Department Foundational Biomedical Sciences, Touro University California, 1310 Club Drive, Vallejo, CA 94592, USA.
Department of Anthropology, University of Arkansas, Old Main 330, Fayetteville, AR 72701, USA.
J Hum Evol. 2024 Dec;197:103601. doi: 10.1016/j.jhevol.2024.103601. Epub 2024 Nov 4.
In primates and other mammals, the capacity to generate a wide maximum jaw gape is an important performance variable related to both feeding and nonfeeding oral behaviors, such as canine gape display and clearing the canines for use as weapons during aggressive encounters. Across sexually dimorphic catarrhine primates, gape is significantly correlated with canine height and with musculoskeletal features that facilitate wide gapes. Given the importance of canine gape behaviors in males as part of intrasexual competition for females, functional relationships between gape, canine height, and musculoskeletal morphology can be predicted to differ between the sexes. We test this hypothesis by investigating sex-specific relationships among these variables in a maximum sample of 32 cercopithecoid species. Using phylogenetic least squares regression, we found that of 18 predicted relationships, 16 of the 18 (89%) were significant in males, whereas only six (33%) were significant in females. Moreover, 15 of the 18 correlations were higher-10 of the 18 significantly higher-in males than in females. Males, but not females, showed strong and significant positive allometry of fiber lengths, indicating that increase in male jaw length is accompanied by allometric increases in the capacity for muscle stretch. While males and females showed significant negative allometry for muscle leverage, only males showed significant negative allometry of muscle leverage relative to jaw gape and canine height. Collectively, these results provide support for the hypothesis that as selection acted to increase relative canine height in male cercopithecoids, one change was an allometric increase in relative maximum jaw gape, along with allometric increases in musculoskeletal morphologies that facilitate gape. Lastly, if gape and canine display/clearance are key targets of selection on masticatory morphology in male cercopithecoids, then cercopithecoid monkeys such as macaques, baboons, and sooty mangabeys may have diminished utility as models for drawing paleobiological inferences from musculoskeletal morphology about feeding behavior and diet in fossil hominins.
在灵长类动物和其他哺乳动物中，产生最大张口幅度的能力是一个重要的表现变量，与进食和非进食口腔行为有关，如犬齿张口展示和在攻击性相遇中清除犬齿以用作武器。在两性异形的猫科灵长类动物中，张口与犬齿高度以及有助于张口的肌肉骨骼特征显著相关。鉴于犬齿张口行为在雄性中作为争夺雌性的内部竞争的重要性，张口、犬齿高度和肌肉骨骼形态之间的功能关系可以预测在两性之间存在差异。我们通过调查 32 种长尾猴科物种的最大样本中这些变量之间的性别特异性关系来检验这一假设。使用系统发育最小二乘法回归，我们发现在 18 个预测关系中，16 个（89%）在雄性中具有统计学意义，而在雌性中只有 6 个（33%）具有统计学意义。此外，在雄性中，18 个相关性中有 15 个更高-18 个中有 10 个具有统计学意义-高于雌性。雄性，但不是雌性，表现出纤维长度的强烈和显著的正异速生长，这表明雄性下颚长度的增加伴随着肌肉伸展能力的异速生长增加。虽然雄性和雌性的肌肉杠杆呈显著的负异速生长，但只有雄性的肌肉杠杆相对于张口和犬齿高度呈显著的负异速生长。总的来说，这些结果支持了这样一种假设，即随着选择作用于增加雄性长尾猴科动物的相对犬齿高度，一个变化是相对最大张口幅度的异速生长增加，同时还有促进张口的肌肉骨骼形态的异速生长增加。最后，如果张口和犬齿展示/清除是雄性长尾猴科动物咀嚼形态选择的关键目标，那么猕猴、狒狒和黑眉长尾猴等长尾猴科动物作为从肌肉骨骼形态推断化石人类的进食行为和饮食的模型，其效用可能会降低。
