Disentangling mechanical and sensory modules in the radiation of Noctilionoid bats

The vertebrate cranium is a complex anatomical structure with diverse
mechanical and sensory functions. Shifts between modularity and
integration in both sets of functions, especially mechanical function,
have been implicated in adaptive diversification. However, how mechanical
and sensory systems and functions have coevolved and how their
interrelationship contributes to phenotypic disparity remains largely
unexplored. To examine the modularity, integration, and evolutionary rates
of sensory and mechanical structures within the head, we analyzed hard and
soft tissue scans from ecologically diverse bats from the superfamily
Noctilionoidea, which range from generalized insectivores to derived
frugivores and nectarivores. We identified eight cranial regions as
distinct modules — five associated with bite force and three linked to the
olfactory, visual, and auditory systems, respectively — whose
interrelationships differ between Neotropical leaf-nosed bats (Family
Phyllostomidae) and other noctilionoids. Our analyses suggest that the
peak rates of sensory module evolution predate those of mechanical
modules. This finding is consistent with transitions to new diets first
involving changes in the detection of novel food items, followed by
adaptations to process them. We propose the coevolution of structures
influencing bite force, olfaction, vision, and hearing constituted a
structural opportunity that allowed the phyllostomid ancestor to take
advantage of existing ecological opportunity and the group to become a
classic example of adaptive radiation.