Genetic stock structure of the swordfish (Xiphias gladius?) inferred by PCR-RFLP analysis of the mitochondrial DNA control region |
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Authors: | S Chow H Okamoto Y Uozumi Y Takeuchi H Takeyama |
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Institution: | (1) National Research Institute of Far Seas Fisheries, Shimizu, Shizuoka 424, Japan, JP;(2) Tokyo University of Agriculture and Technology, Koganei, Tokyo 184, Japan, JP |
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Abstract: | Restriction fragment length polymorphism (RFLP) analysis was performed on PCR amplified DNA fragments containing the control
region of the swordfish (Xiphias gladius Linnaeus, 1758) mitochondrial DNA. A total of 456 individuals comprising 13 local samples (six Pacific, three Atlantic, the
Mediterranean Sea, two Indian Ocean and the Cape of Good Hope) were surveyed with four endonucleases (Alu I, Dde I, Hha I and Rsa I), yielding a total of 52 composite genotypes. Within-sample genotypic diversity (H) was high ranging from 0.702 to 0.962 with a value of 0.922 for the pooled sample. Significant geographic variation in the
frequencies of genotypes and restriction patterns was revealed. The Mediterranean sample was highly distinct from all other
samples. Further, Rsa I digestion revealed high levels of polymorphism in all but the Mediterranean samples, indicating that exogenous swordfishes
rarely enter that body of water. Heterogeneity between the North and South Atlantic samples was significant, both of which
differed from those of the Pacific. In contrast, the Indian Ocean samples were not significantly different from the samples
of South Atlantic and Pacific. Genetic differentiation among the Pacific samples was low. The results indicate that the world-wide
swordfish population is genetically structured not only among, but also within ocean basins and suggest that gene flow is
restricted despite the absence of geographic barriers.
Received: 28 August 1996 / Accepted: 2 October 1996 |
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