Biochemical Characters and the Reconstruction of Turtle Phylogenies: Relationships among Batagurine Genera

Abstract

-Phenetic and cladistic approaches were used to assess relationships among 22 species representing 17 genera of batagurine turtles, and 2 species representing 2 genera of emydine turtles. Phenograms and cladograms were constructed from a total of 90 variable enzyme products (electromorphs) of 14 gene loci. Phenograms were generated by UPGMA clustering using genetic similarity, identity, and distance matrices, and a Wagner tree was constructed from a binary-coded character matrix. A qualitative locus-by-locus cladistic approach was also attempted, and in this as well as in our application of the Wagner algorithm, a species of the sister group family Testudinidae was used as the outgroup taxon. Results of the three approaches are evaluated relative to each other, and relative to relationships that have previously been proposed with other lines of evidence. Some of the clades generated by one or more of the approaches used in this study are particularly strongly corroborated by chromosomal and osteological data sets. High genetic distances between some taxa, and high levels of inferred homoplasy suggest that divergence among many species approaches the limits of electrophoretic resolution and, as a result, several cladistic hypotheses are presented for some taxa. Where results are inconclusive, however, they are useful to the extent that they draw attention to contradictory data sets and alternative hypotheses of intergeneric relationships. [Cladistics; electrophoresis; Emydidae; Emydinae; Batagurinae; turtle systematics.] In the nearly two decades since the widespread application of starch-gel electrophoresis to systematic and evolutionary problems, most studies have focused on spatial genetic variation within species or the degree of relative genetic differentiation among closely related species (reviews by Ayala, 1975; Avise, 1976; Nevo, 1978). Furthermore, most studies of species relationships have been phenetic assessments of intrageneric genetic similarities or distances. Avise (1974) cautioned that electrophoretic data might have only limited value in assessing intergeneric relationships, but elsewhere has shown that the phenetic approach may be of use in some monophyletic groups (Avise et al., 1977). Today few would question the utility of such studies, but only very recently have systematists begun to analyze electrophoretic data using the conceptual phylogenetic approach of Hennig (1966). Some of these studies have involved the coding of character states for all variable loci and the use of computer algorithms to construct the most parsimonious trees (Mickevich and Johnson, 1976; Avise et al., 1980b), while others have been based on a locus-by-locus comparison in an attempt to determine character polarities for polymorphic enzymes (Wake et al., 1978; Baverstock et al., 1979; Avise et al., 1980a; Honeycutt et al., 1981; Patton et al., 1981; Sites et al., 1981; Honeycutt and Williams, 1982; Murphy et al., 1983). We have used all of these approaches in an attempt to clarify phylogenetic relationships among batagurine turtle genera. THE BATAGURINE TURTLES The subfamily Batagurinae is an assemblage of over 20 genera, including over two-thirds of the testudinoid family Emydidae (McDowell, 1964). Except for the Neotropical genus Rhinoclemmys, the subfamily is entirely Old World and, as a