Sylvia Kaiser

Is a wild mammal kept and reared in captivity still a wild animal

This study compared domestic guinea pigs (Cavia aperea f. porcellus; DGP) and two different populations of the wild cavy (Cavia aperea), its ancestor, to examine whether rearing of wild mammals in captivity affects their behavior and physiological stress responses. One population of wild cavies consisted of wild-trapped animals and their first laboratory-reared offspring (WGP-1). The animals of the other population were reared in captivity for about 30 generations (WGP-30). The spontaneous behavior of each of six groups of WGP-1 and WGP-30 and nine groups of DGP, each consisting of one adult male and two adult females, was analyzed quantitatively. Blood samples of the males were taken to determine cortisol, epinephrine, and norepinephrine concentrations. In addition, the exploratory behavior of 60-day-old male WGP-1, WGP-30, and DGP was investigated in an exploration apparatus. The domesticated animals displayed significantly less aggression, but significantly more sociopositive and male courtship behavior than their wild ancestors. In addition, DGP were much less attentive to their physical environment. Surprisingly, no behavioral difference was found between WGP-1 and WGP-30. Basal cortisol concentrations did not differ between wild and domestic guinea pigs. Catecholamine concentrations, however, as well as the challenge values of cortisol, were distinctly reduced in the DGP. WGP-1 and WGP-30 did not differ with respect to their endocrine stress responses. In the exploration apparatus both forms of wild cavies were much more explorative than the domestic animals. These data suggest that the long-term breeding and rearing of wild guinea pigs in captivity do not result in significant changes in behavior and hormonal stress responses. It appears to take much longer periods of time and artificial selection by humans to bring about characters of domestication in wild animals.

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.

Behavioural profiles are shaped by social experience: when, how and why

The comprehensive understanding of individual variation in behavioural profiles is a current and timely topic not only in behavioural ecology, but also in biopsychological and biomedical research. This study focuses on the shaping of behavioural profiles by the social environment in mammals. We review evidence that the shaping of behavioural profiles occurs from the prenatal phase through adolescence and beyond. We focus specifically on adolescence, a sensitive phase during which environmental stimuli have distinctive effects on the modulation of behavioural profiles. We discuss causation, in particular, how behavioural profiles are shaped by social stimuli through behavioural and neuroendocrine processes. We postulate a central role for maternal hormones during the prenatal phase, for maternal behaviour during lactation and for the interaction of testosterone and stress hormones during adolescence. We refer to evolutionary history and attempt to place developmental shaping into broader evolutionary historical trends. Finally, we address survival value. We argue that the shaping of behavioural profiles by environmental stimuli from the prenatal phase through adolescence represents an effective mechanism for repeated and rapid adaptation during the lifetime. Notably, the adolescent phase may provide a last chance for correction if the future environment deviates from that predicted in earlier phases.

A Comparison of Brain Gene Expression Levels in Domesticated and Wild Animals

Domestication has led to similar changes in morphology and behavior in several animal species, raising the question whether similarities between different domestication events also exist at the molecular level. We used mRNA sequencing to analyze genome-wide gene expression patterns in brain frontal cortex in three pairs of domesticated and wild species (dogs and wolves, pigs and wild boars, and domesticated and wild rabbits). We compared the expression differences with those between domesticated guinea pigs and a distant wild relative (Cavia aperea) as well as between two lines of rats selected for tameness or aggression towards humans. There were few gene expression differences between domesticated and wild dogs, pigs, and rabbits (30–75 genes (less than 1%) of expressed genes were differentially expressed), while guinea pigs and C. aperea differed more strongly. Almost no overlap was found between the genes with differential expression in the different domestication events. In addition, joint analyses of all domesticated and wild samples provided only suggestive evidence for the existence of a small group of genes that changed their expression in a similar fashion in different domesticated species. The most extreme of these shared expression changes include up-regulation in domesticates of SOX6 and PROM1, two modulators of brain development. There was almost no overlap between gene expression in domesticated animals and the tame and aggressive rats. However, two of the genes with the strongest expression differences between the rats (DLL3 and DHDH) were located in a genomic region associated with tameness and aggression, suggesting a role in influencing tameness. In summary, the majority of brain gene expression changes in domesticated animals are specific to the given domestication event, suggesting that the causative variants of behavioral domestication traits may likewise be different.

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.

Living in a Dangerous World: The Shaping of Behavioral Profile by Early Environment and 5-HTT Genotype

Anxiety and anxiety disorders are influenced by both, environmental and genetic factors. One genetic factor under scrutiny for anxiety disorders is the genetically encoded variation of the serotonin transporter (5-HTT). The aim of this study was to elucidate the effects of a threatening environment during early phases of life on anxiety-like (ANX) and exploratory behavior (EXP) in adult mice, varying in serotonin transporter (5-HTT) genotype. For this purpose, pregnant and lactating 5-HTT +/− dams were repeatedly exposed to olfactory cues of unfamiliar adult males by introducing small amounts of soiled bedding to their home cage. These stimuli signal the danger of infanticide and simulate a threatening environment. Control females were treated with neutral bedding. The offspring (5-HTT +/+, +/−, −/−) were examined for their ANX and EXP. The main results were: (1) a main effect of genotype existed, with 5-HTT −/− showing higher levels of ANX and lower levels of EXP than 5-HTT +/− and wildtypes. (2) When mothers had lived in a threatening environment, their offspring showed increased ANX and reduced EXP compared to controls. (3) These effects were most pronounced in 5-HTT −/− mice. By applying a new ecologically relevant paradigm we conclude: If 5-HTT +/− mothers live in a threatening environment during pregnancy and lactation, their offspring behavioral profile will, in principle, be shaped in an adaptive way preparing the young for an adverse environment. This process is, however, modulated by 5-HTT genotype, bearing the risk that individuals with impaired serotonergic neurotransmission (5-HTT −/−) will develop an exaggerated, potentially pathological level of anxiety from gene × environment interactions.

Sex-specific difference in social support—a study in female guinea pigs

In challenging situations, the male guinea pigs hormonal stress responses can be ameliorated by the presence of his female bonding partner. Such social support cannot be provided, however, by a female with whom the male is familiar but has no social ties. In this study, we investigated whether the same phenomenon also accounts for female guinea pigs. First, the spontaneous behaviour of 14 females was recorded in their home colonies to determine their male bonding partners. Then, a so-called challenge test was conducted with 22 females: they were placed into an unknown enclosure for 4 h either alone (n=8), or together with their bonding partner (n=7) or with a familiar male from the same colony, who was not their bonding partner (n=7). Immediately before as well as 1, 2 and 4 h after the beginning of the challenge test, blood samples were taken to determine cortisol levels (CORT). Further on, the behaviour was recorded during the first 2 h of the challenge test. Placing a female guinea pig into an unknown enclosure led to significantly increased CORT independently of whether she was tested alone or with a social partner. However, females that were tested together with their bonding partner showed significantly lower CORT than females tested alone. In females who were tested with a familiar male CORT was in between. The behaviour during the challenge tests reflected the magnitude of the stress response. Thus, also in female guinea pigs social support can be provided by social partners. In contrast to males, however, not only the bonding partner is able to reduce the females stress responses, but also a familiar conspecific, though in a less effective way.

Social status and day-to-day behaviour of male serotonin transporter knockout mice

Humans differing in the amount of serotonin transporter (5-HTT) are known to be differentially prone to neuropsychiatric disorders. Genetically modified mice eliciting abrogated transporter function display a number of corresponding phenotypic changes in behavioural tests. However, a characterisation of the effects of serotonergic malfunction on the day-to-day life is still missing. Yet, this is precisely what an animal model is needed for in order to be meaningful for translation into human anxiety disorders. Homozygous 5-HTT knockout mice, heterozygous 5-HTT mice, and wild-type controls were housed in groups of males of the same genotype in spacious and richly structured cages. This enriched environment allowed the animals to show a wide variety of spontaneous behavioural patterns quantified by a trained experimenter. Additionally the mice could emigrate from the cages through a tunnel and a water basin. The results revealed unaltered daily behaviour in heterozygous mice. In knockouts, however, reduced locomotion, increased socio-positive behaviour, and reduced aggressive behaviour were observed. Nevertheless, all groups showed a significant amount of aggressive behaviour and there were no differences regarding the establishment of dominance relationships, emigration, and the number of animals remaining in their groups. In a second step, pairs of heterozygous and wild-type males and pairs of knockout and wild-type males were brought together in order to assess their ability to obtain a dominant social position in a direct encounter. Heterozygous mice did not differ from wild-type mice but knockout mice were significantly inferior in obtaining the dominant position. In addition to confirming multiple effects of abolished 5-HTT function in a real life situation, this study supports the central role of the 5-HTT in the control of social interactions.

Social housing conditions around puberty determine later changes in plasma cortisol levels and behavior

A recent study found that male guinea pigs raised in large, mixed age/sex groups exhibited an unexpected suppression of their cortisol response at 4 mo of age. The present study examined the effect of social experience around the time of puberty on cortisol response suppression and social behavior at 4 mo of age. Males reared in large, mixed age/sex groups were either pair-housed with a female or moved to another large colony at 55 days of age. When tested at 4 mo, pair-housed males exhibited much higher levels of courtship and sexual behavior than did colony-housed males, and a shorter latency to begin courtship when with an unfamiliar adult female. In addition, pair-housed males showed much higher levels of agonistic behavior and a shorter latency to escalated aggression with an unfamiliar adult male. Pair-housed males also had lower basal cortisol concentrations and exhibited a greater increment in cortisol levels when isolated in a novel cage than did colony-housed males. Finally, pair-housed males showed a smaller increment in cortisol levels when with the stimulus female or male than when isolated, but colony-housed males did not. The findings demonstrate that social housing conditions around the time of puberty can have pervasive effects on social behavior and hypothalamic-pituitary-adrenal (HPA) activity in 4-mo-old males. Further, these findings are consistent with the notion that changes in HPA activity contribute to social behavior development beyond the time of sexual maturity.

Social interaction, testosterone, and stress responsiveness during adolescence

Adolescence is the transition from childhood to adulthood, including alterations in the endocrine systems, in neural circuitry and in behavior. During late adolescence, male guinea pigs living in large mixed-sex colonies exhibit a peculiar stress hyporesponsiveness compared with animals in other developmental stages or other housing conditions. In the present study, it was hypothesized that the interaction with conspecifics leads to an increase in testosterone (T) concentrations, which, in turn, reduces cortisol (C) responsiveness. To test this hypothesis, the stress response of pair- and colony-housed animals was compared with that of pair-housed animals that had limited opportunities to interact with unfamiliar animals of both sexes (social stimulation). The main findings were: (1) Social stimulation caused a significant acute increase in T levels. (2) T concentrations increased significantly in colony-housed males from early to late adolescence but not in the other groups. (3) The C response to a novel environment was significantly reduced in late adolescent colony-housed males compared with similarly aged pair-housed males; C responsiveness of socially stimulated males was intermediate. The present data support our general hypothesis that socially induced increases in T during adolescence might organize a reduction of the endocrine stress response.