Maximal indirect development, set-aside cells, and levels of selection

Area of Science:

• Evolutionary developmental biology
• Multicellularity
• Levels-of-selection theory

Background:

• Metazoan development involves complex cell fate determination and division.
• Early bilaterians had features like small size and fixed cell divisions.
• Levels-of-selection theory models conflicts in evolutionary trajectories.

Purpose of the Study:

• To interpret metazoan development through the lens of levels-of-selection conflicts.
• To analyze how early bilaterian features constrain evolutionary models.
• To explain the evolution of "set-aside cells" and germ line sequestration.

Main Methods:

• Applying Michod's levels-of-selection model to Davidson's description of early metazoan development.
• Analyzing constraints on cell division time (t) and cooperation benefits (b).
• Examining the implications of "set-aside cells" on cooperation and competition.

Main Results:

• Early bilaterian traits constrain parameters, favoring between-cell cooperation and multicellularity.
• "Set-aside cells" with indefinite division potential abrogate these constraints.
• The evolution of "set-aside cells" correlates with germ line sequestration to mitigate cell competition.

Conclusions:

• Metazoan development can be understood via levels-of-selection conflicts.
• Constraints in early development facilitate multicellularity.
• "Set-aside cells" co-evolved with germ line sequestration to maintain cooperation.