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Form, function and phylogeny in the cetacean ear complex
Ary, William James
To understand effects of anthropogenic sound on whales, their ear anatomy must be understood, in particular, the tympanoperiotic complex or TPC. The TPC is attached to the mandibular fat body which has been shown to gather environmental sound to the ear and houses the ossicles and cochlea. Twelve TPCs from 10 species were used to examine formfunction relationships in a phylogenetic context. Geometric morphometrics and principal components analysis were used to control for size, position and orientation and summarize variation in TPC shape. Results show closely related animals like the dolphins and porpoises are grouped while phylogenetically isolated species were consistent outliers in TPC shape. TPC structures in contact with the mandibular fat body had larger shape variation. This suggests that these regions may be under selection. Vibrational analysis was used to measure TPC function. Sixty natural resonant frequencies and animations of mode shapes were produced for each species. These frequencies related to body size, their dispersion increased with frequency number. The porpoises, the pygmy sperm whale and striped dolphin grouped together as did the left and right ears for the common and Amazon river dolphins. Motion in the animations was sorted into one of 9 TPC regions, three of which, the sigmoid process, outer lip and anterodorsal crest of the tympanic bone, are also sites of mandibular fat body attachment and were found to have high variability in shape, indicating between species shape variability and TPC vibrational function in these regions are closely linked. Modularity of TPC substructures and covariation with the resonant frequency data were assessed using two-block partial least squares including the effects of phylogeny. The tympanic and periotic were a functional module, as well as the cochlea. Resonant frequency data correlated with TPC morphology. Ancestral state reconstruction was performed to produce phylomorphospaces and estimate the shapes of common ancestors with consistent outliers and grouping in dolphins and porpoises.
Master of Science (M.S.) San Diego State University, 2017
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