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Phylogeny of gregarines (Apicomplexa) as inferred from small-subunit rDNA and -tubulin

¹ Canadian Institute for Advanced Research, Program in Evolutionary Biology, Department of Botany, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
² Division of Science and Technology, Peru State College, Peru, NE 68421, USA

Correspondence
Patrick Keeling
pkeeling{at}interchange.ubc.ca

Gregarines are thought to be deep-branching apicomplexans. Accordingly, a robust inference of gregarine phylogeny is crucial to any interpretation of apicomplexan evolution, but molecular sequences from gregarines are restricted to a small number of small-subunit (SSU) rDNA sequences from derived taxa. This work examines the usefulness of SSU rDNA and -tubulin sequences for inferring gregarine phylogeny. SSU rRNA genes from Lecudina (Mingazzini) sp., Monocystis agilis Stein, Leidyana migrator Clopton and Gregarina polymorpha Dufour, as well as the -tubulin gene from Leidyana migrator, were sequenced. The results of phylogenetic analyses of alveolate taxa using both genes were consistent with an early origin of gregarines and the putative ‘sister’ relationship between gregarines and Cryptosporidium, but neither phylogeny was strongly supported. In addition, two SSU rDNA sequences from unidentified marine eukaryotes were found to branch among the gregarines: one was a sequence derived from the haemolymph parasite of the giant clam, Tridacna crocea, and the other was a sequence misattributed to the foraminiferan Ammonium beccarii. In all of our analyses, the SSU rDNA sequence from Colpodella sp. clustered weakly with the apicomplexans, which is consistent with ultrastructural data. Altogether, the exact position of gregarines with respect to Cryptosporidium and other apicomplexans remains to be confirmed, but the congruence of SSU rDNA and -tubulin trees with one another and with morphological data does suggest that further sampling of molecular data will eventually put gregarine diversity into a phylogenetic context.

Published online ahead of print on 26 July 2002 as DOI 10.1099/ijs.0.02284-0.

The GenBank accession numbers for the small-subunit rDNA sequences from Monocystis agilis, Lecudina sp., Gregarina polymorpha and Leidyana migrator are respectively AF457127–AF457130. The GenBank accession number for the -tubulin sequence from Leidyana migrator is AF457131.

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