[Organization and evolution of animal colonies]

Area of Science:

• Paleontology
• Evolutionary Biology
• Colonial Organisms

Context:

• Bryozoan colonies exhibit complex astogeny, a developmental process influenced by internal and external factors.
• Graptolites, an extinct group of hemichordates, provide a model for understanding colonial organization and evolution.
• The morphogen gradient theory, originally applied to graptolites, offers a framework for interpreting colonial development.

Purpose:

• To investigate the relationship between late astogeny events in bryozoan colonies and their somatic and reproductive cycles.
• To compare the organization and evolutionary mechanisms of bryozoan colonies with those of graptoloid colonies.
• To interpret bryozoan colony structure using the morphogen gradient theory.

Summary:

• Bryozoan colonies were analyzed using the morphogen gradient theory, where a founder-zooid (oozooid) produces a morphogen that diffuses along the colony's axis, regulating zooid size and structure.
• Evolutionary changes in graptoloid colonies involved new character introduction and spread, linked to gradient changes.
• Bryozoan colonies, unlike graptolites, exhibit multiple zones of astogeny changes and repetitions, suggesting evolutionary mechanisms related to gene penetrance and expressivity.

Impact:

• This study provides insights into the evolutionary mechanisms of colonial invertebrates, bridging extinct and extant groups.
• The findings contribute to understanding how developmental processes shape colony morphology and evolution.
• The research highlights the utility of the morphogen gradient theory in diverse colonial systems.