Sensory ecology, morphology and behavior of Neotropical leaf-nosed bats

Abstract

Sensory systems perform fitness-relevant functions, and specialized sensory structures and behavior allow organisms to accomplish challenging tasks. Furthermore, echolocation is a highly complex sense, and in function, is influenced by morphology, phylogeny, behavior, and ecology. This dissertation seeks to deepen the knowledge of how elements of complex sensory systems evolved and how it is ecologically meaningful for an adaptive radiation of bats through coupling acoustics, ecological, morphological, and behavioral data in a phylogenetic context. In chapter 1, I quantify the echolocation calls of 21 genera and 35 species of Neotropical leaf-nosed bats (Phyllostomidae) to explore how dietary guild and body size contribute to echolocation call design and whether call parameters are adapted for prey detection, in a phylogenetic context. These analyses indicate that phyllostomids are more diverse in call design than previously thought and we suggest call structure may primarily be adapted for dealing with acoustic constraints of foraging in a dense habitat, as all phyllostomids are narrow-spaced gleaners and then secondarily specialized in certain species or dietary guilds, whereas phyllostomids vary in diet. This study gives insight to what possible mechanisms shape an organism’s sensory systems and how this influences species’ ecology. In chapter 2, I 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. 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. 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. Our results give insight into the morphological evolution of external sensory structures in bats, and highlight new links between morphological diversity and ecology. In chapter 3, we use the short-tailed fruit bat (Carollia: Phyllostomidae) to investigate behavioral adaptations that allow bats to find ripe fruit effectively, and to test relative importance of different senses in varying foraging scenarios. Within Neotropical ecosystems, short-tailed fruit bats (Carollia: Phyllostomidae) are abundant nocturnal frugivores, relying primarily on plants of the genus Piper as a food resource. Previous research has demonstrated Carollia employ olfaction and echolocation to locate Piper fruit, but it is unknown how their sensory use and foraging decisions are influenced by the complex diversity of chemical cues that fruiting plants produce. Using wild C. castanea and their preferred food, Piper scintillans, we conducted behavioral experiments to test two main hypotheses: (1) foraging decisions in C. castanea are primarily driven by ripe fruit scent and secondarily by vegetation scent, and (2) C. castanea re-weight their sensory inputs to account for available environmental cues, such that bats rely more heavily on echolocation in the absence of adequate scent cues. Our results suggest that C. castanea requires olfactory information and relies almost exclusively on ripe fruit scent to make foraging attempts. Ripe fruit scent is chemically distinct from vegetation scent in P. scintillans, with a greater abundance of β-caryophyllene, germacrene D and β-elemene, and a few unique compounds. Although variation in echolocation call parameters was independent of scent cue presence, bats emitted longer and more frequent echolocation calls in trials where no fruit scent was present. Altogether, these results highlight the adaptations, plasticity, and potential constraints in the sensory system of neotropical fruit bats.