The origin and evolution of chordate nervous systems

Area of Science:

• Evolutionary developmental biology (evodevo)
• Comparative morphology
• Neuroscience

Background:

• Reconstructing ancestral forms relies on comparative morphology and evodevo.
• These methods often yield congruent results only for closely related species.
• The evolution of the chordate central nervous system (CNS) remains a complex challenge.

Purpose of the Study:

• To investigate the evolutionary origins of the chordate CNS.
• To compare developmental gene expression and mechanisms with morphology.
• To understand the ancestral deuterostome CNS and its relation to chordates and hemichordates.

Main Methods:

• Comparative analysis of developmental gene expression (evodevo).
• Electron microscopy.
• Comparative morphology.
• Phylostratigraphy (proposed).

Main Results:

• Evodevo and electron microscopy revealed similarities between amphioxus brains and vertebrate brain regions.
• Genetic mechanisms for structures like the midbrain/hindbrain boundary and neural crest were identified in amphioxus.
• Whole-genome duplications in vertebrates facilitated the evolution of new structures like neural crest.

Conclusions:

• The chordate CNS evolved from an ancestral deuterostome CNS, with differing views on the presence of a discrete ancestral brain.
• Evodevo provides insights into the genetic underpinnings of CNS evolution.
• New techniques like phylostratigraphy are needed to resolve remaining evolutionary questions.