P. de Ley

Lost in worm space: phylogeny and morphology as road maps to nematode diversity

The taxonomic impediment in nematology is expanding rather than receding: in the past decade estimates of nematode species richness have increased by several orders of magnitude, while the number of active nematode taxonomists has continued to decline steadily. In order to survive as a discipline in the new century, nematode taxonomy will therefore have to i) prioritise taxa that are relevant to other scientific investigations, ii) provide identification and classification tools that are easily applicable by nonspecialists, and iii) focus on revealing patterns of relatedness rather than on compiling exhaustive catalogues of species, since the latter will never remotely reach completion. Traditional morphological studies based on light microscopy do not meet these needs because they provide insufficient character resolution and require too much specialist knowledge. Phylogenetic approaches are more promising, especially when incorporating molecular sequence data as well as other non-traditional character suites. En nematologie, les obstacles taxinomiques sont en accroissement plutot qu’en recul: pendant la derniere decennie, les estimations relative a la diversite en especes ont ete accrues par plusieurs ordre de grandeur tandis que le nombre de taxinomistes a continue a decroitre regulierement. Pour se maintenir en tant que discipline au cours du nouveau siecle, la taxinomie nematologique devra donc i) donner priorite a des taxons en relation directe avec d’autres recherches scientifiques, ii) produire des instruments d’identification et de classification plus accessibles aux non-specialistes, et iii) se concentrer sur la decouverte de relations d’affinite plutot que sur la compilation de catalogues d’especes lesquels n’atteindront jamais l’exhaustivite. Les etudes morphologiques traditionnelles basees sur la microscopie optique ne peuvent repondre a ces besoins du fait qu’elles n’ont pas une resolution suffisante pour les caracteres et qu’elles requierent trop de connaissances specialisees. Les approches phylogenetiques sont plus prometteuses, specialement lorsqu’elles sont basees sur des sequences moleculaires et d’autres series de caracteres non-traditionnels.

Patterns and processes in the evolution of animal parasitic nematodes.

The parasitic Nematoda have traditionally been classified distinct from free-living species, and animal parasites treated separately from plant parasites. In classical concepts of phylogenetic relationships within the phylum, parasitic groups are usually afforded ordinal status and their origins are often obscure. We have been using molecular phylogenetics to examine the interrelationships of animal parasites with free-living and plant-parasitic groups, and find that a new view of the origins and radiation of animal parasites is warranted. Using sequence from the nuclear small subunit ribosomal RNA gene, we have constructed an alignment that allows robust phylogenetic inference. With this dataset, we place the Strongylida as a monophyletic clade nested within the Rhabditina. The Ascaridida, Oxyurida and Spirurida are closely related, but currently have no clear closest free-living sister taxon. Strongyloides spp. are rooted in a radiation of cephalobid/tylenchid species. Where available, other sequences in general confirm these relationships. Les Nematoda parasites ont ete traditionnellement classifies separement des especes libres, les parasites d’animaux etant traites separement des parasites de plantes. Suivant les concepts classiques des relations phylogenetiques a l’interieur du phylum, les groupes parasites sont habituellement traites au niveau ordinal et leurs origines sont souvent inconnues. Utilisant la phylogenie moleculaire, les interrelations des parasites animaux avec les groupes d’especes libres et parasites de plantes ont ete etudiees conduisant a la conclusion qu’une nouvelle approche des origines et de l’evolution des parasites animaux est necessaire. Sur la base de la petite sous-unite nucleaire du gene de l’ARN ribosomal, un alignement est propose qui permet une inference phylogenetique solide. Avec cet ensemble de donnees, les Strongylida sont consideres comme un clade monophyletique emboite au sein des Rhabditina. Les Ascaridida, Oxyurida et Spirurida sont etroitement relies, mais jusqu’a present sans relation etroite claire avec des taxons de nematode libre. Les Strongyloides spp. ont evolue a partir des cephalobides/tylenchides. Lorsqu’elles sont disponibles, les donnees issues d’autres sequences confirment le plus souvent ces relations.

Marine nematode taxonomy in the age of DNA: the present and future of molecular tools to assess their biodiversity.

Molecular taxonomy is one of the most promising yet challenging fields of biology. Molecular markers such as nuclear and mitochondrial genes are being used in a variety of studies surveying marine nematode taxa. Sequences from more than 600 species have been deposited to date in online databases. These barcode sequences are assigned to 150 nominal species from 104 genera. There are 41 species assigned to Enoplea and 109 species to Chromadorea. Morphology-based surveys are greatly limited by processing speed, while barcoding approaches for nematodes are hampered by difficulties in matching sequence data with morphology-based taxonomy. DNA barcoding is a promising approach because some genes contain variable regions that are useful to discriminate species boundaries, discover cryptic species, quantify biodiversity and analyse phylogeny. We advocate a combination of several approaches in studies of molecular taxonomy, DNA barcoding and conventional taxonomy as a necessary step to enhance the knowledge of biodiversity of marine nematodes.

Phasmarhabditis hermaphrodita (Nematoda: Rhabditidae), a potential biocontrol agent isolated for the first time from invasive slugs in North America.

Phasmarhabditis hermaphrodita is reported for the first time in North America from cadavers of the invasive slug species Deroceras reticulatum, D. laeve and Lehmannia valentiana collected from three different locations in California, USA. Four isolates were identified using combined morphology, morphometrics and molecular sequence data for complete internal transcribed spacer (ITS-1, 5.8S, ITS-2), D2-D3 expansion segments of the large subunit (LSU or 28S) and nearly complete small subunit (SSU or 18S) ribosomal DNA. Extremely low sequence variations in the COI gene of the mitochondria were observed among US isolates as well as between US isolates and the two UK sequences. The occurrence of P. hermaphrodita in North America has regulatory implications for potential biological control strategies against non-native gastropod species that are pests in ornamental and agricultural cultivation on this continent. The D2-D3 sequence of the LSU rDNA is new for the species.

Nematodes from the Gulf of California. Part 1. The genera Ceramonema Cobb, 1920, Pselionema Cobb in Cobb, 1933 and Pterygonema Gerlach, 1954 (Nematoda: Ceramonematidae)

The morphology and morphometry of nematodes of six species of the family Ceramonematidae is described using light and scanning electron microscopy. In this paper, we describe two new species and redescribe two known species of Ceramonema and one new species each of Pselionema and Pterygonema. Ceramonema altogolfi sp. n. is characterised by the 0.8-1.3 mm long body, 187-247 body annules, weakly developed zygapophyses, presence of intracuticular vacuoles, sexual dimorphism in amphid shape, presence of vaginal sclerotisation, complex gubernaculum and relatively uniform anal and cloacal annules, whilst C. inguinispina sp. n. has a 0.8-1.1 mm long body, 135-191 body annules, weakly developed zygapophyses, presence of intracuticular vacuoles, sexual dimorphism in amphid shape, absence of vaginal sclerotisation, thorn-shaped precloacal projection, plate-like gubernaculum and double cloacal annule. Pselionema psednum sp. n. is distinguished by 1.4-1.7 mm long body, 251-292 body annules, weakly developed zygapophyses, absence of intracuticular vacuoles, sexual dimorphism in amphid shape and Pterygonema mexicanum sp. n. is characterised by having amphids lacking a central thorn-like projection and pharynx with a distinct posterior glandular bulb. Populations of Ceramonema rectum and Ceramonema cf. yunfengi are also described. The male cloacal region of the species examined appears to be a rich potential source of taxonomic characters that have as yet received insufficient attention for this family.

Xyala finneyae sp. n. (Nematoda: Xyalidae) from the intertidal region of the eastern Gulf of California, Mexico.

Xyala finneyae sp. n. from the intertidal zone in the northern Gulf of California, Mexico, is described using light and scanning electron microscopy. The new species is characterised by the first ring of cuticular crests being at least twice as long as the crests on the remaining annules, vulva at 70-76% of body length from anterior end, sexual dimorphism in amphid fovea size with females having a smaller amphidial opening. Xyala finneyae sp. n. is most similar to the type species, X. striata , and to X. oxybiotica . It differs from the former in having the first ring of crests markedly longer than all subsequent ones, in having shorter outer labial and cephalic setae on the lip region (8-9 and 15-18 vs 12 and 22 μ m, respectively), in a more anterior position of vulva (V = 70-76 vs 79-81) and in shorter spicules (29-31 vs 44-47 μ m). From X. oxybiotica , it differs in the more spherical lip region with thinner cuticle on the lips ( vs lips more protruding anteriad and with thicker cuticle in optical section), shorter outer labial and cephalic setae on the lip region (8-9 and 15-18 vs 13 and 23 μ m, respectively), a more anterior vulva (V = 70-76 vs 81-89) and shorter spicules (29-31 vs 35 μ m).

Nematodes from the gulf of California. Part 2. Ceramonema nasobema sp. n. (Nematoda: Ceramonematidae)

An unusual new ceramonematid, Ceramonema nasobema sp. n., is described using light and scanning electron microscopy. It is particularly characterised by the presence of a perioral tube projecting 5.5-7.0 ?m anterior to the lips, moderately long body (0.86-1.09 mm), relatively small number of body annules (121-134), weakly developed zygapophyses, absence of intracuticular vacuoles, pronounced sexual dimorphism in amphid shape with the male ventral amphidial branch extending as far posterior as the 55-80th annule (no extension in females), barrel-shaped stoma, sigmoid and anteriorly inclined vagina without sclerotisations, gubernaculum with dorsal apophyses and relatively uniform cloacal annules. The new species differs from all other known species of Ceramonema especially by the shape of the amphid in males, the strongly projecting perioral tube and the inclined, sigmoid, vagina. Additional data on morphology of Ceramonema algoensis (from Natal Bay, South Africa) are also provided as this species has the most prominent perioral tube among previously described members of the genus.