Data from: The evolution of bat vestibular systems in the face of potential antagonistic selection pressures for flight and echolocation

The vestibular system maintains the body’s sense of balance and, therefore, was probably subject to strong selection during evolutionary transitions in locomotion. Among mammals, bats possess unique traits that place unusual demands on their vestibular systems. First, bats are capable of powered flight, which in birds is associated with enlarged semicircular canals. Second, many bats have enlarged cochleae associated with echolocation, and both cochleae and semicircular canals share a space within the petrosal bone. To determine how bat vestibular systems have evolved in the face of these pressures, we used micro-CT scans to compare canal morphology across species with contrasting flight and echolocation capabilities. We found no increase in canal radius in bats associated with the acquisition of powered flight, but canal radius did correlate with body mass in bat species from the suborder Yangochiroptera, and also in non-echolocating Old World fruit bats from the suborder Yinpterochiroptera. No such trend was seen in members of the Yinpterochiroptera that use laryngeal echolocation, although canal radius was associated with wing-tip roundedness in this group. We also found that the vestibular system scaled with cochlea size, although the relationship differed in species that use constant frequency echolocation. Across all bats, the shape of the anterior and lateral canals was associated with large cochlea size and small body size respectively, suggesting differential spatial constraints on each canal depending on its orientation within the skull. Thus in many echolocating bats, it seems that the combination of small body size and enlarged cochlea together act as a principal force on the vestibular system. The two main groups of echolocating bats displayed different canal morphologies, in terms of size and shape in relation to body mass and cochlear size, thus suggesting independent evolutionary pathways and offering tentative support for multiple acquisitions of echolocation.前庭系统（vestibular system）负责维持机体的平衡感知，因此在运动方式的演化过渡过程中大概率受到了强烈的选择压力。在哺乳动物类群中，蝙蝠拥有独特的性状，这对其前庭系统提出了非同寻常的要求。其一，蝙蝠具备动力飞行（powered flight）能力，而在鸟类中，该能力与扩大的半规管（semicircular canals）密切相关；其二，多数蝙蝠拥有与回声定位（echolocation）相关联的扩大耳蜗（cochleae），且耳蜗与半规管在岩骨（petrosal bone）中共享空间。为探究蝙蝠前庭系统在上述多重压力下的演化规律，我们借助显微CT（micro-CT）扫描技术，对比了飞行与回声定位能力存在差异的蝙蝠物种的半规管形态。研究结果显示，与动力飞行能力获得相关的半规管半径并未出现显著增大；但在阳翼手亚目（Yangochiroptera）蝙蝠，以及隶属于阴翼手亚目（Yinpterochiroptera）的非回声定位旧大陆果蝠中，半规管半径确实与体重呈显著正相关。而在使用喉部回声定位的阴翼手亚目类群中并未观察到此类关联模式，不过该类群的半规管半径与翼尖圆度存在显著相关性。我们还发现，前庭系统与耳蜗大小存在缩放关系，但在使用恒频回声定位（constant frequency echolocation）的物种中，这一关系存在显著差异。在所有蝙蝠类群中，前半规管与外侧半规管的形态分别与较大的耳蜗尺寸和较小的体重相关，这表明每个半规管因其在颅骨内的朝向不同，受到的空间约束存在差异。因此在多数回声定位蝙蝠中，小型体型与扩大耳蜗的共同作用似乎构成了驱动前庭系统演化的核心动力。两类主要的回声定位蝙蝠类群在半规管大小、形态与体重、耳蜗大小的关联模式上存在显著差异，这暗示二者具备各自独立的演化路径，并为回声定位的多次独立起源提供了初步支撑。