Trait macroevolution in the presence of covariates

Area of Science:

• Evolutionary Biology
• Macroevolutionary Studies
• Phylogenetic Comparative Methods

Background:

• Statistical models of trait evolution on phylogenies often conflate unique and shared influences, complicating interpretations of macroevolutionary history.
• The Fabric model (2022) previously identified directional trait shifts and changes in macroevolutionary 'evolvability' over evolutionary time.
• Correlated traits can obscure the independent evolutionary dynamics of a focal trait.

Purpose of the Study:

• To extend the Fabric model to analyze traits that covary with other traits.
• To develop a method that isolates the unique variance component of a trait, independent of its covariates.
• To investigate macroevolutionary patterns of directional change and evolvability while accounting for trait correlations.

Main Methods:

• Introduction of the Fabric-regression model, an extension of the Fabric model.
• The model estimates directional and evolvability effects on a focal trait while controlling for one or more covarying traits.
• Application to a dataset of 1504 mammalian species, analyzing brain size evolution while accounting for body size.

Main Results:

• The Fabric-regression model successfully identifies a unique component of trait variance, free from influences of correlated traits.
• Inferences on mammalian brain size evolution, when accounting for body size, qualitatively differ from analyses of brain size alone.
• New macroevolutionary effects on brain size and its evolvability were identified that were not apparent when analyzing brain size without considering body size.

Conclusions:

• Accounting for trait correlations provides a more nuanced understanding of macroevolutionary history and trait dynamics.
• The Fabric-regression model enables the study of trait variation uniquely attributable to the trait itself.
• This approach opens avenues for applying causal inference methods to phylogenetic comparative studies, addressing fundamental macroevolutionary questions.