Population Genetic and Phylogeographic Structure of Wahoo, Acanthocybium solandri, From the Western Central Atlantic and Central Pacific Oceans
Coastal Sciences, Gulf Coast Research Laboratory
The wahoo, Acanthocybium solandri (Cuvier, 1832), is a pelagic, highly migratory, scombroid fish, distributed worldwide throughout tropical and warm temperate seas. To evaluate population genetic and phylogeographic structure against a null hypothesis of panmixia, the entire mitochondrial DNA control-region (&SIM; 890 base pairs) was sequenced for 231 wahoo. Samples were collected from 1997 to 2001 from seven sites: North Carolina (NC; n=23), east central Florida (CF; n=30), Bimini, Bahamas (BB; n=40), southern tip of Florida (SF; n=21), Cayman Islands (CI; n=23), northern Gulf of Mexico (NG; n=54), and Hawaii (HI; n=40). Inter-annual samples were obtained from four of these locations (NC, BB, SF, NG). Seventeen haplotypes were shared by individuals within and among samples; 187 singleton haplotypes were observed. Within-sample haplotype diversities ranged from 0.995 to 1.000 (overall h=0.999) and within-sample nucleotide diversities ranged from 0.049 to 0.055 (overall π=0.053). A neighbor-joining tree based on inter-haplotypic distances revealed two monophyletic lineages differing by 13.6% nucleotide divergence. Nested within each major lineage were several, well-supported subclades. There was no evidence of temporal heterogeneity in haplotype distributions. Partitioning mtDNA variation, 99.75% of the variance was within samples and 0.25% (P=0.307) between samples; the fixation index (&UPhi;(ST)=0.0025) was not significant. Likewise, pairwise &UPhi;(ST) values were low or negative, and none were significant on a table-wide basis. Exact tests for sample differentiation in haplotypes were also non-significant. All population analyses were consistent with the null hypothesis of panmixia. However, analytical power was limited by sample size. Mismatch distributions were inconsistent with expected distributions based on sudden-expansion and static-growth models. Wahoo exhibit concurrently high haplotype and nucleotide diversities, presumably a consequence of secondary contact between historical subpopulations rather than a long, stable evolutionary history. Given the level of geographic and individual sampling, wahoo thus far represent the sole example of a scombroid or xiphioid fish exhibiting coarse-grain genetic homogeneity across a broad, inter-oceanic range despite a deeply coalescing genealogical structure. Accordingly, cooperative fishery management on a broad, inter-ocean scale may be warranted.
Franks, J. S.
(2005). Population Genetic and Phylogeographic Structure of Wahoo, Acanthocybium solandri, From the Western Central Atlantic and Central Pacific Oceans. Marine Biology, 147(1), 205-214.
Available at: http://aquila.usm.edu/fac_pubs/2775