A Comparison of Branching Diagrams Derived by Various Phenetic and Cladistic Methods

Data for 20 binary characters for 18 hypothetical evolutionary units, members of "Dendrogrammaceae," have been analyzed using various phenetic and cladistic methods. Phenograms from single link, complete link, UPGMA, and WPGMA cluster analysis, shortest spanning tree diagrams, and cladograms from groundplan-divergence, Wagner tree, and character compatibility analyses were con- structed. The phenograms and cladograms derived from these analyses were com- pared with respect to topological distance matrices derived from each. Shortest span- ning tree phenograms and cladograms were compared for the number and sequence of character changes occurring on each. From these comparisons, the advantages and limitations of each method as a means for expressing evolutionary relationships among organisms are discussed and a series of recommendations is outlined. Each method can contribute to the development of an estimate of the evolutionary history for a group of organisms and no single method is best for such studies. Quantitative methods for the examination of similarities and differ- ences among organisms have been developed to assist systematic biolo- gists in assesssing relationships. These methods have usually been ap- plied to morphological data, but geographical distribution, occurrence of chemical compounds, and genetic data have also been used. These methods are operational interpretations of two approaches to the for- mulation of classifications and the estimation of evolutionary relation- ships: phenetics and cladistics. Phenetic methods summarize similarities and differences among organisms without consideration of the number and sequence of changes in characters that have occurred during the evolution of the group being studied (Colless 1967). Cladistic methods attempt to express similarities and differences in terms of the number and sequence of character changes that have occurred during evolution (Estabrook 1972). In both phenetic and cladistic approaches, the results of the assessment of similarities and differences are most frequently ex- pressed as branching diagrams. Diagrams resulting from phenetic meth- 264