Endocrinology Laboratory, German Primate Center, Leibniz Institute for Primate Research, Göttingen, Germany.
Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
Elife. 2022 Aug 30;11:e77227. doi: 10.7554/eLife.77227.
In animals with slow ontogeny and long-term maternal investment, immatures are likely to experience the birth of a younger sibling before reaching maturity. In these species, the birth of a sibling marks a major event in an offspring's early life as the older siblings experience a decrease in maternal support. The transition to siblinghood (TTS) is often considered to be stressful for the older offspring, but physiological evidence is lacking. To explore the TTS in wild bonobos, we investigated physiological changes in urinary cortisol (stress response), neopterin (cell-mediated immunity), and total triiodothyronine (T3, metabolic rate), as well as changes in behaviors that reflect the mother-offspring relationship. Following a sibling's birth, urinary cortisol levels of the older offspring increased fivefold, independent of their age, and remained elevated for 7 months. The cortisol level increase was associated with declining neopterin levels; however, T3 levels and behavioral measures did not change. Our results indicate that the TTS is accompanied by elevated cortisol levels and that this change does not coincide with nutritional weaning and attainment of physical independence. Our results suggest that bonobos and humans experience TTS in similar ways and that this developmental event may have emerged in the last common ancestor.
在发育缓慢且母体长期投入的动物中，幼体在成熟之前很可能会经历更年幼的兄弟姐妹的出生。在这些物种中，兄弟姐妹的出生标志着幼体早期生活中的一个重大事件，因为年长的兄弟姐妹会经历母体支持的减少。向兄弟姐妹关系的转变（TTS）通常被认为对年长的后代是有压力的，但缺乏生理证据。为了探索野生倭黑猩猩的 TTS，我们研究了尿液皮质醇（应激反应）、新蝶呤（细胞介导的免疫）和总三碘甲状腺原氨酸（T3，代谢率）的生理变化，以及反映母子关系的行为变化。在一个兄弟姐妹出生后，年长后代的尿液皮质醇水平增加了五倍，与他们的年龄无关，并持续升高了 7 个月。皮质醇水平的升高与新蝶呤水平的下降有关；然而，T3 水平和行为测量没有变化。我们的结果表明，TTS 伴随着皮质醇水平的升高，这种变化与营养断奶和获得身体独立性不一致。我们的结果表明，倭黑猩猩和人类以相似的方式经历 TTS，并且这种发育事件可能出现在最近的共同祖先中。
