A test between relationships based on phenetic and cladistic taxonomic methods

Abstract

Applying the axiom that hybridizing taxa are, on the average, more closely related than non-hybridizing taxa, a test was devised to evaluate differing methods of determing relationships. A measure of relationship called the cladistic coefficient was created to express the cladistic relationships of Willi Hennig's school of taxonomy and a program in BASIC was written to calculate it. The cladistic coefficient and the simple matching coefficient of numerical taxonomy were calculated for 304 sympatric pairs of genera of North American Cyprinidae using 10 two-state and 18 multistate characters using additive binary coding with 0 for primitive and 1 for advanced states. Fifty of these pairs hybridize.The proportion of simple matching coefficients for hybridizing genera above the mean coefficient, 62%, was not significantly higher than for non-hybridizing genera, 54%. For the cladistic coefficient the proportion of values for hybridizing genera above mean coefficient, 72%, was significantly higher, p < 0.0001, than for non-hybridizing genera, 32%.The cladistic coefficient provided a better measure of phylogenetic relationships than did the simple matching coefficient. The method, which can use indices of relationship other than hybridity, may be used to choose between conflicting classifications or differing taxonomic approaches.