Size and shape variations of the bony components of sperm whale cochleae

Abstract

Several mass strandings of sperm whales occurred in the North Sea during January and February 2016. Twelve animals were necropsied and sampled around 48 h after their discovery on German coasts of Schleswig Holstein. The present study aims to explore the morphological variation of the primary sensory organ of sperm whales, the left and right auditory system, using high-resolution computerised tomography imaging. We performed a quantitative analysis of size and shape of cochleae using landmark-based geometric morphometrics to reveal inter-individual anatomical variations. A hierarchical cluster analysis based on thirty-one external morphometric characters classified these 12 individuals in two stranding clusters. A relative amount of shape variation could be attributable to geographical differences among stranding locations and clusters. Our geometric data allowed the discrimination of distinct bachelor schools among sperm whales that stranded on German coasts. We argue that the cochleae are individually shaped, varying greatly in dimensions and that the intra-specific variation observed in the morphology of the cochleae may partially reflect their affiliation to their bachelor school. There are increasing concerns about the impact of noise on cetaceans and describing the auditory periphery of odontocetes is a key conservation issue to further assess the effect of noise pollution.

Ultra-high matrix mineralization of sperm whale auditory ossicles facilitates high sound pressure and high-frequency underwater hearing

“…We have shown that in human ossicles there is a rapid increase in mineralization during the first years of life [13]. There is also no evidence for relevant postnatal growth of the cochlear structures or ear ossicles with individual shapes [13,17]. This suggests a very early adaptation of the ossicular bone to its function, which persists throughout life.…”

“…The auditory ossicles were taken from three sperm whales of 12, 13 and 15 years of age [16,17]. All specimens were transferred with special documentation of no commercial or trading interests according to the environmental authority of Schleswig-Holstein (Germany) and approved by the Institute for Terrestrial and Aquatic Wildlife Research (ITAW) on behalf of the Schleswig-Holstein Wadden Sea National Park.…”

Bony labyrinth morphology clarifies the origin and evolution of deer

“…This observation has been confirmed in many mammal groups (e.g. cetaceans 68 , 69 ; primates 70 ; primitive artiodactyls 71 ) except for sloths, which exhibit extremely slow locomotion 72 .Thus, the hypothetical specimen mean (consensus of all specimens from a species) was used for the phylogenetic test to not artificially decrease the homoplasy. The phylogenetic tree was created using Mesquite 3.04 software 73 .…”

Inter-individual differences in contamination profiles as tracer of social group association in stranded sperm whales

“…More recent research on sperm whales is equivocal, with some studies illustrating little apparent characteristics of social structure of males 6 , 10 , 11 , 32 , while another recent study even showed that immature males form long-term relationships 33 . A recent study on size and shape variations of the bony components of sperm whale cochleae suggested already that individuals might be affiliated to different bachelor pods 34 . The present study assessed whether variations of the contamination profile are indicative of spatial aggregation (and putatively social structures) of young male sperm whales as they might reflect a variation in feeding preferences and/or in feeding grounds as diet is the main relevant exposure pathway for marine mammals 12 .…”