Vintage helminths yield valuable molecules

The promise of a DNA taxonomy

Not only is the number of described species a very small proportion of the estimated extant number of taxa, but it also appears that all concepts of the extent and boundaries of 'species' fail in many cases. Using conserved molecular sequences it is possible to define and diagnose molecular operational taxonomic units (MOTU) that have a similar extent to traditional 'species'. Use of a MOTU system not only allows the rapid and effective identification of most taxa, including those not encountered before, but also allows investigation of the evolution of patterns of diversity. A MOTU approach is not without problems, particularly in the area of deciding what level of molecular difference defines a biologically relevant taxon, but has many benefits. Molecular data are extremely well suited to re-analysis and meta-analysis, and data from multiple independent studies can be readily collated and investigated by using new parameters and assumptions. Previous molecular taxonomic efforts have focused narrowly. Advances in high-throughput sequencing methodologies, however, place the idea of a universal, multi-locus molecular barcoding system in the realm of the possible.

Molecular phylogenetic analysis of the genus Strongyloides and related nematodes

Strongyloides spp., parasitic nematodes of humans and many other terrestrial vertebrates, display an unusual heterogonic lifecycle involving alternating parasitic and free-living adult reproductive stages. A number of other genera have similar lifecycles, but their relationships to Strongyloides have not been clarified. We have inferred a phylogeny of 12 species of Strongyloides, Parastrongyloides, Rhabdias and Rhabditophanes using small subunit ribosomal RNA gene (SSU rDNA) sequences. The lineage leading to Strongyloides appears to have arisen within parasites of terrestrial invertebrates. Inferred lifecycle evolution was particularly dynamic within these nematodes. Importantly, the free-living Rhabditophanes sp. KR3021 is placed within a clade of parasitic taxa, suggesting that this species may represent a reversion to a non-parasitic lifecycle. Species within the genus Strongyloides are very closely related, despite the disparity of host species parasitised. The highly pathogenic human parasite Strongyloides fuelleborni kelleyi is not supported as a subspecies of the primate parasite S. fuelleborni fuelleborni, but is most likely derived from a local zoonotic source.

New data from old Trypanosomatid preparations

Assessing the diversity of the Trypanosomatidae is difficult because of the relatively small number of species that can be cultured. This same problem thwarts efforts to identify the hosts and insect vectors of Phytomonas, a genus of parasites of plants that includes species responsible for devastating epiphytotics of economically important plantations. Here, Myrna Serrano, Marta Teixeira and Erney Camargo review the studies that have led to the development of a PCR-based technique for processing insect and plant juices fixed on glass slides. The method overcomes the need for cultivation, facilitates field collections and also permits the molecular examination of archival smears of Phytomonas. In principle, the method can be adapted to any trypanosomatid as well as to any fastidious parasitic or free-living organism.

Molecular analysis of nematode diversity and the evolution of parasitism

A thorough and coherent classification of the phylum Nematoda is essential if the evolution of countless phenotypes is to be understood. Here, Mark Dorris, Paul De Ley and Mark Blaxter discuss how the application of molecular phylogenetics is helping to resolve some of the inconsistencies in morphological classification and phylogeny by establishing relationships between free-living and parasitic groups, showing possible patterns underlying the origins of parasitism and placing key nematode species in an evolutionary context for comparative study.

Observations on the phylogeny of the cestode order Pseudophyllidea Carus, 1863

A preliminary phylogenetic analysis of the Pseudophyllidea, based on the 16 type-genera of putative families, indicates that a division into two suborders is reasonable. The subordinal grouping are, on the whole, congruent with those suggested by earlier workers, but the positions of three genera, Hexagonoporus, Cephalochlamys and Parabothriocephalus, are somewhat anomalous with respect to earlier work.