Department of Experimental Psychology, Institute of Psychology, Av. Prof. Mello Moraes, 1721, University of São Paulo, São Paulo, Brazil.
Physiol Behav. 2011 Oct 24;104(5):948-54. doi: 10.1016/j.physbeh.2011.06.006. Epub 2011 Jun 16.
In many mammal species, reproduction is not shared equally among the members of a social unit. Even though reproductive skew seems unlikely in females of solitary species, this phenomenon could result from environmental factors. Although solitary in the wild, captive Syrian hamsters (Mesocricetus auratus) are generally housed in groups. We investigated whether social stress produces some degree of reproductive skew in this solitary species and whether female reproductive success varies as a function of social rank. To assess the physiological relationship between social stress and fertility, we monitored reproductive hormones and glucocorticoids of solitary and pair-housed females during pregnancy by means of recently established non-invasive methods for measuring hormone metabolites in the feces. The patterns of fecal progesterone, estrogen and glucocorticoid metabolites were similar to those found in blood and reported in the literature for pregnant hamsters. As expected, dominant females had higher breeding success than subordinate females. However the rate of reproductive failure was also very high among the singly housed females of our control group. The number of pups per litter, the average sex-ratio in each group, and the mean weight of pups did not differ significantly among groups. Glucocorticoid concentrations were unaffected by housing and social rank and the few differences between the endocrine profiles of singly- and pair-housed females are not sufficient to explain the observed difference in breeding success. It is likely that social isolation impairs reproduction in the same manner as subordination. Our findings suggest that social isolation of animals accustomed to group living was equally as disturbing as cohabitation with an unknown conspecific.
在许多哺乳动物物种中，繁殖并不是在一个社会单位的成员之间平等分配的。尽管在独居物种的雌性中，繁殖偏斜似乎不太可能，但这种现象可能是由环境因素引起的。尽管野生的叙利亚仓鼠（Mesocricetus auratus）是独居的，但在圈养环境中通常会被成群饲养。我们研究了社会压力是否会在这种独居物种中产生一定程度的繁殖偏斜，以及雌性的繁殖成功率是否会随着社会等级的变化而变化。为了评估社会压力和生育力之间的生理关系，我们通过最近建立的非侵入性方法，监测了独居和成对饲养的雌性在怀孕期间的生殖激素和糖皮质激素，这些方法可以测量粪便中的激素代谢物。粪便中孕激素、雌激素和糖皮质激素代谢物的模式与血液中的模式相似，也与文献中报道的怀孕仓鼠的模式相似。正如预期的那样，优势雌性的繁殖成功率高于从属雌性。然而，我们对照组中独居雌性的繁殖失败率也非常高。每窝幼崽的数量、每组的平均性别比和幼崽的平均体重在组间没有显著差异。糖皮质激素浓度不受饲养方式和社会等级的影响，独居和成对饲养的雌性之间的内分泌特征差异很小，不足以解释繁殖成功率的差异。很可能是社会隔离以与从属相同的方式损害繁殖。我们的研究结果表明，习惯于群居的动物的社会隔离与与未知同种动物同居一样令人不安。
