Flatfish: an asymmetric perspective on metamorphosis

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Comparative Anatomy

Background:

• Flatfish are vertebrates known for their extreme asymmetry and behavioral lateralization.
• Unlike most vertebrates, flatfish undergo a secondary asymmetric remodeling during metamorphosis.
• This process deviates significantly from the typical bilateral symmetry seen in vertebrates.

Purpose of the Study:

• To explore the developmental biology of flatfish metamorphosis.
• To understand the genetic, morphological, and behavioral origins of flatfish asymmetry.
• To investigate the evolutionary implications of flatfish developmental processes.

Main Methods:

• Review of current knowledge on flatfish metamorphosis.
• Analysis of gene expression patterns during larval development.
• Comparative study of ontogeny and phylogeny.

Main Results:

• Flatfish metamorphosis involves thyroid hormone-controlled developmental programs.
• Key embryonic gene pathways (nodal-lefty-pitx2) are re-expressed during metamorphosis.
• Metamorphic changes, like eye migration, mirror phylogenetic patterns.

Conclusions:

• Flatfish asymmetry arises from a distinct postembryonic remodeling phase.
• The developmental pathways highlight a link between ontogeny and phylogeny.
• Thyroid hormone plays a crucial role in orchestrating these asymmetric developmental processes.