Tissue Expression Patterns of Avian Isozymes: A Preliminary Study of Phylogenetic Applications

Publisher Website
Google Scholar
Abstract
We conducted cladistic analyses of isozyme tissue expression patterns in representatives of 13 avian genera from two orders (Charadriiformes and Passeriformes) to assess utility of those characters for reconstructing phylogenies. Presence or absence of expression in each of 12 different tissues was determined by means of starch-gel electrophoresis for 30 presumptive gene loci and heteropolymers. Most parsimonious trees were examined for “correct” segregation of the two orders and unification of members of two disparate families (Recurvirostridae and Emberizidae). We found high levels of homoplasy in isozyme expression patterns in the study taxa, with most containing little phylogenetic information. However, some isozyme expression patterns of malic enzyme, aspartate aminotransferase, and aconitate hydratase yielded cladograms approximating the three taxonomic distinctions mentioned above. Reanalysis of isozyme expression characters under the assumption of homologous gains being impossible (Dollo parsimony) resulted in longer (less parsimonious) and less “accurate” trees. S-Acon-A and S-Aat-A showed significantly greater restriction of tissue expression in relatively primitive taxa, whereas Ldh-A4 and, to a lesser degree, S-Me-A showed increased restriction of tissue expression in advanced taxa. These opposite polarities in isozyme expression restriction suggest independent evolutionary histories for various loci. The evolutionary trend of decreasing numbers of expressed LDH isozymes accompanying phyletic advance, as observed in fishes (Markert et al., 1975; Toledo and Ribiero, 1978), was not observed in avian systems. The findings of widespread homoplasy, opposite polarities and limited predictive capability for the isozyme tissue expression patterns suggest that most may be more useful in studies of gene regulation than in higher level taxonomy.

This publication has 1 reference indexed in Scilit: