Manatee Cerebral Cortex and Comparative Volumetrics

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Manatees are endangered species of the Order Sirenia and exhibit several unusual traits in brain anatomy which appear to be related to their unique lifestyle. Manatees have an annual death rate of approximately 150 individuals from a total population of about 1500-2000. This fact, coupled with their slow reproductive replacement rate, leads to the real possibility exists that we are witnessing the last opportunity to study the biology of these unique mammals. Each mammalian species represents an "experiment" by nature and every unusual species helps define the range of possible evolutionary outcomes, increases our understanding of evolutionary potential, and enables the reconstruction of the evolutionary history of the brain. At present, we have some understanding of how certain peculiar features of manatee brains may be correlated with their unique ecological niche; for example, the small brain/body-weight ratio, smooth cerebral hemispheres, and low cell densities in the cortex. The present research will enable the identification of different cortical areas in the manatee based on cellular staining patterns and will suggest functional roles for these regions through comparisons with other mammalian species. Computer-generated three- dimensional reconstructions of cerebral hemispheres and determination of the volumes of the major brain divisions are also major objectives.