Our research in comparative evolutionary biology focuses on the evolution of the multivariate phenotype. Current theoretical research emphasizes the development of phylogenetic comparative methods for multivariate datasets, and morphometric methods for characterizing patterns of shape variation and covariation. Current empirical work focuses largely on vertebrates, and examines macroevolutionary patterns of phenotypic diversification to decipher the tempo and mode by which phenotypic evolution occurs.
Developing Multivariate phylogenetic comparative methods
One current theoretical focus is on the mathematical merger of multivariate shape theory with phylogenetic comparative evolutionary biology. The evolution of multi-dimensional traits (such as shape) is complex, and considerable effort is required to properly merge the mathematical properties of such traits with the tenants of macroevolutionary theory. Our work in this regard has focused on developing new analytical methods that extend the underlying algebra of individual phylogenetic comparative methods, so that macroevolutionary hypotheses may be evaluated in high-dimensional multivariate datasets in the same manner as is presently accomplished with univariate data.
Recent efforts have resulted in the development of approaches for estimating phylogenetic signal in multivariate data, for evaluating multivariate evolutionary rates, for assessing the evolutionary covariation among sets of variables in a phylogenetic context, and approaches that generalize phylogenetic regression and anova for high-dimensional datasets. Our current theoretical work continues to extend the phylogenetic comparative toolkit in new directions to address questions not currently available with standard appraoches, and to extend additional univariate comparative methods to the multivariate arena.
Development of Morphometric Methods
A second theoretical focus is on the development of morphometric methods to address particular questions and hypotheses. Here our work concentrates on developing landmark-based geometric morphometrics for the characterization of shape, and quantification of patterns of shape variation and covariation. Recent efforts have focused on two areas: methods for the characterization of patterns of phenotypic change trajectories, and methods for comparing levels of integration and modularity in morphometric datasets.
Our work also includes the dissemination of software packages for use by the scientific community. To that end we have developed the R-package geomorph; a comprehensive software package for performing all stages of geometric morphometric analyses of landmark data. With geomorph one may read, manipulate, and digitize 2D and 3D landmark data, generate shape variables, perform statistical analyses of shape variation and covariation, and provide graphical depictions of shapes and patterns of shape variation. The analytical methods in geomorph may also be used on other multivariate phenotypic datasets. Finally, all new analytical methods developed in the lab, including phylogenetic comparative methods for high-dimensional multivariate data, are included in geomorph for use by other researchers.
MacroevolutionAry patterns and processes
At the macroevolutionary level, we are investigating how ecological factors, such as species interactions and differences in ecological regime, affect patterns of morphological variation and diversification. We utilize a comparative phylogenetic approach to investigate these patterns, with a focus on plethodontid salamanders (though we work on other taxonomic groups as well). For the former, we leverage decades of empirical discoveries at microevolutionary scales to motivate and generate testable hypotheses at the macroevolutionary level regarding how ecological forces may shape patterns of morphological diversification over time.
To date our work has shed light on how rates of phenotypic evolution relate to patterns of species diversification, and how distinct ecological regimes affect rates of morphological evolution. Our current work examines the tempo and mode of morphological evolution across salamanders experiencing distinct ecological selective regimes. Earlier work demonstrated that these lineages are exposed to distinct ecological selective regimes, and that selection appears to operate on different morphological traits, generating testable predictions at the macroevolutionary level. We are currently testing these predictions in a phylogenetic context to decipher whether rates of morphological evolution, and patterns of morphological convergence, correspond to predictions based on ecological theory.