2 resultados para ITS1

em University of Queensland eSpace - Australia


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The molecular diversity of symbiotic dinoflagellates associated with the widespread western Pacific coral Plesiastrea versipora was explored in order to examine if associations between reef-building corals and symbiotic dinoflagellates change with environment. Several ribosomal DNA genes with different evolutionary rates were used.. including the large subunit (28S), the 5.8S region and the internal transcribed spacers (ITS). The phylogenetic analysis of the 28S and 5.8S rDNA regions indicated that a single endosymbiont species, highly related to one of the species of Symbiodinium in clade C (=Synbiodinium goreaui, Trench et Blank), associates with P. versipora along the Ryukyu Archipelago. The persistence of the same endosymbiont within P. versipora across this wide array of latitudes may be a result of such features as the Kuroshio Current, which brings tropical temperatures as far north as Honshu, Japan. Analysis of the faster evolving ITS rDNA region revealed significant genetic variability within endosymbionts from different populations. This variation was due to a high degree of interpopulation variability, based on the proportion of pairwise variation detected among the populations (0.95% approximately). By comparison with other studies, the results also indicate that some ITS1 haplotypes from P. versipora endosymbionts seem to be widely distributed within the western Pacific Ocean, ranging from the Great Barrier Reef to the northeast of the China Sea.

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In just over a decade, the use of molecular approaches for the recognition of parasites has become commonplace. For trematodes, the internal transcribed spacer region of ribosomal DNA (ITS rDNA) has become the default region of choice. Here, we review the findings of 63 studies that report ITS rDNA sequence data for about 155 digenean species from 19 families, and then review the levels of variation that have been reported and how the variation has been interpreted. Overall, complete ITS sequences (or ITS1 or ITS2 regions alone) usually distinguish trematode species clearly, including combinations for which morphology gives ambiguous results. Closely related species may have few base differences and in at least one convincing case the ITS2 sequences of two good species are identical. In some cases, the ITS1 region gives greater resolution than the ITS2 because of the presence of variable repeat units that are generally lacking in the ITS2. Intraspecific variation is usually low and frequently apparently absent. Information on geographical variation of digeneans is limited but at least some of the reported variation probably reflects the presence of multiple species. Despite the accepted dogma that concerted evolution makes the individual representative of the entire species, a significant number of studies have reported at least some intraspecific variation. The significance of such variation is difficult to assess a posteriori, but it seems likely that identification and sequencing errors account for some of it and failure to recognise separate species may also be significant. Some reported variation clearly requires further analysis. The use of a yardstick to determine when separate species should be recognised is flawed. Instead, we argue that consistent genetic differences that are associated with consistent morphological or biological traits should be considered the marker for separate species. We propose a generalised approach to the use of rDNA to distinguish trematode species.