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Population Structure and Dynamics in Mahimahi (Coryphaena hippurus) as Inferred through Analysis of Mitochondrial DNA

The proposed research will study the spatial scale of population subdivision in C. hippurus collected worldwide using a phylogenetic analysis of mitochondrial DNA (mtDNA). The information generated from this study will benefit pelagic fisheries by providing an evolutionary perspective on the demography of the circumtropical fish, C. hippurus. Such data now exist for salmon and whale populations, and new directions for management have arisen because of the global connections uncovered. Researchers hope to estimate levels of gene flow, effective numbers of reproducing females, and to reconstruct the dynamics of populations that have given rise to the levels of genetic diversity currently maintained in this species, as well as discern population structure. This information will not only provide insights into the stability of tropical and subtropical pelagic fish populations, but will also be useful to other researchers working on similar problems in pelagic fisheries.


Principal Investigator:
Dr. Carol Reeb
c/o Hopkins Marine Station
Stanford University
120 Ocean View Blvd.
Pacific Grove, California 93950-3094
Phone (408) 655-6200
FAX (408) 375-0793
Dr. Rebecca Cann
Department of Genetics & Molecular Biology
University of Hawaii at Manoa
1960 East-West Road, Biomed A-204
Honolulu, Hawaii 96822
Phone (808) 956-5521/6907
FAX (808) 956-5506

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Progress Report - July 1996

Purpose of the Project:
To determine whether populations are structured on a global scale in C. hippurus, and to determine the amount of genetic diversity contained in this commercially exploited species from which historical population stability can be inferred.

Progress during FY 1996:
We have found a repetitive sequencethat shows a high level of size polymorphism. We have been able to show that this difference in size can be explained through the loss or gain of one or more repetitive units and provides a tremendous amount of genetic differentiation with which to study population structure. We have devised a novel and quick method to screen this molecular marker using the automated sequencer and hope to complete this study by the end of 1996.

Between 1991 and 1993, 200 samples of Coryphaena hippurus (mahimahi) were collected from eleven sites worldwide to examine global population structure. Initially, 270 base pairs of Cytochrome b from the mitochondrial DNA (mtDNA) were sequenced in 55 fish to determine the amount of genetic polymorphism contained in this species. Only thirteen mtDNA haplotypes were found. One lineage was found to be very common and distributed worldwide while the remaining twelve were quite rare. While these data were not useful in discerning population subdivision, it did suggest that C. hippurus populations, like a number of other pelagic fish populations, have not been stable during the Pleistocene. These data suggest the following three scenarios: (1) a catastrophic near extinction, (2) demographic parameters favoring males (in vertebrates, mtDNA is thought to be transmitted through females only), or (3) recurrent extinction and recolonization of populations. Recently, more effort has been put into finding a faster-evolving part of the mtDNA to better study population structure in C. hippurus. We have found that these fish possess a very large control region relative to other fish such as the swordfish. We have determined that this size difference is due to a short (8 base pair), tandem, repetitive sequence present 100 times or more. This sequence is analogous to a rapidly-evolving microsatellite sequence, and it appears to provide a significant amount of polymorphism with which to test for population subdivision. We have begun to assay this repeat region for the 200 samples collected worldwide.

Plans for the next Fiscal Year:
We hope to complete the screening of our 200 fish and publish the results.

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This page updated August 16, 2006