A Phenetic and a Phylogenetic Approach to the Classification of a Genus of Seed Beetles (Coleoptera: Bruchidae)

Slobodchikoff, C. N. and C. D. Johnson (Dept. of Biological Sciences, Northern Arizona University, Flagstaff, Arizona 86001) 1973. A Phenetic and Phylogenetic Approach to the Classification of a Genus of Seed Beetles (Coleoptera: Bruchidae). Syst. Zool. 22: 280-294.-To test whether the process of phylogenetic analysis is an unweighted phenetic process, 34 multistate characters were obtained from a recent revision of 29 species of Acanthoscelides, a genus of seed beetles (Bruchidae). Based on these characters, an intuitive unweighted-character phenogram and an intuitive phylogenetic tree were constructed. The intuitive phylogenetic tree was converted to a phenogram format. The characters were treated numerically, generating product-moment and taxonomic distance phenograms for the 29 species. An elementary Wagner tree was constructed from a Prim network. The intuitive and numerical phenograms were analyzed for the topological relationships of closely related OTUs, and the phenograms were compared by means of an "index of positional relationship." This index compares the positions of closely-linked OTUs in two phenograms, regardless of whether the phenogram has been generated by intuitive or numerical means. Within a given numerical technique of calculating similarities (e.g., product-moment), different clustering methods (e.g., weighted-pair and unweightedpair group methods) produced very similar phenograms. Considerably less agreement was obtained between phenograms generated by two different methods of calculating similarities (e.g., product-moment and taxonomic distance). Least agreement was found between the numerical phenograms and the intuitive phylogenetic phenogram, suggesting that the process of intuitive phylogenetic analysis is not solely another form of unweighted phenetic analysis. [Seed Beetles; Acanthoscelides; Phenetic; Phylogenetic.] As originally defined by Cain and Harrison (1960), phenetics involved "the arrangement of overall similarity, based on all available characters without any weighting," while phyletics involved describing an "arrangement that aims to show the course of evolution." Phenetics has since been modified to include weighting of characters (see, for example, Moss, 1972, and Colless, 1971). However, phenetics might generally be defined as a process leading to an arrangement, based on phenotypic similarity, that does not attempt to elucidate the course of evolution. Phylogenetics (or the phyletics of Cain and Harrison, 1960), on the other hand, may be described as a process leading to an arrangement which attempts to elucidate the course of evolution. In practice, most phenetic analyses have involved statistical treatment of characters, usually with the aid of computers, while phylogenetic analyses have been largely intuitive in nature, relying primarily on the taxonomist's ability to structure complex interrelationships within the framework of what purports to be an evolutionary scheme. In recent years there has been some controversy over whether or not the phylogenetic approach to classification is merely an intuitive, unweighted phenetic approach. Colless (1967, 1970, 1971) has pointed out that, in his opinion, this is, indeed, the case, while others, e.g., Hennig (1966), Brundin (1966), maintain that the phylogenetic approach does elucidate evolutionary relationships and is founded on principles that are conceptually very different from those governing a phenetic approach. A solution to the problem of which approach is actually used by taxonomists would be to experimentally test the hypothesis that the phylogenetic approach is only a phenetic one against the available data from taxo-