Assessing trait covariation and morphological integration on phylogenies using evolutionary covariance matrices

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Macroevolutionary studies

Background:

• Morphological integration describes how organismal traits covary.
• Analyzing trait covariation at the macroevolutionary level requires accounting for phylogeny.
• Existing methods like phylogenetic independent contrasts have limitations.

Purpose of the Study:

• To outline a new analytical procedure for evaluating morphological integration across species while considering phylogenetic relationships.
• To provide a flexible and robust complement to existing phylogenetic comparative methods.
• To test hypotheses of morphological integration within a macroevolutionary framework.

Main Methods:

• Development of an analytical procedure based on the evolutionary covariance matrix.
• Utilizing computer simulations under a Brownian motion model to assess statistical properties.
• Application of the method to analyze head shape integration in Plethodon salamanders.

Main Results:

• Statistical tests based on the evolutionary covariance matrix show appropriate Type I error rates and high statistical power.
• Simulation results remain consistent across varying numbers of species and trait dimensions.
• Significant integration was found between cranial shape and mandible shape in Plethodon salamanders.

Conclusions:

• The proposed procedure offers a robust method for testing hypotheses of morphological integration in a phylogenetic context.
• The approach is a valuable complement to phylogenetic independent contrasts.
• The study provides R code for implementing the procedure, facilitating its use in future research.