Patterns and processes of brain diversification within esociform teleosts

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Means, Sheila M.
Lannoo, Michael J.
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Thesis (M.S.)
Department of Physiology and Health Science
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The richness of nervous systems represented by extant fishes has not yet been determined; the brain morphology of many species, indeed, many groups, remain undescribed. For this reason we have examined esociform teleosts and focused on three goals: 1) to provide the first basic descriptions of the brains of two esociform teleosts, Esox masquinongy (muskellunge) and Esox lucius (northern pike); 2) to describe the development of E. masquinongy brains; and 3) to compare the neuronal features between E. masquinongy and E. lucius in light of the ontogenic pattern of E. masquinongy. We demonstrate that a suite of differences exists between the brains of these two congeners. Relative to the brains of E. lucius, the brains of E. masquinongy exhibit a number of paedomorphic features. This heterochronic shift parallels the differences in non-neuralmorphological features previously described between these two species. We identify three features that cannot be explained by this heterochronic shift: 1) the optic nerves of E. masquinongy and E. lucius cross oppositely, E. masquinongy have optic nerves that cross left nerve dorsal, E. lucius cross right nerve dorsal; 2) Esox lucius have a consistent cellular discontinuity in the telencephalon between Dm, and Dd that is not present in E. masquinongy; and 3) adult E. lucius retain a neural canal opening that closes in larval E. masquinongy, a peramorphic exception to the paedomorphic pattern.