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.

Phylogenetic relationships between tuna species of the genus Thunnus (Scombridae: Teleostei): Inconsistent implications from morphology, nuclear and mitochondrial genomes

“…The present results on mtDNA and nDNA are consistent with allozyme analysis by Sharp and Pirages (1978) and Elliott and Ward (1995) for T. alalunga (ALB), which showed it to be the most divergent member of the genus. Although mtDNA of T. t. orientalis (PNB) is very similar to that of T. alalunga (ALB), the allozyme analysis revealed T. t. orientalis (PNB) to have closest affinity to T. t. thynnus (ANB), T. maccoyii (SBT), and even to the species of yellowfin tuna group.…”

“…Bluefin tunas (ANB and SBT) and species of the yellowfin group (BFT, LTT, and YFT) showing less mtDNA divergence from one another may have emerged -500,000 years ago. Elliott and Ward (1995) indicated that the Thunnus tuna species appear to be genetically much more similar one another than are most congeneric fish species and pointed out that the relationships between bluefin tunas (PNB and SBT) and T. albacares (YFT) are too close to infer the branch orders from their allozyme data. MtDNA divergence between T. t. orientalis (PNB) and T. alalunga (ALB) is comparable with those among T. t. thynnus (ANB), T. maccoyii (SBT), and species of the yellowfin group, suggesting an introgression event to have occurred at similar timing with the emergence of the bluefin tunas and tropical tuna species.…”

“…Furthermore, Atlantic northern bluefin and southern bluefin tunas were observed to have restriction profiles more similar to those of the tropical species of the yellowfin tuna group than to those of the Pacific northern bluefin tuna, albacore, and bigeye tuna, which are assigned to be members of the bluefin group. Sharp and Pirages (1978) and Elliott and Ward (1995), using allozyme analysis, observed the albacore to be the most divergent species in the genus. Interestingly, Elliott and Ward (1995) reported that the bluefin tunas were much closer to the yellowfin tuna than to albacore and bigeye tuna.…”

“…Sharp and Pirages (1978) and Elliott and Ward (1995), using allozyme analysis, observed the albacore to be the most divergent species in the genus. Interestingly, Elliott and Ward (1995) reported that the bluefin tunas were much closer to the yellowfin tuna than to albacore and bigeye tuna. Finnerty and Block (1995) also reported that the mitochondrial cytochrome b data are not consistent with the taxonomic subdivision in the genus Thunnus, and suggested that conclusions about phylogenetic relationships between species may be drawn by obtaining mtDNA data from the two tropical species.…”

Interspecific and Intraspecific Genetic Diversity of Thunnus Species

“…Nevertheless, Sharp & Pirages (1978) and Chow & Kishino (1995) indicated that albacore tunas are highly divergent from all other tunas, suggesting that the Thunnus subgenus is not a monophyletic group. Elliott and Ward (1995) reported that bluefin tunas were much closer to the yellow tuna than to albacore and bigeye tunas, and albacore was the most divergent species in the maccoyii was obtained from the Indian Ocean by Taiwanese fishery observers in 2006 as described by Shiao et al (2008). Thunnus thynnus was caught from Martinique waters of the eastern Caribbean Sea in 2008.…”