RAPID EVOLUTION OF GASTRULATION MECHANISMS IN A SEA URCHIN WITH LECITHOTROPHIC LARVAE.

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Marine Biology

Background:

• Echinoid gastrulation typically involves radial cell rearrangements for archenteron elongation.
• The ancestral mode of echinoid gastrulation is conserved across many species with planktotrophic larvae.
• Heliocidaris erythrogramma, an echinoid with lecithotrophic larvae, presents a unique case for studying developmental evolution.

Purpose of the Study:

• To document evolutionary modifications in gastrulation mechanisms in Heliocidaris erythrogramma.
• To compare the developmental processes of H. erythrogramma with ancestral echinoid gastrulation.
• To investigate the timescale of developmental mechanism evolution in echinoids.

Main Methods:

• Cell marking experiments were employed to trace cell movements during gastrulation.
• Observation of archenteron extension and associated cellular behaviors.
• Comparative analysis of gastrulation in H. erythrogramma versus other echinoids.

Main Results:

• Gastrulation in H. erythrogramma involves prolonged cell movement over the blastopore lip, extending the archenteron.
• This process utilizes a different type of cellular movement compared to ancestral echinoids.
• Dorsoventral asymmetry in cellular movements is imposed during archenteron extension in H. erythrogramma.

Conclusions:

• Evolutionary modifications in echinoid gastrulation include altered cell movement types and the introduction of asymmetry.
• Despite conserved mechanisms in planktotrophic echinoids over millions of years, H. erythrogramma shows rapid evolutionary change in development.
• Morphogenetic mechanisms of early development can evolve substantially even after long periods of evolutionary stasis.