The 18S ribosomal RNA gene of a crustacean decapod Oedignathus inermis: a comparison with Artemia salina gene

The monophyletic origin of freshwater crayfish estimated from nuclear and mitochondrial DNA sequences

Despite their widespread use as model organisms, the phylogenetic status of the around 520 species of freshwater crayfish is still in doubt. One hypothesis suggests two distinct origins of freshwater crayfish as indicated by their geographical distribution, with two centres of origin near the two present centres of diversity; one in south-eastern United States and the other in Victoria, Australia. An alternative theory proposes a single (monophyletic) origin of freshwater crayfish. Here we use over 3000 nucleotides from three different gene regions in estimating phylogenetic relationships among freshwater crayfish and related Crustacea. We show clear evidence for monophyly of freshwater crayfish and for the sister-group relationship between crayfish and clawed lobsters. Monophyly of the superfamilies Astacoidea and Parastacoidea is also supported. However, the monophyly of the family Cambaridae is questioned with the genus Cambaroides being associated with the Astacidae.

Sequences of the 18S rDNAs from two Collembolan insects: shorter sequences in the V4 and V7 regions

The complete 18S rDNA sequences were determined for Hypogastrura sp. and Crossodonthina koreana (Insecta: Collembola) using PCR cloning and Taq dideoxy sequencing. These two wingless insects show high sequence similarity to each other, without large insertions and/or deletions, and are clearly distinguished from the two dipteran insects Drosophila melanogaster and Aedes albopictus by shorter sequences in the V4 (61-76 bp) and in the V7 (89-104 bp). regions.

Sequence of the 18S ribosomal RNA-encoding gene of the crustacean Philyra pisum: longer sequences of decapods in the V9 region

The complete sequence of the 18S rRNA gene of Philyra pisum was determined by using PCR cloning and Taq sequencing. The sequence was compared with those known from other crustaceans. The decapods (Oedignathus inermis, Pugettia quadridens, Philyra pisum) were distinguished from the other crustaceans (Artemia salina, Bosmina longirostris, Diastylis sp.) by longer sequences (17-41 bp) in the V9 region.