Background Genetic and ecological factors influence morphology, and morphology is compatible with function. The morphology and bite performance of skulls of bats show a number of characteristic feeding adaptations. The great evening bat, Ia io (Thomas, 1902), eats both insects and birds (Thabah et al. J Mammal 88: 728-735, 2007), and as such, it is considered to represent a case of dietary niche expansion from insects to birds. How the skull morphology or bite force in I. io are related to the expanded diet (that is, birds) remains unknown. We used three-dimensional (3D) geometry of the skulls and measurements of bite force and diets from I. io and 13 other species of sympatric or closely related bat species to investigate the characteristics and the correlation of skull morphology and bite force to diets. Results Significant differences in skull morphology and bite force among species and diets were observed in this study. Similar to the carnivorous bats, bird-eaters (I. io) differed significantly from insectivorous bats; I. io had a larger skull size, taller crania, wider zygomatic arches, shorter but robust mandibles, and larger bite force than the insectivores. The skull morphology of bats was significantly associated with bite force whether controlling for phylogeny or not, but no significant correlations were found between diets and the skulls, or between diets and residual bite force, after controlling for phylogeny. Conclusions These results indicated that skull morphology was independent of diet, and phylogeny had a greater impact on skull morphology than diet in these species. The changes in skull size and morphology have led to variation in bite force, and finally different bat species feeding on different foods. In conclusion, I. io has a larger skull size, robust mandibles, shortened dentitions, longer coronoid processes, expanded angular processes, low condyles, and taller cranial sagittal crests, and wider zygomatic arches that provide this species with mechanical advantages; their greater bite force may help them use larger and hard-bodied birds as a dietary component.

中文翻译：

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食鸟蝙蝠（Ia io; Vespertilionidae）头骨形态和咬合力的相关性。

背景遗传和生态因素影响形态，形态与功能相适应。蝙蝠头骨的形态和咬合表现显示出许多特征性的摄食适应。夜蝠 Ia io (Thomas, 1902) 既吃昆虫又吃鸟 (Thabah et al. J Mammal 88: 728-735, 2007)，因此，它被认为代表了从昆虫到鸟类。I.io 中的头骨形态或咬合力如何与扩展饮食（即鸟类）相关仍然未知。我们使用头骨的三维 (3D) 几何形状以及 I. io 和其他 13 种同域或密切相关的蝙蝠物种的咬合力和饮食测量来研究头骨形态和咬合力与饮食的特征和相关性。结果在本研究中观察到物种和饮食之间的颅骨形态和咬合力存在显着差异。与食肉蝙蝠相似，食鸟者 (I. io) 与食虫蝙蝠有显着差异；与食虫动物相比，I.io 的头骨更大，颅骨更高，颧弓更宽，下颌骨更短但结实，咬合力更大。蝙蝠的头骨形态与是否控制系统发育的咬合力显着相关，但在控制系统发育后，饮食与头骨之间或饮食与残余咬合力之间没有显着相关性。结论这些结果表明，颅骨形态与饮食无关，系统发育对这些物种的颅骨形态的影响大于饮食。头骨大小和形态的变化导致咬合力的变化，最终导致不同的蝙蝠物种以不同的食物为食。总之，I.io 具有较大的颅骨尺寸、坚固的下颌骨、较短的牙列、较长的冠状突、扩大的角突、较低的髁突、较高的颅矢状嵴和较宽的颧弓，为该物种提供了机械优势；它们更大的咬合力可能有助于它们使用更大、更强壮的鸟类作为饮食成分。