Guinea-pig maternal-young attachment behaviour

Female Chemical Signalling Underlying Reproduction in Mammals

Chemical communication plays many key roles in mammalian reproduction, although attention has focused particularly on male scent signalling. Here, we review evidence that female chemical signals also play important roles in sexual attraction, in mediating reproductive competition and cooperation between females, and in maternal care, all central to female reproductive success. Female odours function not only to advertise sexual receptivity and location, they can also have important physiological priming effects on male development and sperm production. However, the extent to which female scents are used to assess the quality of females as potential mates has received little attention. Female investment in scent signalling is strongly influenced by the social structure and breeding system of the species. Although investment is typically male-biased, high competition between females can lead to a reversed pattern of female- biased investment. As among males, scent marking and counter-marking are often used to advertise territory defence and high social rank. Female odours have been implicated in the reproductive suppression of young or subordinate females across a range of social systems, with females of lower competitive ability potentially benefiting by delaying reproduction until conditions are more favourable. Further, the ability to recognise individuals, group members and kin through scent underpins group cohesion and cooperation in many social species, as well as playing an important role in mother-offspring recognition. However, despite the diversity of female scent signals, chemical communication in female mammals remains relatively understudied and poorly understood. We highlight several key areas of future research that are worthy of further investigation.

Can but don't: olfactory discrimination between own and alien offspring in the domestic cat

Mammalian maternal care usually comes at a large energetic cost. To maximize their fitness, mothers should preferentially care for their own offspring. However, the majority of studies of mother-offspring recognition have focused on herd- or colony-living species and there is little information on maternal discrimination in more solitary-living species. Olfaction has been found to play a major role in mother-offspring recognition across various taxa. Therefore, our aim was to study this in a species evolved from a solitary-living ancestor, the domestic cat. We asked whether cat mothers distinguish between their own and alien offspring when providing maternal care, and whether cat mothers use olfactory cues in the offspring discrimination process. Results of Experiment 1 showed that cat mothers do not discriminate between own and alien young when retrieving them to the nest. They treated own and alien young similarly with respect to latency and order of retrieval. However, the results of Experiments 2 and 3, where we used an olfactory habituation-discrimination technique, showed that mothers were able to distinguish between the odours of their own and alien kittens. We discuss what ecological and/or behavioural factors might influence a mother's decision when faced with discriminating between own and alien young, and why mothers might not discriminate between them when they are able to do so. Our findings support the view that maternal care alone should not be used as a measure of offspring recognition, and equal maternal care of own and alien young should not be immediately interpreted as an inability to discriminate between them.

Parental potentiation of vocalization as a marker for filial bonds in infant animals

Maternal and paternal potentiation of vocalization are two parts of a promising model of early life social bonds that has been and can be a useful tool in research. Most mammalian infants vocalize when isolated. Interactions with adult females just before isolation have been found to increase vocalizations in several species. Interactions with littermates and other social stimuli do not. In guinea pigs and pigs, the response is specific to the dam. In rats and octagon degus, an unrelated adult female from the colony is sufficient. The presence of an intact adult male in the test chamber with dam-reared pups evokes behavioral inhibition, a fear response. Previous exposure to the male in the home cage, biparental rearing, dramatically transforms the response of the pup. The pup treats the adult male as it does its dam, including potentiation of vocalization during a subsequent isolation. This article outlines the methods, advantages, and disadvantages of parental potentiation as a research tool, as well as a brief review of the evidence supporting its use as a marker for filial attachment. Future research directions are outlined.

An investigation of the effects of maternal separation and novelty on central mechanisms mediating pituitary-adrenal activity in infant guinea pigs (Cavia porcellus)

In mammalian species in which the young exhibit a strong filial attachment (e.g., monkeys, guinea pigs), numerous studies have shown that even brief separation from the attachment figure potently elevates circulating concentrations of glucocorticoids and adrenocorticotropic hormone (ACTH). However, effects of separation on central regulation of this stress response are not known. Therefore, we investigated central mechanisms mediating pituitary-adrenal activation during maternal separation and novelty exposure in guinea pig (Cavia porcellus) pups. Corticotropin-releasing factor (CRF) mRNA expression in the hypothalamic paraventricular nucleus (PVN), and plasma cortisol and ACTH levels, were elevated only during separation in a novel environment. C-Fos activity was elevated in the medial amygdala (MeA) and reduced in the bed nucleus of the stria terminalis (BNST) during novelty exposure, regardless of separation. On the other hand, c-Fos activity was elevated in the PVN during separation, regardless of novelty exposure. These results demonstrate independent and combined effects of separation and novelty in regions of the guinea pig CNS that regulate pituitary-adrenal activity. Moreover, they suggest that a pathway from MeA to BNST to PVN mediates responses to novelty in the guinea pig pup, as in the adult rat, though inputs from other cell populations appear required to fully account for the HPA activity observed here.

Olfactory regulation of maternal behavior in mammals

In mammals, olfactory cues are extensively used in many aspects of maternal care to ensure the coordination of mother-infant interactions and consequently the normal development of the offspring. Outside the period of parturition and lactation, when the young are not a behavioral priority, olfactory cues play an inhibitory role on maternal responsiveness since in most mammalian species studied so far, nonpregnant females find the odor of young aversive. On the contrary at the time of parturition, a shift in the hedonic value of infantile odors occurs so that the young now become a very potent stimulus and this sensorial processing constitutes an important part of the maternal motivational system. Moreover, infants' odors provide a basis for individual recognition by their mothers and some species (ungulates) have developed highly specialized mechanisms for processing of the infant signals. Perception of the smell of the young also regulates various aspects of maternal behavior. Dodecyl propionate, a compound released by of pup's preputial glands, has been shown to influence anogenital licking behavior, a fundamental pattern of maternal behavior in rodents. While there is no functional specificity of either the main or the accessory olfactory systems in the development of maternal behavior amongst species, it appears that only the main olfactory system is implicated when individual odor discrimination of the young is required. Neural structures, such as the main olfactory bulb, undergo profound changes when exposed to offspring odors at parturition. These changes in synaptic circuitry contribute both to maternal responsiveness to these odors, to their memorization, and to effects of long-term maternal experience.

Enduring maternal influences in a precocial rodent

The guinea pig is highly developed at birth and requires little active maternal care. Yet the mother and other social figures markedly influence biobehavioral processes of the offspring. Here, responses of guinea pigs and nonhuman primates to maternal and other social separation procedures are compared, and influences of social partners on endocrine responses and behavior in periadolescent guinea pigs are described.

Social influences on endocrine activity in guinea pigs, with comparisons to findings in nonhuman primates

Guinea pigs exhibit a rich and varied social organization. Studies in recent years have demonstrated that social stimuli have widespread neuroendocrine effects in guinea pigs. Here, effects on the hypothalamic-pituitary-adrenal, adrenal medullary/sympathetic, and hypothalamic-pituitary-gonadal systems of both adult and developing guinea pigs are reviewed. These systems respond to various social variables, or factors that affect social variables, including: separation from attachment objects, housing conditions, changes in housing, the familiarity of the environment in which social interactions occur, foraging conditions, surrogate-rearing, agonistic interactions, and the establishment of dominance rank. Similarities and differences between these findings and those in nonhuman primates are discussed. It is argued that the guinea pig is well suited for the study of socioendocrine effects throughout the life span, and can provide a valuable complement to nonhuman primate research in this area.

Hypothalamic-pituitary-adrenal responses to brief social separation

Involuntary separation from close social companions is widely held to lead to pathophysiological outcomes. Presumably, the relationship with, or category of, the separated individual determines the nature of the physiological response. Here, experiments examining the consequences of brief involuntary separation on the activity of the stress-responsive hypothalamic-pituitary-adrenal (HPA) system are reviewed. Only those studies designed specifically to assess the effect of the absence of the social partner are considered. Evidence for HPA activation in response to social separation has been obtained in a number of species; yet, many studies find no effect of separation of affiliative partners on HPA activity. The occurrence of an HPA response to separation does not appear to be related to the phylogenetic position or cognitive capacity of the species studied, nor is it a universal response to mother-infant separation. Rather, it is suggested that the pattern of results can be largely understood in the context of attachment. Separation of partners exhibiting signs of emotional attachment leads to an immediate and persistent HPA response, whereas separation of partners that are affiliative, but do not exhibit attachment, has little or no effect on HPA activity.

Hormonal and behavioral attachment responses in infant guinea pigs

Infant guinea pigs, 11/12 and 18/19 days of age, exhibited high rates of vocalizing and increases in plasma concentrations of cortisol when separated from their mothers for 30 min in a novel environment (unfamiliar cage in an unfamiliar room). Levels of vocalizations and plasma cortisol were significantly reduced when the pup was exposed to the novel environment with its own conscious or anesthetized mother, but not when it was exposed with an unfamiliar anesthetized lactating female. Pups spent equivalent amounts of time in physical contact with their own conscious mother, their own anesthetized mother and an unfamiliar anesthetized lactating female. Unexpectedly, when the unfamiliar cage was placed in an environmental chamber during separation, pups showed negligible increases in vocalizations and plasma cortisol levels, even when administered footshock just prior to exposure. These findings demonstrate that guinea pig pups exhibit adrenocorticoid as well as behavioral responses to maternal separation, provide further evidence for the existence of filial attachment in this species, and document an unexpected role of the test environment in determining responses during maternal separation. The guinea pig may afford a rodent model for examining the effects of attachment-object separation on the activity of the pituitary-adrenal system.

Cortisol and behavioral responses to separation in mother and infant guinea pigs

In Experiment 1, lactating guinea pigs 3 days postpartum exhibited an elevation of plasma levels of cortisol when their litters were taken from the home cage and placed out of auditory range for 30 min. If pups were left within auditory range during the period of separation, or if the litter was disturbed but not removed, no increase in plasma cortisol levels was observed. In Experiment 2, 11/12- and 18/19-day-old guinea pig pups placed alone in a novel environment for 30 min displayed levels of plasma cortisol and vocalizations that were greater than those of pups tested in the same environment but with their mother. Pups tested with littermates but not with their mother exhibited plasma cortisol levels that were as great as those of pups tested alone. Pups tested with littermates vocalized much less than pups tested alone but more than pups tested with their mother. These results indicate that brief mother-infant separation can activate the pituitary-adrenal system in mother as well as infant guinea pigs and they provide further evidence for the existence of a reciprocal mother-infant attachment in this species.

Home odor preferences in young hares (Lepus capensis syriacus): effects of age and role of maternal presence

The odor preferences of mother-reared and hand-reared young hares between 1-30 days of age were studied. Subjects were exposed daily to three choice tests in which the following pairs of odors were presented: home cage odor (HCO)-neutral odor (NO); HCO-strange cage odor (SCO); SCO-NO. All young strongly preferred their HCO over SCO throughout the 30-day period. HCO was preferred over NO until the age of 20 days, while avoidance of SCO was shown during the first 10 or 20 days. The same experiment conducted on postweaned hares (31-50 days of age) revealed a strong preference for SCO over both HCO and NO. These findings may be interpreted with respect to the natural history of the hare and its unusual mother-young relationship, which, in the wild, is limited to a single daily meeting for nursing. It is suggested that the highly precocial hare recognizes and prefers its home odor independently of any maternal contribution to that odor, possibly relying on odor cues from its own body to return to its nursing site. Other possible advantages of these olfactory preferences, including predation avoidance and facilitation of social relationships, are discussed.

Pup recognition in Mus musculus: parental discrimination between their own and alien young

The responses of male and female mice each presented with a sequence of 4 pups from their own litter, a pup from another litter but of the same age and strain, and finally their own pup were noted. Both sexes spent longer sniffing the alien pup than the preceding own pup regardless of the age of pups at testing, and more time licking the alien pup on some test days. Young pups (Days 0-3; birth = Day 0) emitted fewer ultrasounds in the presence of a male than a female, but there was no quantitative difference in the vocalizations of own and alien pups. These data indicate that adult mice are able to discriminate between their own and alien offspring; this discrimination appears to be based upon olfactory and possibly gustatory cues rather than auditory ones.

Attachment and separation distress in the infant guinea pig

This study systematically examined separation-induced distress vocalization in the infant guinea pig. Experiment I found that under maximum separation from both social and physical surroundings, the distress vocalization rate remained high for the 1st 4 weeks and then continuously declined to near zero by Week 12. Repeated testings had no effect on habituation of the rate during Week 5. Experiment II, using separation distress vocalization responses to the social (the mother) and the physical (the home pen) environments, showed that when the mother was present the vocalization rate was extremely low, and when she was absent the rate was moderate if the subject was isolated in the home box and high if the subject was in an unfamiliar box. Experiment III confirmed the finding that primary social attachment took place toward the mother. These results corroborate other attachment measures, and indicate the usefulness of the vocalization technique for the study of attachment in the infant guinea pig.

The responses of one-day old Acomys cabirinus pups to naturally occurring chemical stimuli

The role of olfactory stimuli in the mediation of the behavior of 26--36 hour old spiny mice (Acomys cabirinus) was assessed through a series of six experiments. The major results of these experiments are: 1. One day old spiny mice showed a preference for soiled bedding from their own home-cage as compared to clean bedding in a simultaneous two-choice preference test. 2. No significant preference was displayed for home-cage bedding vs. bedding from the cage of a conspecific litter and parents. 3. Soiled bedding from the home-cage was preferred over soiled bedding from the cage of a nulliparous adult female conspecific. 4. A reduced mean latency to leave an area of clean bedding was found in comparison to mean latencies to leave soiled bedding from the subjects' home-cage or from the cage of a conspecific litter. 5. No differential activity levels were displayed on home-cage vs. clean bedding. It was concluded that by the second day of life, Acomys pups have developed attachment to chemical stimuli produced by specific classes of conspecifics--and that the early appearance of such attachments is a function of the high degree of sensory and motor precocity of the Acomys pups at birth. The adaptive value of such rapidly developed attachments in precocial as contrasted to altricial species was discussed.