ISSN:
1550-7408
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
Apostome ciliates are exclusively symbionts, typically of crustaceans. Their life cycles are complex, but show remarkable similarities to ophyroglenines and to other symbiotic oligohymenophoreans, particularly those that undergo microstome–macrostome transformations. The highly modified structures around the cytostome—the rosette and x, y, and z kineties—have made the assessment of homologies to other groups of ciliates difficult. A description of the apostome somatic kinetids with well-developed overlapping kinetodesmal fibrils suggested affinities with hymenostomes (Bradbury 1966. J. Protozool., 13:591). Further analysis of the ultrastructural features of the oral region of the tomite of Hyalophysa demonstrated homologies to the paroral and adoral ciliature of hymenostomes, confirming these affinities (Bradbury 1989. J. Protozool., 36:95). To test this hypothesis, we proposed to sequence the small subunit rRNA (SSrRNA) genes of apostomes. Specimens of Gymnodinioides sp. were collected from molts of the amphipod Marinogammarus obtusatus collected off the coast of Eastport, ME. Seawater was decanted from the substrate upon which tomonts had settled, and the dish was flooded with 70% ethanol. The ethanol-fixed ciliates were collected by a micropipette, rinsed with distilled water, and DNA was extracted using the modified Chelex® protocol. The SSrRNA genes were amplified by PCR, and sequences obtained in both directions. Initial BLAST searches of the GenBank databases clearly demonstrated affinities with oligohymenophorean ciliates, particularly scuticociliates. In preliminary phylogenetic analyses which use likelihood, distance and parsimony methods, this relationship was confirmed. However, the apostome sequence diverged basal to the Subclasses Astomatia and Scuticociliatia consistent with the assignment of a Subclass Apostomatia within the Class Oligohymenophorea. We have made collections of Hyalophysa chattoni and anticipate that the SSrRNA gene sequences of this genus will confirm the relationship of apostomes to the oligohymenophoreans.Funded by NSERC Canada Discovery Grant to D. H. L.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1550-7408.2005.05202003_1_54.x
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