Phylogeny of the Haplosporidia (Eukaryota: Alveolata) Based on Small Subunit Ribosomal RNA Gene Sequence

Abstract

The phylogenetic position of the phylum Haplosporidia was investigated with the complete small subunit rRNA gene sequences from 5 species in the phylum: Haplosporidium nelsoni and Haplosporidium costale, parasites of the eastern oyster Crassostrea virginica; Haplosporidium louisiana, a parasite of the mudcrab Panopeus herbstii; Minchinia teredinis, a parasite of shipworms (Teredo spp.) and Urosporidium crescens, a hyperparasite found in metacercariae of the trematode Megalophallus sp. in the blue crab, Callinectes sapidus. Multiple alignments of small subunit rRNA gene sequences included the 5 haplosporidian taxa and 14 taxa in the alveolate phyla Ciliophora, Dinoflagellida, and Apicomplexa. Maximum parsimony analysis placed the phylum Haplosporidia as a monophyletic group within the alveolate clade, as a taxon of equal rank with the other 3 alveolate phyla, and as a sister taxon to the clade composed of the phyla Dinoflagellida and Apicomplexa. Transversionally weighted parsimony placed the haplosporidians as a sister taxon to the ciliates. A separate analysis focused on the relationships of species in the genus Haplosporidium. Analyses were conducted with the haplosporidians as a functional ingroup, using each of the alveolate phyla individually as functional outgroups. The results indicated that species in the genus Haplosporidium do not form a monophyletic assemblage. As such, the present morphological criteria for distinguishing the genera Haplosporidium and Minchinia are insufficient.