Negrey Jacob D, Deschner Tobias, Langergraber Kevin E
School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, U.S.A.
Center for Evolution and Medicine, Arizona State University, Tempe, AZ, U.S.A.
Anim Behav. 2023 Aug;202:99-109. doi: 10.1016/j.anbehav.2023.06.004. Epub 2023 Jul 4.
Testosterone promotes mating effort, which involves intraspecific aggression for males of many species. Therefore, males with higher testosterone levels are often thought to be more aggressive. For mammals living in multimale groups, aggression is hypothesized to link male social status (i.e. dominance rank) and testosterone levels, given that high status predicts mating success and is acquired partly through aggressive intragroup competition. In male chimpanzees, , dominance rank has been repeatedly linked to interindividual variation in testosterone levels, but evidence directly linking interindividual variation in testosterone and aggression is lacking. In the present study, we test both aggression levels and lean muscle mass, as measured by urinary creatinine, as links between dominance rank and testosterone levels in a large sample of wild male chimpanzees. Multivariate analyses indicated that dominance rank was positively associated with total rates of intragroup aggression, average urinary testosterone levels and average urinary creatinine levels. Testosterone was positively associated with creatinine levels but negatively associated with total aggression rates. Furthermore, mediation analyses showed that testosterone levels facilitated an association between dominance rank and creatinine levels. Our results indicate that (1) adult male chimpanzees with higher average testosterone levels are often higher ranking but not more aggressive than males with lower testosterone and (2) lean muscle mass links dominance rank and testosterone levels in Ngogo males. We assert that aggression rates are insufficient to explain links between dominance rank and testosterone levels in male chimpanzees and that other social variables (e.g. male-male relationship quality) may regulate testosterone's links to aggression.
睾酮会促进交配行为，而这对许多物种的雄性来说都涉及种内攻击行为。因此，睾酮水平较高的雄性通常被认为更具攻击性。对于生活在多雄性群体中的哺乳动物而言，鉴于高社会地位预示着交配成功，且部分是通过群体内的攻击性竞争获得的，所以人们推测攻击行为将雄性的社会地位（即优势等级）与睾酮水平联系了起来。在雄性黑猩猩中，优势等级一直与个体间睾酮水平的差异存在关联，但缺乏直接将个体间睾酮差异与攻击性联系起来的证据。在本研究中，我们在一大群野生雄性黑猩猩样本中，测试了攻击水平以及用尿肌酐测量的瘦肌肉量，以此作为优势等级与睾酮水平之间的联系。多变量分析表明，优势等级与群体内攻击行为的总发生率、平均尿睾酮水平和平均尿肌酐水平呈正相关。睾酮与肌酐水平呈正相关，但与总攻击率呈负相关。此外，中介分析表明，睾酮水平促进了优势等级与肌酐水平之间的关联。我们的结果表明：（1）平均睾酮水平较高的成年雄性黑猩猩通常比睾酮水平较低者具有更高的等级，但并非更具攻击性；（2）在恩戈戈雄性黑猩猩中，瘦肌肉量将优势等级与睾酮水平联系了起来。我们认为，攻击率不足以解释雄性黑猩猩优势等级与睾酮水平之间的联系，其他社会变量（如雄性之间的关系质量）可能会调节睾酮与攻击行为之间的联系。
