Patterns and processes of brain diversification within esociform teleosts.

Area of Science:

• Neuroscience
• Ichthyology
• Evolutionary Biology

Background:

• The full diversity of fish nervous systems, particularly brain morphology, remains largely undescribed.
• Esociforms, representing basal euteleosts, offer a valuable model for understanding brain evolution in teleosts.

Purpose of the Study:

• To provide initial descriptions of the brains of muskellunge (Esox masquinongy) and northern pike (Esox lucius).
• To detail the neuronal development in Esox masquinongy.
• To compare neuronal differences between E. masquinongy and E. lucius, referencing E. masquinongy's ontogeny.

Main Methods:

• Comparative neuroanatomy of adult specimens.
• Histological examination of brain tissue to describe neuronal morphology and development.
• Ontogenetic analysis of neuronal features in Esox masquinongy.

Main Results:

• The brains of Esox masquinongy exhibit paedomorphic features in nuclear position and morphology compared to Esox lucius and other basal euteleosts.
• These paedomorphic brain features correlate with observed differences in non-neural morphology between the two species.
• Neuronal development in E. masquinongy shows specific patterns that contribute to the observed adult brain morphology.

Conclusions:

• Paedomorphosis in brain structure is a significant feature distinguishing Esox masquinongy from Esox lucius.
• Evolutionary transformations affecting all body systems, including neural and non-neural features, drive diversification within fish groups like esocids.
• Heterochronic shifts in development can explain observed morphological differences at finer taxonomic levels.