Detecting diversifying selection for a trait from within and between-species genotypes and phenotypes.

Area of Science:

• Evolutionary biology
• Quantitative genetics
• Macroevolutionary studies

Background:

• Current methods for quantifying selection on traits use either within- or between-species variation.
• Within-species methods fail to integrate macro-evolutionary changes.
• Between-species methods often ignore micro-evolutionary processes.

Purpose of the Study:

• To develop a novel neutrality index for quantitative traits by integrating both within- and between-species variation.
• To provide a method for detecting deviations from neutral evolution and identifying diversifying selection.
• To apply the index to mammalian brain and body mass evolution.

Main Methods:

• Developed a neutrality index that incorporates nucleotide polymorphism and divergence to normalize trait variation.
• The index does not require estimation of population size or speciation time.
• Applied the index to a dataset of mammalian brain and body mass.

Main Results:

• The developed neutrality index successfully combines within- and between-species variation.
• Analysis of mammalian brain and body mass revealed that brain mass is under diversifying selection.
• The test demonstrated robustness against assumptions of constant population sizes, mutation rates, and generation times.

Conclusions:

• The new neutrality index offers a comprehensive approach to studying trait evolution.
• Diversifying selection plays a significant role in the evolution of mammalian brain mass.
• The method is reliable across diverse phylogenetic scales and evolutionary parameters.