Effects of social influence on neonatal approach responses of Gallus chicks

Although most laboratory studies of imprinting rear and test subjects individually, in the natural setting birds are imprinted in groups. In order to approximate and evaluate naturally occuring conditions, the present study compared the approach responses of chicks reared and trained alone to those reared and trained in pairs to an audio-visual imprinting stimulus. The responses of both groups were virtually identical during the presence of the imprinting stimulus. However, under conditions of experimental extinction, the paired trained birds (now tested alone) were more resistant to extinction than their isolated counterparts, thus suggesting that birds with prior social experience are more strongly imprinted than has been previously reported.     

Effects of social isolation and crowding upon adrenocortical reactivity and behavior in the rat

The effects of social isolation and crowding on adrenocortical function and upon behavioral responsiveness to electric shock have been studied in male and female rats. All female experimental groups showed higher corticosterone levels and heavier adrenals than their male counterparts. The major effect of housing condition concerned the corticosterone response to stress, while basal hormone concentration was not modified. Socially housed rats showed a more intense adrenocortical response and also a greater behavioral reactivity to electric shock than the isolates.     

Effects of social and inanimate enrichment on the behavior of yearling rhesus monkeys

Certain types of inanimate environmental enrichment have been shown to positively affect the behavior of laboratory primates, as has housing them in appropriate social conditions. While social housing is generally advocated as an important environmental enhancement, few studies have attempted to measure the influence of social conditions on the effects of inanimate enrichment or to compare the relative merits of social and inanimate enhancements. In the present study, inanimate enrichment (predominately physical and feeding enhancements) resulted in increased species-typical behavior for socially restricted subjects. However, social enrichment (living in groups) appeared to be more beneficial for young rhesus monkeys, leading to increased species-typical activities and decreased abnormal activities. The behavior of one cohort of yearling rhesus monkeys (Macaca mulatta) housed in small peer groups was compared with the behavior of four yearling cohorts housed in single cages. Half the animals in each cohort received a three-phase enrichment program and the rest served as controls. Group-housed yearlings spent significantly more time feeding and exploring and significantly less time behaving abnormally, self-grooming, and drinking than did singly housed yearlings. Enriched subjects spent significantly more time playing by themselves, and significantly less time self-grooming and exploring than did controls. Among group-housed subjects only, there were no differences between enriched and control monkeys. Captive primates should be housed socially, whenever appropriate, as the first and most important step in an enrichment program, with the provision of inanimate enhancements being considerably less important. Limited resources for inanimate enrichment programs instead should be focused on those individuals who can not be housed socially. © 1996 Wiley-Liss, Inc.     

Effects of social isolation on growth,stress response,and immunity of zebrafish

Stressful housing conditions like social isolation have been shown to profoundly affect the physiology and health of various organisms which is rarely addressed in fish species. In the present study, we used a shoaling species, zebrafish, to investigate the stress reactivity of grouped and individually housed fish. We also hypothesized if isolation is a stressful condition may disrupt growth performance and innate immune response of individuals. To this end, fish were housed individually (social isolated treatment) or in groups of five fish (control treatment) for 60 days. Growth indices of fish were not affected by social isolation. Sixty-day social isolation did insignificant effect on baseline cortisol levels of specimens; however, individually housed zebrafish showed lower plasma cortisol to chasing stress than the control grouped fish. On the contrary, exposure to predator caused higher cortisol levels in social isolated fish. Serum lysozyme activity of isolated individuals was significantly lower than control fish, but activity of serum complement remained unchanged. Our results represent evidences that zebrafish experienced social isolation showed broad changes in physiological and immunological functions which may affect the quality of life.     

Prenatal light exposure affects early feather-pecking behaviour in the domestic chick

Recently we proposed that early feather pecking is a form of social exploration. Social recognition, important for exploration, is a lateralized function in the domestic chick. Lateralization of functions can be influenced by light exposure late in embryonic development. Therefore, we investigated whether this light exposure affected early posthatching feather-pecking behaviour in domestic chicks, Gallus gallus domesticus. White leghorn embryos either were exposed to light or remained in darkness in the last week of incubation. After hatching, they were housed in groups of two light-exposed and two dark-incubated chicks. Light-exposed chicks showed more feather pecking than did their dark-incubated cagemates. Dark-incubated chicks preferred to direct feather pecks to unfamiliar peers than to familiar peers; light-exposed chicks showed no preference. These effects were present in the first week after hatching and remained at least another 3 weeks. These results support the hypothesis that early gentle feather pecking is part of the normal behavioural repertoire of young chicks and influences social exploration. We discuss a possible mechanism underlying these results. We also suggest that it may be worthwhile not to expose embryos to light during the last week of incubation when housing hatchlings in commercial conditions, where feather pecking is a serious problem.     

Assessing the effects of social environment on blood pressure and heart rates of baboons

The objective of this publication is to report on the feasibility of using a tether system for obtaining data on blood pressure and heart rates of socially housed primates and to evaluate the extent to which housing environment alters cardiovascular responses (mean arterial blood pressure and heart rate). Blood pressure and heart rates of adult male baboons (Papio cynocephalus hamadryas) were evaluated over a 6 week period under three different housing conditions: social companion, individual, and socially unfamiliar. Social environment was manipulated in a specially designed cage that incorporated removable panels of either woven wire or solid sheet metal. The design of the cage permitted nonhuman primates to engage in species-typical social behaviors such as grooming and aggression. Using a tether and catheter system, we monitored cardiovascular physiology. We tested the hypothesis that individual housing, housing with social companions, and housing with social strangers would produce different mean arterial blood pressure and heart rate responses. Individual housing and housing with strangers produced resting mean arterial blood pressures that were elevated relative to blood pressure responses with social companions. Individual housing and housing with social strangers produced different patterns of cardiovascular response. Individual housing resulted in lowered heart rates and elevated blood pressures relative to the social companion condition. Housing with social strangers resulted in both elevated blood pressure and elevated heart rate, relative to the social companion condition. Responses observed during this study demonstrated the sensitivity of blood pressure and heart rates to differences in social environment.     

Alternatives to continuous social housing.

Although social housing is desirable for social species of nonhuman primates, circumstances arise whereby social housing is precluded (for example, certain kinds of infectious disease or toxicologic research, when the health of the animal(s) would be compromised by social housing, and animals which respond behaviorally in an inappropriate manner to social housing). Nonsocial alternatives that provide increased environmental complexity to the home cage should then be considered. Nonsocial "environmental enrichment" schemes can be designed to enhance the expression of an individually housed nonhuman primate's locomotive/postural, manipulative, and foraging behaviors. In this way, nonsocial, but species-typical, behaviors can be promoted in the single cage housing condition.     

Old,socially housed rhesus monkeys manipulate objects

Recent research has indicated that old, individually housed monkeys show little interest in novel objects. Yet unanswered is whether this effect is caused primarily by age or housing condition. The purpose of this study was to assess the role of social living in promoting responsiveness to objects. We measured the rates of object manipulation in older animals, assessed responsiveness over time to particular objects as a measure of habituation, and examined social influences on object use. Several social groups of rhesus monkeys that contained older adults were studied. These groups were housed in indoor pens or in an outdoor enclosure, and all monkeys had continuous access to a variety of objects in their home environment. In contrast to previous studies of individually housed monkeys, our group-housed monkeys showed sustained interest in objects. Old monkeys manipulated objects extensively, and this response was all the more significant, given that the objects were not novel. Monkeys housed in an outdoor enclosure showed object manipulation patterns that were not different from monkeys housed in indoor pens. However, females exhibited much higher object-related responses than males. Social facilitation played a role in the reactions of some monkeys to objects. Patterns of social facilitation as well as avoidance were present in two of the three indoor groups that were observed. Failure to manipulate objects in rhesus macaques appears to be more a function of individual housing than of old age. Factors such as environmental complexity, social needs, and early experience should be considered in order to understand why individually housed rhesus monkeys are unresponsive to objects. © 1993 Wiley-Liss, Inc.     

Affiliation and social discrimination produced by brief exposure in day-old domestic chicks.

Discrimination between individual strangers and companions was examined in day-old domestic chicks. In one experiment, pecking rates at companions and strangers were observed in pairwise bouts after 16 hr of cohabitation. The discriminability of strangers and companions was varied by means of pre-hatch colouring. Reliable discriminations between individual strangers and companions emerged as early as the first minute of the encounter. Discriminative cues provided by artificial colouring were found not to be necessary in establishing social discrimination. In a second experiment, undyed chicks were housed in pairs for 1, 4 or 16 hr. Half of the pairs lived in cages that separated companions by a wire screen, and half were housed in undivided cages. Observations of pecking in four-way bouts confirmed previous findings and demonstrated that the opportunity to peck during exposure may be a necessary condition in producing social discrimination. Antecedent conditions that lead to the development of affiliative bonds simultaneously appear to establish social discrimination.     

A comparison of cell-mediated immune responses in rhesus macaques housed singly, in pairs, or in groups

A variety of psychosocial factors have been shown to influence immunological responses in laboratory primates. The present investigation examined the effects of social housing condition on cell-mediated immune responses, comparing rhesus macaques (Macaca mulatta) in three housing conditions (single, pair, and group). Subjects included 12 adults of both sexes in each housing condition (N=36). Multiple blood samples (0, 4, 8, and 12 months) were collected for immunological analyses, including lymphocyte subsets, lymphocyte proliferation to pathogens and nonspecific mitogens, natural killer cell activity, and cytokine production. CD4(+) to CD8(+) ratios differed significantly across housing conditions and singly caged subjects had significantly lower CD4(+)/CD8(+) after the 4-month timepoint than did socially housed (pair and group) subjects. CD4(+) to CD8(+) ratios were positively correlated within subjects, suggesting a trait-like aspect to this parameter. Lymphocyte proliferation responses to all four gastrointestinal pathogens differed across housing conditions (at least at the 0.08 level), as did proliferation responses to StaphA, and the production of cytokines (IFN-gamma, IL-2, and IL-10). Proliferation responses of singly caged monkeys did not differ from socially housed monkeys and the highest levels of both IFN-gamma and IL-10 were produced by group housed subjects. The data demonstrate that social housing condition affects immune responses. While not unidirectional, these effects generally suggest enhanced immune responses for socially housed animals. Since rhesus monkeys live socially in nature, and the immune responses of singly housed animals differed from those housed socially, there is considerable motivation and justification for suggesting that the use of singly housed rhesus macaques may complicate interpretations of normal immunological responses. This may have important implications for the management, treatment, and selection of primate subjects for immunological studies.     

Impact of 'living apart together' on postoperative recovery of mice compared with social and individual housing

Social housing is the optimal way of housing female laboratory mice. However, individual housing may be required in experimental designs, for example after surgery. We therefore investigated whether housing two female mice in a cage, separated by a grid partition ('living apart together', LAT), counters the adverse effects of individual housing on postoperative recovery. Ten individually housed (IND) mice, nine socially housed (SOC) mice and nine mice, housed LAT, were surgically implanted with a telemetry transmitter. From one week prior to surgery until three weeks thereafter, several physiological and behavioural parameters were measured in the mice subjected to surgery. The telemetry transmitter measured heart rate (HR), body temperature and activity continuously. Body weight, food and water intake were scored regularly, as were wound healing, ease of handling, nest building and behaviour. Results indicated that SOC mice appear to be less affected by abdominal surgery than IND mice, as indicated by HR and behaviour. LAT, however, did not appear to be beneficiary to the mice. Increased HR levels and differences in behaviour as compared with both SOC and IND animals indicate that LAT may even be the most stressful of the three housing conditions. We therefore conclude that mice benefit most from social housing after surgery. If, however, social housing is not possible, individual housing appears to be a better option than separating mice by a grid partition.     

Sensitiveness to social stress in female rats with alteration of the pituitary-adrenal axis stress reactivity

The sensitiveness of female rats to social stress induced by increasing group density, was investigated. It was shown that female rats were housed in groups of 9-10 animala per cage in pubertal period and demonstrated significant alteration of oestrous cycle duration and anxiety level. This housing condition increased basal level of corticostcrone in prenatal stressed female rats who have high stress reactivity of the hypothalamic-pituitary-adrenal axis, as well as a more profound effect on anxiety level and oestrous cycle. Prenatal stressed rats retained impairment of oestrous cycle and behavior after optimization of housing condition, whereas control rats demonstrated normalization of oestrous cycle duration and anxiety level. These data suggest that high stress reactivity females rats are more sensitive to crowding-induced stress.     

Behavioral assessment of intermittent wheel running and individual housing in mice in the laboratory

Physical cage enrichment—exercise devices for rodents in the laboratory—often includes running wheels. This study compared responses of mice in enriched physical and social conditions and in standard social conditions to wheel running, individual housing, and open-field test. The study divided into 6 groups, 48 female BALB/c mice group housed in enriched and standard conditions. On alternate days, the study exposed 2 groups to individual running wheel cages. It intermittently separated from their cage mates and housed individually 2 groups with no running wheels; 2 control groups remained in enriched or standard condition cages. There were no significant differences between enriched and standard group housed mice in alternate days' wheel running. Over time, enriched, group housed mice ran less. Both groups responded similarly to individual housing. In open-field test, mice exposed to individual housing without running wheel moved more and faster than wheel running and home cage control mice. They have lower body weights than group housed and wheel running mice. Intermittent withdrawal of individual housing affects the animals more than other commodities. Wheel running normalizes some effects of intermittent separation from the enriched, social home cage.     

Training Nonhuman Primates Using Positive Reinforcement Techniques

Physical cage enrichment—exercise devices for rodents in the laboratory—often includes running wheels. This study compared responses of mice in enriched physical and social conditions and in standard social conditions to wheel running, individual housing, and open-field test. The study divided into 6 groups, 48 female BALB/c mice group housed in enriched and standard conditions. On alternate days, the study exposed 2 groups to individual running wheel cages. It intermittently separated from their cage mates and housed individually 2 groups with no running wheels; 2 control groups remained in enriched or standard condition cages. There were no significant differences between enriched and standard group housed mice in alternate days' wheel running. Over time, enriched, group housed mice ran less. Both groups responded similarly to individual housing. In open-field test, mice exposed to individual housing without running wheel moved more and faster than wheel running and home cage control mice. They have lower body weights than group housed and wheel running mice. Intermittent withdrawal of individual housing affects the animals more than other commodities. Wheel running normalizes some effects of intermittent separation from the enriched, social home cage.     

Social stimuli, testosterone, and aggression in gull chicks: support for the challenge hypothesis

We tested the challenge hypothesis for the hormonal regulation of aggression in chicks of the black-headed gull, Larus ridibundus. Chicks of this species are highly aggressive toward conspecifics, but never to peers that hatched from the same clutch (modal clutch size is three). Therefore, in the first experiment small families were housed together in large groups (challenged condition) and compared to families kept isolated (nonchallenged condition). As expected, in the challenged condition during the initial stage of territory establishment basal levels of testosterone (T) were clearly higher than those in the nonchallenged condition. In the second experiment we tested the effect of a short social challenge on short-term T-fluctuations. The design was based on an earlier experiment, showing that after temporary T-treatment chicks become very sensitive to social challenges while having low basal T-levels. We now show that these social challenges induce brief elevations in plasma T-levels. These peaks are similar to those in previously untreated chicks but untreated chicks do not respond with aggression to a challenge. Therefore, we conclude that the initial exposure to elevated T-levels increases the sensitivity to brief changes in T induced by social challenges. In this way exposure to T, that may be detrimental for development, is minimized while birds remain able to defend territories. This is the first report showing that the challenge hypothesis as established for adult birds, is also applicable for aggressive behavior in young birds outside the sexual context. Furthermore we suggest that a phase of priming with T is necessary to obtain the high behavioral responsiveness to a challenge.     

Ontogeny of magnetoreception in chickens (Gallus gallus domesticus)

Chickens are precocial birds, capable of moving independently from within a few hours of hatching, and thus provide a useful model to investigate the development of magnetoreception in young birds. Chicks show some sharply-timed behavioural changes at around 11 days of age that may be indicative of improvements in navigation ability around this age. We trained Young (<10 days, n = 7) and Old (11 days or older, n = 6) chicks to find a hidden imprinting stimulus behind one of four screens in a square arena. Once criterion was reached, the directional choices of chicks were recorded in unrewarded tests in the geomagnetic field and in an experimental field shifted by 90° clockwise. These tests were separated with rewarded training trials to avoid extinction. In the first, and the first 3 tests, no indication was found that chicks chose the correct unimodal magnetic direction. Instead, in all tests, Old chicks preferred the screens in the same magnetic axis as the training direction in tests in the geomagnetic and shifted experimental fields significantly more than Young chicks (P < 0.05). Choices of Young chicks were no different to chance in tests, whereas choices by Old chicks were significantly different from chance (P < 0.05). Our findings support the hypothesis that magnetoreception appears in the second week of life in the chicken. It is, however, unclear when a truly directional magnetic response (i.e. an unimodal, rather than axial, response in our test) develops that could be used by the chicks for accurate navigation.     

Effect of differential housing in mice on natural killer cell activity, tumor growth, and plasma corticosterone.

Various forms of stress have been shown to alter natural killer (NK) cell activity and tumorigenesis; however, few studies have measured these two variables simultaneously. Isolation of mice was utilized as a model of stress by which to study NK cell activity and pulmonary metastatic response following a tumor challenge. Male C3H mice were group or individually housed for 3 weeks, after which CIRAS 3 fibrosarcoma tumor cells or the tumor vehicle was injected intravenously (tail vein), NK cell activity, pulmonary metastasis, and plasma corticosterone were measured 1, 7, and 21 days following tumor cell inoculation. Individually housed mice, irrespective of tumor or vehicle condition, had a higher NK response on Day 1 relative to group-housed animals (P less than 0.001). By Day 21, tumor condition, rather than housing, was the major significant factor affecting NK activity (P less than 0.001). Nevertheless, individually housed, tumor-injected mice still had higher NK activity compared with the other treatment groups on Day 21. No effect of housing condition was present for the incidence of pulmonary metastases or frequency of metastases in affected animals. Plasma corticosterone levels generally increased over the study period, with no housing or injection effects at Days 1 and 7. Individually housed, vehicle-injected mice had higher corticosterone levels at Day 21 (P less than 0.01). These data suggest that in response to housing condition, NK cell activity differs in tumor-bearing mice and vehicle controls. Furthermore, CIRAS 3 pulmonary tumor formation is not affected by differences in NK activity consequent to housing condition. Plasma corticosterone does not appear to be a major in vivo regulator of NK activity in this experimental tumor system. Finally, the interpretation of housing effects on NK activity and plasma corticosterone levels depends on the temporal window in which sampling occurs.     

Influence of juvenile housing conditions on the ventilatory, thermoregulatory, and endocrine responses to hypoxia of adult male rats

"Extreme" housing conditions, such as isolation (single housing) or crowding, are stressful for rats, and their deleterious impact on behavior is well documented. To determine whether more subtle variations in housing can affect animal physiology, the present study tested the hypothesis that the hypoxic ventilatory response (HVR) of adult male rats housed in pairs during the juvenile period (postnatal day 21 to adulthood) does not differ from that of animals housed in triads. Because neonatal stress augments the neuroendocrine responsiveness to stress and HVR, experiments were performed both on "control" (undisturbed) animals and rats subjected to neonatal maternal separation (NMS; 3 h/day, postnatal days 3-12). At adulthood, ventilatory activity was measured by whole body plethysmography under normoxic and hypoxic conditions (inspired fraction of O(2) = 0.12; 20 min). The ventilatory and body temperature responses to hypoxia of rats raised in triads were less than those of rats housed in pairs. For the HVR, however, the attenuation induced by triad housing was more important in NMS rats. Triad housing decreased "basal" plasma corticosterone, but increased estradiol and testosterone levels. Much like the HVR, housing-related decrease in corticosterone level was greater in NMS than control rats. We conclude that modest changes in housing conditions (pairs vs. triads) during the juvenile period can influence basic homeostatic functions, such as temperature, endocrine, and respiratory regulation. Housing conditions can influence (even eliminate) the manifestations of respiratory plasticity subsequent to deleterious neonatal treatments. Differences in neuroendocrine function likely contribute to these effects.     

Resurgence: the role of extinction

Three hens were trained to door push and three were trained to head bob using food as the reinforcer (Behaviour 1 training). A period of extinction followed. Each hen was then trained to perform the other behaviour (Behaviour 2) and this was followed by seven sessions of extinction. This whole sequence was repeated six times, with two sessions of extinction following Behaviour 1 training. Over the repeated extinction conditions there were decreases in responding early in extinction, for both Behaviours 1 and 2, compared with the first condition. Behaviour in the later extinction sessions could be studied for Behaviour 2 only, and it was found to increase relative to the first condition, over repeated extinction conditions. The occurrence of Behaviour 1 during the extinction following the training of Behaviour 2, that is the resurgence of Behaviour 1, both over the whole of and in the first session of each extinction phase, was variable and tended to increase over these six conditions. Thus it is possible to study resurgence using a within-subject design but the effect of repeated extinction conditions needs to be considered. The period of extinction immediately following Behaviour 1 training was then increased to nine sessions for two replications of the whole sequence. This was followed by two repeats of the sequence with no sessions of this extinction and then by another repeat, with nine sessions of this extinction phase. Over these five conditions the total resurgence of Behaviour 1 was generally greater when there were no sessions of extinction immediately following Behaviour 1 training, than when there were nine sessions. This result was more marked for the resurgence of Behaviour 1 in the first session of the extinction of Behaviour 2. Thus, these data support the hypothesis that the resurgence of Behaviour 1 is the result of the prevention of the extinction of Behaviour 1 by training Behaviour 2. At a similar point in extinction, the number of occurrences of Behaviour 1 in its own extinction was not significantly different from the number of occurrences of Behaviour 1 during the extinction of Behaviour 2. This fails to support the hypothesis that resurgence is induced by the extinction of Behaviour 2.     

Close Proximity of the Heterosexual Partner Reduces the Physiological and Behavioral Consequences of Novel-Cage Housing in Black Tufted-Ear Marmosets (Callithrix kuhli)

The present studies assessed the extent to which heterosexual pairmates could buffer marmosets (Wied's black tufted-ear marmoset,Callithrix kuhli)against stress. Six male and six female marmosets from established groups were exposed to two experimental manipulations together with a control condition. Each condition lasted a total of 4 days. For the two experimental conditions, animals were removed from the family group and housed in a novel cage for 48 h in either the presence or the absence of the heterosexual pairmate. During the 48-h novel-cage housing period and for 48 h upon reunion of the subjects with the family group, concentrations of urinary cortisol were measured in the first void sample of the day and behavioral observations were conducted. When animals were housed alone in a novel cage they exhibited significant elevations in levels of urinary cortisol after 24 and 48 h of novel-cage exposure. In contrast, when marmosets were housed in the novel cage in the presence of the pairmate, levels of urinary cortisol did not change across the 4-day period. The presence of the social partner also reduced the behavioral manifestations of exposure to novelty. Upon reunion with the family group, animals that had been housed in the novel cage alone spent significantly more time in close proximity to the pairmate than animals that had been housed with the partner. A second experiment was conducted to determine the effect that separation from the pairmate, only (independent of any effects of novelty), had on levels of cortisol. Concentrations of urinary cortisol were measured in subjects housed in the familiar home cage, but in the absence of the pairmate, over a 48-h period and compared to concentrations of excreted cortisol immediately prior to separation. Separation from the pairmate did not elevate cortisol levels when the subject was housed in the home cage, suggesting that elevated cortisol levels in animals housed alone in the novel cage were in response to novelty exposure rather than to separation from the pairmate. Since the physical presence of the heterosexual partner reduced the physiological and behavioral effects of novel-cage housing, social attachments might function as homeostatic regulators of HPA function in marmosets.