The repeated, independent evolution of traits (convergent evolution) is often attributed to shared environmental selection pressures. However, developmental dependencies among traits can limit the phenotypic variation available to selection and bias evolutionary outcomes. Here we determine how changes in developmentally correlated traits may impact convergent loss of the tympanic middle ear, a highly labile trait within toads that currently lack adaptive explanation. The middle ear’s lability could reflect evolutionary trade-offs with other skull features under selection, or the middle ear may evolve independently of the rest of the skull, allowing it to be modified by active or passive processes without pleiotropic trade-offs with other skull features. We compare the skulls of 55 species (39 eared, 16 earless) within the family Bufonidae, spanning six hypothesized independent middle ear transitions. We test whether shared or lineage-specific changes in skull shape distinguish earless species from eared species and whether earless skulls lack other late-forming skull bones. We find no evidence for pleiotropic trade-offs between the middle ear and other skull structures. Instead, middle ear loss in anurans may provide a rare example of developmental independence contributing to evolutionary lability of a sensory system.
.ply meshes of skulls used in this study
Procrustes' fit data (landmark data) that was used in geomorph analyses. Averaged by species.
Bone presence/absence data plus the species names and identifiers of all skull files.
Museum specimens used in this study
Field-caught specimens used in this study
a .tps file with raw landmark coordinates for each specimen. Specimen numbers can be matched with species names using the bone analysis spreadsheet (SI_3).
National Science Foundation, Award: #IOS-13503461350346 & #PRFB-1611752