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Present study investigates the genetic diversity and genetic distribution of the longtail tuna Thunnus tonggol collected from east Malaysia (Borneo states of Sabah and Sarawak) based on mitochondrial DNA D-loop sequence analysis. 58 fish samples were obtained, specifically from Kota Kinabalu, KK (n = 22), Miri, MR (n=20) and Bintulu, BT (n = 17). DNA template was isolated using the salt extraction method. Final length of 404 base pair (bp) D-loop sequences revealed 52 haplotypes that comprise of 77 variable sites (38 of parsimony informative and 39 singleton). A total of 20 haplotypes were found in KK, 19 haplotypes in MR and 16 haplotypes in BT. Molecular diversity indices revealed high haplotype diversity and low nucleotide diversity in all populations; KK (h = 0.9913 ± 0.0165, π = 0.00239 ± 0.0127), MR (h = 0.9942 ± 0.0193, π = 0.0226 ± 0.0121) and BT (h = 0.9926 ± 0.0230, π = 0.0196 ± 0.0171). Population comparison pairwise FST show that KK and BT were significantly genetically differentiated. The result from this study will be beneficial for fisheries management and also to provide information on the population genetics of T. tonggol in East Malaysian waters.

The population genetic diversity and demographic history of the longtail tunaThunnus tonggolin Malaysian waters was investigated using mitochondrial DNA D-loop and NADH dehydrogenase subunit 5 (ND5). A total of 203 (D-loop) and 208 (ND5) individuals ofT. tonggolwere sampled from 11 localities around the Malaysian coastal waters. Low genetic differentiation between populations was found, possibly due to the past demographic history, dispersal potential during egg and larval stages, seasonal migration in adults, and lack of geographical barriers. The gene trees, constructed based on the maximum likelihood method, revealed a single panmictic population with unsupported internal clades, indicating an absence of structure among the populations studied. Analysis on population pairwise comparison ФSTsuggested the absence of limited gene flow among study sites. Taken all together, high haplotype diversity (D-loop = 0.989–1.000; ND5 = 0.848–0.965), coupled with a low level of nucleotide diversity (D-loop = 0.019–0.025; ND5 = 0.0017–0.003), “star-like” haplotype network, and unimodal mismatch distribution, suggests a recent population expansion for populations ofT. tonggolin Malaysia. Furthermore, neutrality and goodness of fit tests supported the signature of a relatively recent population expansion during the Pleistocene epoch. To provide additional insight into the phylogeographic pattern of the species within the Indo-Pacific Ocean, we included haplotypes from GenBank and a few samples from Taiwan. Preliminary analyses suggest a more complex genetic demarcation of the species than an explicit Indian Ocean versus Pacific Ocean delineation.

The population genetic diversity and demographic history of the longtail tuna Thunnus tonggol in Malaysian waters was investigated using mitochondrial DNA D-loop and NADH dehydrogenase subunit 5 (ND5). A total of 203 (D-loop) and 208 (ND5) individuals of T. tonggol were sampled from 11 localities around the Malaysian coastal waters. Low genetic differentiation between populations was found, possibly due to the past demographic history, dispersal potential during egg and larval stages, seasonal migration in adults, and lack of geographical barriers. The gene trees, constructed based on the maximum likelihood method, revealed a single panmictic population with unsupported internal clades, indicating an absence of structure among the populations studied. Analysis on population pairwise comparison ФST suggested the absence of limited gene flow among study sites. Taken all together, high haplotype diversity (D-loop = 0.989–1.000; ND5 = 0.848–0.965), coupled with a low level of nucleotide diversity (D-loop = 0.019–0.025; ND5 = 0.0017–0.003), “star-like” haplotype network, and unimodal mismatch distribution, suggests a recent population expansion for populations of T. tonggol in Malaysia. Furthermore, neutrality and goodness of fit tests supported the signature of a relatively recent population expansion during the Pleistocene epoch. To provide additional insight into the phylogeographic pattern of the species within the Indo-Pacific Ocean, we included haplotypes from GenBank and a few samples from Taiwan. Preliminary analyses suggest a more complex genetic demarcation of the species than an explicit Indian Ocean versus Pacific Ocean delineation.