Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
John E. Graves
Intraspecific genetic relationships within yellowfin tuna, Thunnus albacares, and three mackerels of the genus Scomber were studied by restriction fragment length polymorphism (RFLP) analysis of mitochondrial DNA (mtDNA). The comparison of these scombrids, with different larval distributions, adult distributions, and vagilities, served to investigate the hypothesis that population structure in marine fishes results from geographic and physical oceanographic processes that limit dispersal of early life history stages. Samples of 20 yellowfin tuna were examined from each of five Pacific locations and one Atlantic location. MtDNA analysis with 12 informative restriction endonucleases demonstrated considerable genetic variation, as evidenced by overall nucleon diversity of 0.84 and mean nucleotide sequence diversity of 0.31%. Estimates of within-sample variation were consistent across all six locations. Common genotypes occurred with similar frequencies in all samples, and with one exception, all genotypes that were represented by more than one individual occurred at more than one location. The null hypothesis that the sampled populations of yellowfin tuna share a common gene pool was not rejected. In contrast, analysis of species of Scomber revealed considerable intraspecific differentiation. A total of 15 samples averaging 19 individuals each of Scomber japonicus, S. australasicus, and S. scombrus were collected from geographically isolated populations throughout the ranges of each species. Genotypic diversities ranged from 0.28 to 0.95, and nucleotide sequence diversities from 0.13 to 0.76%. East and west Atlantic populations of S. scombrus exhibited significant differentiation, but no fixed restriction site differences. This species differed by 11.9% nucleotide sequence divergence from the other two species. In S. japonicus, fixed restriction site differences were revealed among Pacific samples, but not among Atlantic samples; although significant heterogeneity occurred within the Atlantic. In S. australasicus, North and South Pacific samples were highly differentiated. One of two divergent mtDNA matrilines observed in this species was restricted to southern samples. The study demonstrated that population structure is greater in the species of Scomber than in yellowfin tuna. It further revealed that adult dispersal, in addition to geographic and physical oceanographic processes that control dispersal of early life history stages, are of significant importance in shaping population structure in scombrids.
© The Author
Scoles, Daniel R., "Global phylogeography of yellowfin tuna, Thunnus albacares, and mackerels of the genus Scomber" (1994). Dissertations, Theses, and Masters Projects. Paper 1539616844.