A novel nectar drinking adaptation: Function and morphology of the grooved tongue of nectar-feeding Neotropical lonchophylline bats

以花蜜为食的形态和行为上的专门化主要存在于昆虫中，然而，也有一些专门化的访花哺乳动物。在新热带叶鼻蝙蝠（Phyllostomidae）中，舌鼻蝠亚科（舌鼻蝠亚科）和长鼻蝠亚科（Lonchophyllinae）显示出独立进化的食蜜适应。然而，两者都有舌头的伸长，舌头的形态，以及——正如我们最近所展示的——两个亚科之间的饮酒行为明显不同。舌蝠有一个刷状的舌尖，舌尖上细长的乳头有助于吸收花蜜。这些蝙蝠在采食花朵时，以一种正弦动作反复地伸展和收回舌头。相比之下，长鼻舌没有这些毛发状的乳头状突起，但有两个横向纵向凹槽。最近，我们发现lonchophylline蝙蝠在赏花时伸出舌头，将舌尖浸入花蜜中，然后保持这个姿势，不缩回，直到喝完，而花蜜则从凹槽中上升到嘴里。这种饮用模式的潜在机制与迄今为止描述的花蜜摄取机制都不相符。我们假设花蜜是通过毛细血管力和蠕动肌肉运动的结合在凹槽内运输的。我们想研究这种独特的饮酒方式的生理基础和潜在的生态后果。在生理层面上，我们首先想通过进行微CT（高分辨率x射线计算机断层扫描）和SEM（扫描电子显微镜）成像来收集不同大小lonchophylline蝙蝠舌沟的形态学数据。获得的数据将允许开发基于Hagen-Poiseuille方程的假设流体动力学模型，其中流体流动仅由毛细管作用驱动。此外，我们计划对巴拿马和秘鲁的lonchophylline蝙蝠进行行为实验，包括通过高速视频进行运动分析。通过将我们的模型与lonchophyline蝙蝠对改变粘度和表面张力的人工花蜜的饮用性能的经验数据进行比较，我们将确定活性机制对花蜜摄取的相对贡献。为了评估生态后果，我们将分析两个亚科之间潜在的资源分配机制。使用具有不同花蜜呈现的3d打印人造花朵，我们将比较亚科的进食性能，使用我们在乌尔姆大学的殖民地的舌蝠和野外的lonchophylline蝙蝠。该项目提供了独特的机会来了解一种新的自然流体输送系统，探索觅食适应如何影响资源分配，从而影响采蜜蝙蝠物种的群落生态，甚至可能对开发仿生微泵（例如用于医疗应用）感兴趣。

Morphological and behavioural specialisations on a nectar diet are mostly found in insects, however, there are also a few specialized flower-visiting mammals. Within the Neotropical leaf-nosed bats (Phyllostomidae), the two subfamilies Glossophaginae and the Lonchophyllinae show independently evolved adaptations towards nectarivory. Both share an elongation of the tongue, however, tongue morphology, and - as we could recently show - drinking behaviour differ distinctly between the subfamilies. Glossophagine bats have a brush-tipped tongue, where elongated papillae on the tip of the tongue aid in nectar uptake. These bats extend and withdraw their tongue repeatedly in a sinusoidal lapping movement when feeding at a flower. In contrast, the lonchophylline tongue lacks these hair-like papillae but shows two lateral longitudinal grooves. Recently we found that lonchophylline bats extend during a flower visit their tongue, immerse the tip into the nectar and then maintain this position without retractions to the end of the drinking bout, while nectar rises within the grooves into the mouth. The underlying mechanism of this drinking mode fits none of the so far described nectar uptake mechanisms. We hypothesised that nectar is transported within grooves through a combination of capillary forces and peristaltic muscle movements. We want to investigate the physiological base and potential ecological consequences of this unique drinking mode. On a physiological level, we first want to collect morphological data on the tongue grooves of different sized lonchophylline bat species by performing µCT (high resolution X-ray computed tomography) and SEM (scanning electron microscope) imaging. The obtained data will allow to develop a hypothetical fluid dynamic model based on the Hagen-Poiseuille equation, where fluid flow is just driven by capillarity. Additionally, we plan to perform behavioural experiments with lonchophylline bat species in Panama and Peru, including a motion analysis through high speed video. By comparing our model to empirical data on drinking performance of lonchophylline bats on artificial nectar with modified viscosity and surface tension we will determine the relative contribution of active mechanisms to nectar uptake. For assessing ecological consequences, we will analyse potential resource partitioning mechanisms between both subfamilies. Using 3D-printed artificial flowers with different nectar presentation we will compare the feeding performance of the subfamilies, using glossophagine bats from our colony at the Ulm University and lonchophylline bats in the field. The project provides unique opportunities to understand a novel, natural fluid transport system, to explore how foraging adaptations may affect resource partitioning and thus community ecology of nectar-feeding bat species, and might even be of interest for developing biomimetic micro pumps, e.g., for medical applications.