Submitted to: Comparative Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2008
Publication Date: 8/14/2009
Citation: Carta, L.K., Handoo, Z.A., Hoberg, E.P., Erbe, E.F., Wergin, W.P. 2009. Evaluation of some vulval appendages in nematode taxonomy. Comparative Parasitology. 76(2):191-209. Interpretive Summary: Plant parasitic nematodes are microscopic worms that cause ten billion dollars of crop losses each year in the United States. Determining which nematodes are causing crop damage is difficult because of two problems facing nematode identifiers: the minuteness of the anatomical structures used for identification and the different names used to describe similar anatomical structures. Therefore, this paper documents and illustrates the numerous structures on the nematode surface in the vicinity of the nematode vulva; moreover, uniform terminology is used instead of the multiple terms present in scientific literature. The results are significant because these structures can now be reliably compared to each other in order to more accurately identify nematodes or compare the relationships between different groups of nematodes. Therefore, this information will be used by other researchers to identify nematodes or study the relationships between them.
Technical Abstract: A survey of the nature and phylogenetic distribution of nematode vulval appendages revealed three major classes based on composition, position and orientation: membranes, flaps, and epiptygma. Minor classes included cuticular inflations, vulval tubes of extruded gonadal tissues, vulval ridges, and peri-vulval pits. Vulval membranes were found in Mermithida, Chromadorida, Rhabditidae, Panagrolaimidae, Tylenchida and Trichostrongylidae. Vulval flaps were found in Desmodoroidea, Mermithidae, Oxyurida, Tylenchida, Rhabditida and Trichostrongyloidea. Epiptygmata were present within Aphelenchida, Tylenchida, Rhabditida, Steinernematidae (recently moved to Panagrolaimomorpha), and Enoplida. Within the Rhabditida, vulval ridges occurred in Cervidellus (Cephalobidae), peri-vulval pits in Strongyloides spp. (Strongyloidoidea), and cuticular inflations in Trichostrongylidae. Vulval membranes have been confused with persistent copulatory sacs deposited by males, and some putative appendages may be artifactual. Vulval appendages occurred almost exclusively in commensal or parasitic nematode taxa. Nematodes with vulval membranes also had caudal alae within Tylenchida, Aphelenchida and Rhabditoidea but not in parasitic Mermithida. Appendages are discussed based on their relative taxonomic reliability, ecological associations, and distribution in the context of a molecular phylogenetic tree for the nematodes. Characters were found to be distributed across subsets of terminal and phylogenetically distant taxa, demonstrating considerable homoplasy. Accurate definitions, terminology and documentation of the taxonomic distribution of vulval appendages are important in evaluations of hypotheses for either parallelism and developmental constraint or convergence and adaptation using a candidate gene approach to the evolution of these characters.