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

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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.