Trends in Ecology & Evolution
The evolution of echolocation in bats
Section snippets
Echolocation and the diversity of bats
Bats are perhaps the most unusual and specialized of all mammals. Together with birds, they are the only extant vertebrates that are capable of powered flight. Bats have mastered the night skies largely by using echolocation (biosonar) to perceive their surroundings 1, 2. Indeed flight and echolocation are largely responsible for the global success, species richness and the ability of bats to exploit diverse niches (see Online Supplementary Material). How, when and why did bats evolve these
The position of bats in the mammalian phylogenetic tree
Questions concerning the evolutionary origin of bats have long intrigued biologists and resulted in many phylogenetic studies, the results of which have caused heated and lengthy debates 3, 4, 5, 6. The position of bats within Mammalia and the monophyly of the order itself were questions that dominated the 1980s and 1990s. Currently, there is overwhelming molecular and morphological evidence to support the monophyly of bats and, thus, a single origin of flight in mammals 7, 8, 9, 10. Recent
Morphological consensus
Before the dawn of molecular studies, bat systematics was dominated by palaeontological and morphological data. The most prominent morphological tree in the literature during the 1970s and 1980s was derived from the classification system of Miller [18] and was proposed by Smith [19] and Van Valen [20]. This tree was later modified by Koopman [21] and has been supported mainly by both large morphological datasets 17, 22 and supertree consensus studies [23]. The first major division in this tree
Emerging molecular consensus
The major structure of the bat phylogenetic tree based on molecular data (i.e. microbat paraphyly) was apparent with the first molecular phylogenetic studies. Based on transferrin immunological distance data, microbats were found to be paraphyletic; however, this result was initially reported as an artifact because it was so unexpected (E.D. Pierson, PhD dissertation, University of California, Berkeley, 1986). Whole genome DNA–DNA hybridization studies also supported the association of
Adaptive radiation and convergent evolution of echolocation calls in extant bats
One recent attempt to categorize bat echolocation calls considered three major types of echolocation call: broadband, narrowband and long constant frequency (CF) with Doppler-shift compensation (DSC) [35]. Other than differing in the pattern of frequency structure over time, bat signals also vary in their intensity and harmonic composition. Sophisticated methods for reconstructing bat flight tracks in three-dimensions 36, 37 have enabled the accurate localization of flying bats in relation to
Mapping call structure onto phylogeny highlights the presence of convergence
Attempts to map echolocation call structure onto phylogeny can be informative and have shown, for example, that the single clicks used by cave swiftlets have evolved from double clicks at least twice [64]. However, the large variation in call diversity within and between bat families renders the evolutionary reconstruction of signal types unclear (Figure 1). Overall, our perspective on the evolution of echolocation is clouded by the diversity and plasticity of signals that we see in extant
Conclusions and future directions
It is important that echolocation calls are recorded from some little studied species (e.g. those in Furipteridae, Thyropteridae and Natalidae) to complete our understanding of call diversity in bats. Recording the low-intensity echolocation calls produced by many of these bats in nature remains a challenge. Field studies are essential because familiarity with surroundings might influence how the bat uses echolocation under laboratory conditions [67]. Clearly, many of the diverse echolocation
Acknowledgements
We thank Brock Fenton and two anonymous referees for comments on the article.
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