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.

Comparative population genetics and evolutionary history of two commonly misidentified billfishes of management and conservation concern

“…The reason for this discrepancy between the observed multimodal mismatch distribution curve and statistical fit is unclear. Collectively, however, the majority of the demographic results overwhelmingly support the scenario that both species have experienced substantial historical growth throughout the Pleistocene, consistent with findings for a number of other large pelagic species (e.g., [3,78,79]). Interestingly, the roundscale spearfish and white marlin mismatch distributions suggest that a population expansion began between~200 000 ?…”

“…These parameters are generally associated with shallow levels of genetic differentiation across large geographic regions [1][2][3]. More recently, however, low but statistically significant levels of genetic differentiation have been detected among populations of pelagic fishes, introducing exceptions to the traditional paradigm of little if any genetic structure across local and even broad spatial scales for such taxa [4,5].…”

Comparative phylogeography of the ocean planet

“…A primary phylogeographic pattern for these oceanic migrants is low to no genetic structure within ocean basins, and strong genetic structure between the Atlantic and Indo-Pacific. Some pelagic species seem to cross the Benguela Barrier (southern Africa) often enough to preclude the development of evolutionary partitions, including albacore tuna (124,125), wahoo (126), and the common dolphinfish (127). However, these species are likely exceptions, with many large, vagile species demonstrating structured populations across this barrier, including the scalloped hammerhead shark (50), whale shark (128), and blue marlin (129).…”

“…For tunas in particular, a recurring pattern is two mtDNA lineages: one confined to the Atlantic and an Indo-Pacific lineage that is also found in the Atlantic (table 6 in ref. 126). This pattern indicates extended periods of isolation, punctuated by dispersal around southern Africa.…”

Per-recruit stock assessment of wahoo (Acanthocybium solandri) in the southwest Pacific Ocean

“…Although the species is reputed to exist as a single panmictic population worldwide (Theisen et al, 2008), recent evidence suggests that wahoo may exist as multiple phenotypic populations throughout the Pacific Ocean (Zischke et al, 2013c). A fine-scale, spatially explicit analysis of morphometrics and parasites has indicated that wahoo off eastern Australia form part of a single stock in the southwest Pacific Ocean (Zischke et al, 2013c).…”