Accuracy of phylogenetic reconstructions from continuous characters analyzed under parsimony and its parametric correlates

Quantitative traits are a source of evolutionary information often difficult to handle in cladistics. Tools exist to analyze this kind of data without subjective discretization, avoiding biases in the delimitation of categorical states. Nonetheless, the ability of continuous characters to accurately infer relationships is incompletely understood, particularly under parsimony analysis. This study evaluates the accuracy of phylogenetic reconstructions from simulated matrices of continuous characters evolving under alternative evolutionary processes and analyzed by parsimony. We sampled 100 empirical trees to simulate 9,000 matrices, each containing between 25 and 50 taxa and 50 and 150 continuous characters evolving under three evolutionary processes: Brownian-Motion (BM), Ornstein-Uhlenbeck (OU) and Early-Burst (EB) with variable parametrizations. Our cladogram comparisons revealed that continuous character matrices, when discretized objectively and analyzed by parsimony in TNT, carry phylogenetic signals to infer species relationships, regardless of the evolutionary models and parameterization schemes. Interestingly, implementing Equal Weighting (EW) or Implied Weighting (IW) with varying penalization strengths against homoplasies did not affect cladogram reconstructions on the basis of continuous characters. Finally, the accuracy of continuous characters in resolving species relationships is skewed toward apical nodes of the recovered trees. Our findings provide general insights of the utility of quantitative traits in cladistics and demonstrate that their effectiveness in estimating shallower nodes is independent of the underlying evolutionary model, parameters and weighting schemes.