Skull morphological adaptations to acoustic emissions: peak frequency in bats

Chiropteran species developed different sound emission systems (i.e. oral
or nasal) implying divergent skull morphological adaptations. Species
combining multiple sensory strategies to locate their food might present a
weaker selection pressure on their skulls due to echolocation compared to
species that use echolocation as main sensory system. Consequently, we
predicted that skull shape of non-insectivorous bats should not present
associations between skull morphology and peak frequency. We tested for
the relationship between skull morphology (size and shape, derived from 3D
geometric morphometrics) and peak frequency (FP) in a macroevolutionary
dataset including ~65% of extant bat genera. Phylogenetic comparative
methods were employed to assess skull morphological variation associated
to FP. Unexpectedly, we found that also frugivorous nasal emitters
presented significant skull shape (but not size) adaptations to the
frequency emitted. In both insectivorous and frugivorous species, high
frequencies were associated with a relatively short rostrum. Our study
indicates that FP constrains skull shape variation of nasal emitters more
strongly compared to mouth emitters. These results suggest that
echolocation parameters play an important role in bat skull evolution.