Asymmetric craniofacial remodeling and lateralized behavior in larval flatfish

Area of Science:

• Developmental biology
• Comparative physiology
• Neuroethology

Background:

• Flatfishes (e.g., flounder) exhibit extreme vertebrate asymmetry.
• The cause of their lateralized swimming behavior during metamorphosis is debated.

Purpose of the Study:

• To investigate the developmental basis of lateralized swimming behavior in southern flounder (Paralichthys lethostigma).
• To determine if behavior is an adaptive response to eye asymmetry or a result of thyroid hormone signaling.

Main Methods:

• Studied larval development in left-sided, right-sided, and bilaterally symmetric southern flounder variants.
• Observed behavior and skull morphology.
• Administered thyroid hormone to larvae.

Main Results:

• Behavioral and skull asymmetries were observed before metamorphosis.
• Lateralized behaviors developed independently of eye position in thyroid hormone-treated and symmetric larvae.

Conclusions:

• Lateralized swimming behavior in flatfish is not an adaptive response to eye asymmetry.
• It arises from altered vestibular responses to thyroid hormone during development.