TY - JOUR

T1 - Ecomorphological correlates of inner ear shape in Australian limb-reduced skinks (Scincidae: Sphenomorphini)

AU - Camaiti, Marco

AU - Wiles, James

AU - Aguilar, Rocio

AU - Hutchinson, Mark N

AU - Hipsley, Christy A

AU - Chapple, David G

AU - Evans, Alistair R

N1 - Funding Information: We wish to thank Dr Jay Black for the technical expertise for acquiring our scans, and the reviewers for kindly reviewing our manuscript. This project was supported by the Holsworth Wildlife Research Endowment (Equity Trustees Charitable Foundation and the Ecological Society of Australia; to M.C.), the Monash-Museums Victoria Robert Blackwood scholarship (to M.C.), an Australian Research Council Linkage Project grant (LP170100012; to D.G.C., A.R.E., and M.N.H.), an Australian Research Council Future Fellowship grant (FT200100108; to D.G.C.), and a Discovery Early Career Researcher Award (DECRA: DE180100629, to C.A.H.). The authors declare no conflict of interest. Publisher Copyright: © 2023 The Linnean Society of London.

PY - 2023

Y1 - 2023

N2 - The inner ear labyrinth is an organ able to perceive balance and spatial orientation, but the drivers of its morphological variation across and within vertebrate lineages are unclear. We assess two competing hypotheses whether this organ, and specifically the semicircular canals, modifies its shape as a functional adaptation to ecology and locomotion, or according to the constraints of skull morphology. We test these using 52 species of Australian sphenomorphines, a group of scincid lizards that evolved changes in body shape and locomotory adaptations to fossoriality multiple times independently, by reducing their limbs. We find a correlation between semicircular canal shape and degree of limb reduction in these lizards, supporting a functional hypothesis. The interaction between body shape and substrate ecology is also a significant predictor. The wider and more eccentric semicircular canals of limb-reduced skinks indicate higher balance sensitivity and manoeuvrability compared with fully limbed skinks, probably as an adaptation to navigating cluttered environments. Conversely, our results show only a minimal influence of skull constraints on semicircular canal shape, having instead significant effects on size. This supports the hypothesis that in these skinks inner ear shape evolution is driven by specific locomotory strategies more than it is constrained by cranial anatomy.

AB - The inner ear labyrinth is an organ able to perceive balance and spatial orientation, but the drivers of its morphological variation across and within vertebrate lineages are unclear. We assess two competing hypotheses whether this organ, and specifically the semicircular canals, modifies its shape as a functional adaptation to ecology and locomotion, or according to the constraints of skull morphology. We test these using 52 species of Australian sphenomorphines, a group of scincid lizards that evolved changes in body shape and locomotory adaptations to fossoriality multiple times independently, by reducing their limbs. We find a correlation between semicircular canal shape and degree of limb reduction in these lizards, supporting a functional hypothesis. The interaction between body shape and substrate ecology is also a significant predictor. The wider and more eccentric semicircular canals of limb-reduced skinks indicate higher balance sensitivity and manoeuvrability compared with fully limbed skinks, probably as an adaptation to navigating cluttered environments. Conversely, our results show only a minimal influence of skull constraints on semicircular canal shape, having instead significant effects on size. This supports the hypothesis that in these skinks inner ear shape evolution is driven by specific locomotory strategies more than it is constrained by cranial anatomy.

KW - bony labyrinth

KW - ecomorphologylimb reduction

KW - inner ear

KW - skinks

U2 - 10.1093/zoolinnean/zlad074

DO - 10.1093/zoolinnean/zlad074

M3 - Journal article

VL - 199

SP - 994

EP - 1012

JO - Zoological Journal of the Linnean Society

JF - Zoological Journal of the Linnean Society

SN - 0024-4082

IS - 4

ER -