Beyond size – morphological predictors of bite force in a diverse insectivorous bat assemblage from Malaysia

1. Bite force is used to investigate feeding performance in a variety of vertebrates. In all taxa studied, bite force is strongly correlated with body and head size. Studies of bite force in bats have largely centred on neotropical species with a particular focus on species that maximize dietary differences. Little is known about the bite force of bats from the Old World tropics, nor of variation in bite force within diverse assemblages of obligate insectivores. Moreover, factors other than size are poorly known but may be important in driving interspecific differences in bite force, and thereby diet. 2. Here, we examine the correlation between morphological variation and bite force of 35 species of insectivorous bats from a single palaeotropical assemblage. We confirmed the overall relationship between size and bite force across species, but found that bite force is predicted more strongly by head length than body mass or forearm length. 3. From the combined action of jaw muscles and muscle-bone mechanisms, bats generate a mechanical advantage that creates pressure during biting. We calculated the size-independent mechanical advantage for each of five mandible lever systems (three delineated by the temporalis muscle and two delineated by the masseter muscle) operating through three function points (molar, canine, and incisor). Size-independent mechanical advantage of the suprazygomatic portion of the temporalis muscle at the molar function point was the only significant predictor of size-independent maximum bite force across all species. 4. Within families, the size-independent mechanical advantage of the superficial portion of the masseter muscle plays a significant role in predicting size-independent maximum bite force in both the Rhinolophidae and Vespertilionidae. For the family Hipposideridae, however, size-independent mechanical advantage showed no role in predicting size-independent maximum bite force, suggesting that size really matters in predicting the maximum bite force capacity for this family.

1. 咬合力（bite force）被广泛用于探究多种脊椎动物的摄食性能。在所有已研究的类群（taxa）中，咬合力均与体型及头部大小呈显著正相关。目前针对蝙蝠咬合力的研究多集中于新热带区物种，且重点聚焦于食性差异最大化的类群。学界对旧世界热带区蝙蝠的咬合力，以及多样专性食虫类群内部的咬合力变异情况仍知之甚少。此外，除体型外的其他驱动种间咬合力差异、进而影响食性的因素，也尚未得到充分解析。
2. 本研究针对来自单一古热带类群的35种食虫蝙蝠，探究了形态变异与咬合力之间的相关性。我们验证了跨物种的体型与咬合力间的整体相关性，但发现头部长度对咬合力的预测能力显著强于体质量或前臂长度。
3. 依托颌肌与肌骨机制的协同作用，蝙蝠可在咬合过程中产生具备机械优势的压力。我们针对5个下颌杠杆系统（其中3个由颞肌（temporalis muscle）调控、2个由咬肌（masseter muscle）调控），在三个功能位点（臼齿、犬齿与门齿）分别计算了体型独立的机械优势值。结果显示，仅颧上颞肌部分在臼齿功能位点的体型独立机械优势，可显著预测所有物种的体型独立最大咬合力。
4. 在科级分类单元内，浅部咬肌的体型独立机械优势，可显著预测菊头蝠科（Rhinolophidae）与蝙蝠科（Vespertilionidae）的体型独立最大咬合力。但对于蹄蝠科（Hipposideridae）而言，体型独立的机械优势无法有效预测其最大咬合力，这表明体型确实是该类群最大咬合力能力的核心预测因子。