Noctilionoid bats comprise more than 200 species that span nearly the entire ecological diversity of land mammals. They range from tiny insectivores and nectarivores to large carnivores, and even vampire bats. This superfamily provides an unparalleled system for understanding how, when, and where bats evolved new diets, changed roosting habits and developed different kinds of echolocation. This project will use DNA sequences and comparison of morphological variations to reconstruct evolutionary relationships among these bats, including the fossils of >20 extinct species. Together with powerful methods for estimating the timing of historical events, this extensive fossil series will provide a timeline for investigating patterns and processes of ecological adaptation, speciation, and extinction across all species.
This project will mentor and train postgraduate, graduate, and undergraduate students in molecular and morphological laboratory techniques and research methods. The data generated during the course of this study -- including photographs and DNA sequences -- will be freely available to the public through existing databases and online repositories heavily used by educators at all levels. Extensive documentation of morphological data through Morphobank will facilitate future research. Finally, this project will provide a robust framework for exploring the mechanisms driving ecological and species diversity in a hyperdiverse group of mammals.
One of the biggest puzzles in evolution is why some groups of organisms evolve many species with different ecological adaptations while others are much less diverse. Noctilionoid bats are among the most ecologically diverse mammals on the planet. These bats comprise 200 living species, including species that are specialized to eat insects, other animals (including frogs, lizards, birds, and other bats), fish, fruit, nectar, pollen, and even blood (vampire bats). Over 20 extinct, ecologically distinctive noctilionoid bats are known, and their evolutionary relationships were largely unexplored. This project sought to determine how, why, and when this ecological diversity evolved through a series of studies of gene sequences, anatomy, fossils, and diet. We described 6 new living species of bats and 2 new fossil species, and generated the most complete evolutionary tree ever developed for noctilionoids using data from 8 genes. Because genetic data cannot be obtained from fossil species, we also included information on anatomy of the teeth in our analyses. Teeth fossilize well and provide information about diet, but they also change quickly over evolutionary time, and animals with similar diets independently evolve similar features. We developed new analytical methods to correct for these possible biases when inferring evolutionary trees. Using these methods, we were able to place fragmentary fossils in the evolutionary tree for noctilionoid bats, providing firm dates for many diversification events, and discovering for the first time the evolutionary relationships of key Miocene fossils from South America. Evolutionary analyses of diet, skull shape, and bite force showed that the evolution of a skull shape that enables a strong bite allowed New World Leaf-nosed bats (the most diverse family of noctilionoid bats) to expand their diet to hard fruits, leading to an explosive increase in species numbers. This new shape was a low, broad skull that allowed even small bats to produce the strong bites needed to eat hard fruits. Since there were no nocturnal competitors for this resource when the new skull shape evolved, we propose the access to these new plant resources constitutes a new adaptive zone—a set of ecological resources that populations can move into through evolutionary adaptation. As soon as this new skull shape evolved, about 15 million years ago, many new species evolved rapidly to include more and more fruits in their diets. Subsequent analyses of the evolution of the skulls of New World Leaf-nosed bats coupled with an engineering model that was able to mimic skull shape and estimate physical properties revealed three distinct skull types. Each of these were defined by how well they could transfer mechanical force, and corresponding to adaptive zones determined by nectar, animals and most fruits, and hard fruits. Additional studies of genes involved in sensory systems showed that there are distinctive patterns of olfactory receptors (responsible for the sense of smell) among bats that specialize in eating fruit. The distinctive pattern has arisen twice, once among New World Leaf-nosed bats that feed primarily on figs, and another among Old World Fruit bats. Although the kinds of olfactory receptors involved are similar, the distinctive repertoire has arisen in different ways. This suggests different, independent mechanisms shaping this part of the genome in response to the challenge of finding fruit in the twilight and dark. Our findings illustrate the impact of the evolution of new traits in shaping the diversity of ecological functions and species on Earth. This project contributed to the research training of many young scientists including 7 high school students, 12 undergraduates, 6 graduate students, and 2 postdoctoral researchers. In addition, several project participants helped to design and run a day-long digital-learning program for high school students at the American Museum of Natural History.
