Durand Jean-Dominique, Collet Adeline, Chow S., Guinand B., Borsa Philippe. (2005). Nuclear and mitochondrial DNA markers indicate unidirectional gene flow of Indo-Pacific to Atlantic bigeye tuna (Thunnus obesus) populations, and their admixture off southern Africa. Marine Biology, 147 (2), p. 313-322. ISSN 0025-3162.
Titre du document
Nuclear and mitochondrial DNA markers indicate unidirectional gene flow of Indo-Pacific to Atlantic bigeye tuna (Thunnus obesus) populations, and their admixture off southern Africa
Durand Jean-Dominique, Collet Adeline, Chow S., Guinand B., Borsa Philippe
Source
Marine Biology, 2005,
147 (2), p. 313-322 ISSN 0025-3162
A sharp genetic break separates Atlantic from Indo-Pacific bigeye tuna (Thunnus obesus) populations, as the frequencies of two major mitochondrial (mt) DNA types (alpha and beta) found in this species are different across the tip of southern Africa. The level of nucleotide divergence between mtDNA types alpha and beta is of the same order as that between reproductively isolated taxa. To further investigate the genetic structure of bigeye tuna over its distribution range and in the contact zone off southern Africa, bigeye tuna samples collected between 1992 and 2001 (including samples from a previous mtDNA survey) were characterized for four nuclear DNA loci and for mtDNA. Nuclear markers did not support the hypothesis that alpha and beta mitochondria characterize sibling species. Significant allele-frequency differences at one intronic locus (GH2) and one microsatellite locus (mu 208) were found between Atlantic and Indo-Pacific samples, although the level of nuclear genetic differentiation (Weir and Cockerham's (theta) over cap = 0.025 to 0.042) was much lower than in mtDNA ((theta) over cap = 0.664 to 0.807). Probabilistic Bayesian assignment of individuals to a population confirmed that southern African bigeye tuna samples represent a simple mixture of individuals from Atlantic and Indian stocks that do not interbreed, with a higher contribution from Indian Ocean individuals (about 2/3 vs. 1/3).
