Description of Rotylenchus rhomboides n. sp. and a Belgian population of Rotylenchus buxophilus (Tylenchomorpha: Hoplolaimidae).

During a survey in the Botanical garden of Ghent University, a new species Rotylenchus rhomboides n. sp. and a population of Rotylenchus buxophilus were found. Rotylenchus rhomboides n. sp. is characterized by the presence of a rhomboid-like widening of the mid-ridge of lateral field at the level of vulva, a feature previously unknown within the genus. The population of the new species, composed only by females, has a rounded labial region with 4 to 5 annuli, robust stylet (31-37 µm long), short dorsal esophageal gland (9-19 µm) overlap of the intestine, vulva located slightly posterior to mid-body, and hemispherical or rounded tail shape with large phasmids located 3 to 5 annuli anterior to the level of anus. The hierarchical cluster analysis based on morphological features indicated that the new species closely resembles R. corsicus, R. gracilidens, and R. rugatocuticulatus. The DNA analyses of the D2-D3 of 28S rDNA, ITS rDNA, and COI mtDNA sequences of Rotylenchus rhomboides n. sp. show a close relationship with R. buxophilus, R. goodeyi, R. laurentinus, R. pumilus, and R. incultus, all of which can also be differentiated from the new species by morphological features. The combination of morphological, morphometric, and molecular characteristics confirmed the new species and the first report of R. buxophilus on yam (Dioscorea tokoro) in Belgium.During a survey in the Botanical garden of Ghent University, a new species Rotylenchus rhomboides n. sp. and a population of Rotylenchus buxophilus were found. Rotylenchus rhomboides n. sp. is characterized by the presence of a rhomboid-like widening of the mid-ridge of lateral field at the level of vulva, a feature previously unknown within the genus. The population of the new species, composed only by females, has a rounded labial region with 4 to 5 annuli, robust stylet (31­37 µm long), short dorsal esophageal gland (9­19 µm) overlap of the intestine, vulva located slightly posterior to mid-body, and hemispherical or rounded tail shape with large phasmids located 3 to 5 annuli anterior to the level of anus. The hierarchical cluster analysis based on morphological features indicated that the new species closely resembles R. corsicus, R. gracilidens, and R. rugatocuticulatus. The DNA analyses of the D2-D3 of 28S rDNA, ITS rDNA, and COI mtDNA sequences of Rotylenchus rhomboides n. sp. show a close relationship with R. buxophilus, R. goodeyi, R. laurentinus, R. pumilus, and R. incultus, all of which can also be differentiated from the new species by morphological features. The combination of morphological, morphometric, and molecular characteristics confirmed the new species and the first report of R. buxophilus on yam (Dioscorea tokoro) in Belgium.

First Report of Scutellonema brachyurus (Steiner, 1938) Andrassy, 1958 and Occurrence of Meloidogyne incognita (Kofoid & White, 1919) Chitwood, 1949 in Belgium.

A study of plant-parasitic nematodes in the Botanical garden at Ghent University in Belgium revealed the presence of two tropical nematode species, i.e. Scutellonema brachyurus and Meloidogyne incognita. Scutellonema brachyurus was recovered, only once, for the first time in Belgium from Musa basjoo and is morphologically characterized. M. incognita, forming galls on Hedychium greenii, was recovered in all seasons over three consecutive years and is morphologically and molecularly characterized. Although no unequivocal evidence was found to indicate that these nematodes pose a current threat in Belgium, in the light of climate change, it is crucial to improve our knowledge of potential tropical nematode activity in more Northern countries.

Characterisation of a new species of Trichodorus Cobb, 1913 (Triplonchida: Trichodoridae) from Iran based on morphological and molecular data.

Trichodorus zanjanensis n. sp., collected from the rhizosphere of wild almond tree (Amygdalus scoparia Spach) in Zanjan Province, Iran, is described and illustrated based on morphological and molecular data. The new species is characterised by its body length (772-819 µm in males; 704-953 µm in females), and in having medium-sized onchiostyle (60-64 µm in males; 59-65 µm in females) and a short dorsal overlap of the intestine. Males of the new species have two ventromedian cervical papillae posterior to onchiostyle region, ventrally curved spicules, smooth, long and wide manubrium, gradually continuing in a narrower anterior part of the blade provided with bristles and marked from the wider and transversely striated main part of the blade, tapered towards distal end, three ventromedian precloacal supplements, the posterior one (SP1) situated at the level of anterior blade and gubernaculum situated at 24-25 µm from the cloaca. Females have one pair of sublateral body pores in the vulva region, medium rounded triangular to oval sclerotised vaginal pieces in lateral view, and pear-shaped vagina. The new species resembles T. persicus De Waele & Sturhan, 1987, T. minzi De Waele & Cohn, 1992 and T. taylori De Waele, Mancini, Roca & Lamberti, 1982. The results of morphological and morphometric comparisons and molecular data based on sequences of the partial 18S and D2-D3 expansion segments of 28S rRNA genes, clearly separated T. zanjanensis n. sp. from these known species and supported the description of T. zanjanensis n. sp. as a new species.

Molecular diversity of Photorhabdus and Xenorhabdus bacteria, symbionts of Heterorhabditis and Steinernema nematodes retrieved from soil in Benin.

The diversity of 43 bacterial strains isolated from Beninese entomopathogenic nematodes was investigated molecularly by analyzing the 16S rRNA, recA, and gyrB genes. Based on 16S rRNA sequence analysis, 15 bacterial strains were identified as Xenorhabdus sp., 27 strains as Photorhabdus sp., and one as Serratia sp. The Xenorhabdus strains were isolated from Steinernema nematodes and identified as Xenorhabdus indica based on 16S rRNA gene and concatenated recA and gyrB sequence analysis. However, analysis of 16S rRNA and concatenated recA and gyrB gene sequences of the Photorhabdus strains, all isolated from Heterorhabditis nematodes, resulted in two separate sub-clusters (A) and (B) within the Photorhabdus luminescens group, distinct from the existing subspecies. They share low sequence similarities with nearest phylogenetic neighbors Photorhabdus luminescens subsp. luminescens HbT, Photorhabdus luminescens subsp. caribbeanensis HG29T, and Photorhabdus luminescens subsp. noenieputensis AM7T.

Disparate gain and loss of parasitic abilities among nematode lineages.

Plant parasitism has arisen time and again in multiple phyla, including bacteria, fungi, insects and nematodes. In most of these organismal groups, the overwhelming diversity hampers a robust reconstruction of the origins and diversification patterns of this trophic lifestyle. Being a moderately diversified phylum with ≈ 4,100 plant parasites (15% of total biodiversity) subdivided over four independent lineages, nematodes constitute a major organismal group for which the genesis of plant parasitism could be mapped. Since substantial crop losses worldwide have been attributed to less than 1% of these plant parasites, research efforts are severely biased towards this minority. With the first molecular characterisation of numerous basal and supposedly harmless plant parasites as well as their non-parasitic relatives, we were able to generate a comprehensive molecular framework that allows for the reconstruction of trophic diversification for a complete phylum. In each lineage plant parasites reside in a single taxonomic grouping (family or order), and by taking the coverage of the next lower taxonomic level as a measure for representation, 50, 67, 100 and 85% of the known diversity was included. We revealed distinct gain and loss patterns with regard to plant parasitism per se as well as host exploitation strategies between these lineages. Our map of parasitic nematode biodiversity also revealed an unanticipated time reversal in which the two most ancient lineages showed the lowest level of ecological diversification and vice versa.

Low genetic but high morphological variation over more than 1000 km coastline refutes omnipresence of cryptic diversity in marine nematodes.

BACKGROUND: The resilience of ecosystems to negative impacts is generally higher when high gene flow, species diversity and genetic diversity are present. Population genetic studies are suitable to investigate genetic diversity and estimate gene flow between populations. Seaweed beds form a dynamic shallow water ecosystem influenced by climate change and human exploitation, as such, seaweed beds are a particularly powerful model to investigate ecosystem resilience in coastal areas. We studied the population genetic structure of the new nematode species Paracanthonchus gynodiporata associated with seaweeds in northeastern Brazil. Nematodes are generally believed to have a limited dispersal capacity because of the lack of planktonic larvae. Yet, they can drift on seaweeds, and water currents might be a natural barrier for their dispersal. Populations of P. gynodiporata were sampled over more than 1000 km coastline in regions across major oceanic currents with and without historical exploitation of seaweed. RESULTS: P. gynodiporata is described in an integrative way using mitochondrial and nuclear sequences and morphological data. The 3D model of the head region shows for the first time a detailed view of the ventrosublateral teeth, a character often overlooked in older taxonomic studies of the genus. A total of 17 mitochondrial COI haplotypes were found with one haplotype representing 63 to 83% of the frequencies in each population. AMOVA showed overall little population genetic structure (F ST = 0.05204), and no genetic subdivision between the populations under the influence of the two different water currents were found. Effects of historical seaweed exploitation on population genetic diversity were not detected. In contrast, significant differences between populations were found in morphometric characters. This discrepancy in genetic and morphological differentiation between populations across 1000 km of coastline is surprising in view of the frequently observed presence of several cryptic species at small geographical scale in other macroalgal associated nematodes. CONCLUSIONS: Our results show that cryptic species are not omnipresent in marine nematode species, suggesting that nematodes associated with seaweeds have been able to disperse over large distances across well-known biogeographic barriers.

High-pressure freezing and freeze-substitution fixation reveal the ultrastructure of immature and mature spermatozoa of the plant-parasitic nematode Trichodorus similis (Nematoda; Triplonchida; Trichodoridae).

The spermatozoa from testis and spermatheca of the plant-parasitic nematode Trichodorus similis Seinhorst, 1963 (Nematoda; Triplonchida; Trichodoridae) were studied with transmission electron microscopy (TEM), being the first study on spermatogenesis of a representative of the order Triplonchida and important to unravel nematode sperm evolution. Comprehensive results could only be obtained using high-pressure freezing (HPF) and freeze-substitution instead of chemical fixation, demonstrating the importance of cryo-fixation for nematode ultrastructural research. The spermatozoa from the testis (immature spermatozoa) are unpolarized cells covered by numerous filopodia. They contain a centrally-located nucleus without a nuclear envelope, surrounded by mitochondria. Specific fibrous bodies (FB) as long parallel bundles of filaments occupy the peripheral cytoplasm. No structures resembling membranous organelles (MO), as found in the sperm of many other nematodes, were observed in immature spermatozoa of T. similis. The spermatozoa from the uterus (mature or activated spermatozoa) are bipolar cells with an anterior pseudopod and posterior main cell body (MCB), which include a nucleus, mitochondria and MO appearing as large vesicles with finger-like invaginations of the outer cell membrane, or as large vesicles connected to the inner cell membrane. The peripheral MO open to the exterior via pores. In the mature sperm, neither FBs nor filopodia were observed. An important feature of T. similis spermatozoa is the late formation of MO; they first appear in mature spermatozoa. This pattern of MO formation is known for several other orders of the nematode class Enoplea: Enoplida, Mermithida, Dioctophymatida, Trichinellida but has never been observed in the class Chromadorea.

First report, morphological and molecular characterization of Xiphinemaelongatum and X.pachtaicum (Nematoda, Longidoridae) from Ethiopia.

A total of six soil samples were collected around rhizosphere of citrus plants during 2010 from Melkassa Agricultural Research Center experimental station, Ethiopia. From these samples two most important ecto-plant parasitic nematodes of the genus Xiphinema were found and analysed. The genus Xiphinema is a large group of the phylum nematoda which constitutes more than 260 species. They are polyphagous root- ectoparasites of many crop plants and some species of this genus cause damage by direct feeding on root tips and transmit nepoviruses. The delimitation and discrimination of two species in the genus is presented, described herein as Xiphinemaelongatum and Xiphinemapachtaicum. Morphological and morphometric data were done using light microscopy and results of both species were fit within the previously described nematode species of Xiphinemaelongatum and Xiphinemapachtaicum. 18S rDNA were analysed using Bayesian inference (BI) method to reconstruct phylogenetic relationships of the studied Xiphinema sp. (KP407872Xiphinemaelongatum and KP407873Xiphinemapachtaicum) with other Xiphinema species. The 18S rDNA sequence of Xiphinemapachtaicum was alike to previously described species from the GenBank but Xiphinemaelongatum exhibited very small levels of nucleotides differences (0.4%) which might be possible intra-specific divergence. Though this region of rDNA has less resolution on complex species, its combination with morphological and morphometric analyses, suggests these species as Xiphinemaelongatum and Xiphinemapachtaicum with the GenBank accession number of KP407872 and KP407873, respectively. Short notes, morphological measurements, illustrations, and molecular data are given to these species. These species are reported for the first time from Ethiopia and it provides new geographical information of these organisms.

Utility of Classical α-Taxonomy for Biodiversity of Aquatic Nematodes.

"Classical α-taxonomy" has different interpretations. Therefore, within the framework of an integrated taxonomic approach it is not relevant to divide taxonomy in different components, each being allocated a different weight of importance. Preferably, taxonomy should be seen in a holistic way, including the act of delimiting and describing taxa, based on different features and available methods, and taxonomy can not be interpreted without looking at evolutionary relationships. The concept of diversity itself is quite diverse as is the measure of diversity. Taxonomic descriptions of free-living aquatic nematodes are very valuable as they provide basic phenotypic information that is necessary for the functional ecological, behavioral, and evolutionary interpretation of data gathered from molecular analyses and of the organism as a whole. In general, molecular taxonomic analyses have the advantage of being much faster and of being able to deal with a larger number of specimens but also possess the important advantage of dealing with a huge amount of features compared to the morphology-based approach. However, just as morphological studies, molecular analyses deal only with partial of an organism.

Nematodes from terrestrial, freshwater and brackish water habitats in Belgium: an updated list with special emphasis on compost nematodes.

A study of nematodes from a semi-artificial and controlled composting process in Eastern Flanders revealed 35 taxa, 21 of which were new records for Belgium. An updated checklist of free-living, plant-parasitic and entomopathogenic nematodes from terrestrial, freshwater and brackish water habitats in Belgium is presented. The Belgian non-marine nematofauna comprises 418 taxa, representing 4 subclasses, 14 orders, and 76 families. In total 127 new records were added: i.e. 21 from the newly explored compost habitat, 7 from freshwater samples and 99 from published data in literature.

Megadraconema cornutum, a new genus and species from Korea, with a discussion of its classification and relationships within the family Draconematidae (Nematoda, Desmodorida) based on morphological and molecular characters.

A new genus and species of Draconematidae Filipjev, 1918, Megadraconema cornutum gen. nov., sp. nov., inhabiting subtidal sediments in Jejudo, Korea is described. Megadraconema cornutum gen. nov., sp. nov. is mainly characterized by a long body (1630-2220 µm), presence of a transverse circle of well-developed papillae-like cuticular protrusions at the base of the lip region, a head capsule with reticular structure of subcuticle, an amphid with a pore-like opening, and an internal, bar-shaped fovea. The diagnosis of the family Draconematidae is emended and a key to genus is provided based on their major differential diagnostic characteristics, summarized in a table. Phylogenetic relationships of all the genera within the Draconematidae are discussed for the first time, based on molecular analyses and morphological features. The phylogenetic position of the new genus and relationships within the family Draconematidae based on analysis of molecular sequence data are examined. Analysis of 18S rRNA gene sequences does not support the currently accepted classification, and indicates paraphyly of the subfamily Draconematinae.

Effects of organic enrichment on nematode assemblages in a microcosm experiment.

Marine nematodes from subtidal tropical sediments of Cienfuegos Bay were subjected to organic enrichment in a microcosm experiment for 32 days. Nematode abundance and diversity decreased, and the taxonomic and trophic structure was altered. The results suggested that the nematodes were not food limited in the microcosms or in their natural environment. Chemical stressors such as ammonia and hydrogen sulfide derived from reduced conditions in sediments may be important factors affecting the assemblages. Hypoxic conditions occurred in all experimental units, as well as in the field, suggesting a nematode assemblage adapted to naturally enriched sediments. However, tolerant species showed a grade of sensitivity to reduced conditions. In agreement with the model by Pearson and Rosenberg (1978), we predict that further organic enrichment in sediments from Cienfuegos Bay may cause a phase shift into a strongly depleted benthic fauna and reduced conditions in water and sediments.

Monophyly of the family Desmoscolecidae (Nematoda, Demoscolecida) and its phylogenetic position inferred from 18S rDNA sequences.

To infer the monophyletic origin and phylogenetic relationships of the order Desmoscolecida, a unique and puzzling group of mainly free-living marine nematodes, we newly determined nearly complete 18S rDNA sequences for six marine desmoscolecid nematodes belonging to four genera (Desmoscolex, Greeffiella, Tricoma and Paratricoma). Based on the present data and those of 72 nematode species previously reported, the first molecular phylogenetic analysis focusing on Desmoscolecida was done by using neighbor joining (NJ), maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) methods. All four resultant trees consistently and strongly supported that the family Desmoscolecidae forms a monophyletic group with very high node confidence values. The monophyletic clade of desmocolecid nematodes was placed as a sister group of the clade including some members of Monhysterida and Araeolaimida, Cyartonema elegans (Cyartonematidae) and Terschellingia longicaudata (Linhomoeidae) in all the analyses. However, the present phylogenetic trees do not show any direct attraction between the families Desmoscolecidae and Cyartonematidae. Within the monophyletic clade of the family Desmoscolecidae in all of the present phylogenetic trees, there were consistently observed two distinct sub-groups which correspond to the subfamilies Desmoscolecinae [Greeffiella sp. + Desmoscolex sp.] and Tricominae [Paratricoma sp. + Tricoma sp].

Postembryonic morphology in epsilonematidae, with a discussion on the variability of caudal gland outlets.

A new species of Akanthepsilonema and the first-stage juvenile of Glochinema trispinatum are described. Furthermore, additional morphological information is provided for Triepsilonema tripapillata. Animals originate from a cold-water coral degradation zone in the Porcupine Seabight area (North-East Atlantic Ocean). Akanthepsilonema sinecornibus sp. n. differs from A. heUeouetae in number of body annules, sexual dimorphism in amphid size, absence of copulatory thorns in males, absence of large spines and horns, shape of the copulatory apparatus, and position of ambulatory setae relative to vulva in females. The genus diagnosis for Akanthepsilonema is adjusted to incorporate the new species. Akanthepsilonema mainly differs from every other genus in the family by the combination of six rows of ambulatory setae situated around the vulva in females and eight subcephalic setae not displaced toward the anterior part of the head capsule. Small differences between the Papua New Guinea and the Porcupine Seabight populations of T. tripapillata indicate minimal intraspecific variability. Second-stage juveniles from Papua New Guinea have two rows of three ambulatory setae, whereas Porcupine Seabight specimens have two rows of four ambulatory setae. First- and fourth-stage juveniles of T. tripapillata are described for the first time. Literature data and personal observations showed that the molting of first-stage juveniles into second-stage juveniles and of third-stage juveniles into fourth-stage juveniles involves a decrease in the number of body rings, resulting in a loss of flexibility which is possibly compensated for by the development (I-II) or the doubling of the number of rows (III-IV) of ambulatory setae. This decrease is also linked with the formation of the head capsule and the smooth tail tip, although intergeneric variability is evident. The molting of second-stage juveniles into third-stage juveniles and of fourth-stage juveniles into adults is also subject to intergeneric variability. The variability in the number and orientation of caudal gland outlets among different nematode taxa is discussed. The presence of separate outlets for the caudal glands seems to be widespread within the family Epsilonematidae and has also been observed in various other, unrelated taxa of free-living aquatic nematodes, although their arrangement in Epsilonematidae is opposite. This aberrant arrangement is probably related to the aberrant locomotory pattern in this family.

Review of the ultrastructure of the nematode body cuticle and its phylogenetic interpretation.

The phylogenetic interpretation of the nematode cuticle ultrastructure is reviewed within the framework of recent DNA-sequence data. In particular, the structure of the median and basal zones is discussed. Several structural elements of the cuticle seem to have arisen independently several times within the Nematoda and thus are highly homoplasious (e.g. the cortical or basal radial striae, spiral fibre layers and a fluid matrix with struts). Moreover, identifying the homology of the nematode cuticle ultrastructures is often very difficult at deep taxonomic levels. Hence, the cuticle appears to be unreliable regarding resolution of deep-level relationships in the Nematoda. However, at less inclusive taxonomic levels (e.g. families, genera, ...) the cuticle seems to be a more reliable phylogenetic marker.