Worldwide molecular phylogeny of common estuarine polychaetes of the genus Hediste (Annelida: Nereididae), with special reference to interspecific common haplotypes found in southern Japan

摘要

The nucleotide sequences of two mitochondrial genes (16S rDNA and COI) were compared among all species of Hediste, including five nominal and two cryptic species (H. atoka and H. diversicolor both consisting of two cryptic species, H. diadroma, H. japonica, and H. limnicola), as well as a newly found undescribed species (H. sp.), to estimate their phylogenetic relationships. The analysis using 16S rDNA sequence supported the monophyly of all five nominal species and H. sp., with no detection of the genetic differentiation between the two cryptic species in both H. atoka and H. diversicolor. However, analysis using COI sequence detected a marked differentiation between the cryptic species, and indicated that the two forms of H. atoka were separated into distinct clades; form A was included in a clade together with H. diversicolor, H. limnicola, and H. sp., whereas form B was included in another clade together with H. diadroma. Based on the topology of our phylogenetic analysis using the combined data set of 16S rDNA and COI, a hypothesis on the evolutionary history of the worldwide speciation in Hediste is proposed. This hypothesis seems to correspond well with the geographical distributions of current species and their morphological differentiation, supporting the previous hypothesis that the unique epitokous swarming and planktic larval development evolved independently in H. diadroma and H. japonica in eastern Asia. We also show that no or few interspecific substitutions have occurred in sequences of nuclear DNA (18S rDNA, 28S rDNA, and histone H3) in Hediste.