Molecular phylogeny of pelagic chaetognaths

Abstract

We have studied the intra- and inter-species phylogeography of chaetognaths by molecular biological methods to understand their speciation processes in the open sea. An outline of part of our study is described here. Firstly, we sequenced and analyzed part of the mitochondrial cytochrome c oxidase subunit I gene for various chaetoganths species to clarify the genetic distances indicative of intra- and inter-species relationships. The interspecies genetic distance between Eukrohnia bathyantarctica and E. fowleri was the smallest among the analyzed species. Also, monophyly for clades that are comprised by a single morphological species was supported by high statistical values, except for in the case of E. hamata and E. bathypelagica, for which the morphological classification was not supported by our molecular analysis. On the other hand, the present study showed that morphological species often comprised more than two genetic groups where the genetic distance was larger between these groups than within that morphological species clade, and this was supported by a high bootstrap values. In some groups of several species, differences in the morphology and distribution between groups were discovered by detailed observations on the meso- and bathypelagic species. These results suggest that both classification by molecular methods and new observations on of morphology are needed to understand the real species diversity of chaetoganths.