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Abstract
Largehead hairtail, Trichiurus japonicus, is a valuable commercially exploited demersal species. We gathered mtDNA control region sequences (3′ mtDNA CR) of T. japonicus to investigate its genetic diversity and population genetic structure. Fifty-four specimens were collected from the nearshore localities along the coastline of China. A total of 42 polymorphic sites were found, which defined 40 haplotypes. A pattern with high level of haplotype diversity (h = 0.98 ± 0.01) and very low level of nucleotide diversity (π = 0.008 ± 0.005) were detected in the examined range. Comparing π with other fish species shows that T. japonicus has remarkable low genetic diversity values compared with other Pacific Ocean marine fishes. AMOVA and conventional Fst values revealed no significant genetic structure throughout the examined range, which is inconsistent with the previous findings based on the morphological and ecological studies. Using a variety of phylogenetic methods, coalescent reasoning, and molecular dating interpreted in conjunction with paleoclimateic and physiographic evidence, we infer that the genetic make-up of extant populations of T. japonicus was shaped by Pleistocene environmental impacts on the historical demography of this species. Coalescent analyses (Neutrality tests, Mismatch distribution analysis, Bayesian skyline analyses) showed that the species along the coastline of China has experienced population expansions originated in its most recent history at about 153–216 kyr.