A quantitative morphological analysis of the inner ear of galliform birds.

The function of the inner ear is dependent on its physical structure and there is therefore a strong correspondence between inner ear morphology and hearing capabilities. In this study, we examine the morphology of the inner ear and use this relationship to predict the hearing range and sensitivities of species within the Order Galliformes (chicken, quail and allies). All galliforms share a similar inner ear morphology, which is characterized by gradients in hair cell morphology that are similar to other birds. Most galliforms did have an area of morphologically similar hair cells at the apical end of the BP, indicative of a low frequency specialization. We suggest that, in general, the galliform inner ear is tuned for detecting low frequencies, with most hair cells and more than half of the BP dedicated to frequencies below 1 kHz. Whether this is a specialization or associated with their basal lineage remains to be determined. We also determined that body and brain size are associated with the number of hair cells and basilar papilla length across galliform birds, such that as body size increases, there are correlated increases in BP length and the number of hair cells. Our data therefore corroborate patterns observed across a wide range of bird species and provides significant insight into how species differences in BP morphology evolve and putative relationships with size, vocalizations and life history.