Distinguishing Evolutionary Conservation from Derivedness

Area of Science:

• Evolutionary biology
• Developmental biology
• Genomics

Background:

• Evolutionary conservation explains shared ancestral traits but can be misused to assess evolutionary change.
• Derivedness, the degree of change from a common ancestor, encompasses novel or lost traits, differing from conservation.

Purpose of the Study:

• To distinguish between evolutionary conservation and derivedness for a clearer understanding of phenotypic and organismal evolution.
• To introduce a novel molecular method for quantifying phenotypic derivedness.

Main Methods:

• Developed the "transcriptomic derivedness index" using whole-embryonic transcriptomes as a molecular phenotype.
• Applied the method to analyze the transcriptomic derivedness of echinoderm and chordate embryos.

Main Results:

• The transcriptomic derivedness index quantifies evolutionary changes beyond conserved traits.
• Echinoderm embryos, despite common assumptions, show transcriptomic derivedness comparable to chordate embryos.
• Conservation-focused methods may underestimate evolutionary changes in certain lineages.

Conclusions:

• Distinguishing conservation from derivedness is essential for accurate evolutionary assessments.
• The transcriptomic derivedness index offers a quantitative molecular approach to measure phenotypic evolution.
• Future derivedness-oriented methods could identify traits with high or low evolvability.