Mitochondrial DNA analysis reveals a unique population structure of the amphidromous sculpin Cottus pollux middle-egg type (Teleostei: Cottidae)

In this study, we examined nucleotide sequences from the first half of the mitochondrial control region gene to test for genetic differentiation in an amphidromous sculpin, Cottus pollux middle-egg type (ME) (Cottidae), obtained from 19 localities across its distribution range. Spatial analysis of molecular variance revealed five divergent groups of related haplotypes among this populations. Analysis with Migrate software revealed that gene flow was quite restricted among the groups, although it occurred practically between neighboring groups. It has previously been reported that the population structure among the amphidromous fishes of the various islands is low or non-existent, and is characterized mainly by the duration of the pelagic larval life. However, the present study demonstrated that the various C. pollux ME populations were different both among the islands, and within the island of the Japanese Archipelago. Our finding indicate that the unique population structure of C. pollux ME may be influenced not only by the extent of the pelagic larval phase of the species but also by the seasonal differentiation of its dispersal phase.

► Unique population structure of the amphidromous fishes.
► The population structure of amphidromous fish, Cottus pollux ME is formed by 5 divergent groups.
► The population structure of C. pollux ME may be influenced by the extent of the pelagic larval phase of the species.
► The population structure of C. pollux ME may be influenced by the seasonal differentiation of the dispersal phases.