Species and morphs in the Ostertagiinae: an allozyme study of seven species

Insight into species diversity of the Trichostrongylidae Leiper, 1912 (Nematoda: Strongylida) in ruminants

This paper focuses on the species diversity among the Trichostrongylidae Leiper, 1912 (Nematoda: Strongylida), and complexity of the family systematics. Polymorphism (subfamilies: Ostertagiinae, Cooperiinae and Haemonchinae), the presence of cryptic species (genus: Teladorsagia) and hybridization (genera: Cooperia, Haemonchus and Ostertagia) are presented and discussed, considering both morphological and molecular evidence. Some of these phenomena are common, nevertheless not sufficiently understood, which indicates the need for expanding the current state of knowledge thereof. Within the Trichostrongylidae, species distinction supported merely by morphological features is difficult, and requires confirmation by means of molecular methods. The parasitic nematode taxonomy is complicated mainly by the genus Teladorsagia, but complexity may also be expected among other Ostertagiinae (e.g. in the genera Ostertagia and Marshallagia). The data presented here show that the members of the Trichostrongylidae can significantly complicate unambiguous species identification. Hence, it is essential to consider the phenomena mentioned, to gather valid and comparable data on the biodiversity of this family.

Molecular genetic conspecificity of Spiculopteragia houdemeri (Schwartz, 1926) and S. andreevae (Dróżdż, 1965) (Nematoda: Ostertagiinae) from wild ruminants in Japan

Male dimorphism of the subfamily Ostertagiinae (Nematoda: Trichostrongylidae) is a well-known phenomenon, and two or more morphotypes of a single species have previously been described as different species. Two Spiculopteragia spp., S. houdemeri (syn. S. yamashitai) and S. andreevae (syn. Rinadia andreevae) recorded in Asian cervids and wild bovids, are considered to represent major and minor morphs of S. houdemeri, respectively, based solely on their co-occurrence in the same host individual along with monomorphic females. In this study, males of morph houdemeri ( = S. houdemeri) and morph andreevae ( = S. andreevae) as well as females with three different vulval ornamentations were collected from sika deer (Cervus nippon) and Japanese serows (Capricornis crispus) distributed on the mainland of Japan. Morphologically characterized worms were subjected to molecular genetic analyses based on the internal transcribed spacer region of the ribosomal RNA gene and a partial region of the cytochrome c oxidase subunit I gene of mitochondrial DNA. Of 181 collected sika deer, 177 (97.8%) and 73 (40.3%) deer harboured males of morphs houdemeri and andreevae, respectively. Worm numbers of the former morph were found to range between 1 and 444 per individual, whereas only 1–25 worms per individual were detected for the latter morph. Five out of six serows harboured 47–71 or 2–9 males of morphs houdemeri and andreevae per individual, respectively. Females with one or two vulval flaps were predominant, but there was a substantial presence of flapless females in both host species. All the morphs of male and female adults had an identical genetic background, thus directly confirming the morphological polymorphism of S. houdemeri.

Spiculopteragia mathevossianiRuchliadev, 1948 is the minor morph ofSpiculopteragia spiculoptera(Gushanskaya, 1931): molecular evidence

Although Spiculopteragia spiculoptera is primarily a parasite of cervids, it can also but less often contaminate domestic livestock. Little is known about its epidemiology and its pathogenicity in domestic ruminants and other unusual cervid species. Its taxonomic status remains unclear since the hypothesis of morphological polymorphism among males has been proposed. However, accurate taxonomy is fundamental in the identification and survey of potentially pathogenic species of parasites. The second internal transcribed spacer of rDNA (ITS-2) and the mitochondrial (mt) DNA-derived ND4 gene were used to study the polymorphism hypothesis for S. spiculoptera. ND4 evolves more quickly than ITS-2 and is considered to be more discriminant in the characterization of closely related species. DNA sequences of ITS-2 and ND4 were studied in 18 individual males of morphological type spiculoptera and in 3 of morphological type of mathevossiani from Red deer (Cervus elaphus), Roe deer (Capreolus capreolus) and Chamois (Rupicapra rupicapra). Intraindividual ITS-2 variations were detected within and between each morphotype of Spiculopteragia but these differences did not separate the two morphs mathevossiani and spiculoptera. Similarly, although ND4 showed a high level of nucleotide substitution, the morphotypes S. mathevossiani and S. spiculoptera were clustered together. Our genetic data support the dimorphic male hypothesis for the species S. spiculoptera.

Identical ITS-1 and ITS-2 sequences suggest Spiculopteragia asymmetrica and Spiculopteragia quadrispiculata (Nematoda: Trichostrongylidae) constitute morphologically distinct variants of a single species

Sequences of ITS-1 and ITS-2 rDNA for adult males of Spiculopteragia asymmetrica and Spiculopteragia quadrispiculata in red deer (Cervus elaphus) were determined. They were found to be identical, suggesting that S. asymmetrica and S. quadrispiculata represent a single species and do not refute the concept of dimorphic species in the Spiculopteragia.

New molecular evidence that Teladorsagia circumcincta (Nematoda: Trichostrongylidea) is a species complex

In the polymorphic Teladorsagia circumcincta (morphs circumcincta and trifurcata), a sheep and goat line (SGL) and a goat line (GL) have been previously described on the basis of the malate dehydrogenase allozyme polymorphism (MDH-2) and of the morphology of the dorsal ray. The GL were never found alone in 1 host, so the status of species was not given to these 2 lines. To investigate further whether there are other genetic markers that will delineate them, we collected T. circumcincta worms from goat and sheep at 8 farms in Touraine (west-central France). The worms were identified individually as being SGL or GL on the basis of MDH-2 polymorphism. This distinctiveness was corroborated by sequences of the beta-tubulin isotype I gene, the second internal transcribed spacer (ITS2) of their rDNA, and the nicotinamide dehydrogenase (ND4) gene of their mDNA. The extent of the divergence in the 3 additional genetic markers was such that SGL and GL may be considered as 2 species. A third putative species was found in the SGL line based exclusively on the ND4 gene. These findings suggest that T. circumcincta is a species complex and that further investigation is required on a wider geographic scale.

DNA evidence that Marshallagia marshalli Ransom, 1907 and M. occidentalis Ransom, 1907 (Nematoda: Ostertagiinae) from Svalbard reindeer are conspecific

The gastro-intestinal parasitic nematodes of ruminants Marshallagia marshalli and M. occidentalis are morphs of a single species according to indirect evidence. In this study, their taxonomic status and molecular identification were assessed more directly in isolates from the abomasal nematode community of Svalbard reindeer using genetic data. DNA sequences of the first and second internal transcribed spacers of nuclear ribosomal RNA genes were obtained from individual nematodes by the polymerase chain reaction (PCR). Both taxa contained virtually identical sequences of each ITS and shared most of the polymorphisms detected. A PCR assay based on ITS-2 sequences previously developed to identify M. marshalli and Ostertagia gruehneri, the second common species in this community, gave identical results for M. marshalli and M. occidentalis. Genetic data thus confirmed that M. marshalli and M. occidentalis are conspecific.

Evidence for continued transmission of parasitic nematodes in reindeer during the Arctic winter

Living in the high Arctic, the Svalbard reindeer (Rangifer tarandus platyrhynchus) and its trichostrongyle nematodes experience a long cold winter from October to late May/early June. Over this period, transmission would be expected to be low. However, in culled reindeer the abundance of infection increased from autumn to late winter, providing evidence for continued transmission within this period. To our knowledge this is the first time this has been demonstrated in a climate with temperatures consistently below 0 degrees C. In one winter (1996-1997), the average fraction of nematodes found as larvae in the abomasal mucosa increased from around 10% to 50% between October and March. This suggests that arrested development took place throughout the winter. We found no evidence for an efficient acquired immune response towards the nematodes. The abundance of infection did not tend to decrease with increasing host age after an earlier peak, but levelled off instead, as predicted by a simple immigration-death model. In the late winter when the nutritional plane is low, both adult reindeer and calves had high worm burdens at intensities that may affect their condition and fitness.

Multilocus enzyme electrophoresis: a valuable technique for providing answers to problems in parasite systematics

The aim of this review is to highlight the effectiveness of the technique of multilocus enzyme electrophoresis in answering questions relating to the systematics of parasites and to highlight errors in the way the technique has been used and the results interpreted. We have approached this topic by answering specific questions that we have been asked by colleagues and students not necessarily familiar with the technique, the method of data analysis and its application. Although the technique has been applied to provide answers for taxonomic and population genetics studies, it remains under-utilised, perhaps because of recent advances in newer molecular technology. Rather than not acknowledge or dismiss the value of more traditional technology, we suggest that researchers examine problems in the systematics of parasites by the comparison of data derived from morphological, biochemical and molecular techniques.

Systematics of gastrointestinal nematodes of domestic ruminants: advances between 1992 and 1995 and proposals for future research

The systematics of trichostrongyloid nematodes of ruminants provides a foundation for diagnostics and responds to the need to identify eggs in feces, free-living larvae from pastures or fecal cultures and larval or adult nematodes collected from hosts. These needs are associated with diagnostic problems or research projects. Difficulties in identifying all developmental stages of trichostrongyloid nematodes of domestic ruminants still severely limit the effective diagnosis and control of these parasites. Phylogenetic hypotheses as the basis for predictive classifications have been developed only for the subfamilies of the Trichostrongylidae. This report briefly describes recent progress in the development of improved tools for identification, phylogenetic analyses and predictive classifications. It also describes future research needed on the identification and classification of trichostrongyloid nematode parasites of domestic ruminants. Nematodes included are species of the super-family Trichostrongyloidea known to be important pathogens of domestic ruminants. The information summarized is presented by nematode developmental stage and by taxonomic groups. Eggs: While eggs of some trichostrongyloid nematode parasites of ruminants can be readily identified to their genus (Nematodirus), and some to species (e.g. Nematodirus battus), most of the important pathogens (including the Ostertagiinae and Haemonchinae) cannot be identified morphologically or morphometrically even to family level. However, DNA technology has been developed for determining not only the presence of specific pathogens in eggs from fecal samples, but also for estimating the percentage of the total eggs that each pathogen comprises. This new method will make possible a rapid determination of which individual animals in a herd should be treated. Larvae: The most commonly-used method for identifying infective larvae is time-consuming (several weeks), unreliable for estimating intensities of individual species as components of mixed populations and requires highly trained specialists. Available identification keys for larvae are not well illustrated and need to be augmented. Adults: Recent advances in the identification of adult trichostrongyloids and their systematics are organized by taxonomic group. Genera included are Ostertagia, Haemonchus, Cooperia, Trichostrongylus and Nematodirus. Recently, the first phylogenetic analysis of the Trichostrongylidae family established monophyly for the family. A similar analysis of the Molineidae is needed. Ostertagia: Several studies of polymorphism summarized the phenomenon and listed 19 polymorphic species in five genera. Two studies of DNA differences within and among polymorphic species of Ostertagiinae supported earlier hypotheses that the species pairs represent polymorphic species. A phylogenetic analysis of the Ostertagiinae and generic concepts are needed. Haemonchus: A key to three species of Haemonchus provides, for the first time, morphological characteristics for the microscopical identification to species of individual adult nematodes of either sex. The Food and Drug Administration is now requiring that results of drug trials include identification of Haemonchus to species. Cooperia: Studies using random amplified polymorphic DNA methods showed a high degree of variation within and among C. oncophora/C. surnabada, but supported a polymorphic relationship for the species pair. A phylogenetic analysis of the Cooperiinae is needed. Trichostrongylus: Restriction Fragment Length Polymorphisms (RFLPs) of genomic DNA of two strains of T. colubriformis indicated a high degree of intra- and inter-strain DNA polymorphism. However, other studies demonstrated expected species level differences between T. colubriformis and T. vitrinus using Random Amplified Polymorphic DNA (RAPD) methods. Sequences of the second Internal Transcribed Spacer Region (ITS-2) ribosomal repeat showed sequence differences of 1.3-7.6% among five

Morphological polymorphism in the nematode Teladorsagia circumcincta in relation to age of larvae, infection mode and lamb characteristics in experimental conditions

Variations in the proportion of the less-frequent morph of Teladorsagia circumcincta, T. c. trifurcata, were studied under experimental conditions. Infections with older larvae (over 7 months of age at 4 degrees C) yield a lower proportion of T. c. trifurcata compared with those obtained from fresh larvae (15 days). This phenomenon could account for the reduction in the proportion of the morph trifurcata in two isolates that were acclimated to laboratory rearing for several generations. The infection mode (single or trickle infections did not significantly modify the proportions of both morphs. The morph trifurcata was found in higher proportions (> 5.5%) in more susceptible male and/or Romanov lambs, and in lower proportions (< 2.5%) in less susceptible female and/or Mérinos d'Arles lambs.

Use of random amplified polymorphic DNA for identification of ruminant trichostrongylid nematodes

The aim of this work was to evaluate random amplified polymorphic DNA (RAPD) as a source of markers for species identification and phylogenetic analysis of ruminant trichostrongylid nematodes. As these nematodes are often polymorphic, species identification may be difficult. We tested eight species and several of their morphs: Haemonchus contortus (three vulvar morphotypes: flap, smooth, and knobbed), Teladorsagia circumcincta, Ashworthius gagarini, Spiculopteragia boehmi, Ostertagia leptospicularis (and its morph Ostertagia kolchida), Cooperia oncophora (and its morph C. surnabada), Trichostrongylus colubriformis, and T. vitrinus. With five chosen 10-mer primers, genetic variations were assessed among individuals of each species or morphotype. In trichostrongylid nematodes, the identification of species is possible by means of RAPD on adult or larva DNA extracts, although the variability observed within species was very important for most species studied. The use of RAPD in phylogenetics studies is conversely questionable for this superfamily of parasitic nematodes. The interspecific distances were always larger than the intraspecific ones and did not vary much (between 0.8 and 0.9); they would not be of much use in the construction of a phylogenetic tree, at least for the species and the primers involved in this study.