Diplogastrid Nematodes Research Articles

Feeding-structure morphogenesis in "rhabditid" and diplogastrid nematodes is not controlled by a conserved genetic module.

Disentangling the evolution of the molecular processes and genetic networks that facilitate the emergence of morphological novelties is one of the main objectives in evolutionary developmental biology. Here, we investigated the evolutionary history of a gene regulatory network controlling the development of novel tooth-like feeding structures in diplogastrid nematodes. Focusing on NHR-1 and NHR-40, the two transcription factors that regulate the morphogenesis of these feeding structures in Pristionchus pacificus, we sought to determine whether they have a similar function in Caenorhabditis elegans, an outgroup species to the Diplogastridae which has typical "rhabditid" flaps instead of teeth. Contrary to our initial expectations, we found that they do not have a similar function. While both receptors are co-expressed in the tissues that produce the feeding structures in the two nematodes, genetic inactivation of either receptor had no impact on feeding-structure morphogenesis in C. elegans. Transcriptomic experiments revealed that NHR-1 and NHR-40 have highly species-specific regulatory targets. These results suggest two possible evolutionary scenarios: either the genetic module responsible for feeding-structure morphogenesis in Diplogastridae already existed in the last common ancestor of C. elegans and P. pacificus, and subsequently disintegrated in the former as NHR-1 and NHR-40 acquired new targets, or it evolved in conjunction with teeth in Diplogastridae. These findings indicate that feeding-structure morphogenesis is regulated by different genetic programs in P. pacificus and C. elegans, hinting at developmental systems drift during the flap-to-tooth transformation. Further research in other "rhabditid" species is needed to fully reconstruct the developmental genetic changes which facilitated the evolution of novel feeding structures in Diplogastridae.

Onthodiplogaster japonica n. gen., n. sp. (Rhabditida: Diplogastridae) isolated from Onthophagus sp. (Coleoptera: Scarabaeidae) from Japan

A diplogastrid nematode was isolated from a dung beetle, Onthophagus sp., collected from a rotten mushroom in Kyoto, Japan. The species is characterised by its cheilostomatal shape, separated into 12 narrow plates (rugae), deep stegostom, large ellipsoidal amphids, conical female tail and characteristic receptaculum seminis in the female. Based on its phylogenetic status and stomatal composition, the species is typologically similar to two other diplogastrid genera, Neodiplogaster and Mononchoides. The species can be distinguished from these two genera by the size and shape of the amphid (small pore in Neodiplogaster), female tail shape (long and filiform in Mononchoides) and presence of receptaculum seminis (absence in the two nominal genera), and is described as a monotypic member of a new genus, Onthodiplogaster japonica n. gen., n. sp. Observation of feeding behaviour suggested that O. japonica n. gen., n. sp. does not show clear stomatal dimorphism or polymorphism, which is found in its close relatives, but the species can feed on nematodes (predation), fungi and bacteria. This monomorphic omnivory possibly represents its habitat of dung and other rotten materials, where the environment is biologically divergent, and its condition changes rapidly.

Analysis of repeat elements in the Pristionchus pacificus genome reveals an ancient invasion by horizontally transferred transposons

BackgroundRepetitive sequences and mobile elements make up considerable fractions of individual genomes. While transposition events can be detrimental for organismal fitness, repetitive sequences form an enormous reservoir for molecular innovation. In this study, we aim to add repetitive elements to the annotation of the Pristionchus pacificus genome and assess their impact on novel gene formation.ResultsDifferent computational approaches define up to 24% of the P. pacificus genome as repetitive sequences. While retroelements are more frequently found at the chromosome arms, DNA transposons are distributed more evenly. We found multiple DNA transposons, as well as LTR and LINE elements with abundant evidence of expression as single-exon transcripts. When testing whether transposons disproportionately contribute towards new gene formation, we found that roughly 10–20% of genes across all age classes overlap transposable elements with the strongest trend being an enrichment of low complexity regions among the oldest genes. Finally, we characterized a horizontal gene transfer of Zisupton elements into diplogastrid nematodes. These DNA transposons invaded nematodes from eukaryotic donor species and experienced a recent burst of activity in the P. pacificus lineage.ConclusionsThe comprehensive annotation of repetitive elements in the P. pacificus genome builds a resource for future functional genomic analyses as well as for more detailed investigations of molecular innovations.

Nematode epibionts on skin of the Florida manatee, Trichechus manatus latirostris

A survey for the presence of nematodes on the skin of the native Florida manatee, Trichechus manatus latirostris from Crystal River, Florida was conducted during annual manatee health assessments. A putative isolate of Cutidiplogaster manati (Diplogastridae) and two other nematodes belonging to the same family were recovered from mid-dorsal tail skin-scrapings from all sampled winter-collected healthy wild adult manatees during two successive years (2018–2019). Qualitative abundance estimates of these three species of diplogastrid nematodes suggest that an average wild Florida manatee adult might possess between 30,000 and 120,000 nematodes on its tail dorsum and that the entire body dorsum including the tail might possess 160,000–640,000 nematodes in roughly equal ratios. Attempts to culture these nematodes on a variety of different culture media were unsuccessful but examination of the mouth (stomatal) morphology suggests specialized feeding on microbes such as diatoms or predation on other nematodes. No skin lesions were observed during the 2018–2019 samplings suggesting that under normal conditions these nematodes are highly specialized free-living epibionts of the skin that are tightly bound to this niche and horizontally transferred between individual manatees in an analogous fashion to human skin mites (Demodex folliculorum and D. brevis). Molecular phylogenetic inferences using sequences of near full length SSU and D2–D3 expansion segments of LSU rRNA genes revealed a putative new morphospecies in Cutidiplogaster sister to C. manati that was monophyletic with several named Mononchoides species, and another putative new morphospecies that formed a clade with several undescribed species similar in appearance to Mononchoides as well as Tylopharyx, Eudiplogasterium, Paroigolaimella and Sachsia.

Acrostichus ziaelasi n. sp. (Nematoda: Diplogastridae) isolated from the beetle Ziaelas formosanus, a tenebrionid symbiont of the termite Odontotermes formosanus with remarks on the genus Acrostichus Rahm, 1928

A diplogastrid nematode species was isolated from a termite-associated tenebrionid beetle, Ziaelas formosanus, collected from several localities in Taiwan. The new species shares a characteristic feeding structure, i.e., an extremely long and thin stoma with two genera, Rhabditolaimus and Mehdinema. However, the new species has highly characteristic male and female reproductive system, i.e., arrangement of male genital papillae, spicule and gubernaculum morphologies, and presence of female receptaculum seminis, that are similar to those of Acrostichus. A molecular phylogenetic analysis based on near-full-length small subunit and D2-D3 expansion segments of large subunit of ribosomal RNA gene sequences suggested that the species belongs to Acrostichus. The highly derived feeding characters of the new species accentuates the plasticity of the feeding structures of diplogastrid nematodes. In addition to the species description, the generic characters of Acrostichus are emended, and a list of the species in the genus is provided.

De Novo, Divergence, and Mixed Origin Contribute to the Emergence of Orphan Genes in Pristionchus Nematodes.

Homology is a fundamental concept in comparative biology. It is extensively used at the sequence level to make phylogenetic hypotheses and functional inferences. Nonetheless, the majority of eukaryotic genomes contain large numbers of orphan genes lacking homologs in other taxa. Generally, the fraction of orphan genes is higher in genomically undersampled clades, and in the absence of closely related genomes any hypothesis about their origin and evolution remains untestable. Previously, we sequenced ten genomes with an underlying ladder-like phylogeny to establish a phylogenomic framework for studying genome evolution in diplogastrid nematodes. Here, we use this deeply sampled data set to understand the processes that generate orphan genes in our focal species Pristionchus pacificus. Based on phylostratigraphic analysis and additional bioinformatic filters, we obtained 29 high-confidence candidate genes for which mechanisms of orphan origin were proposed based on manual inspection. This revealed diverse mechanisms including annotation artifacts, chimeric origin, alternative reading frame usage, and gene splitting with subsequent gain of de novo exons. In addition, we present two cases of complete de novo origination from non-coding regions, which represents one of the first reports of de novo genes in nematodes. Thus, we conclude that de novo emergence, divergence, and mixed mechanisms contribute to novel gene formation in Pristionchus nematodes.

The bacterial community of entomophilic nematodes and host beetles.

Insects form the most species-rich lineage of Eukaryotes and each is a potential host for organisms from multiple phyla, including fungi, protozoa, mites, bacteria and nematodes. In particular, beetles are known to be associated with distinct bacterial communities and entomophilic nematodes. While entomopathogenic nematodes require symbiotic bacteria to kill and reproduce inside their insect hosts, the microbial ecology that facilitates other types of nematode-insect associations is largely unknown. To illuminate detailed patterns of the tritrophic beetle-nematode-bacteria relationship, we surveyed the nematode infestation profiles of scarab beetles in the greater Los Angeles area over a five-year period and found distinct nematode infestation patterns for certain beetle hosts. Over a single season, we characterized the bacterial communities of beetles and their associated nematodes using high-throughput sequencing of the 16S rRNA gene. We found significant differences in bacterial community composition among the five prevalent beetle host species, independent of geographical origin. Anaerobes Synergistaceae and sulphate-reducing Desulfovibrionaceae were most abundant in Amblonoxia beetles, while Enterobacteriaceae and Lachnospiraceae were common in Cyclocephala beetles. Unlike entomopathogenic nematodes that carry bacterial symbionts, insect-associated nematodes do not alter the beetles' native bacterial communities, nor do their microbiomes differ according to nematode or beetle host species. The conservation of Diplogastrid nematodes associations with Melolonthinae beetles and sulphate-reducing bacteria suggests a possible link between beetle-bacterial communities and their associated nematodes. Our results establish a starting point towards understanding the dynamic interactions between soil macroinvertebrates and their microbiota in a highly accessible urban environment.

Gene inactivation using the CRISPR/Cas9 system in the nematode Pristionchus pacificus.

The diplogastrid nematode Pristionchus pacificus is a nematode model system for comparative studies to Caenorhabditis elegans and integrative evolutionary biology aiming for interdisciplinary approaches of evo-devo, population genetics, and ecology. For this, fieldwork can be combined with laboratory studies, and P. pacificus has a well-developed methodological toolkit of forward genetics, whole genome sequencing, DNA-mediated transformation, and various -omics platforms. Here, we establish CRISPR/Cas9-based gene inactivation and describe various boundary conditions of this methodology for P. pacificus. Specifically, we demonstrate that most mutations arise within the first 9 hours after injections. We systematically tested the efficiency of sgRNAs targeting different exons in Ppa-dpy-1 and characterized the molecular nature of the induced mutations. Finally, we provide a protocol that might also be useful for researchers working with other non-Caenorhabditis nematodes.

Conserved behavioral and genetic mechanisms in the pre-hatching molt of the nematode Pristionchus pacificus.

BackgroundDuring development, juvenile nematodes undergo four molts. Although the number of molts appears to be constant within the Nematoda, the timing of the first molt can occur either before or after hatching. A previous study indicates that, as in some parasitic nematode lineages, a pre-hatching juvenile stage also exists in Diplogastrid nematodes. A detailed description of these sequence of events has yet to be shown for any single species.FindingsTo delineate the timing of the pre-hatching molt in the beetle-associated Pristionchus pacificus, we tracked individual mid-J1 stage worms inside the eggshell through the J1-J2 transition and hatching. We found that active movement ended 21 hours after egg-laying, followed by lethargus and hatching. We inferred that lethargus behavior represents the onset of the first molt, which precedes each post-hatching molt in C. elegans and P. pacificus. The onset of the J1-J2 molt was also marked by the upregulation of the P. pacificus molting marker Ppa-pnhr-1. We further corroborated the pre-hatching molt with the isolation of two genetic mutants that exhibited aberrant molting both inside the egg and after hatching, as characterized by protracted and often-aborted shedding of the old cuticle.ConclusionOur results describe in detail the pre-hatching juvenile molt in P. pacificus, provide strong visual evidence of a pre-hatching molt, and show support for common genetic mechanisms regulating molting in the pre-hatching and post-hatching developmental stages. Our findings support the hypothesis that the evolution of pre-hatching development in Diplogastrid nematodes is likely due to a heterochronic shift between the timing of the first molt and hatching.

Levipalatum texanum n. gen., n. sp. (Nematoda: Diplogastridae), an androdioecious species from the south-eastern USA

A new species of diplogastrid nematode,Levipalatum texanumn. gen., n. sp., was isolated from scarab beetles (Coleoptera: Scarabaeidae) in Texas and baited from soil in Virginia, USA.Levipalatumn. gen. is circumscribed by stomatal and pharyngeal morphology, namely a long, hooked dorsal tooth connected to a ‘palate’ projecting anteriad and mediad, subventral telostegostomatal ridges of denticles, and the dorsal radius of the pharynx bulging anteriad. The males of the new species are distinguished from most other Diplogastridae by the frequent presence of ten pairs of genital papillae. Phylogenetic relationships inferred from 11 ribosomal protein-coding genes and a fragment of the small subunit rRNA gene strongly supportL. texanumn. gen., n. sp. to be a sister group toRhabditolaimus, which lacks all the stegostomatal and pharyngeal characters diagnosing the new genus. The new species expands comparative studies of the radiation of feeding morphology that are anchored on the model organismPristionchus pacificus. The phylogenetic position ofL. texanumn. gen., n. sp. indicates a new case of convergent evolution of hermaphroditism in Diplogastridae.

Three new species ofPristionchus(Nematoda: Diplogastridae) show morphological divergence through evolutionary intermediates of a novel feeding-structure polymorphism

Developmental plasticity is often correlated with diversity and has been proposed as a facilitator of phenotypic novelty. Yet how a dimorphism arises or how additional morphs are added is not understood, and few systems provide experimental insight into the evolution of polyphenisms. Because plasticity correlates with structural diversity in Pristionchus nematodes, studies in this group can test the role of plasticity in facilitating novelty. Here, we describe three new species, Pristionchus fukushimae sp. nov., Pristionchus hoplostomus sp. nov., and the hermaphroditic Pristionchus triformis sp. nov., which are characterized by a novel polymorphism in their mouthparts. In addition to showing the canonical mouth dimorphism of diplogastrid nematodes, comprising a stenostomatous (‘narrow-mouthed’) and a eurystomatous (‘wide-mouthed’) form, the new species exhibit forms with six, 12, or intermediate numbers of cheilostomatal plates. Correlated with this polymorphism is another trait that varies among species: whereas divisions between plates are complete in P. triformis sp. nov., which is biased towards a novel ‘megastomatous’ form comprising 12 complete plates, the homologous divisions in the other new species are partial and of variable length. In a reconstruction of character evolution, a phylogeny inferred from 26 ribosomal protein genes and a partial small subunit rRNA gene supported the megastomatous form of P. triformis sp. nov. as the derived end of a series of split-plate forms. Although split-plate forms were normally only observed in eurystomatous nematodes, a single 12-plated stenostomatous individual of P. hoplostomus sp. nov. was also observed, suggesting independence of the two types of mouth plasticity. By introducing these new species to the Pristionchus model system, this study provides further insight into the evolution of polymorphisms and their evolutionary intermediates. © 2013 The Linnean Society of London

Sudhausia aristotokia n. gen., n. sp. and S. crassa n. gen., n. sp. (Nematoda: Diplogastridae): viviparous new species with precocious gonad development

Two new species of diplogastrid nematodes,Sudhausia aristotokian. gen., n. sp. andS. crassan. gen., n. sp., were isolated from dung beetles (Coleoptera: Scarabaeidae) in Ghana and South Africa, respectively.Sudhausian. gen. is circumscribed by stomatal morphology, namely the presence of a tube-shaped gymnostom, a pair of conical subventral denticles in the metastegostom, and a disk-like telostegostom bearing minute conical denticles. Other characters distinguishing the new genus are the presence of a bursa in the male and a vulva lined anteriorly and posteriorly by columns of sac-like cells. The two new species, both of which are hermaphroditic, are distinguished from each other by spicule and gubernaculum morphology, male papillae arrangement, bursal shape, vaginal morphology, and phasmid position. A suite of unusual developmental traits that distinguishesSudhausian. spp. includes maturation of the gonad and development of juvenile progeny before moulting to adulthood, a two-fold increase in embryo size during development, and constitutive vivipary. A phylogeny inferred from 11 ribosomal protein-coding genes and a fragment of the small subunit rRNA gene showSudhausian. gen. to be divergent from other sequenced diplogastrid taxa, including those characterised by a tube-like stoma. The two new species represent useful new reference points for the study of feeding-structure evolution in Diplogastridae.

Validation of Rhabditolaimus Fuchs, 1914 (Nematoda: Diplogastridae) supported by integrative taxonomic evidence

Rhabditolaimus leuckarti, type species of Rhabditolaimus, was isolated from its type host, Hylobius abietis (Coleoptera: Curculionidae), at several locations in central Europe. The position of the species among other diplogastrid nematodes was revised using morphological characters and molecular phylogenetic analysis. The revealed common apomorphic features and the inferred evolutionary tree strongly indicates a close relationship between R. leuckarti and Myctolaimus. Our findings suggest that the historical classifications do not reflect the natural relationships of some diplogastrid taxa. Therefore, we reject all previous synonymisations of Rhabditolaimus and consider it to be valid within the Diplogastridae. Five species are transferred from Diplogasteroides to Rhabditolaimus. Myctolaimus sensu lato is regarded as a junior synonym of Rhabditolaimus and the following new combinations are proposed: R. anoplophorae comb. n., R. carolinensis comb. n., R. curzii comb. n., R. dendrophilus comb. n., R. erectus comb. n., R. goodeyi comb. n., R. inevectus, comb. n., R. kishtwarensis comb. n., R. macrolaimus comb. n., R. nacogdochensis comb. n., R. neolongistoma comb. n., R. pellucidus comb. n., R. platypi comb. n., R. rifflei comb. n., R. robiniae comb. n., R. ulmi comb. n., R. vitautasi comb. n., R. walkeri comb. n. and R. zamithi comb. n.

Parapristionchus giblindavisi n. gen., n. sp. (Rhabditida: Diplogastridae) isolated from stag beetles (Coleoptera: Lucanidae) in Japan

A new species of diplogastrid nematode, isolated in a previous survey of nematodes associated with stag beetles in Japan, is described as Parapristionchus giblindavisi n. gen., n. sp. Parapristionchus n. gen. differs from other diplogastrid genera chiefly by its stomatal morphology. Distinguishing the genus are the presence of a claw-like dorsal tooth in both the eurystomatous and stenostomatous forms and the division of the cheilostom into 12 plates lacking apical flaps. According to phylogenetic analysis of nine ribosomal protein gene sequences, Parapristionchus n. gen. shows deep divergence from other known genera. Molecular evidence strongly supports P. giblindavisi n. gen., n. sp. + Pristionchus spp. as monophyletic with respect to all other diplogastrids examined. Congruent with a clade of P. giblindavisi n. gen., n. sp. + Pristionchus spp. is the shared presence of a bifurcate P7 genital papilla. Discovery and description of a close sister group to Pristionchus, a model biological system, enables character polarisation in macroevolutionary studies of Pristionchus nematodes.

Horizontal gene transfer of microbial cellulases into nematode genomes is associated with functional assimilation and gene turnover

BackgroundNatural acquisition of novel genes from other organisms by horizontal or lateral gene transfer is well established for microorganisms. There is now growing evidence that horizontal gene transfer also plays important roles in the evolution of eukaryotes. Genome-sequencing and EST projects of plant and animal associated nematodes such as Brugia, Meloidogyne, Bursaphelenchus and Pristionchus indicate horizontal gene transfer as a key adaptation towards parasitism and pathogenicity. However, little is known about the functional activity and evolutionary longevity of genes acquired by horizontal gene transfer and the mechanisms favoring such processes.ResultsWe examine the transfer of cellulase genes to the free-living and beetle-associated nematode Pristionchus pacificus, for which detailed phylogenetic knowledge is available, to address predictions by evolutionary theory for successful gene transfer. We used transcriptomics in seven Pristionchus species and three other related diplogastrid nematodes with a well-defined phylogenetic framework to study the evolution of ancestral cellulase genes acquired by horizontal gene transfer. We performed intra-species, inter-species and inter-genic analysis by comparing the transcriptomes of these ten species and tested for cellulase activity in each species. Species with cellulase genes in their transcriptome always exhibited cellulase activity indicating functional integration into the host's genome and biology. The phylogenetic profile of cellulase genes was congruent with the species phylogeny demonstrating gene longevity. Cellulase genes show notable turnover with elevated birth and death rates. Comparison by sequencing of three selected cellulase genes in 24 natural isolates of Pristionchus pacificus suggests these high evolutionary dynamics to be associated with copy number variations and positive selection.ConclusionWe could demonstrate functional integration of acquired cellulase genes into the nematode's biology as predicted by theory. Thus, functional assimilation, remarkable gene turnover and selection might represent key features of horizontal gene transfer events in nematodes.

Molecular phylogeny of beetle associated diplogastrid nematodes suggests host switching rather than nematode-beetle coevolution

BackgroundNematodes are putatively the most species-rich animal phylum. They have various life styles and occur in a variety of habitats, ranging from free-living nematodes in aquatic or terrestrial environments to parasites of animals and plants. The rhabditid nematode Caenorhabditis elegans is one of the most important model organisms in modern biology. Pristionchus pacificus of the family of the Diplogastridae has been developed as a satellite model for comparison to C. elegans. The Diplogastridae, a monophyletic clade within the rhabditid nematodes, are frequently associated with beetles. How this beetle-association evolved and whether beetle-nematode coevolution occurred is still elusive. As a prerequisite to answering this question a robust phylogeny of beetle-associated Diplogastridae is needed.ResultsSequences for the nuclear small subunit ribosomal RNA and for 12 ribosomal protein encoding nucleotide sequences were collected for 14 diplogastrid taxa yielding a dataset of 5996 bp of concatenated aligned sequences. A molecular phylogeny of beetle-associated diplogastrid nematodes was established by various algorithms. Robust subclades could be demonstrated embedded in a phylogenetic tree topology with short internal branches, indicating rapid ancestral divergences. Comparison of the diplogastrid phylogeny to a comprehensive beetle phylogeny revealed no major congruence and thus no evidence for a long-term coevolution.ConclusionReconstruction of the phylogenetic history of beetle-associated Diplogastridae yields four distinct subclades, whose deep phylogenetic divergence, as indicated by short internal branch lengths, shows evidence for evolution by successions of ancient rapid radiation events. The stem species of the Diplogastridae existed at the same time period when the major radiations of the beetles occurred. Comparison of nematode and beetle phylogenies provides, however, no evidence for long-term coevolution of diplogastrid nematodes and their beetle hosts. Instead, frequent host switching is observed. The molecular phylogeny of the Diplogastridae provides a framework for further examinations of the evolution of these associations, for the study of interactions within the ecosystems, and for investigations of diplogastrid genome evolution.

Teratodiplogaster fignewmanigen. nov., sp. nov. (Nematoda: Diplogastridae) from the Syconia ofFicus racemosein Australia

During the course of a survey of fig-associated nematodes in eastern Australia, we discovered an unusual diplogastrid nematode that we describe herein as Teratodiplogaster fignewmani gen. nov., sp. nov. This nematode was isolated as adults and juveniles from the syconia of Ficus racemose in Queensland and Western Australia. It is presumed to be associated with the agaonid fig wasp, Ceratosolen fusciceps, for dispersion to new phase-B sycones. Teratodiplogaster fignewmani gen. nov., sp. nov. was inferred to be the sister taxon to the genus Parasitodiplogaster based upon molecular phylogeny using nearly full-length sequences of the SSU and D2/D3 LSU ribosomal RNA genes. It is sufficiently distinct in morphology (with many autapomorphies) to justify a new monotypic genus with the hypothesis that further species of Teratodiplogaster gen. nov. will be discovered when sycones from other Ficus from tropical Australasia and possibly Africa are sampled.

Nematodes of the order Rhabditida from India. Description of Diplogasteroides uriceus sp. n. and Rhabditidoides papillatus sp. n. (Diplogastrina)

Abstract Two new species of diplogastrid nematodes from India are described and illustrated. Diplogasteroides uriceus sp. n. has a medium-sized body, monoprodelphic reproductive system lacking a post-uterine sac, anteriorly directed muscular vagina and vulva located far posterior; long, slender, arcuate spicules; gubernaculum with proximal thread-like flexible part and nine pairs of genital papillae of which four pairs are precloacal and five pairs postcloacal. The new species resembles D. crassus but can be most easily differentiated by the structure of the cheilorhabdions, shape and structure of the gubernaculum, arrangement of the genital papillae and the complete absence of a bursa. The new species also resembles D. proprius but can be differentiated by stoma structure, more anteriorly located vulva, longer spicules, gubernaculum shape and tail form. Rhabditidoides papillatus sp. n. is characterised by the presence of three pairs of post-deirids in the lateral fields, posteriorly curved tubular stoma, amphidelphic female reproductive system, strongly developed, arcuate spicules with bilobed capitulum and a slender gubernaculum provided with a sleeve distally and anteriorly directed bifid ends proximally. It can be distinguished from R. stigmatus by the structure of the spicule head, gubernaculum shape and arrangement of the genital papillae; from R. mastigurus by spicule structure and the gubernaculum shape; and from R. quercophilus by a more slender female body, stoma structure, absence of a male bursa, spicule form and arrangement of the genital papillae.

Molecular variability of Schistonchus caprifici (Nematoda: Aphelenchoididae) from Ficus carica in Turkey

Abstract An extensive biogeographical survey was conducted from 2004 through part of 2007 of nematodes associated with the edible fig, Ficus carica, in seven different regions of Turkey. Figs (syconia) were collected, dissected and harvested for nematodes from 308 apparently wild or naturalised F. carica trees along roadsides and trails. Nematode specimens were examined morphologically and molecular analyses of sequences of the D2/D3 expansion segments of the large subunit (LSU) rDNA and partial mitochondrial DNA COI (mtCOI) were done. Of the 308 fig trees, 150 (49%) were positive for what was morphologically confirmed to be Schistonchus caprifici. Figs on one tree in Kahramanmaras city, South East Turkey, were found to contain S. caprifici and dauer juveniles of what appears to be a diplogastrid nematode. Molecular analyses produced congruent trees for both sequenced loci supporting the hypothesis that S. caprifici from different locations in Turkey are part of a well supported clade with some inherent variability. No geographic patterns were observed for either locus suggesting that the sequences generated represent inherent intraspecific variation for S. caprifici and that human activities related to the culture of the edible fig have allowed for mixing of any previously allopatric lineages.

Nematodes of the genus Pristionchus are closely associated with scarab beetles and the Colorado potato beetle in Western Europe

Evolutionary developmental biology examines how changes in developmental programmes give rise to developmental and, ultimately, morphological novelty. To this end, comparisons of related but distinct organisms have to be performed. The diplogastrid nematode Pristionchus pacificus has been developed as a satellite system for a detailed comparison of various developmental processes to the model organism Caenorhabditis elegans, a rhabditid nematode. In addition to developmental and genetic studies, a genomic platform has been established to analyse the biology of this organism. However, only little is known about where and how Pristionchus pacificus and its relatives live in the wild. Here we show that nematodes of the genus Pristionchus live in close association with scarabaeoid beetles and the Colorado potato beetle. In total, we generated 371 isogenic female lines from 4242 beetles collected at 25 sampling sites all over Europe. Isogenic female lines were subjected to sequence analysis and mating experiments for species determination. The 371 isolates fell into six species. Two hermaphroditic species account for about 60% of the collected nematodes. We found Pristionchus maupasi almost exclusively on cockchafers and Pristionchus entomophagus predominantly on dung beetles. Colorado potato beetles carried the gonochoristic species Pristionchus uniformis, which was only rarely observed on scarabaeoid beetles. We describe the initial evidence for the association of Pristionchus nematodes with beetles and provide a phylogeny based on sequence analysis of the small subunit ribosomal RNA gene.