2020 Fiscal Year Annual Research Report
Large brain evolution in cetaceans
| Project/Area Number |
18K14833
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| Research Institution | Hokkaido University |
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Principal Investigator |
PATZKE NINA 北海道大学, 高等教育推進機構, 助教 (20801690)
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| Project Period (FY) |
2018-04-01 – 2021-03-31
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| Keywords | Brain / Evolution / Comparative neruoanatomy / Cetaceans / Odontocete / MRI / Morphology / Histology |
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| Outline of Annual Research Achievements |
1. Specimen acquisition: We collected the brain of a Pacific white sided dolphin.
2. MRI analysis: All brains collected were suspected to MRI scans and analyzed for morphology and volumetric. The external and internal anatomical organization revealed typical characteristics, which were previously observed in other dontoceti. In addition, we measured the cortical area external perimeter of a sequence of coronal MR images and used those to calculate the volume and the exposed surface area of the entire cortical hemisphere. The cortical volume and exposed surface, of all whales analyzed, reveal the same scaling relationship as that of a multi-species data set previous reported. This finding indicates that overall external shape of the 2 cetaceans is typical mammalian, despite its unusual detailed shape, large size and high gyrification level. However the brains seem to be more spherical than that of land mammals.
3. Cellular and neuropil architecture: we analyzed the hippocampus and the amygdala and could clearly demonstrate that both are smaller and have a more simplified neuroanatomy when compare to terrestrial mammals.
4. Cell counting: Using the isotropic fractionator technique we estimated the total number of neurons and glia in the harbor porpoise, the Baird's beaked whale and the Pacific white sided dolphin. Interestingly toothed whales seem to have more neurons in the cortex when compared to baleen whales and terrestrial non-primate mammals. This finding indicates that toothed whales, in parallel evolution to primates have evolved a higher neuronal cortical density.
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