Abstract
The population genetic structure of the messmate pipefish, Corythoichthys haematopterus, in the northwest Pacific was investigated based on the partial mitochondrial DNA cytochrome b (589 bp) and 16S rRNA (528 bp) region sequences of 108 individuals collected from six sites along the coast of the Japanese archipelago and one site on Mactan Island, the Philippines. A total of 60 and 28 haplotypes were obtained from the cytochrome b and 16S rRNA regions, respectively. Two genetically distinct lineages were detected: lineage A and B, which are separated by mean pairwise genetic distances of 23.3 and 14.1% in the partial cytochrome b and 16S rRNA genes, respectively. Such a huge genetic divergence between lineages, which is comparable to or even higher than the interspecific level, and the difference in their geographical distributions and habitat preferences suggests that they are distinct species, although there is no marked difference in their morphology. Haplotype network and gene and nucleotide diversity statistics indicate that the two lineages have different biogeographic histories: lineage A experienced rapid population expansion after a population bottleneck whereas lineage B has a long evolutionary history in a large stable population. In contrast, the levels of genetic variation among populations are relatively low in both lineages, probably because of frequent gene flow among populations resulting from the dispersal of pelagic larvae by the Kuroshio Current. These results indicate that past climatic events and contemporary oceanographic features have played a major role in establishing the population genetic structure of C. haematopterus.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-2-408) contains supplementary material, which is available to authorized users.
Highlights
Elucidating the population genetic structure of a species can aid conservation decisions, enable us to identify demographically independent populations that should be managed as separate units (i.e. Evolutionarily Significant Unit, ESU; Fraser and Bernatchez 2001), and assess connectivity among local populations providing useful information for reservation design (Palumbi 2003)
For the partial 16S rRNA region gene (h) and nucleotide diversity (π) ranged from 0.538 to 0.895 and 0.0012 to 0.0625, respectively (Table 2). Both gene and nucleotide diversity estimates were highest in Kin in both mitochondrial regions, but the lowest values were found in the Morode and Bounotsu populations for cytochrome b and 16S rRNA, respectively
Lineage B has a broad range from Okinawa Island southward, indicating that some biogeographic boundary exists between the two lineages
Summary
Elucidating the population genetic structure of a species can aid conservation decisions, enable us to identify demographically independent populations that should be managed as separate units (i.e. Evolutionarily Significant Unit, ESU; Fraser and Bernatchez 2001), and assess connectivity among local populations providing useful information for reservation design (Palumbi 2003). High population genetic structure is expected to develop when gene flow among populations is severely restricted. This is the case for marine organisms, especially sessile or sedentary species, when larval dispersal is prevented by short pelagic larval duration or oceanographic features, or when migrating larvae have no chance of growing and entering non-natal breeding grounds because of crucial differences in selection regimes among populations (i.e. local adaptation), even though transportation of larvae may occur (Palumbi 2003). In the northwest Pacific, two strong ocean currents, the Kuroshio and North Equatorial Currents, should facilitate the dispersal of pelagic larvae. The Kuroshio Current originates in the westward-flowing North Equatorial Current of the central Pacific Ocean and deflects towards the northeast offshore of the Philippine Islands. There are many examples that marine organisms having a pelagic larval phase show strong regional genetic differentiation in the area of the Kuroshio Current (Ogoh and Ohmiya 2005; Kojima et al 2006; Liu et al 2008; Yorifuji et al 2012)
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