TABLE CONTENTS

Mitochondrial DNA Frameshift Mutations in the Heteroderidae
Nematodes: A New Phylogenetic Marker for the Cyst-forming Nematodes?
Riepsamen, A.H. (1), T. Gibson (1), V.C. Blok (2), M. Phillips (2) & M. Dowton (1)
(1) School of Biological Sciences, University of Wollongong, New South Wales 2522; (2)
Department of Nematology, Scottish Crop Research Institute, Dundee DD2 D5A, Scotland
Mitochondrial genomes (mtDNA) are used extensively in phylogenetics due to their sole
maternal inheritance, apparent lack of recombination, and sequence conservation within a
taxon. Typically, animal mtDNA have a highly compact gene arrangement with no introns,
minimal non-coding sequence, and with intra-individual variation limited to infrequent silent
mutations. However, the mtDNA of cyst-forming, plant-parasitic nematodes (Tylenchida:
Heteroderidae) is unusual, with recombination apparent in the Globodera genus, as well as
abundant intra-individual variation. Our research found that nematodes of the Heterodera and
Gobodera genera have extensive variation in the length of long poly-thymidine tracts within
protein-coding genes, such that the reading frame would not be maintained in all gene copies
if they were coded for directly. Comparisons with expressed sequence tag (EST) data
indicated that this variation was also present at the mRNA level. Further studies are required
to determine whether these copies are translated or edited, and what effect they have on the
physiology of the cyst nematodes.
Thus far we have observed poly-T variation only in cyst-forming nematodes, but not in their
close relatives, the root knot nematodes (Tylenchida: Meloidogynidae). We therefore
hypothesise that poly-T variation is a synapomorph for the Heteroderidae, and as such may
provide a new phylogenetic character for the cyst-forming nematodes.
Symbiotic Association of a Monhysterid Nematode in Perianal Folds of
Stinkpot Turtles
Sharma, J. (1) & T. Platt (2)
(1) University of Texas at San Antonio, San Antonio, TX 78249; (2) Department of Biology, Saint Mary's
College, Notre Dame, IN 46556,
The Monhysteridae is a family of free-living nematodes that is associated with fresh and
marine benthic habitats. An examination of perianal folds of the stinkpot turtles,
Sternotherus odoratus, from Virginia, USA, found several monhysterid nematodes.
Morphological characters such as circular amphids, unstriated cuticle, single outstretched
ovary, single testis, caudal glands, terminal spinnerette and the absence of a apophysis on the
gubernaculum suggest close affinity to the Monhysteridae. Confocal microscope
observations of the buccal morphology note distinct teeth and denticles on the extensions of
the buccal wall and suggest that this is a new genus. The systematic position of this genus is
compared to other commensal monhysterids. Affinities of this genus with Gammarinema,
Monhystrium and Tripylium that are ectocommensals of crustaceans are discussed. The
genus Tridentulus has denticles on the base of the stoma but lacks the buccal wall extensions.
A monhysterid, Odontobius ceti, has also been described from baleen plates of whales.
Stinkpot turtles feed on benthic fauna and may acquire the symbionts when sediment is
disturbed. The significance and evolutionary aspects of the transition to commensalism of
this genus and related adenophorean genera are discussed. The feeding behavior of stinkpot
turtles that may facilitate acquisition of these commensal nematodes is discussed as a
pathway to symbiosis.
5 th International Congress of Nematology, 2008 191