Correlating Cochlear Morphometrics from Parnell’s Mustached Bat (Pteronotus parnellii) with Hearing

Abstract

Morphometric analysis of the inner ear of mammals can provide information for cochlear frequency mapping, a species-specific designation of locations in the cochlea at which different sound frequencies are encoded. Morphometric variation occurs in the hair cells of the organ of Corti along the cochlea, with the base encoding the highest frequency sounds and the apex encoding the lowest frequencies. Changes in cell shape and spacing can yield additional information about the biophysical basis of cochlear tuning mechanisms. Here, we investigate how morphometric analysis of hair cells in mammals can be used to predict the relationship between frequency and cochlear location. We used linear and geometric morphometrics to analyze scanning electron micrographs of the hair cells of the cochleae in Parnell's mustached bat (Pteronotus parnellii) and Wistar rat (Rattus norvegicus) and determined a relationship between cochlear morphometrics and their frequency map. Sixteen of twenty-two of the morphometric parameters analyzed showed a significant change along the cochlea, including the distance between the rows of hair cells, outer hair cell width, and gap width between hair cells. A multiple linear regression model revealed that nine of these parameters are responsible for 86.9 % of the variation in these morphometric data. Determining the most biologically relevant measurements related to frequency detection can give us a greater understanding of the essential biomechanical characteristics for frequency selectivity during sound transduction in a diversity of animals.

Ultrastructure of the organ of Corti in harbor seals (Phoca vitulina)

“…This analysis reveals the existence of clusters that share similarities in hair cell morphology related to their location in the cochlear spiral without previously assuming the location variable as a grouping factor. The hair cell morphology trend continued to show an association with their tonotopic organization, as previously described in mustached bats Pternonotus parnellii (Girdlestone et al, 2020). The clusters that were visualized in the PCA were identified using k-means clustering analysis.…”

“…Established methods used for linear morphometry (LM) analysis (Yarin et al, 2014;Girdlestone et al, 2020) were followed. At each position, 19 measurements based on the form and spatial positions of OHCs and IHCs were obtained from image analysis (Figure 3 and Table 2).…”

Selective Inner Hair Cell Loss in a Neonate Harbor Seal (Phoca vitulina)

“…Specific points on each image were identified to achieve an accurate consecutive delineation of length. Contiguous measurements avoided overlapping or gaps in the calculation of the structure (see Girdlestone and colleagues [ 23 ]).…”