High connectivity on a global scale in the pelagic wahoo, Acanthocybium solandri (tuna family Scombridae)

Abstract

The population genetic structure and phylogeography of wahoo, Acanthocybium solandri, were investigated on a global scale with intron six of lactate dehydrogenase-A (ldhA6, 8 locations, N = 213) and mtDNA cytochrome b (Cytb, 10 locations, N = 322). Results show extensive sharing of haplotypes across the wahoo's entire global range, and analyses were unable to detect significant structure (nuclear F(ST) = 0.0125, P = 0.106; mtDNA Phi(ST) < 0.0001, P = 0.634). Power analyses indicated 95% confidence in detecting nuclear F(ST) > or = 0.0389 and mtDNA Phi(ST) > or = 0.0148. These findings appear unique, as most other tunas, billfishes, and oceanic sharks exhibit significant population structure on the scale of East-West Atlantic, Atlantic vs. Indian-Pacific, or East-West Pacific. Overall nuclear heterozygosity (H = 0.714) and mtDNA haplotype diversity (h = 0.918) are both high in wahoo, while overall mtDNA nucleotide diversity (pi = 0.006) and nuclear nucleotide diversity (pi = 0.004) are uniformly low, indicating a recent increase in population size. Coalescence analyses yield an estimate of effective female population size (NeF) at approximately 816,000, and a population bottleneck approximately 690,000 years ago. However, conclusions about population history from our Cytb data set are not concordant with a control region survey, a finding that will require further investigation. This is the first example of a vertebrate with a single globally distributed population, a finding we attribute to extensive dispersal at all life stages. The indications of a worldwide stock for wahoo reinforce the mandate for international cooperation on fisheries issues.