Genetic relationships of eight species of Pacific tunas (Teleostei: Scombridae) inferred from allozyme analysis

Abstract

A phylogenetic analysis of eight species of Pacific tunas was made after examining allozyme variation at 23 muscle and liver enzymes encoded by 35 loci. The eight species of tuna were: Thunnus alalunga, albacore; T. obesus, bigeye; T. thynnus orientalis, northern bluefin; T. maccoyii, southern bluefin; T. albacares, yellowfin; Auxis thazard, frigate; Euthynnus affiizii kawakawa; Katsuwonus pelamis, skipjack. All species except the northern bluefin were also examined for variation at three eye-specific loci. The average heterozygosity per locus ranged from 0.038 (frigate) to 0.070 (bigeye). Genetic relationships were examined on the basis of the 35 loci screened in all species. Genetic identities among the five Thunnus species were high, averaging 0.864 and ranging from 0.788 to 0.923. Whereas the albacore appeared to be the most divergent of the Thunnus species (mean identity to other Thunnus species of 0.825, range 0.788-0.452), there was little differentiation between yellowfin, southern bluefin and northern bluefin tunas (mean identity 0.905, range 0.892-0.923), and phylogenetic analyses failed to resolve the branch order among the Thunnus species. The non-Thunnus tunas were quite divergent both from one another and from Thunnus species (mean identity 0.358, range 0.280-0.606). Diagnostic allozyme loci were identified, allowing the discrimination of all species.