MULTILOCUS PHYLOGENY OF CICHLID FISHES (PISCES, PERCIFORMES) - EVOLUTIONARY COMPARISON OF MICROSATELLITE AND SINGLE-COPY NUCLEAR LOCI

Among vertebrates, cichlid fishes are the paradigmatic example of adap tive radiation and ecological specialization. In turn, molecular genet ic studies of cichlids have focused primarily on more recently diverge d groups. Here, we present an evolutionary hypothesis of the major Lin eages of cichlid fishes based on DNA sequence data from two nuclear lo ci. One marker, Tmo-4C4, is a single-copy locus containing a region of amino acid similarity to the muscle protein TITIN. Flanking sequence from a second, microsatellite, locus, Tmo-M27, shows similarity to mam malian RAS guanine nucleotide-releasing factor. We compare and combine data from these loci to evaluate phylogenetic performance. In separat e and combined analyses, the sequence data support and clarify previou s morphological hypotheses of cichlid major-group relationships. India n and Malagasy cichlids form a basal, paraphyletic group. Neotropical cichlids are the sister clade to an African assemblage composed of the paraphyletic west and Pan-African lineages and a group of east Africa n rift lake taxa. We use a consensus phylogeny of the Cichlidae to tra ce evolutionary changes in the microsatellite repeat motif at Tmo-M27. Analysis reveals that the repeat region was nearly lost in the ancest or to cichlids and then amplified extensively in African taxa. Results demonstrate that these two new DNA markers could be widely applied in perciform systematics. Furthermore, the comparative approach can unve il mutational dynamics of simple-sequence repeat loci over long period s of fish evolution. Simple-sequence repeat regions are increasingly b eing found in introns of important regulatory genes. We address issues involving their function and suggest caution in making assumptions of strict neutrality.