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Cell Size Predicts Morphological Complexity in the Brains of Frogs and Salamanders

Gerhard Roth, Jens Blanke and David B. Wake
Proceedings of the National Academy of Sciences of the United States of America
Vol. 91, No. 11 (May 24, 1994), pp. 4796-4800
Stable URL: http://www.jstor.org/stable/2364856
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Cell Size Predicts Morphological Complexity in the Brains of Frogs and Salamanders
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Abstract

The morphological organization of the brain of frogs and salamanders varies greatly in the degree to which it is subdivided and differentiated. Members of these taxa are visually oriented predators, but the morphological complexity of the visual centers in the brain varies interspecifically. We give evidence that the morphological complexity of the amphibian tectum mesencephali, the main visual center, can be predicted from knowledge of cell size, which varies greatly among these taxa. Further, cell size is highly correlated with genome size. Frogs with small cells have more complex morphologies of the tectum than do those with large cells independent of body and brain size. In contrast, in salamanders brain-body size relationships also are correlated with morphological complexity of the brain. Small salamanders with large cells have the simplest tecta, whereas large salamanders with small cells exhibit the most complex tectal morphologies. Increases in genome, and consequently cell size, are associated with a decrease in the differentiation rate of nervous tissue, which leads to the observed differences in brain morphology. On the basis of these findings we hypothesize that important features of the structure of the brain can arise independently of functional demands, from changes at a lower level of organismal organization-in this case increase in genome size, which induces simplification of brain morphology.

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