Data from: The evolution of bat vestibular systems in the face of potential antagonistic selection pressures for flight and echolocation

The vestibular system maintains the body’s sense of balance and,
therefore, was probably subject to strong selection during evolutionary
transitions in locomotion. Among mammals, bats possess unique traits that
place unusual demands on their vestibular systems. First, bats are capable
of powered flight, which in birds is associated with enlarged semicircular
canals. Second, many bats have enlarged cochleae associated with
echolocation, and both cochleae and semicircular canals share a space
within the petrosal bone. To determine how bat vestibular systems have
evolved in the face of these pressures, we used micro-CT scans to compare
canal morphology across species with contrasting flight and echolocation
capabilities. We found no increase in canal radius in bats associated with
the acquisition of powered flight, but canal radius did correlate with
body mass in bat species from the suborder Yangochiroptera, and also in
non-echolocating Old World fruit bats from the suborder
Yinpterochiroptera. No such trend was seen in members of the
Yinpterochiroptera that use laryngeal echolocation, although canal radius
was associated with wing-tip roundedness in this group. We also found that
the vestibular system scaled with cochlea size, although the relationship
differed in species that use constant frequency echolocation. Across all
bats, the shape of the anterior and lateral canals was associated with
large cochlea size and small body size respectively, suggesting
differential spatial constraints on each canal depending on its
orientation within the skull. Thus in many echolocating bats, it seems
that the combination of small body size and enlarged cochlea together act
as a principal force on the vestibular system. The two main groups of
echolocating bats displayed different canal morphologies, in terms of size
and shape in relation to body mass and cochlear size, thus suggesting
independent evolutionary pathways and offering tentative support for
multiple acquisitions of echolocation.