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Symmetry breaking and the evolution of development.
1Systematics and Evolution Group, Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada. rich.palmer@ualberta.ca
Science (New York, N.Y.)
|October 30, 2004
Summary
Left-right asymmetry in organisms offers evolutionary insights. Studies show genetic assimilation is common, developmental pathways evolve, and heart development becomes more robust over time.
Area of Science:
- Developmental Biology
- Evolutionary Biology
- Genetics
Background:
- Left-right asymmetry is a fundamental biological trait allowing for comparative studies across diverse organisms.
- Understanding the evolution of developmental mechanisms underlying asymmetry provides insights into broader evolutionary processes.
Purpose of the Study:
- To analyze patterns of asymmetry variation, inheritance, and molecular mechanisms across different species.
- To investigate the evolutionary origins and modifications of developmental pathways controlling asymmetry, particularly in heart development.
Main Methods:
- Phylogenetic analysis of asymmetry variation and inheritance.
- Comparative analysis of molecular mechanisms, focusing on the nodal cascade in vertebrates.
Main Results:
- Directional asymmetry frequently arises from nonheritable sources, indicating genetic assimilation is a significant evolutionary mechanism.
- The molecular pathway for leftward heart development (nodal cascade) shows considerable variation among vertebrates, suggesting developmental pathway co-option.
- A decrease in spontaneous asymmetry reversal frequency during vertebrate evolution points to increased canalization of heart development.
Conclusions:
- The study highlights the dynamic nature of developmental evolution, where genetic assimilation and pathway co-option are key drivers.
- Heart development has become increasingly canalized throughout vertebrate evolution, leading to more robust and predictable leftward asymmetry.
- Comparative analysis of asymmetry provides a powerful lens for understanding how developmental processes evolve.
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