A Concern for Evidence and a Phylogenetic Hypothesis of Relationships among Epicrates (Boidae, Serpentes)

Abstract

-Character congruence, the principle of using all the relevant data, and character independence are important concepts in phylogenetic inference, because they relate directly to the evidence on which hypotheses are based. Taxonomic congruence, which is agreement among patterns of taxonomic relationships, is less important, because its connection to the underlying character evidence is indirect and often imperfect. Also, taxonomic congruence is difficult to justify, because of the arbitrariness involved in choosing a consensus method and index with which to estimate agreement. High levels of character congruence were observed among 89 biochemical and morphological synapomorphies scored on 10 species of Epicrates. Such agreement is consistent with the phylogenetic interpretation attached to the resulting hypothesis, which is a consensus of two equally parsimonious cladograms: (cenchria (angulifer (striatus ((chrysogaster, exsul) (inornatus, subflavus) (gracilis (fordii, monensis)))))). Relatively little (11.4%) of the character incongruence was due to the disparity between the biochemical and morphological data Each of the clades in the consensus cladogram was confirmed by two or more unique and unreversed novelties, and six of the eight clades were corroborated by biochemical and morphological evidence. Such combinations of characters add confidence to the phylogenetic hypothesis, assuming the qualitatively different kinds of data are more likely to count as independent than are observations drawn from the same character system. Most of the incongruence occurred in the skeletal subset of characters, and much of that independent evolution seemed to be the result of paedomorphosis. [Biochemical data; character congruence; character independence; Epicrates; evidence; morphological data; paedomorphosis; phylogenetic systematics; taxonomic congruence; total evidence.] The goals of cladistics and phenetics are different. The former estimates phylogeny (Hennig, 1966), the latter seeks stability and convenience in classification (Sokal, 1986:424). Unfortunately, these objectives have become confused, especially where stability is concerned. For example, Hillis (1987:35) stated that [c]lassifications are best based on information in common among multiple data sets (i.e., consensus trees), whereas the best estimate of phylogeny and best estimate of character evolution are represented in the analysis of the combined data sets. The importance of a conservative information storage-retrieval system is undeniable (e.g., International Code of Zoological Nomenclature, 1985:3), and pheneticists sought justification for their methods in this simple truth (Sokal and Sneath, 1963). Even cladists attributed some significance to stability per se, because the lack of it confounds attempts to discover the single historical pattern (Schuh and Farris, 1981). Not unexpectedly, cladists responded (e.g., Farris, 1971) to the proposition that phenetic methods produce more stable classifications (e.g., Sokal and Sneath, 1963: 264). Analytical precision was demanded by the contestants, and an incredible array of consensus methods and indexes were developed (see lists below). It is important to bear in mind that only information on taxonomic grouping can be used to evaluate the pheneticists' claims, because character congruence is difficult to judge in phenetic analyses. Eventually, the controversy over stability became a relative issue, with cladists arguing greater stability for classifications produced by their methods, as if stability was a goal of phylogenetic systematics. Further, Nelson and Platnick (1981:219; see also Nelson, 1979) attempted to justify cla-