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Structure and evolution of the horizontal septum in vertebrates
1Evolution, Bio-Geosphere Dynamics Program (EBID), Systematic Zoology, Auf der Morgenstelle 28, Tübingen, Germany. sven.gemballa@uni-tuebingen.de
Journal of Evolutionary Biology
|November 26, 2003
Summary
The horizontal septum (HS) in fish is not as conserved as previously thought, showing significant evolutionary changes in its collagen fibre structure across species. This impacts biomechanical models and understanding of its developmental roles.
Area of Science:
- Comparative anatomy
- Evolutionary biology
- Fish biomechanics
Background:
- The horizontal septum (HS) is crucial for fish biomechanics and cell development.
- Its detailed morphology and evolutionary conservation are not well understood.
Purpose of the Study:
- To investigate the evolutionary conservation of the horizontal septum (HS) morphology.
- To analyze the collagen fibre architecture of the HS across major gnathostome clades.
Main Methods:
- Utilized a novel combination of techniques to examine the HS.
- Analyzed 35 species from diverse gnathostome lineages.
- Visualized collagen fibre architecture.
Main Results:
- The HS is conserved only in the presence of epicentral and posterior oblique fibre tracts.
- Significant evolutionary variations exist in the condensation and presence of these tracts (epicentral tendons and posterior oblique tendons).
- Multiple independent losses and evolutions of these tracts occurred across vertebrate evolution.
Conclusions:
- The horizontal septum (HS) exhibits homoplasy, not strict conservation, across vertebrates.
- Generalizing biomechanical models of fish swimming that include the HS is problematic.
- The pathfinding role of the HS in zebrafish may extend to gnathostomes, but not agnathans, sarcopterygians, or tetrapods.