DNA evolution in krill : molecular phylogenetics and population genetics of Euphausiacea (Crustacea: Malacostraca) and their close relatives

The evolutionary history of krill (Euphausiacea: Crustacea) was studied through information held in their DNA. The earliest events in the evolution of this group were investigated by phylogenetic analysis of slowly evolving nuclear DNA sequences of krill and their near relatives. These analyses established the sister taxon of krill to be the Mysida. Molecular dating techniques suggested that krill diverged from the Mysida in the upper Carboniferous, two lineages of krill survived the end Cretaceous extinctions, and the extant genera of Euphausiidae radiated during the early Palaeogene. More recent speciation events in the krill genus Euphausia were studied by phylogenetic analysis of mitochondrial DNA sequences. A comparison between the speciation history of Euphausia and that of freshwater crustaceans in the Anaspididae was made because the Anaspididae are close relatives of krill and have undisputable barriers to migration between populations that are not present for krill. This comparison suggests that genetic differentiation in Euphausia may involve parapatric or even sympatric processes. Microevolution in the krill species Euphausia crystallorophias was studied by comparing allele frequencies between populations of krill from different parts of its range. Features of the genome of Euphausia superba were characterized in order to compare its qualities with the genomes of other metazoans.