estrus

Simple Summary

Canine reproductive behavior can be easily observed; however, the mechanism of semiochemical signaling in this species is still not well understood. Despite numerous studies, no efficient, artificial canine sex pheromones are available. In most studies of canine semiochemical communication, female urine was believed to be a source of volatile compounds that attract males. We hypothesized that urine is also a source of compounds that are very important in the process of the mating decision but are not so volatile. These compounds are collected by licking urine or the vulva and are transferred into the vomeronasal organ. Such behavior always precedes the male’s mating decision. In two experiments, we assessed the reactions of male dogs in response to air containing odor molecules from estrous females’ urine, from a live female in estrus, and from food, as well as during direct sniffing of urine samples from females in estrus, in anestrus, from male dogs and from humans. It was concluded that urine odor is not used for long-distance semiochemical communication in dogs but rather for close distance signaling.

Abstract

This study aimed to assess the mechanisms of semiochemical signal detection in dogs. In the first experiment, five males were exposed to volatile semiochemicals emitted by a live female in estrus and the female’s urine sample collected during estrus. The odor of canine food and clean air were used as controls. In the second experiment, 25 males could directly sniff and lick the urine samples from females in estrus, from females in anestrus, from males and from humans, placed in a lineup. Sniffing, licking and salivation, as well as keeping dogs at different distances from the source of odor, were recorded in both experiments. Experiment 1 showed that food odor was sniffed by males longer than estrous urine. Volatile semiochemicals from females in estrus evoked interest in males but without visual cues did not cause overt symptoms of sexual arousal. In Experiment 2, the estrous urine evoked interest in males and provoked significantly longer sniffing. Licking accompanied by salivation was observed in all instances only during direct contact with estrous urine. The results suggest a complex character of detection of female reproductive status, in which both volatile and nonvolatile compounds emitted by females and present in female urine are involved.

Processing by the main olfactory system of chemosignals that facilitate mammalian reproduction

This article is part of a Special Issue "Chemosignals and Reproduction". Most mammalian species possess two parallel circuits that process olfactory information. One of these circuits, the accessory system, originates with sensory neurons in the vomeronasal organ (VNO). This system has long been known to detect non-volatile pheromonal odorants from conspecifics that influence numerous aspects of social communication, including sexual attraction and mating as well as the release of luteinizing hormone from the pituitary gland. A second circuit, the main olfactory system, originates with sensory neurons in the main olfactory epithelium (MOE). This system detects a wide range of non-pheromonal odors relevant to survival (e.g., food and predator odors). Over the past decade evidence has accrued showing that the main olfactory system also detects a range of volatile odorants that function as pheromones to facilitate mate recognition and activate the hypothalamic-pituitary-gonadal neuroendocrine axis. We review early studies as well as the new literature supporting the view that the main olfactory system processes a variety of different pheromonal cues that facilitate mammalian reproduction.

Intermale sexual effect elicited by volatile urinary ether extract inMicrocebus murinus (Prosimian, Primates)

The effect of volatiles of diethyl ether-extracted dominant male mouse lemur urine on conspeciflc testosterone plasma concentrations was determined in an apparatus permitting olfactory isolation of the experimental subjects. Two experimental groups were exposed to air odorized with either ether or aqueous extracts of dominant male urine, while a third group received nonodorant air. Testosterone concentrations were measured before, during, and after the period of stimulation. The group submitted to the lipid fraction of dominant urine (N = 15) showed a significant decrease in testosterone concentrations. In contrast, no difference was observed between the group submitted to the aqueous fraction (N = 10) and the controls (N = 11). This physiological effect, which occurs in response to conditions of persistent stress, appears to be due to lipophilic components present in the urine of dominant males. The results are discussed in terms of the social structure of this primitive primate species.

Chemical communication and reproduction in the gray short-tailed opossum (Monodelphis domestica)

The gray short-tailed opossum is one of the most widely studied of all marsupials and an important model for study of olfactory communication, particularly as it relates to pheromonal activation of reproduction. Males respond to differentially to female skin gland secretions and urine from anestrous females, while females respond only skin gland secretions, particularly that of the suprasternal gland. Divergent responses by male and female opossums to odors from these different body sources are most likely related to sex-specific production and deposition of chemical signals in this species. Female opossums do not have an estrous cycle but are stimulated to estrus by male pheromone. Females nuzzle scent marks from male suprasternal gland secretions, and thereby facilitate delivery of a nonvolatile estrus-inducing pheromone to the chemosensory epithelium of vomeronasal organ. Neuroendocrine correlates of pheromonal induction of estrus include elevated plasma estradiol and upregulation of progesterone receptors in hypothalamic regions that control reproductive behavior.

Skin, gland, and urine odors elicit intense investigation by male gray short-tailed opossums, Monodelphis domestica

Chemical signaling between animals of the same species is common among vertebrates. We have reported this phenomenon in the gray short-tailed opossum, Monodelphis domestica (Wagner, 1842). We now find that male opossums investigate odors derived from the mandibular and flank regions and from urine of male and female opossums and from the sternal gland of male opossums significantly more than distilled water. Males investigate female odors significantly more than male odors. They also investigate strange male odors significantly more than their own odors when similar body parts were compared. The males investigate female flank odors significantly longer than female urine odors when these were paired, but the time spent investigating other pairings of female odors was not significantly different. Furthermore, experimental males, unlike females tested in former studies, discriminate between urine of male and of female conspecifics when compared with water control. We hypothesize that male opossums require information about the presence of male conspecifics that recently traversed their home range to avoid potential conflicts. Urine from diestrous females signals the proximity of a female that has not already mated.

Pregnant female guinea pigs adapt easily to a new social environment irrespective of their rearing conditions

For male guinea pigs, the social rearing conditions are crucial for the course of social interactions and endocrine stress responses in later life. While colony-reared males adjust easily to new social situations, high levels of aggression and extreme endocrine responses are found in males that were raised in pairs [Psychoneuroendocrinology 23 (1998) 891]. This study investigated whether the same finding also applies to females. Therefore, 8 females reared in mixed-sexed colonies of 8-10 males and 12-13 females (designated as CF) and 8 females reared in mixed-sexed pairs (designated as PF) were transferred to an unknown colony for 3 days. Control females remained in their respective housing conditions. Serum cortisol concentrations (CORT) were determined before, during and after the transfer. The behavior of the CF and PF was recorded on the first, second and third day of transfer. All females adjusted easily to the new social situation, but frequencies of some behavioral patterns were significantly different between CF and PF. In the new social situation, PF displayed social orientation as well as defensive aggressive and avoidance behavior more frequently than CF. On the day of transfer, resident males displayed courtship behavior more frequently towards PF than CF. CORT did not differ between PF and CF either before, during or after the transfer. Furthermore, the transfer to the new social situation did not result in significantly increased CORT 4 h later either in CF or PF. We conclude that-in contrast to male guinea pigs-females are able to adapt to unfamiliar conspecifics independently of their social rearing conditions.

The ability of red squirrels (Tamiasciurus hudsonicus) to discriminate conspecific olfactory signatures

Using a habituation-dishabituation procedure, we investigated the ability of male red squirrels (Tamiasciurus hudsonicus) to discriminate olfactory signatures of different male conspecifics. Our results indicate that they effectively pay attention to odours from unfamiliar male conspecifics and that they invest more time sniffing litter impregnated with these unfamiliar social odours than control litters. They can also habituate themselves to a given social odour and can discriminate olfactory signatures of different male conspecifics. The role of olfactory communication in this territorial species from the boreal forest is discussed with regard to the "dear enemy" phenomenon and to the fact that these squirrels are known to use vocal communication intensively to advertise their territories.

Consequences of the presence of the mother or unfamiliar adult female on cortisol, ACTH, testosterone and behavioral responses of periadolescent guinea pigs during exposure to novelty

Periadolescent guinea pigs were exposed to a novel environment for 10, 30, 60, or 90 min while either alone or with either their biological mother or an unfamiliar adult female. Both classes of females reduced plasma cortisol, ACTH and vocalization responses to the novel environment, and did so to an equivalent degree. However, behavioral interactions with the mother and unfamiliar female differed considerably. The offspring exhibited more defensive behavior and were the targets of more agonistic acts when with the unfamiliar female, though one agonistic behavior, kicking, was observed more often in tests with the mother. Males displayed more social/courtship behavior and tumescence with the unfamiliar female. Further, males exhibited higher plasma testosterone levels when with the unfamiliar female than when either with the mother or alone. These data in conjunction with earlier findings suggest that the ability of unfamiliar adult females to moderate hypothalamic-pituitary-adrenal activity fully emerges during the periadolescent period, is not dependent on nurturant behavior by the adult female, and may facilitate the redirection of social behavior from the mother to unrelated adults. Further, mothers appear to inhibit maternally directed sexual behavior and plasma testosterone elevations in their periadolescent sons, effects which likely serve to inhibit inbreeding.

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.

Nuzzling in the gray short-tailed opossum. I: Delivery of odors to vomeronasal organ

Nuzzling in the gray short-tailed opossum (Monodelphis domestica) is exhibited in response to conspecific odor deposits and is involved in chemosensory recognition. Nuzzling consists of bouts of repeated forward rubbing motions (with intermittent tapping) with the ventral aspect of the snout over the odor source, while moistening it with naso-oral secretions. The role of nuzzling in odorant d delivery to the vomeronasal organ (VNO) was investigated. Five opossums were allowed to nuzzle conspecific odor deposits mixed with 3H-proline. Histological sections of the snouts processed for autoradiography revealed very strong labeling of the VNOs, primarily the nonsensory epithelium. No labeling was observed in the olfactory epithelium. Unilateral closure of the oral opening to the nasopalatine canal resulted in labeling of the contralateral VNO only, implicating oral access to the VNO. Several distinctive structures appear to be associated with chemical access. An experiment in which 16 males and 16 females were given a preference test of dried nuzzling secretion versus dried distilled water established that the naso-oral secretions deposited during nuzzling do not have properties of scent marks.

Olfactory discrimination of estrous condition by the male golden hamster (Mesocricetus auratus)

After repeated exposure to receptive and nonreceptive females, male golden hamsters were tested for olfactory preferences in a four-choice olfactometer. Males discriminated between the odor of anesthetized females in different stages of their estrous cycle when the airstreams carrying the stimulus odors were diluted. Previous failures to demonstrate such an ability were probably due to ceiling effects resulting from laboratory testing. Males preferred the odor of females on the day before receptivity (a day coincident with maximal scent marking by the female) and least preferred the odor of females on diestrus-1 (the day on which females attacked and chased males during pretesting encounters). Detection and quick response to an impending estrus would be especially important for males of a solitary and promiscuous species in which there is a first male mating advantage.

Behavioral responses of male guinea pigs to conspecific chemical signals following neonatal vomeronasal organ removal

Following vomeronasal organ removal or sham surgery at 4-7 days of age, male guinea pigs were tested for responsiveness to conspecific chemical uses as infants and again as adults. In the first experiment, vocalizations in response to soiled home cage bedding and male bedding were monitored twice prior to surgery and twice weekly for four weeks. Home cage cues elicited more vocalizations than did male bedding in both groups; however, there was no effect of vomeronasal organ removal. When tested as adults in a second experiment, animals without vomeronasal organs exhibited depressed investigative responsiveness and vocalizations to female genital smears. The data from the first experiment fail to indicate a role for the vomeronasal organ in infantile response to conspecific odor. However, the second experiment demonstrates that adult responses to similar odors are substantially depressed by an absence of the vomeronasal organ.

Female discrimination of male dominance by urine odor cues in hamsters

Female hamsters have been found to differentially respond to the odors of dominant as opposed to subordinate males. This study reexamined these responses in an olfactometer allowing the females to choose between urinary odors obtained from males differing in dominance status and clean air source. The behavior of the estrous females was consistent with previous research which indicated that such females exhibit a preference for stimuli obtained from dominant males. Contrary to previous findings in a two-choice apparatus, diestrous females failed to prefer the odors of subordinates. These females spent significantly more time in the area infused with unscented air. These data emphasize the importance of odor cues as they relate to male attractivity and possibly mate choice. They also underscore the need to allow animals to avoid conspecific odors in order to reduce the possibility of forcing animals into an unrealistic choice situation.

Responses to conspecifics' urine by the degu (Octodon degus)

In nature the degu has been observed to deposit and to investigate scents. This study employed a captive group of these animals to investigate their responses to conspecific urinary marks in a neutral arena. Both sex classes served as subjects. They were presented with urine obtained from males, from females and a saline control. The females were found to be more active in responding. On the basis of sniffing frequency, they exhibited greater discriminative abilities than did the males. The urine from female donors was sniffed more frequently by all subjects. The frequency of approaching a mark and the time spent in the vicinity of a stimulus are interpreted as being investigatory responses. It seems that the marks deposited by females have a greater salience and that females are more sensitive to olfactory stimuli.

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.

Access of urinary nonvolatiles to the mammalian vomeronasal organ

Guinea pigs were allowed to investigate urine that contained rhodamine, a nonvolatile fluorescent dye. Guinea pigs given free access to dyed urine exhibited fluorescence in their vomeronasal and septal organs but not on their olfactory epithelium. Fluorescence was not seen when unadulterated urine was presented. Thus compounds of low volatility, which do not reach the olfactory epithelium, may stimulate the vomeronasal system and provide information that is normally not provided by gustation or olfaction.

Chemical communication in Cavia: responses of wild (C. aperea), domestic (C. porcellus) and F1 males to urine

Urine preferences of wild (Cavia aperea), domestic (C. porcellus), and F1 adult male guinea pigs were investigated. Males of all three types preferred female urine to male urine regardless of donor type. When given a choice between female urine of each type, males preferred conspecific urine. In choices between male urine of the three types, a conspecific preference was evident for wild and domestic but not F1 subjects. These data indicate that a loss of distinctive male and female odours had not occurred as a result of domestication. However, the urine odours of wild and domestic types have diverged. The possible effects of previous individual experience on the preferential response is discussed.