Mitochondrial and nuclear rRNA based copepod phylogeny with emphasis on the Euchaetidae (Calanoida)

Phylogenetic relationships within the copepod family Euchaetidae and betwee n representatives of three copepod orders (Calanoida, Harpacticoida, and Po ecilostomatoida) were investigated using partial nucleotide sequences of th e mitochondrial 16S rRNA and the nuclear 28S rRNA genes. DNA isolation, pol ymerase chain reaction, cloning, and DNA sequencing techniques were customi zed for these crustaceans. Our results support the monophyly of each copepo d order, but in contrast to traditional morphology-based phylogenies of cop epod orders, the Poecilostomatoida are basal to the Calanoida and Harpactic oida on our DNA-based phylogenetic tree. Phylogenetic trees generated by ma ximum parsimony, neighbor-joining, and maximum-likelihood analyses support the classification of the genera Euchaeta and Paraeuchaeta in the family Eu chaetidae; results, however, suggest that Euchaeta acuta Giesbrecht is more closely related to species of the genus Paraeuchaeta than to those of Euch aeta, although limited taxon sampling may be partially responsible for this result. Phylogenetic mapping using the most parsimonious 16S tree suggests that the morphological synapomorphies distinguishing the genus Euchaeta ev olved independently twice during the history of the Euchaetidae. Further, p hylogenetic mapping suggests that the most recent common ancestor of the Eu chaetidae and the Aetideidae was a deep-living, vertically migrating copepo d, and that a bathypelagic, vertically migrating lifestyle characteristic o f Paraeuchaeta is an ancestral trait of the family Euchaetidae which was lo st apomorphically by Euchaeta. The application of a molecular clock suggest s that the sibling species Euchaeta rimana Bradford and Euchaeta marina (Pr estandrea) diverged due to the emergence of the Panamanian land bridge.