Integrating Ontogeny of Echolocation and Locomotion Gives Unique Insights into the Origin of Bats

Abstract

The evolutionary sequence of events that led to flight and echolocation in bats is a compelling question in biology. Fundamentally lacking from this discussion is the ontogeny of how these two systems become functionally integrated producing an evolutionary developmental model. We build such a model by integrating growth and development of the cochlea, larynx, and sound production with the ontogeny of locomotion in newborn bats. In addition, we use available fossil and molecular data along with patterns of high frequency vocalization in extant mammals to model probable evolutionary transitions in bats. We find clear evidence that the ability to hear high frequency echolocation-like sounds preceded the ability to produce it and that a simple echolocation system was likely inherited from a shrew-like ancestor and was not an in situ evolutionary innovation of bats. Refinement of this system coevolved with sustained flight, both ontogenetically and evolutionarily, leading to the sophisticated echolocation observed today.