Male-female associations in the domestic guinea pig

Family first! Influence of parental investment in Guinea pigs (Cavia porcellus) prosocial choices

Literature often assumed that prosocial behaviours (behaviours that benefit others with or without a cost for the actor) would have evolved many species to improve the effectiveness of parental care (Decety and Cowell 2014). While this hypothesis is rarely questioned at a phylogenetic scale, it was never tested at an individual scale to the best of our knowledge. Therefore, we chose to study the impact of effective parental care on prosociality by comparing the prosocial tendencies of Guinea pigs before mating, during mating and after parturition. We conducted Prosocial Choice Tests on three groups of Guinea pigs (males, multiparous females, and nulliparous females). Subjects had to choose between three options: a prosocial option (subject and recipient being rewarded), a selfish option (only subject was rewarded), and a null option (no reward). Our results showed high prosociality towards their mating partner and their young both in male and in female subjects. Males became selfish towards other males after parturition. Among other interesting results, we found a direct reciprocity phenomenon. We also highlighted an ability in our subjects to consider both the identity and relationship shared with the recipient, such as tolerance (enhancing prosociality), dominance rank (being tested with a dominant recipient increasing selfish responses), and its behaviour (begging calls eliciting prosociality, while threatening ones decreasing it), to choose an option. These findings suggested that prosociality could be modulated by many factors and that the constraints and stakes induced by breeding would highly influence prosocial strategies.

Social buffering of the stress response: diversity, mechanisms, and functions

Protracted or repeated activation of the hypothalamic-pituitary-adrenocortical (HPA) system is associated with a variety of physical and psychological pathologies. Studies dating back to the 1970s have documented many cases in which the presence of a social companion can moderate HPA responses to stressors. However, there also are many cases in which this "social buffering" of the HPA axis is not observed. An examination of the literature indicates that the nature of the relationship between individuals is crucial in determining whether or not social buffering of the HPA response will occur. Other factors that affect social buffering, either directly or by influencing the social relationship, include the social organization of the species, previous experience, gender, integration into a social unit, and the developmental stage at which individuals are examined. Current evidence suggests that social buffering involves mechanisms acting at more than one level of the CNS. It is suggested that, in addition to promoting health, social buffering may have evolved to direct the establishment of social relationships, and to facilitate developmental transitions in social interactions appropriate for different life stages.

Social buffering of the cortisol response of adult female guinea pigs

When housed in spacious, mixed age/sex colonies, male guinea pigs form small harems of females with which attachment-like social bonds are established. A previous study indicated that the bonded male, but not an unfamiliar male from the same colony, could reduce the plasma cortisol response of a female when exposed to a novel environment. We examined the effect of several classes of social partners on the cortisol response of females maintained under standard laboratory housing conditions. Eight "artificial harems" comprised of one adult male and two adult females were formed in standard group-housing cages 2 weeks prior to the study. Behavior observed in these home cages indicated that interactions between males and females of the triads were overwhelmingly positive in nature. When exposed to a novel environment for 2 h, the presence of either the male or female cage mate reduced the subject female's plasma cortisol response, whereas the presence of an unfamiliar adult male did not. Changes in plasma cortisol levels were not predicted by the frequency of various social behaviors observed in the novel environment. These findings: (1) demonstrate that the buffering effect of male partners on the cortisol response of adult females can be observed in guinea pigs maintained in conventional laboratory housing; (2) indicate that unfamiliar adult males are ineffective at reducing cortisol responses of females under these conditions; and, (3) appear to be the first to show buffering effects by adult female guinea pigs on the cortisol responses of other adult females.

Cortisol responses and social buffering: a study throughout the life span

The ability of specific adult females to moderate plasma cortisol responses throughout the life span was examined in male guinea pigs maintained in large mixed age/sex groups. At four critical life stages of social development (preweaning, periadolescent, sexually but not socially mature, and sexually and socially mature), the same male guinea pigs were exposed to the stressor of exposure to a novel environment for 4 h while either alone, with an unfamiliar adult female, or with a favored adult female, as based on objective criteria from behavioral observation at that life stage. In preweaning males (9-19 days of age), the favored female (biological mother), but not an unfamiliar female, reduced the cortisol response in the novel environment. In periadolescents (49-61 days), an unfamiliar female, but not the favored female, buffered the cortisol response. At the sexually but not socially mature stage (114-126 days), the cortisol response to novelty was depressed in all conditions, and not affected by either female. At the sexually and socially mature stage (270-330 days), the favored female, but not the unfamiliar female, moderated cortisol levels. These results corroborate previous findings in infants and full adults, demonstrate marked age-specific changes in the ability of females to buffer hypothalamic-pituitary-adrenal responses, and identify a heretofore undescribed period of cortisol response suppression in maturing male guinea pigs. The changing pattern of social buffering during the life span described here for the guinea pig might represent a more general pattern for males of other group-living mammals.

Increases in the circulating testosterone of maturing male guinea pigs appear neither necessary nor sufficient for heightened maternally directed sexual and social/courtship behavior

Periadolescent male guinea pigs housed continuously with their mother since birth exhibit little maternally directed sexual behavior. However, if rehoused apart from the mother for 24 h, they show elevations in circulating testosterone concentrations and display frequent sexual responses and increased social/courtship behavior upon reunion with her. We investigated the role of testosterone in the disinhibition of maternally directed sexual and social/courtship behavior. Subcutaneous implants of testosterone (Experiment 1) did not trigger maternally directed sexual behavior or an increase in social/courtship behavior among males housed continuously with their mothers. Further, neither blocking androgen receptors (Experiment 2) nor preventing the surge in testosterone (Experiment 3) prevented males housed without the mother from exhibiting increased maternally directed sexual and social/courtship behavior upon reunion. These findings indicate that the increase in testosterone that males exhibit when rehoused apart from the mother is neither sufficient nor necessary for the disinhibition of maternally directed sexual and social/courtship behavior observed when mother and son are reunited.

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.

Early social stress in female guinea pigs induces a masculinization of adult behavior and corresponding changes in brain and neuroendocrine function

This study was undertaken to investigate, in guinea pigs, the effects of pre- and early postnatal social stress on the functioning of hormonal-, autonomic-, behavioral-, and limbic-brain systems. Dams had either lived in groups with a constant composition (i.e. stable social environment) or in groups with changing compositions, that means every 3 days two females were transferred from one group to another (i.e. unstable social environment). The subjects studied were female offspring of dams who had either lived in a stable social environment during pregnancy and lactation (i.e. control daughters, CF) or in an unstable social environment during this period of life (i.e. early stressed daughters, SF). After weaning, each five groups of CF and SF, consisting of two females each, were established. The spontaneous behavior of the females was recorded, blood samples were taken to determine cortisol, testosterone, dehydroepiandrosterone, dehydroepiandrosterone sulfate and estrogen levels, the adrenals were prepared to determine tyrosinehydroxylase (TH) activities and the brains to investigate the distribution of sex hormone receptors. SF showed not only a behavioral and endocrine masculinization, but also an upregulation of androgen receptor and estrogen receptor-alpha in the medial preoptic area and the nucleus arcuatus of the hypothalamus, the nucleus paraventricularis of the thalamus, and the CA1 region of the hippocampus. These findings corresponded with distinctly elevated serum-concentrations of testosterone and increased activities of the adrenal TH. In conclusion, early social stress caused by an unstable social environment induces in female guinea pigs a permanent behavioral masculinization that is accompanied by changes in the endocrine and autonomic system as well as by changes in the distribution of sex hormone receptors in the limbic system.

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.

Sexual interactions of maturing male guinea pigs with their mothers, sisters, and unfamiliar adult females in the home cage

During observations in the home cage in the light and dark on days 5, 15, 25, 35, and 45, male guinea pigs mounted and exhibited anogenital investigation of the mother, though appropriately directed mounting occurred infrequently and was not shown by all males. Mothers nipped and kicked advancing males. No mounting of a female sibling was observed. When behavioral interactions of approximately 35-day-old males with the mother or an unfamiliar adult female were compared during 1-hr tests in the home cage, males exhibited much higher levels of mounting and anogenital investigation, and received many more nips and kicks, when with the unfamiliar female. The results 1) demonstrate that limited maternally directed sexual behavior occurs in the home cage, 2) support earlier findings indicating that continuous housing with the mother suppresses maternally directed sexual behavior in periadolescent guinea pig males, and 3) suggest that sexual behavior toward female siblings also is suppressed.

Presence of mother and unfamiliar female alters levels of testosterone, progesterone, cortisol, adrenocorticotropin, and behavior in maturing Guinea pigs

Although the guinea pig is characterized by precocial physical development and minimal active maternal care, studies suggest the presence of the mother can influence neuroendocrine and behavioral activity of offspring even well beyond weaning. Previous results may have been influenced by the procedure of housing weaned subjects with the mother to within 2 days of testing. The present study examined approximately 40-day-old guinea pigs housed apart from the mother for 0 (not rehoused), 2, or 10 days. Rehousing without the mother led to elevations in plasma testosterone (measured in males), progesterone (measured in females), cortisol, and adrenocorticotropin (ACTH) (both measured in males and females). Offspring housed without the mother for 10 days had the highest progesterone, cortisol, and ACTH levels. Testosterone elevations were observed in 2-day-, but not 10-day-, rehoused animals. Regardless of rehousing condition, 60 min isolation in a novel test cage elevated progesterone, cortisol, and ACTH, and reduced testosterone. These effects were all moderated if the subject was tested with the mother or another female. Sexual behavior toward the mother was observed frequently, but only in males housed apart from her prior to testing. Overall, males and females that had been housed apart from the mother interacted with her as they would an unfamiliar female. Our results corroborate previous findings, suggest the effect of housing apart from the mother on male testosterone is transitory, and indicate that continuous housing with the mother past weaning suppresses circulating progesterone in females and cortisol and ACTH in both sexes.

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.

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.

Social relationships and the management of stress

Two different types of social relationships exist in mammalian social systems: dominance relationships and social bondings. This article shows that both are crucial for the management of stress. The following general conclusions are derived: (1) In stable social systems, established dominance relationships result in predictable behaviour. As a consequence, low positions in the hierarchy do not necessarily lead to enhanced endocrine stress responses. Under conditions of instability, however, distinct increases in the activities of the pituitary-adrenocortical- and the sympathetic-adrenomedullary systems are found; (2) The ability to establish and to respect dominance relationships is a prerequisite to build up stable social systems. Whether this ability is realized, however, depends on social experiences made during behavioural development. The time around puberty seems to be essential for the acquisition of those social skills needed to adapt to unfamiliar conspecifics in a non-stressful and non-aggressive way; (3) Stress responses can be ameliorated by the presence of members of the same species. This phenomenon is called social support. In general, social support cannot be provided by any conspecific, but the ability to give social support is restricted to bonding partners. In most mammalian species mothers are important bonding partners for their infants. In some species bondings also occur between adult individuals; and (4) On a physiological level the bonding partner reduces the activities of the pituitary-adrenocortical- and the sympathetic-adrenomedullary systems. On a psychological level he/she can be regarded as a 'security-giving and arousal-reducing structure'. This is true irrespective of whether the bonding partner is the mother, in the case of an infant, or a male or a female in the case of an adult individual.

The social environment during pregnancy and lactation affects the female offsprings' endocrine status and behaviour in guinea pigs

This study investigated the influence of the social environment during pregnancy and lactation on the female offsprings' endocrine parameters and behaviour. The subjects studied were daughters whose mothers had either lived in a stable social environment (SSE) during pregnancy and lactation (SE-mothers) or in an unstable social environment (USE) during this period of life (UE-mothers). The SSE was made by keeping the group composition (one male, five females) constant; in the USE situation every third day two females from different groups were exchanged. After weaning, 3 groups of daughters from UE-mothers (UE-daughters) and 3 groups of daughters from SE-mothers (SE-daughters), consisting of four females each, were established. From their 60th through their 80th day of age the spontaneous behaviour of the daughters was recorded in their home cages. On the endocrine level, cortisol and testosterone (T) concentration in serum as well as adrenal tyrosinehydroxylase activities in both adrenals and their weight were determined. UE-daughters displayed significantly higher amounts of male-typical courtship and play behaviour than SE-daughters. This behavioural masculinization corresponded with significantly higher T in UE- than SE-daughters. Cortisol levels did not differ between both categories of females. Significantly higher tyrosinehydroxylase activities and adrenal weight in UE- than SE-daughters pointed, however, to higher degrees of stress response in UE-daughters. Thus, the instability of the social environment during pregnancy and lactation has distinct effects on the behaviour and endocrine system of the female offspring.

Prenatal social stress masculinizes the females' behaviour in guinea pigs

This study investigated the influence of the social environment during pregnancy and lactation on the female offsprings' behaviour and body weight. The subjects studied were daughters whose mothers had lived: a) in a stable social environment (SSE) during pregnancy and lactation; b) in an unstable social environment (USE) during pregnancy and lactation; c) in a SSE during pregnancy but in an USE during lactation; d) in an USE during pregnancy but in a SSE during lactation. The SSE was made by keeping the group composition (one male, five females) constant; in the USE situation every third day two females from different groups were exchanged. After weaning (n = 4 x 3 = 12), groups of daughters, consisting of four females each, were established, originating from the different categories of mothers. From their 41st through their 80th day of age the spontaneous behaviour of the daughters was recorded in their home cages. When the mothers had lived in an USE during pregnancy, the daughters displayed significantly higher amounts of male-typical courtship, play, and social orientation behaviour compared to daughters whose mothers had lived in a SSE during pregnancy. The stability and instability, respectively, of the social environment during lactation, however, had no significant influence on the daughters' prospective behaviour. The four categories of daughters did not differ in their body weights either at birth or at 80 days of age. Thus, the instability of the social environment during pregnancy obviously represented a mild stressor that nevertheless caused a distinct masculinization of the daughters' behaviour.

Social experience, behavior, and stress in guinea pigs

This study examined the effect of varying rearing and testing conditions on guinea pig aggression, courting behavior, endocrine responses and body weight. Pairs of 7-8-month-old males were placed in chronic confrontations for 6-50 days in 2 m2 enclosures. Social behavior was recorded with a total of 882 h observation time. Body weight as well as plasma glucocorticoid, testosterone and norepinephrine titers were determined for each male 20 h before, and 4, 52 and 124 h after, the onset of the chronic encounters. Three experiments were conducted: in Experiment I, 7 pairs of males, each male raised singly with one female (FRM), were confronted in the presence of an unfamiliar female, in Experiment II, 6 pairs of FRM were confronted with no female present, and in Experiment III, 7 pairs of males which were raised in different large colonies were confronted in the presence of an unfamiliar female. In Experiment II and III low levels of aggression, no distinct endocrine changes and no indications of physical injury occurred in winners or losers, whereas in Experiment I high levels of aggression and courting behavior, extreme increases in glucocorticoid titers and distinct decreases in body weights were found in both males. Losers, however, were affected to a much greater extent than winners. These findings suggest that in guinea pigs a causal relationship exists between social rearing conditions, behavior as adults and degree of social stress in chronic encounters.

Social stress in guinea pigs

Confrontation studies between eight pairs of two 7-8 months old male guinea pigs, each raised with one female from their 30th day of age, were conducted in an enclosure of 2 m2 in the presence of an unfamiliar female. The opponents were chronically kept together for up to 8 days. When they were not separated after 52 hr, one or (in 1 case) both males fell into a comatose state and died 5-8 days after the onset of the confrontation. Four hr after the onset of the confrontations both opponents showed significantly increased plasma glucocorticoid (CS) titers. At this time as well as 24 hr earlier, prospective winners (PW) and prospective losers (PL) did not yet differ in any physiological parameter measured. Forty-eight hr later, PW were characterized by a low body weight loss, low CS, high testosterone (T) and elevated plasma-catecholamine (CA) values. In contrast, PL showed a high body weight loss, very high CS titers, low T-titers and more elevated CA values than PW. Despite these highly significant differences in physiological parameters, PL and PW did not yet differ in the frequency of any agonistic behavioral element recorded. Seventy-two hr after the onset of the chronic cohabitation, losers began to behave more and more passive, they ceased feeding and drinking and were less and less involved in social interactions. The physiological differences between winners and losers intensified.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of long-term isolation on physiology and behavior in male guinea pigs

Studied were isolation induced effects in guinea pigs. Males (CM) living in two colonies (12 males, 12 females, each) were compared to males (IM) born in the colonies and kept isolated from their 2nd month of age. The findings were: At 19 months of age CM showed higher testosterone and cortisol titers, higher adrenal tyrosine hydroxylase activities and higher seminal vesicles weights than IM. Body, spleen, and adrenal weights did not differ. Thus gonadal, adrenomedullary, and adrenocortical activities appear higher in CM. Adrenal functioning indicates that isolation per se is no more stressful than group living. At their 13th month of age CM and IM did not differ in their behaviors during a 1 hr open-field exposure. This is not considered to result from similar 'emotional temperaments' but rather from an inappropriate procedure to study 'emotionality' in adult guinea pigs. At their 14th month of age CM and IM were placed into the home cage of a male experienced fighter for 15 min. The agonistic encounters between the resident and CM occurred more frequently and were more escalated than between the resident and IM. IM may be a weaker stimulus for attack possibly due to a decreased production of androgen dependent pheromones as indicated by the decreased seminal vesicles weights. Eight IM placed into the colonies at their 16th month of age lost 16.3 to 20.9% of their initial body weights. Three IM died within 8 days although they were not attacked by CM. The 5 surviving males gained low ranking social positions, showed a high degree of arousal and probably were not able to reproduce.(ABSTRACT TRUNCATED AT 250 WORDS)