Variation and disparity within the inner ear and trigeminus of the tenrecomorpha

TL;DR

This study examines the inner ear and trigeminal nerve of tenrecomorph mammals to understand how their sensory systems evolved in response to different ecological niches.

Contribution

The study reveals conflicting evolutionary signals in the inner ear and trigeminal nerve of tenrecomorphs, challenging expectations of convergent sensory adaptation.

Findings

Tenrecomorphs show cross-taxon differences in sensory structures, but no single factor explains most of the variation.

Inner ear and trigeminal nerve structures do not share convergent evolutionary patterns.

The results contrast with prior findings on the tenrec cranial endocast, where habitat and ecotype strongly influence shape.

Abstract

Evolutionary theory predicts that sensory systems should adaptively respond to environmental selection. Different ecological niches should, in theory, then correlate with changes in sensory anatomy in lineages that have undergone extensive radiation. The afrotherian clade Tenrecomorpha, comprising of African potamogalines and Malagasy tenrecines, is of particular interest because of its variety: the clade reportedly includes fossorial, arboreal, semiaquatic, and even echolocating taxa. To investigate their sensory ecology, we provide geometric morphometric analyses of inner ear endocasts of 24 tenrec species. We expand this dataset with 9 iodine-stained specimens to study trigeminal organization. Although tenrecomorphs display cross-taxon differences in sensory structures, our analyses distinguish signals of conflicting strength and direction within the tenrec ear, with no single factor that might explain a substantial portion of observed variation when accounting for phylogeny. This contrasts with prior studies of the tenrec cranial endocast, where sensory ecotype and habitat are strongly associated with shape. Iodine-enhanced scans of the trigeminal nerve align with this, and other studies based on bony anatomy. The disparate patterns of shape evolution in Tenrecomorpha and the contrasts exhibited by the inner ear and trigeminal nerve provide a nuanced portrait of neurosensory adaptation, differing from expectations set by other mammalian groups.

The inner ear and trigeminal nerves of tenrecomorph mammals are analyzed and compared; while sensory specialists may exhibit extreme features, the semicircular canals, cochlea, and trigeminal nerve do not share convergent evolutionary trajectories.

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