Collen, AL; (2012) The evolution of echolocation in bats: a comparative approach. Doctoral thesis , UCL (University College London).

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Abstract

The evolutionary history of echolocation in bats is poorly understood, as fossils provide little direct evidence, and most studies into echolocation have taken an ecological approach. Bats use a wide variety of echolocation call structures despite facing similar sensory challenges, and it is not clear how and why these echolocation call types evolved, or what impact they have on other aspects of the evolution of bats. Here, I use phylogenetic comparative methods and newly-collated echolocation call data from 410 species in 120 genera and all 19 families to investigate the origination and evolution of echolocation in bats (Chiroptera). I construct an updated phylogenetic supertree of the bats using source phylogenies from the literature between 1970 and 2009. I ask three main questions: (1) Are echolocation call structures really a product of present-day ecological conditions, or are they much more constrained by evolutionary history than is currently thought? (2) What did the first echolocation calls sound like? (3) Are echolocation calls ‘key innovations’ that promote diversification? I found that early divergences and subsequent constraints in evolutionary history have resulted in a greater variety of bat call structures than appear to be functionally necessary. The structure of the first echolocation calls was predicted to be short duration, multi-harmonic, and narrowband, suggesting that the proto-bat was a slow and manoeuvrable flier with an opportunistic and omnivorous diet, and may have used a perch-hunting foraging strategy. Finally, some echolocation call types were found to correlate with higher diversification rates such that they may be considered key innovations, but, unexpectedly, the most rapidly diversifying clades were those in which species either did not use echolocation at all (Pteropodidae), or where less sensory reliance was placed on echolocation (Stenodermatinae: Phyllostomidae).

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