Table_1_Phylogenetic Patterns in Mouth Posture and Echolocation Emission Behavior of Phyllostomid Bats.XLSX

While phyllostomid bats show an impressive range of feeding habits, most of them emit highly similar echolocation calls. Due to the presence of an often prominent noseleaf, it has long been assumed that all phyllostomids emit echolocation calls exclusively through the nostrils rather than through the mouth. However, photo evidence documents also phyllostomid bats flying with an opened mouth. We hypothesized that all phyllostomid species emit echolocation calls only through the nostrils and therefore fly consistently with a closed mouth, and that observations of an open mouth should be a rare and random behavior among individuals and species. Using a high-speed camera and standardized conditions in a flight cage, we screened 40 phyllostomid species. Behavior varied distinctly among the species and mouth posture shows a significant phylogenetic signal. Bats of the frugivorous subfamilies Rhinophyllinae and Carolliinae, the nectarivorous subfamilies Glossophaginae and Lonchophyllinae, and the sanguivorous subfamily Desmodontinae all flew consistently with open mouths. So did the animalivorous subfamilies Glyphonycterinae, Micronycterinae and Phyllostominae, with the notable exception of species in the omnivorous genus Phyllostomus, which consistently flew with mouths closed. Bats from the frugivorous subfamily Stenodermatinae also flew exclusively with closed mouths with the single exception of the genus Sturnira, which is the sister clade to all other stenodermatine species. Further, head position angles differed significantly between bats echolocating with their mouth closed and those echolocating with their mouths opened, with closed-mouth phyllostomids pointing only the nostrils in the direction of flight and open-mouth phyllostomids pointing both the nostrils and mouth gape in the direction of flight. Ancestral trait reconstruction showed that the open mouth mode is the ancestral state within the Phyllostomidae. Based on the observed behavioral differences, we suggest that phyllostomid bats are not all nasal emitters as previously thought and discuss possible reasons. Further experiments, such as selectively obstructing sound emission through nostrils or mouth, respectively, will be necessary to clarify the actual source, plasticity and ecological relevance of sound emission of phyllostomid bats flying with their mouths open.

尽管叶口蝠科（Phyllostomidae）蝙蝠展现出极为多样的取食习性，但其绝大多数类群的回声定位叫声却高度相似。由于多数类群具有显著的鼻叶（noseleaf），长期以来学界普遍认为，所有叶口蝠科蝙蝠均仅通过鼻孔而非口腔发射回声定位叫声。然而，影像证据显示，部分叶口蝠科蝙蝠会以张开的口腔飞行。我们曾提出两项假说：其一，所有叶口蝠科蝙蝠均仅通过鼻孔发射回声定位叫声，因此飞行时始终保持口腔闭合；其二，观察到口腔张开的情况应仅为个体与物种间罕见且随机的行为。本研究借助高速摄像机，在标准化飞行笼环境中对40个叶口蝠科物种的飞行姿态进行了筛查。结果显示，不同物种间的口腔姿态存在显著差异，且口腔开合状态具有显著的系统发育信号。食果性的鼻叶蝠亚科（Rhinophyllinae）、卡罗利蝠亚科（Carolliinae），食蜜性的长舌蝠亚科（Glossophaginae）、尖叶长舌蝠亚科（Lonchophyllinae），以及吸血性的吸血蝠亚科（Desmodontinae）蝙蝠，飞行时均始终保持口腔张开。食虫性的纤毛蝠亚科（Glyphonycterinae）、微叶口蝠亚科（Micronycterinae）以及叶口蝠亚科（Phyllostominae）的类群亦是如此，但杂食性的叶口蝠属（Phyllostomus）物种是显著例外，它们飞行时始终保持口腔闭合。食果性的狭叶蝠亚科（Stenodermatinae）蝙蝠同样几乎全程以闭合口腔飞行，仅有的例外是食果蝠属（Sturnira）——该类群是其余所有狭叶蝠亚科物种的姊妹演化支。进一步分析显示，以闭合口腔发射回声定位叫声的蝙蝠，与以张开口腔发射叫声的蝙蝠，其头部指向角度存在显著差异：保持口腔闭合的叶口蝠科蝙蝠，仅将鼻孔朝向飞行方向；而口腔张开的类群，则同时将鼻孔与口腔裂隙朝向飞行方向。祖先性状重建结果表明，口腔张开的发声模式为叶口蝠科的祖征。基于上述行为差异，我们提出：叶口蝠科蝙蝠并非如以往研究所认为的那样，均为鼻腔发声类群，并对可能的成因进行了讨论。后续还需开展针对性实验，例如分别选择性阻塞鼻孔与口腔的声音发射通路，以明确叶口蝠科蝙蝠张开口腔飞行时的声音发射实际来源、发声可塑性及其生态相关性。