Morphological Diversity in the Sensory System of Phyllostomid Bats: Implications for Acoustic and Dietary Ecology

1. Sensory systems perform fitness-relevant functions, and specialized sensory structures allow organisms to accomplish challenging tasks. However, broad comparative analyses of sensory morphologies and their performance are lacking for diverse mammalian radiations. 2. Neotropical leaf-nosed bats (Phyllostomidae) are one of the most ecologically diverse mammal groups; including a wide range of diets and foraging behaviours, and extreme morphological variation in external sensory structures used in echolocation (nose leaf and pinnae). 3. We coupled 3D geometric morphometrics and acoustic field recordings under a phylogenetic framework to investigate the mechanisms underlying the diversification of external sensory morphologies in phyllostomids, and explored the potential implications of sensory morphological diversity to functional outputs and dietary ecology. 4. We found that the nose leaf consists of two evolutionary modules-spear and horseshoe-suggesting that modularity enabled morphological and functional diversification of this structure. 5. We found a significant association between some aspects of nose leaf shape and maximum frequency and bandwidth of echolocation calls, but not between pinnae shape and echolocation call parameters. This may be explained by the use of multiple sensory modes across phyllostomids and plasticity of some echolocation call parameters. 6. Species with different diets significantly differed in nose leaf shape, specifically in spear breadth, presence of a midrib, and cupping and anterior rotation of the horseshoe. This may relate to different levels of prey type specificity within each diet. Pinnae shape significantly differed between species that consume nonmobile, non-evasive prey (broad rounded, cupped pinnae) and mobile, evasive prey (flattened pinnae with a sharp tapering apex). This may reflect the use of different sound cues to detect prey. 7. Our results give insight into the morphological evolution of external sensory structures in bats, and highlight new links between morphological diversity and ecology.