MORPHOLOGICAL CORRELATIONS IN EVOLUTION - CONSEQUENCES FOR PHYLOGENETIC ANALYSIS

Methods of inferring phylogenetic relationships have received an enorm ous amount of attention in recent years. One missing component in much of this work concerns the analysis of the data being wed. Most techni ques of phylogenetic inference, including parsimony, assume the indepe ndence of characters, and the assignment of equal weights to character s assumes that they have an equal probability of change. Although syst ematists wing molecular data have begun to deal with issues of charact er correlation and weighting, they are generally avoided by those wing morphological data. Systematists have paid relatively little attentio n to morphological characters that may be correlated for reasons other than commonality of descent. We review some of the reasons that the a ssumption of independence of characters may be violated for morphologi cal features, and suggest ways in which detailed analysis of the pheno type may bad to both a priori and a posteriori rationales for weightin g of morphological characters. Just as it seems prudent to explore phy logenetic hypotheses that are less than the most parsimonious, systema tics would be well served if researchers more fully explored the cause s and consequences of character correlations that may exist in morphol ogical data sets. Our two examples, the evolution of sexual dimorphism in voiceless frogs and the rob of heterochrony in the evolution of ch aenopsid fishes, illustrate that character weighting provides potentia l insights into both systematic relationships and the evolution of cha racter complexes.