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Rudolf A Raff1, Elizabeth C Raff
1Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Novartis Foundation Symposium
|August 23, 2007
Summary
The evolution of sea urchin development can be rapid, with conserved gene pathways shifting timing to create new larval forms. This study examines how direct-developing larvae evolved from feeding larvae in Heliocidaris species.
Area of Science:
- Developmental biology
- Evolutionary developmental biology
- Marine biology
Background:
- Marine embryos and larvae exhibit diverse life histories and body plans.
- Evolutionary modifications in larval forms can occur rapidly among closely related species.
Purpose of the Study:
- To investigate the evolutionary mechanisms behind the direct-developing larva of Heliocidaris erythrogramma.
- To understand how this evolved from an indirect-developing feeding larva (pluteus).
Main Methods:
- Comparative embryology between Heliocidaris erythrogramma and Heliocidaris tuberculata.
- Cross-species hybridization experiments.
- Gene expression manipulation in embryos.
Main Results:
- Heliocidaris erythrogramma diverged from its sister species within 4 million years.
- Radical developmental evolution allows metamorphosis in 3-4 days, compared to weeks for the pluteus.
- Evolutionary changes largely resulted from heterochronies (shifts in timing of conserved regulatory pathways).
Conclusions:
- Rapid evolution of larval forms is driven by shifts in the timing of conserved developmental pathways.
- Changes in gene regulation, including novel tissue identities, contribute to rapid larval evolution.
- Heterochrony is a key mechanism in the evolution of developmental patterns in sea urchins.
