Molecular characterisation and evolution of the hemocyanin from the European spiny lobster, Palinurus elephas

The hemocyanin of the European spiny lobster Palinurus elephas (synonym: Palinurus vulgaris) is a hexamer composed by four closely related but distinct subunits. We have obtained the full cDNA sequences of all four subunits, which cover 2275-2298 bp and encode for native polypeptides of 656 and 657 amino acids. The P. elephas hemocyanin subunits belong to the alpha-type of crustacean hemocyanins, whereas beta- and gamma-subunits are absent in this species. An unusual high ratio of non-synonymous versus synonymous nucleotide substitutions was observed, suggesting positive selection among subunits. Assuming a constant evolution rate, the P. elephas hemocyanin subunits emerged from a single hemocyanin gene around 25 million years ago. The alpha-type hemocyanins of P. elephas and the American spiny lobster Panulirus interruptus split around 100 million years ago. This is about five times older than the assumed divergence time of the species and suggests that the genera may have split with the formation of the Atlantic Ocean. The application of the Bayesian method for phylogenetic inference allows for the first time a solid reconstruction of the evolution of the decapod hemocyanins, showing that the beta-subunit types diverged first and that the crustacean pseudo-hemocyanins are associated with the gamma-type subunits.