Evidence for translational selection in codon usage in Echinococcus spp.

We analysed the intragenomic variation in codon usage in Echinococcus spp. by correspondence analysis. This approach detected a trend among genes which was correlated with expression levels. Among the (presumed) highly expressed sequences we found an increased usage of a subset of codons, almost all of them G- or C- ending. Since an increase in these bases at the synonymous sites is against the mutational bias (these genomes are slightly A+T-rich), we conclude that codon usage in Echinococcus is the result of an equilibrium between compositional pressure and selection, the latter acting at the level of translation, mainly on highly expressed genes. This is the first report where translational selection for codon usage is detected among Platyhelminthes.