Emmerson Michael G, Spencer Karen A
University of St Andrews, School of Psychology & Neuroscience, St Mary's Quad, South Street, St Andrews, Fife KY16 9JP, Scotland, United Kingdom.
Gen Comp Endocrinol. 2018 Jan 15;256:71-79. doi: 10.1016/j.ygcen.2017.07.008. Epub 2017 Jul 8.
Adolescent social interactions can have long-term effects on physiological responses to stressors in later-life. A larger adolescent group size can result in higher stressor-induced secretion of glucocorticoids in adulthood. The effect may be due to a socially-mediated modulation of gonadal hormones, e.g. testosterone. However, group size (number of animals) has been conflated with social density (space per animal). Therefore it is hard to determine the mechanisms through which adolescent group size can affect the stress response. The current study aimed to tease apart the effects of group size and social density during adolescence on the physiological stress response and gonadal hormone levels in adulthood. Adolescent zebra finches were housed in groups varying in size (2 vs. 5 birds per cage) and density (0.03m vs. 0.06m per bird) during early adolescence (day 40-60). Density was only manipulated in birds raised in groups of five. Glucocorticoid concentration secreted in response to a standard capture and restraint stressor was quantified in adolescence (day 55±1) and adulthood (day 100+). Basal gonadal hormone concentrations (male testosterone, female estradiol) were also quantified in adulthood. Female birds housed in larger groups, independent of social density, secreted a higher glucocorticoid concentration 45min into restraint regardless of age, and had higher peak glucocorticoid concentration in adulthood. Adult gonadal hormone concentrations were not affected by group size or density. Our results suggest that group size, not density, is a social condition that influences the development of the endocrine response to stressors in female zebra finches, and that these effects persist into adulthood. The findings have clear relevance to the social housing conditions necessary for optimal welfare in captive animals, but also elucidate the role of social rearing conditions in the emergence of responses to stressors that may persist across the lifespan and affect fitness of animals in wild populations.
青少年时期的社会互动会对其成年后对应激源的生理反应产生长期影响。青少年群体规模越大，成年后应激源诱导的糖皮质激素分泌就越高。这种影响可能是由于社会介导的性腺激素调节，例如睾酮。然而，群体规模（动物数量）与社会密度（每只动物的空间）一直被混淆。因此，很难确定青少年群体规模影响应激反应的机制。当前的研究旨在区分青少年时期群体规模和社会密度对成年后生理应激反应和性腺激素水平的影响。在青少年早期（第40 - 60天），将青少年斑胸草雀按不同的群体规模（每个笼子2只或5只鸟）和密度（每只鸟0.03米或0.06米）饲养。密度仅在五只一组饲养的鸟中进行了调整。在青少年期（第55±1天）和成年期（第100 +天），对因标准捕捉和束缚应激源而分泌的糖皮质激素浓度进行了量化。成年期还对基础性腺激素浓度（雄性睾酮、雌性雌二醇）进行了量化。无论年龄大小，饲养在较大群体中的雌性鸟，无论社会密度如何，在束缚45分钟时分泌的糖皮质激素浓度更高，并且成年期糖皮质激素峰值浓度也更高。成年性腺激素浓度不受群体规模或密度的影响。我们的研究结果表明，群体规模而非密度是影响雌性斑胸草雀对应激源内分泌反应发展的社会条件，并且这些影响会持续到成年期。这些发现对于圈养动物最佳福利所需的社会饲养条件具有明确的相关性，同时也阐明了社会饲养条件在应激源反应出现中的作用，这些反应可能会持续一生并影响野生种群中动物的适应性。
