engrailed duplication events during the evolution of barnacles

Barnacles (Cirripedia) are a subclass of Crustacea. Their peculiar segmentation pattern (few segments, absence of abdominal segments, and, in the parasitic rhizocephalan, loss of segmentation at the adult stage) prompted us to study the engrailed gene, which encodes a homeodomain transcription factor and is expressed in arthropods in the posterior half of each segment. We searched for engrailed genes by PCR in a representative cross section of the Cirripedia. Eight unambiguous engrailed genes were cloned from five species, three genes belonging to the same species (Elminius modestus). This implies two duplication events. Molecular phylogenies were constructed and a cladistic approach was applied to the most informative sites. The results indicate that the older duplication (en.a/en.b) is probably very ancient and concerns the whole cirripedean subclass, whereas the other (en.a1/en. a2) is specific to the Elminius lineage.