Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Blue marlin diversity was assessed at mtDNA, scnDNA, microsatellite DNA, and allozyme molecular markers. Hierarchical analysis of molecular variance (AMOVA) revealed that most genetic variation was maintained within populations, with a non-significant fraction attributable to variation among temporal replicates and between locations within oceans. In contrast, inter-ocean divergence was highly significant for a majority of loci within each marker class. Previous studies of mitochondrial DNA (mtDNA; n = 104) genetic variation within the blue marlin revealed two distinct clades of haplotypes, one of which was present only in the Atlantic (the 'Atlantic clade'), at a frequency of 40% &(F\sb{lcub}st{rcub}& = 0.39). ScnDNA and allozyme markers exhibited lower levels of diversity and inter-ocean divergence than mtDNA (average &F\sb{lcub}st{rcub}& = 0.08). Enhanced genetic drift among populations, due to the four-fold lower effective population size of mtDNA, was emphasized as causing the greater mtDNA inter-ocean divergence. The low mutation rate of nuclear markers, and greater male dispersal may have contributed to the difference detected. Microsatellite loci were hypervariable, and displayed a wide range of divergence estimates (average &F\sb{lcub}st{rcub}& = 0.14). A nuclear 'Atlantic clade' of alleles was detected at one locus, indicating that the historical forces that generated the mitochondrial Atlantic clade (Pleistocene allopatry) also strongly influenced the nuclear genome. Although some microsatellite loci were much more sensitive than scnDNA markers, on average, these differences were not significant, due to the wide range of microsatellite patterns detected. The mean and variance of inter-ocean divergence &(F)& estimates were not significantly different among marker classes, suggesting a minor influence of selection. Correlations between diversity and divergence within and among marker classes were non-significant, indicating that difference in mutation rate can not explain the lower nuclear divergence. The patterns of diversity obtained within and among marker classes is consistent with expected values under migration-drift equilibrium.



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