The Utility of Morphological Data in Resolving Phylogenetic Relationships of Darters as Exemplified with Etheostoma (Teleostei: Percidae)

Recent investigations of darter phylogeny have been based almost entirely on analyses of DNA sequence data. External morphological characters have, at times, been used to infer phylogenetic relationships among species in specific darter clades, but these types of characters are most often used in the discovery and description of darter species. Datasets that comprise more than a dozen discretely coded characters from osteology and myology are surprisingly absent from the investigation of darter phylogeny. It is unknown whether phylogenetic analyses of discretely coded morphological characters can result in resolved hypotheses of darter phylogeny, and whether these inferences would agree with those resulting from phylogenetic analyses of DNA sequence data. This study uses a dataset of 135 discretely coded morphological characters scored for 83 darter species originally presented in an unpublished doctoral dissertation. The phylogenetic utility of this morphological dataset was investigated with both maximum parsimony and a model-based Bayesian method. The phylogenies resulting from these analyses had limited phylogenetic resolution, with limited bootstrap pseudoreplicate and Bayesian posterior probability support for inferred nodes. Aspects of the morphological phylogenies were in agreement with previous analyses using DNA sequence data. Many darter taxonomic groups (e.g., subgenera) sampled with more than one species were not monophyletic in the resulting parsimony and Bayesian inferred phylogenies, including Percina, Belophlox, Hololepis, Catonotus and Oligocephalus. On the other hand, Ozarka, Microperca and Nothonotus were monophyletic in both analyses. In the context of these results, we conclude that morphological data have limited utility in resolving the phylogenetic relationships of darters; however, the phylogenies inferred using this dataset could highlight problematic areas of the darter phylogeny and may offer results that contrast with trees inferred in molecular phylogenetic analyses. Discretely coded morphological characters could find their greatest value in advancing the investigation of darter phylogeny when used in combination with DNA sequence data sampled from mitochondrial and nuclear genes.