Occurrence of Belonolaimus in Sinaloa, Northwestern Mexico: A New Report on Distribution and Host Range

The present study reports the occurrence of the genus Belonolaimus in the state of Sinaloa, Mexico, associated with native plants (i.e., Ziziphus amole and Stenocereus alamosensis) in a natural coastal ecosystem. Both morphological and molecular approaches were employed to characterize the Sinaloa population. Notwithstanding of some morphological and morphometric variation between Belonolaimus from Sinaloa and other valid species, the characterization indicates that this population might belong to the Belonolaimus longicaudatus species complex. Molecular analyses based on the 28S gene and ITS1-5.8S-ITS2 regions of the ribosomal RNA (rRNA) identified four major clades within Belonolaimus; however, none of the species including B. longicaudatus, B. gracilis, and B. euthychilus were supported as monophyletic; yet monophyly is argued to be a basic requirement of species status. Sequence divergence among different Belonolaimus populations and species varied according to the rRNA dataset (i.e., ITS1-5.8S-ITS2 > 28S > 18S) used, thus showing the importance of using genes with different rates of evolution to estimate species relationships. The fact that Belonolaimus has not been found in other cultivated (including on suitable hosts) areas in Sinaloa and that this population is relatively distant from the common B. longicaudatus groups (i.e., clades A and B) suggests that its appearance was not due to a recent introduction associated with the local agriculture.

Periosteum tissue engineering in an orthotopic in vivo platform

The periosteum plays a critical role in bone homeostasis and regeneration. It contains a vascular component that provides vital blood supply to the cortical bone and an osteogenic niche that acts as a source of bone-forming cells. Periosteal grafts have shown promise in the regeneration of critical size defects, however their limited availability restricts their widespread clinical application. Only a small number of tissue-engineered periosteum constructs (TEPCs) have been reported in the literature. A current challenge in the development of appropriate TEPCs is a lack of pre-clinical models in which they can reliably be evaluated. In this study, we present a novel periosteum tissue engineering concept utilizing a multiphasic scaffold design in combination with different human cell types for periosteal regeneration in an orthotopic in vivo platform. Human endothelial and bone marrow mesenchymal stem cells (BM-MSCs) were used to mirror both the vascular and osteogenic niche respectively. Immunohistochemistry showed that the BM-MSCs maintained their undifferentiated phenotype. The human endothelial cells developed into mature vessels and connected to host vasculature. The addition of an in vitro engineered endothelial network increased vascularization in comparison to cell-free constructs. Altogether, the results showed that the human TEPC (hTEPC) successfully recapitulated the osteogenic and vascular niche of native periosteum, and that the presented orthotopic xenograft model provides a suitable in vivo environment for evaluating scaffold-based tissue engineering concepts exploiting human cells.

Microsporidia-nematode associations in methane seeps reveal basal fungal parasitism in the deep sea

The deep sea is Earth's largest habitat but little is known about the nature of deep-sea parasitism. In contrast to a few characterized cases of bacterial and protistan parasites, the existence and biological significance of deep-sea parasitic fungi is yet to be understood. Here we report the discovery of a fungus-related parasitic microsporidium, Nematocenator marisprofundi n. gen. n. sp. that infects benthic nematodes at methane seeps on the Pacific Ocean floor. This infection is species-specific and has been temporally and spatially stable over 2 years of sampling, indicating an ecologically consistent host-parasite interaction. A high distribution of spores in the reproductive tracts of infected males and females and their absence from host nematodes' intestines suggests a sexual transmission strategy in contrast to the fecal-oral transmission of most microsporidia. N. marisprofundi targets the host's body wall muscles causing cell lysis, and in severe infection even muscle filament degradation. Phylogenetic analyses placed N. marisprofundi in a novel and basal clade not closely related to any described microsporidia clade, suggesting either that microsporidia-nematode parasitism occurred early in microsporidia evolution or that host specialization occurred late in an ancient deep-sea microsporidian lineage. Our findings reveal that methane seeps support complex ecosystems involving interkingdom interactions between bacteria, nematodes, and parasitic fungi and that microsporidia parasitism exists also in the deep-sea biosphere.

Redescription of Filenchus annulatus (Siddiqui & Khan, 1983) Siddiqi, 1986 based on specimens from Iran with contributions to the molecular phylogeny of the Tylenchidae

Filenchus annulatus is redescribed and males are characterised for the first time based on a population found in Northern Khorasan province, Iran. New morphological characterisation is based on light and scanning electron microscopy. In addition, molecular analyses based on 18S and 28S genes are included to test monophyly of the genus. Females from the Iranian population have a spermatheca typically filled with sperm. Generally males are similar to females, ranging from 306 to 426 μm long. Spicules are arcuate, cephalated and 11.5-14.0 μm long, the gubernaculum is minute and trough-shaped and the caudal alae are adanal. Phylogenetic analyses differed in results depending on the gene used: 28S gene strongly supports Filenchus as monophyletic whereas 18S shows Filenchus as polyphyletic. In both gene phylogenies, F. annulatus is placed as a sister taxon of F. quartus from Wyoming, USA. Although sequence divergence between these two species is only 3 base pairs and 1 base pair for 28S and 18S genes, respectively, strong morphological differences support their species status. Relationships between Filenchus and other Tylenchidae genera are also gene dependent. Such differences in tree topologies and branch support are related to the number of Filenchus species used in the analyses (greater for 18S gene) and gene resolution (greater for 28S gene). Molecular phylogenies also suggest that other Tylenchidae genera (i.e., Psilenchus, Cephalenchus and Eutylenchus) belong to separate clades, as is also suggested by some morphology-based classifications. The inclusion of more taxa and perhaps additional genes is needed further to clarify Filenchus relationships and further to test its monophyly.

Metagenetic community analysis of microbial eukaryotes illuminates biogeographic patterns in deep-sea and shallow water sediments

Microbial eukaryotes (nematodes, protists, fungi, etc., loosely referred to as meiofauna) are ubiquitous in marine sediments and probably play pivotal roles in maintaining ecosystem function. Although the deep-sea benthos represents one of the world's largest habitats, we lack a firm understanding of the biodiversity and community interactions amongst meiobenthic organisms in this ecosystem. Within this vast environment, key questions concerning the historical genetic structure of species remain a mystery, yet have profound implications for our understanding of global biodiversity and how we perceive and mitigate the impact of environmental change and anthropogenic disturbance. Using a metagenetic approach, we present an assessment of microbial eukaryote communities across depth (shallow water to abyssal) and ocean basins (deep-sea Pacific and Atlantic). Within the 12 sites examined, our results suggest that some taxa can maintain eurybathic ranges and cosmopolitan deep-sea distributions, but the majority of species appear to be regionally restricted. For Operationally Clustered Taxonomic Units (OCTUs) reporting wide distributions, there appears to be a taxonomic bias towards a small subset of taxa in most phyla; such bias may be driven by specific life history traits amongst these organisms. In addition, low genetic divergence between geographically disparate deep-sea sites suggests either a shorter coalescence time between deep-sea regions or slower rates of evolution across this vast oceanic ecosystem. While high-throughput studies allow for broad assessment of genetic patterns across microbial eukaryote communities, intragenomic variation in rRNA gene copies and the patchy coverage of reference databases currently present substantial challenges for robust taxonomic interpretations of eukaryotic data sets.

Cervidellus sonorensis n. sp. (Nematoda: Cephalobidae) from the desert of Anza-Borrego, CA, USA

Abstract

Cervidellus sonorensis n. sp. is described from sand near the roots of creosote bush (Larrea tridentata) from Anza-Borrego Desert State Park, CA, USA. It is distinguished from others in the genus by the combination of a greatly distended, guitar-shaped corpus and the morphology of the lips and labial probolae. Distinctive features include a large pharyngeal metacorpus with a double swelling, a knob-like ledge at the base of each labial probola and lips with five filamentous tines, the most apical of which are those closest to the primary axil. One male individual was discovered in this parthenogenetic species. Characters used to diagnose C. sonorensis n. sp. are not definitive with respect to other genera and are probably plesiomorphic or convergent in light of DNA-based phylogenetic hypotheses. The position of C. sonorensis n. sp. and morphologically close congeners in relation to species of Nothacrobeles and Paracrobeles is discussed.

Identification, phylogeny and phylogeography of circumfenestrate cyst nematodes (Nematoda: Heteroderidae) as inferred from analysis of ITS-rDNA

Abstract

Some 134 ITS rRNA gene sequences for circumfenestrate cyst nematodes and two sequences for non-cyst nematodes of the family Heteroderidae, of which 46 were newly obtained, were analysed by phylogenetic and phylogeographic methods. Sequence and phylogenetic analysis combined with known morphological, biological and geographical data allowed the identification, amongst samples original to this study, of several belonging to known valid species as well as others that might be new species. The phylogenetic analysis revealed six major clades for circumfenestrate cyst nematodes: i) Globodera from South and North America; ii) Globodera from Europe, Asia, Africa and Oceania; iii) Paradolichodera; iv) Punctodera; v) Cactodera; and vi) Betulodera. Monophylies of Punctodera, Cactodera and Betulodera were highly supported. The Betulodera clade occupied a basal position on all trees. Phylogeographic analysis suggested a North American origin of Punctoderinae with possible further long distance dispersal to South America, Africa and other regions. Molecular data supported synonymisation of G. achilleae with G. millefolii and of G. hypolysi with G. artemisiae. PCR-RFLP diagnostic profiles for some Globodera and Cactodera species are given. Problems of diagnostics for Globodera species using PCR with specific primers are discussed.

Resolving phylogenetic incongruence to articulate homology and phenotypic evolution: a case study from Nematoda

Modern morphology-based systematics, including questions of incongruence with molecular data, emphasizes analysis over similarity criteria to assess homology. Yet detailed examination of a few key characters, using new tools and processes such as computerized, three-dimensional ultrastructural reconstruction of cell complexes, can resolve apparent incongruence by re-examining primary homologies. In nematodes of Tylenchomorpha, a parasitic feeding phenotype is thus reconciled with immediate free-living outgroups. Closer inspection of morphology reveals phenotypes congruent with molecular-based phylogeny and points to a new locus of homology in mouthparts. In nematode models, the study of individually homologous cells reveals a conserved modality of evolution among dissimilar feeding apparati adapted to divergent lifestyles. Conservatism of cellular components, consistent with that of other body systems, allows meaningful comparative morphology in difficult groups of microscopic organisms. The advent of phylogenomics is synergistic with morphology in systematics, providing an honest test of homology in the evolution of phenotype.

Comparative, three-dimensional anterior sensory reconstruction of Aphelenchus avenae (nematoda: Tylenchomorpha)

The anterior sensory anatomy (not including amphids) of the nematode Aphelenchus avenae (Tylenchomorpha) has been three-dimensionally reconstructed from serial, transmission electron microscopy thin sections. Models, showing detailed morphology and spatial relationships of cuticular sensilla and internal sensory receptors, are the first computerized reconstruction of sensory structures of a Tylenchomorpha nematode. Results are analyzed with respect to similarly detailed reconstructions of Rhabditida outgroup nematodes, Acrobeles complexus (Cephalobomorpha) and Caenorhabditis elegans (Rhabditomorpha). Homologies identified in A. avenae demonstrate the general conservation of the anterior sensory system between freeliving nematodes and the largely plant parasitic Tylenchomorpha. A higher degree of similarity is shown between A. avenae and A. complexus, with common features including: the presence of a second, internal outer labial dendrite (OL1); a second cephalic dendrite in the female (CEP2/CEM); an accessory process loop of inner labial dendrite 1; and terminus morphology and epidermal associations of internal sensory receptors BAG and URX. Unique to A. avenae is a pair of peripheral, lateral neurons of unknown homology but with axial positions and intercellular relationships nearly identical to the "posterior branches" of URX in A. complexus. Knowledge of homologies and connectivity of anterior sensory structures provides a basis for expansion of the experimental behavioral model of C. elegans to the economically important nematodes of Tylenchomorpha.

Three-dimensional reconstruction of the stomatostylet and anterior epidermis in the nematode Aphelenchus avenae (Nematoda: Aphelenchidae) with implications for the evolution of plant parasitism

A three-dimensional model of the stomatostylet and associated structures has been reconstructed from serial thin sections of Aphelenchus avenae, a representative of Tylenchomorpha, a group including most plant parasitic nematodes. The reconstruction is compared with previous work on bacteriovorous cephalobids and rhabditids to better understand the evolution of the stylet and its associated cells. Two arcade syncytia ("guide ring") line the stylet shaft, supporting the hypothesis that the stylet shaft and cone (into which the shaft extends and which is not lined by syncytia) are homologous with the gymnostom of cephalobids, the sister taxon of tylenchids. Epidermal syncytia, HypA, HypB, HypC, and HypE, line the cephalic framework, vestibule, and vestibule extension, congruent with the hypothesis that these components are homologous with the cephalobid cheilostom. Relative to outgroups, HypC is expanded in A. avenae, enclosing sensilla that fill most of the cephalic framework. The homolog of syncytium HypD in the cephalobid Acrobeles complexus is not observed in A. avenae. Arcade syncytia are reduced compared with those of cephalobids. Stylet protractor muscles in A. avenae are homologous with the most anterior set of radial muscles of cephalobids. Observations to date test and verify our previous hypotheses of homology of the stomatostylet with respect to the stoma of bacteriovorous outgroups. Reconstruction of the stegostom and pharynx will provide further tests of homology and evolution of feeding structure adaptations for plant parasitism.

Three-dimensional reconstruction of the amphid sensilla in the microbial feeding nematode, Acrobeles complexus (Nematoda: Rhabditida)

Amphid sensilla are the primary olfactory, chemoreceptive, and thermoreceptive organs in nematodes. Their function is well described for the model organism Caenorhabditis elegans, but it is not clear to what extent we can generalize these findings to distantly related nematodes of medical, economic, and agricultural importance. Current detailed descriptions of anatomy and sensory function are limited to nematodes that recent molecular phylogenies would place in the same taxonomic family, the Rhabditidae. Using serial thin-section transmission electron microscopy, we reconstructed the anatomy of the amphid sensilla in the more distantly related nematode, Acrobeles complexus (Cephalobidae). Amphid structure is broadly conserved in number and arrangement of cells. Details of cell anatomy differ, particularly for the sensory neurite termini. We identify an additional sensory neuron not found in the amphid of C. elegans and propose homology with the C. elegans interneuron AUA. Hypotheses of homology for the remaining sensory neurons are also proposed based on comparisons between C. elegans, Strongyloides stercoralis, and Haemonchus contortus.

Apratylenchus vietnamensis gen. n., sp. n. and A. binhi gen. n., sp. n., sedentary Pratylenchidae (Nematoda: Tylenchida) from coffee in Vietnam, with proposal of Apratylenchinae subfam. n

Abstract

Apratylenchinae subfam. n. is proposed within the Pratylenchidae to include Apratylenchus gen. n. and two new species, A. vietnamensis gen. n., sp. n. and A. binhi gen. n., sp. n., from coffee plantations in Vietnam. Apratylenchus gen. n. is distinguished by the presence of transverse rows of cuticular tubercles on the annuli and by sexual dimorphism in which the males are stout and cylindrical, but mature sedentary females are club-shaped. The sedentary females are broadest in the posterior third although narrowing posterior to the vulva (V ≥ 85%). The female cephalic region is low and dome-shaped with all labial sectors fused to one another and the oral disc and the pharyngeal glands overlap the intestine ventrally. Males have a weak stylet with reduced knobs and a conical tail with a blunt terminus, arcuate spicules and a non-protrusible gubernaculum. Apratylenchus vietnamensis gen. n., sp. n. is characterised by a sedentary mature female with a 368-515 μm long club-shaped body, cephalic region low, dome shaped with three annuli, body annuli bearing a single or double row of refractive tubercles, stylet 17.0-19.9 μm long, V = ca 88-92, spermatheca filled with sperm and males known, if rarely found, in the type population. Males have a weak, 15 μm long stylet with reduced knobs, 16 μm spicules, a non-protrusible gubernaculum and low bursa. It differs from A. binhi gen. n., sp. n., the only other nominal species of the new genus, by longer female body (368-515 vs 326-364 μm), longer distance from anterior end to anus (353-512 vs 310-348 μm) and longer stylet (17.0-19.9 vs 14.7-16.9 μm). In addition, the spermatheca is filled with round sperm vs empty in A. binhi gen. n., sp. n. and the cuticle has less densely spaced and less pronounced tubercles. D2/D3 sequences of the 28 rDNA gene clearly support the separation of Apratylenchus gen. n. from other Pratylenchidae and further distinguish the two new species from each other.

A phylogenetic framework for root lesion nematodes of the genus Pratylenchus (Nematoda): Evidence from 18S and D2-D3 expansion segments of 28S ribosomal RNA genes and morphological characters

The root lesion nematodes of the genus Pratylenchus Filipjev, 1936 are migratory endoparasites of plant roots, considered among the most widespread and important nematode parasites in a variety of crops. We obtained gene sequences from the D2 and D3 expansion segments of 28S rRNA partial and 18S rRNA from 31 populations belonging to 11 valid and two unidentified species of root lesion nematodes and five outgroup taxa. These datasets were analyzed using maximum parsimony and Bayesian inference. The alignments were generated using the secondary structure models for these molecules and analyzed with Bayesian inference under the standard models and the complex model, considering helices under the doublet model and loops and bulges under the general time reversible model. The phylogenetic informativeness of morphological characters is tested by reconstruction of their histories on rRNA based trees using parallel parsimony and Bayesian approaches. Phylogenetic and sequence analyses of the 28S D2-D3 dataset with 145 accessions for 28 species and 18S dataset with 68 accessions for 15 species confirmed among large numbers of geographical diverse isolates that most classical morphospecies are monophyletic. Phylogenetic analyses revealed at least six distinct major clades of examined Pratylenchus species and these clades are generally congruent with those defined by characters derived from lip patterns, numbers of lip annules, and spermatheca shape. Morphological results suggest the need for sophisticated character discovery and analysis for morphology based phylogenetics in nematodes.

Synonymy of Afenestrata with Heterodera supported by phylogenetics with molecular and morphological characterisation of H. koreana comb. n. and H. orientalis comb. n. (Tylenchida: Heteroderidae)

Abstract

Phylogenetic analysis of five gene fragments: ITS-rRNA, D2 and D3 of 28S rRNA, 18S rRNA, Hsp90 and actin, of Heterodera species and two representative Afenestrata species, A. koreana and A. orientalis, form a clade with H. cynodontis, H. bifenestra and an unidentified Heterodera sp. infecting grasses. Based on these results and the consideration that the key diagnostic characters of Afenestrata are convergent and do not define a clade, synonymisation of Afenestrata with Heterodera is proposed. The following new combinations are made: H. africana comb. n., H. axonopi comb. n., H. koreana comb. n., and H. orientalis comb. n. Furthermore, H. (= Afenestrata) sacchari is renamed as H. saccharophila nom. nov. to avoid homonymy. All these species, together with H. bamboosi, are regarded as members of a paraphyletic ‘Afenestrata group’ within Heterodera. Whilst recognised as artificial, the Afenestrata group is nevertheless an aid to discussion about these similar species. Morphological and molecular characterisation of populations of H. koreana comb. n. from Florida and H. orientalis comb. n. from Florida and Guatemala verify the identification of these populations as valid representatives for molecular studies of the species. Light and SEM observations also provide new detail and a broader understanding of the morphological range of both species. These include a longer stylet for females of H. koreana comb. n. and H. orientalis comb. n. than reported in the original descriptions. In addition, previously unreported tuberculate ridges are noted on the surface of vulval lips of H. orientalis comb. n. The lip region of second-stage juveniles of H. koreana comb. n. and H. orientalis comb. n. both include fused adjacent submedian lips that also fuse with the labial disc and the second lip annulus. The ITS-rRNA gene sequences of H. orientalis comb. n. populations from Florida and Guatemala were similar to those from the Russian type locality. Diagnostic PCR-RFLP of ITS-rRNA profiles with six enzymes for H. orientalis comb. n. and H. koreana comb. n. are given. A key for the morphological identification of species of the Afenestrata group is provided.

Three-dimensional fine structural reconstruction of the nose sensory structures of Acrobeles complexus compared to Caenorhabditis elegans (Nematoda: Rhabditida)

Nematode sensory structures can be divided into two classes; cuticular sensillae, with dendrites ending outside the epidermis, and internal receptors, that typically are single dendrites terminating within the body cavity. Fine structure of the former has been described completely in more than a dozen nematode taxa, while the latter were previously only well understood in the microbial feeder Caenorhabditis elegans. The distantly related nematode Acrobeles complexus has a similar ecology and together the two span a clade representing a large proportion of nematode biodiversity. The cuticular sensillae and internal receptors of A. complexus are here shown to be remarkably similar in number, arrangement, and morphology to those of C. elegans. Several key differences are reported that likely relate to function, and suggest that this nematode has a cuticular sensillum morphology that is closer to that of the common ancestor of the two taxa. Internal sensory receptors have more elaborate termini than those of C. elegans. The existence of a novel form of mechanoreceptor in A. complexus and spatial relationships between sensillum dendrites suggest differences between two classes of sensillae in how a touch-response behavior may be mediated.

Three-dimensional reconstruction of the nose epidermal cells in the microbial feeding nematode, Acrobeles complexus (Nematoda: Rhabditida)

The epidermis of the anterior end (nose) plays an important role in the evolution, development, and functional feeding morphology in nematodes, but information on this complex organ system is limited. Here, we produce a 3D model of 13 of the cells making up this organ system reconstructed from serial transmission electron micrographs of the microbial feeding nematode, Acrobeles complexus. Nose epidermal cells were found to be broadly similar to those of the distantly related model organism Caenorhabditis elegans in the number and arrangement of nuclei in these largely syncytial cells; this similarity demonstrates striking evolutionary conservation that allows for robust statements of homology between the taxa. Examining details of cell shape, however, revealed surprisingly complex subcellular specialization, which differed markedly from C. elegans in the number and arrangement of cell processes. Anterior toroid processes of the anterior arcade, posterior arcade, and HypB syncytia form a nested complex at the base of the labial probolae. Anterior toroid processes of HypC and the inner labial socket cells are associated with the base of the cephalic probolae and radial ridge processes. Extracellular filaments (tendon organs) and radiating cytoskeletal filaments of the posterior arcade syncytium form a connection between the body wall muscle cells and the pharynx. An epidermal cell with no known homolog in other nematodes is identified. Findings provide a basis to propose hypotheses related to the development and evolutionary origin of specialized feeding appendages (probolae) in the Cephalobinae (including Acrobeles), and hypotheses of homology are revised for epidermal cells in the nose of the closely related and primarily plant parasitic group, Tylenchida.

Application of the secondary structure model of rRNA for phylogeny: D2-D3 expansion segments of the LSU gene of plant-parasitic nematodes from the family Hoplolaimidae Filipjev, 1934

Knowledge of rRNA structure is increasingly important to assist phylogenetic analysis through reconstructing optimal alignment, utilizing molecule features as an additional source of data and refining appropriate models of evolution of the molecule. We describe a procedure of optimization for alignment and a new coding method for nucleotide sequence data using secondary structure models of the D2 and D3 expansion fragments of the LSU-rRNA gene reconstructed for fifteen nematode species of the agriculturally important and diverse family Hoplolaimidae, order Tylenchida. Using secondary structure information we converted the original sequence data into twenty-eight symbol codes and submitted the transformed data to maximum parsimony analysis. We also applied the original sequence data set for Bayesian inference. This used the doublet model with sixteen states of nucleotide doublets for the stem region and the standard model of DNA substitution with four nucleotide states for loops and bulges. By this approach, we demonstrate that using structural information for phylogenetic analyses led to trees with lower resolved relationships between clades and likely eliminated some artefactual support for misinterpreted relationships, such as paraphyly of Helicotylenchus or Rotylenchus. This study as well as future phylogenetic analyses is herein supported by the development of an on-line database, NEMrRNA, for rRNA molecules in a structural format for nematodes. We also have developed a new computer program, RNAstat, for calculation of nucleotide statistics designed and proposed for phylogenetic studies.

Phylogeny of Cephalobina (Nematoda): Molecular evidence for recurrent evolution of probolae and incongruence with traditional classifications

Nematodes of the suborder Cephalobina include an ecologically and morphologically diverse array of species that range from soil-dwelling microbivores to parasites of vertebrates and invertebrates. Despite a long history of study, certain of these microbivores (Cephaloboidea) present some of the most intractable problems in nematode systematics; the lack of an evolutionary framework for these taxa has prevented the identification of natural groups and inhibited understanding of soil biodiversity and nematode ecology. Phylogenetic analyses of ribosomal (LSU) sequence data from 53 taxa revealed strong support for monophyly of taxa representing the Cephaloboidea, but do not support the monophyly of most genera within this superfamily. Historically these genera have primarily been recognized based on variation in labial morphology, but molecular phylogenies show the same general labial (probolae) morphotype often results from recurrent similarity, a result consistent with the phenotypic plasticity of probolae previously observed for some species in ecological time. Phylogenetic analyses of LSU rDNA also recovered strong support for some other groups of cephalobs, including taxa representing most (but not all) Panagrolaimoidea. In addition to revealing homoplasy of probolae, molecular trees also imply other unexpected patterns of character evolution or polarity, including recurrent similarity of offset spermatheca presence, and representation of complex probolae as the ancestral condition within Cephaloboidea. For Cephalobidae, molecular trees do not support traditional genera as natural groups, but it remains untested if deconstructing probolae morphotypes or other structural features into finer component characters may reveal homologies that help delimit evolutionary lineages.

A position paper on the electronic publication of nematode taxonomic manuscripts

Several nematode species have now attained 'model organism' status, yet there remain many niches in basic biological inquiry for which nematodes would be ideal model systems of study. However, furthering the model system approach is hindered by lack of information on nematode biodiversity. The shortage of taxonomic resources to inventory and characterize biodiversity hinders research programs in invasion biology, ecosystem functioning, conservation biology, and many others. The disproportion between numbers of species to be described and numbers of available taxonomic specialists is greater for Nematoda than for any other metazoan phylum. A partial solution to the taxonomic impediment is the adoption of recent advances in electronic publishing. Electronic publishing has the potential to increase the rate at which taxonomic papers are published, the breadth of their distribution, and the type, quantity, quality, and accessibility of data. We propose that the Journal of Nematology implement the advantageous aspects of electronic publication as a means to help ameliorate the limitations of an underdeveloped taxonomy and empower the nematological disciplines currently hindered by it.

An integrated approach to fast and informative morphological vouchering of nematodes for applications in molecular barcoding

Molecular surveys of meiofaunal diversity face some interesting methodological challenges when it comes to interstitial nematodes from soils and sediments. Morphology-based surveys are greatly limited in processing speed, while barcoding approaches for nematodes are hampered by difficulties of matching sequence data with traditional taxonomy. Intermediate technology is needed to bridge the gap between both approaches. An example of such technology is video capture and editing microscopy, which consists of the recording of taxonomically informative multifocal series of microscopy images as digital video clips. The integration of multifocal imaging with sequence analysis of the D2D3 region of large subunit (LSU) rDNA is illustrated here in the context of a combined morphological and barcode sequencing survey of marine nematodes from Baja California and California. The resulting video clips and sequence data are made available online in the database NemATOL (http://nematol.unh.edu/). Analyses of 37 barcoded nematodes suggest that these represent at least 32 species, none of which matches available D2D3 sequences in public databases. The recorded multifocal vouchers allowed us to identify most specimens to genus, and will be used to match specimens with subsequent species identifications and descriptions of preserved specimens. Like molecular barcodes, multifocal voucher archives are part of a wider effort at structuring and changing the process of biodiversity discovery. We argue that data-rich surveys and phylogenetic tools for analysis of barcode sequences are an essential component of the exploration of phyla with a high fraction of undiscovered species. Our methods are also directly applicable to other meiofauna such as for example gastrotrichs and tardigrades.

Morphology and Description of Bursaphelenchus platzeri n. sp. (Nematoda: Parasitaphelenchidae), an Associate of Nitidulid Beetles

Bursaphelenchus platzeri n. sp., an associate of nitidulid beetles in southern California, is described and illustrated. Adult males and females of B. platzeri n. sp. were examined by scanning electron microscopy for ultrastructural comparisons with other members of the genus. Bursaphelenchus cocophilus (red ring nematode) appears to be the closest related taxon to B. platzeri n. sp. based upon shared morphological features of the fused spicules, female tail shape, phoresy with non-scolytid beetles, and molecular analysis of the near full-length small subunit (SSU) rDNA. Unfortunately, sequence data from the D2D3 expansion segments of the large subunit (LSU) rDNA and partial mitochondrial DNA COI did not help resolve the relationship of nearest relative. In addition to significant molecular sequence differences in SSU, LSU, and COI, B. platzeri n. sp., which is an obligate fungal feeder, can be differentiated from B. cocophilus because it is an obligate parasite of palms. Bursaphelenchus platzeri n. sp. can be differentiated from all other species of Bursaphelenchus by the length and shape of the female tail and spicule morphology. The spicules are fused along the ventral midline and possess unfused cucullae; the fused unit appears to function as a conduit for sperm. Population growth of B. platzeri n. sp. was measured in a time-course experiment at 25 degrees C in the laboratory on cultures of the fungus Monilinia fructicola grown on 5% glycerol-supplemented potato dextrose agar (GPDA). Nematode population densities rapidly increased from 25 to approximately 200,000/culture within 14 d and then plateaued for up to 28 d.

Phylogenetic analysis of Tylenchida Thorne, 1949 as inferred from D2 and D3 expansion fragments of the 28S rRNA gene sequences

Abstract

The evolutionary relationships of 82 species of tylenchid and aphelenchid nematodes were evaluated by use of sequence data of the D2 and D3 expansion fragments of the 28S ribosomal RNA genes. Nine automatic and one culled sequence alignments were analysed using maximum parsimony and Bayesian inference approaches. The molecular data sets showed that the order Tylenchida comprises lineages that largely correspond to two suborders, Hoplolaimina and Criconematina, and other taxonomic divisions as proposed by Siddiqi (2000). Several significant results also derived from our study include: i) the basal position of groups that include entomoparasitic nematodes within tylenchid trees; ii) paraphyly of the superfamily Dolichodoroidea sensu Siddiqi (2000); iii) evidence for a Pratylenchus, Hirschmanniella and Meloidogyne clade; and iv) lack of support for widely held traditional placement of Radopholus within Pratylenchidae and placement of this genus within Hoplolaimidae or Heteroderidae. Congruence and incongruence of molecular phylogeny and traditional classifications and morphological-based hypotheses of phylogeny of tylenchids are discussed.

Phylogenetic Relationships Among Selected Heteroderoidea Based on 18S and ITS Ribosomal DNA

In a study of relationships among selected cyst-forming and noncyst-forming species of Heteroderoidea, combined sequences comprised of DNA from part of the conserved 18S ribosomal RNA gene (rDNA) plus the complete ITS rDNA segment were more similar to analyses based on the ITS data alone than to analyses based on the 18S data alone. One of the two noncyst-forming species, Ekphymatodera thomasoni, grouped with cyst-forming species of Heteroderoidea. Bilobodera flexa, also a noncyst-forming species, was separated from all the other taxa by a long branch. Afenestrata koreana, with a weakly sclerotized cyst, grouped closely with H. bifenestra. These observations suggest that phylogenetic analyses using molecular data may aid in our understanding of the evolution of cyst formation in nematodes, including the possibility of secondary loss. The usefulness of molecular phylogenetic analyses in nematodes may depend more on the particular selection of taxa than on mere addition of data from additional genes.

Evolution of plant parasitism among nematodes

Despite extraordinary diversity of free-living species, a comparatively small fraction of nematodes are parasites of plants. These parasites represent at least three disparate clades in the nematode tree of life, as inferred from rRNA sequences. Plant parasites share functional similarities regarding feeding, but many similarities in feeding structures result from convergent evolution and have fundamentally different developmental origins. Although Tylenchida rRNA phylogenies are not fully resolved, they strongly support convergent evolution of sedentary endoparasitism and plant nurse cells in cyst and root-knot nematodes. This result has critical implications for using model systems and genomics to identify and characterize parasitism genes for representatives of this clade. Phylogenetic studies reveal that plant parasites have rich and complex evolutionary histories that involve multiple transitions to plant parasitism and the possible use of genes obtained by horizontal transfer from prokaryotes. Developing a fuller understanding of plant parasitism will require integrating more comprehensive and resolved phylogenies with appropriate choices of model organisms and comparative evolutionary methods.

Molecular phylogenetics and diagnosis of soil and clinical isolates of Halicephalobus gingivalis (Nematoda: Cephalobina: Panagrolaimoidea), an opportunistic pathogen of horses

Phylogenetic relationships among six isolates of Halicephalobus gingivalis (Stefanski, 1954), a species with pathogenic potential in horses and humans, were evaluated using DNA sequences from the nuclear large-subunit ribosomal RNA (LSU rDNA) gene. Sequences from nematodes obtained from in vitro cultures (soil or clinical sources), or isolated from infected horse tissues, were compared. Gene sequences from a fatal equine clinical case from southern California and a free-living isolate recovered from southern California soil showed no fixed differences. Sequences from isolates representing two fatal equine cases from North America, one from Ontario, Canada and another from Tennessee also showed no fixed differences. In contrast, two equine cases from Tennessee had 18 fixed differences for this LSU region, the greatest observed among isolates from horses. Phylogenetic analysis of six Halicephalobus sequences and four outgroup taxa by maximum parsimony yielded one tree with five well-supported clades. This phylogeny did not group isolates of Halicephalobus strictly by region of geographic isolation or source of sample, and depicted one clinical and one soil isolate as sister taxa. These results confirm that free-living environmental isolates are potential sources of infection for horses. The phylogeny also reveals that diverse isolates can cause infections in horses within a relatively limited geographic region, and conversely that genetically similar sister taxa can be recovered from geographically distant localities. PCR primers that selectively amplify Halicephalobus DNA were designed and tested based on comparison of closely related nematodes as inferred from phylogenetic analysis.

Fine Structure of the Stoma of Bunonema sp. and Teratorhabditis palmarum (Nematoda) and Its Phylogenetic Significance

Fine structure of the stoma, including the cheilostom, gymnostom, and stegostom of Bunonema sp. and Teratorhabditis palmarum was compared with Caenorhabditis elegans to consider fine structural characters that may be phylogenetically informative. The stegostom, enclosed by the anterior end of the pharynx, includes a triradiate lumen surrounded by radial cells (interradial or pairs of adradial cells) repeated in the dorsal and subventral sectors; in Rhabditina, typically the stegostom includes anteriorly two sets of epithelial and posteriorly two sets of muscular radial cells. These muscle cells are anteriorly m1 and posteriorly m2. In Bunonema sp., unlike T. palmarum and C. elegans, the stegostom has a third set of interradial epithelial cells. In Bunonema sp., m1 is expressed by three interradial cells, whereas in T. palmarum and C. elegans m1 is three pairs of adradial muscle cells (i.e., six cells). In all three taxa m2 is expressed as three pairs of adradial muscle cells. Posterior processes of adjacent adradial cells fuse, and closely apposed nuclei may present a figure-eight shape. However, in Bunonema the three interradial m1 cells each have a long posterior process enclosing two separate round nuclei. In combination with additional characters, these diverse stoma features may prove phylogenetically informative. Specifically, the radial epithelial cells of the stegostom appear to be a synapomorphy consistent with a bunonemid-diplogastrid-rhabditid clade, whereas a thickening in the dorsal sector of the stoma cuticle lining is interpreted as a synapomorphy supporting a bunonemid-diplogastrid clade.

Comparative survey of early embryogenesis of Secernentea (Nematoda), with phylogenetic implications

Insight into the evolution of class Secernentea (Nematoda) for the purpose of providing a phylogenetic context for the model Caenorhabditis elegans is being gained from the use of molecular character sets. Such phylogenies provide a framework for mapping the evolution of diversity in some early-development characters for 70 species and 19 families of Secernentea. These characters include (i) whether AB and P1 blastomeres initially develop at the same (synchronous) or different (asynchronous) rates, (ii) whether AB and P1 are initially aligned along the linear axis of the embryo (tandem pattern) or obliquely (rhomboidal pattern), and (iii) whether the founder germ cell, P4, is established early, i.e., by the sixth cleavage, or later. Evolutionary polarity of characters was evaluated through outgroup comparisons. From our data the following inferences are made. The derived character, late establishment of P4, evolved primarily in the ancestor of the monophyletic groups Diplogastrina, Rhabditina, and Panagrolaimidae. Asynchronous development is convergent, defining one clade of Tylenchina as well as Cephalobina, and also arising independently in Aphelenchina. The rhomboidal embryo is ancestral to the tandem-pattern embryo that defines a second clade of Tylenchina. Early-embryo characters are congruent with the polyphyly of Cephalobina and Aphelenchina, as has been demonstrated by molecular phylogenies. Many aspects of early embryogenesis, rather than being highly conserved, evolve at a rate appropriate to defining taxa within Secernentea.

Ultrastructure of the postcorpus of the esophagus of Teratocephalus lirellus (Teratocephalida) and its use for interpreting character evolution in Secernentea (Nematoda)

The ultrastructure of the postcorpus of the putative outgroup of Secernentea (Nematoda), Teratocephalus lirellus (Teratocephalida), is compared with previous observations of representative species Zeldia punctata (Cephalobina), Caenorhabditis elegans (Rhabditina), and Diplenteron sp. (Diplogastrina) in order to interpret the evolution of feeding structures within Secernentea. The postcorpus of T. lirellus consists of 6 marginal, 13 muscle, 3 gland, and 11 nerve cells. In both T. lirellus and Z. punctata, one duct from each of two subventral glands opens into the esophageal lumen at the junction of the isthmus and the basal bulb, whereas in C. elegans and Diplenteron sp., homologous openings are at the posterior end of the median bulb. Caenorhabditis elegans and Z. punctata each have two additional glands that open within the basal bulb. The postcorpus of each taxon has four anterior-to-posterior layered sets of radial muscle cells, except in Diplenteron sp., which lacks a grinder and has homologs to the anterior two sets only. The anterior set of muscles of T. lirellus and Z. punctata includes six mononucleate cells, whereas the homolog in C. elegans and Diplenteron sp. includes three binucleate cells. Evaluation of character polarity defines Rhabditina and Diplogastrina as sister taxa, and suggests that the character of five glands may result from functional convergence.

Ultrastructure of the post-corpus of Zeldia punctata (Cephalobina) for analysis of the evolutionary framework of nematodes related to Caenorhabditis elegans (Rhabditina)

The ultrastructure of the post-corpus of Zeldia punctata (Cephalobina) was compared with previous observations of Caenorhabditis elegans (Rhabditina) and Diplenteron sp. (Diplogastrina) with the goal of interpreting the morphological evolution of the feeding structures in the Secernentea. The post-corpus of Z. punctata consists of six marginal, 13 muscle, five gland and seven nerve cells. The most anterior of four layers of muscle cells consists of six mononucleate cells in Z. punctata. The homologous layer in C. elegans and Diplenteron consists of three binucleate cells, suggesting a unique derived character (synapomorphy) shared between the Rhabditina and Diplogastrina. Contrary to Diplenteron sp. where we observed three oesophageal glands, Z. punctata and C. elegans have five oesophageal glands. We question this shared character as reflecting a common evolution between the Cephalobina and Rhabditina, because there are strong arguments for functional (adaptive) convergence of the five glands in these bacterial feeders. Convergence is further suggested by the mosaic distribution of three versus five glands throughout the Nemata; this distribution creates difficulties in establishing character polarity. Although morphological data are often laborious to recover and interpret, we nevertheless view 'reciprocal illumination' between molecular and morphological characters as the most promising and robust process for reconstructing the evolution of the Secernentea and its feeding structures.

Ultrastructural variation of cuticular layers in cephalobinae (nemata: rhabditida)

The ultrastructure of the body wall cuticle in Acrobeles complexus, Cervidellus alutus, and Zeldia punctata was studied as a step toward understanding biological diversity within Cephalobinae, and to discover new characters for phylogeny-based classification of the suborder. In each species the cuticle consists of cortical, median, and basal layers. The cortical layer includes an external trilaminate and internal granular zone; the basal layer is striated. In Z. punctata the median layer is electron-lucent, vacuolar, and penetrates the cortical layer; it also includes periodically dense columns that apparently correspond to punctuations visible with light microscopy. In contrast, the median layer of the body wall cuticle in A. complexus and C. alutus is bisected by a zone that undulates parallel to the nematode surface and with periodicity corresponding to annuli. Phylogenetic analysis, using derived cuticle patterns of Cephalobinae, requires an understanding of ecological pressures that could result in convergent evolution of cuticle characters.

Three new species of nothacrobeles (nemata: cephalobidae) from the mojave desert, california

Three new species of Nothacrobeles are described from localities in the Mojave Desert, southern California. Nothacrobeles triniglarus n. sp. is characterized by the presence of a long post-vulval sac and three tubular adoral projections. Both N. spatulatus n. sp. and N. nanocorpus n. sp. are smaller than any other known species within the genus. Nothacrobeles spatulatus n. sp. has labial probolae that are short and spatulate without a basal ridge, whereas those of N. nanocorpus n. sp. are flattened and plate-like. Furthermore, N. nanocorpus n. sp. is unique by its extremely short esophageal corpus (less than 25 microm long in adult females) and the small size of its guard processes. An emended diagnosis of the genus is given to accommodate distinctive characteristics of these new species. A table comparing the 11 valid species of Nothacrobeles is presented.

Ultrastructure of the Esophagus of Diplenteron sp. (Diplogasterida) to Test Hypotheses of Homology with Rhabditida and Tylenchida

The ultrastructure of the isthmus and basal bulb (postcorpus) of Diplenteron sp. (Diplogasterida) was revealed through transmission electron micrographs of serial sections. The postcorpus is glandular and muscular. There are 26 cells in the postcorpus, including 6 marginal (two sets of three), 6 muscle (two sets of three), 3 gland, and 11 nerve cells. Most of the cell bodies, including the nuclei, are in the basal bulb. Unlike Caenorhabditis elegans, Diplenteron sp. has three gland cells. The glands are embedded in a muscular framework in both taxa, but each gland cell is much bigger in Diplenteron sp. than in C. elegans. Each of the anterior set of three marginal cells is located at the apex of the esophageal lumen and overlaps slightly with one of the posterior sets of three marginal cells. All six marginal cells in Diplenteron sp. have homologs in C. elegans. The anterior set of radial muscle cells is V-shaped and is homologous to m5 muscle cells in C. elegans. The posterior set of muscle cells appears to be homologous to m6 muscle cells in C. elegans. Diplenteron sp. does not have muscle cells corresponding to the m7 cells associated with the "grinder" in C. elegans, which is absent in diplogasterids. The single saucer-shaped muscle cell, m8, covering the posterior wall of the basal bulb in C. elegans was not observed in Diplenteron sp. The structure of the esophageal-intestinal junction in Diplenteron sp. is similar to that of C. elegans in being composed of five epithelial cells. Neurons appear to be more abundant in Diplenteron sp. than in C. elegans. Ultrastructure of the esophagus in diplogasterids, rhabditids, cephalobids, and tylenchids will be useful in testing classical and recent competing hypotheses of secernentean phylogeny.

Buccal capsule development as a consideration for phylogenetic analysis of Rhabditida (Nemata)

Bacterial feeding nematodes in the order Rhabditida including Zeldia punctata (Cephalobidae) and Caenorhabditis elegans (Rhabditidae) differ profoundly in the buccal capsule parts and associated cells. We carried out a range of tests to determine which buccal capsule parts and cells are evolutionarily homologous between the representative species of the two families. Tests included reconstruction of the buccal capsule and procorpus with transmission electron microscopy (TEM), nuclei position and morphology using 4, 6-diamidino-2-phenylindole (DAPI) staining, and cell lineage using four dimensional (4D) microscopy. The lining of the buccal capsule of Z. punctata and additional Cephalobidae includes four sets of muscular radial cells, ma, mb, mc and md, in contrast to C. elegans and additional Rhabditidae, which has two sets of epithelial cells (e1, e3) and two sets of muscle cells (m1, m2). Cell lineage of a nematode closely related to Z. punctata, Cephalobus cubaensis, supports the hypothesis that in cephalobids the e1 and e3 cells become hypodermal cells or are programmed to die. Our findings contradict all previous hypotheses of buccal capsule homology, and suggest instead that ma and mb in Z. punctata are homologous to m1 and m2 in C. elegans respectively. We also hypothesize that ma and mb could be homologous to primary and secondary sets of stylet-protractor muscle cells in the plant parasitic Tylenchida.

Changes in Esophageal Gland Activity During the Life Cycle of Nacobbus aberrans (Nemata: Pratylenchidae)

Electron and light microscopy were used to study the dorsal gland (DG) and the two subventral glands (SvG) of seven developmental phases of Nacobbus aberrans: pre-parasitic second-stage juveniles (J2), parasitic J2, third- (J3) and fourth- (J4) stages, migratory females, young sedentary females, and mature sedentary females. In each developmental phase the level of esophageal gland activity, was estimated by the abundance of organelles associated with secretory pathways, including endoplasmic reticulum, ribosomes, Golgi, multivesicular bodies, and secretory granules. All esophageal glands were metabolically active in all J2 examined, although only in parasitic J2 were there numerous secretory granules in the esophageal gland extensions and ampullae. No evidence of secretory activity was observed in the esophageal glands of the coiled and relatively inactive J3 and J4, nor in migratory females; these stages apparently do not feed. Observations suggest that reserves stored by J2 sustain three ecdyses and the migratory female's search for a feeding site and induction of a syncytium. Feeding activity is resumed in young and mature sedentary females, in which the DG is highly active and enlarged. The SvG are metabolically active, but with little synthesis of secretory granules, suggesting that in sedentary females the SvG may have physiological roles other than digestion.

Cactodera salina n. sp. from the Estuary Plant, Salicornia bigelovii, in Sonora, Mexico

Cactodera salina n. sp. (Heteroderinae) is described from roots of the estuary plant Salicornia bigelovii (Chenopodiaceae), in Puerto Pefiasco, Sonora, Mexico, at the northern tip of the Sea of Cortez. The halophyte host is grown experimentally for oilseed in plots flooded daily with seawater. Infected plants appear to be adversely affected by C. salina relative to plants in noninfested plots. Cactodera salina extends the morphological limits of the genus. Females and cysts have a very small or absent terminal cone and deep cuticular folds in a zigzag pattern more typical of Heterodera and Globodera than of Cactodera spp. Many Cactodera spp. have a tuberculate egg surface, whereas C. salina shares the character of a smooth egg with C. amaranthi, C. weissi, and C. acnidae. Only C. milleri and C. acnidae have larger cysts than C. salina. Face patterns of males and second-stage juveniles, as viewed with scanning electron microscopy, reveal the full complement of six lip sectors as in other Cactodera spp. Circumfenestrae of C. salina are typical for the genus.

An evolutionary framework for the study of developmental evolution in a set of nematodes related to Caenorhabditis elegans

Nematodes are known to be a useful system for studies of comparative development. Here we perform a molecular phylogenetic analysis to allow for the independent interpretation of the developmental and morphological changes observed among a selected set of nematode species. Our molecular phylogenetic analysis is based on coding regions of the genes for RNA polymerase II, the small subunit rRNA and an expansion segment of the large subunit rRNA. Sequences were compared from five species in the family (Rhabditidae) that includes the developmental model organism Caenorhabditis elegans and from an outgroup taxon Aduncospiculum halicti (Diplogasterina). The phylogenetic analysis does not support the monophyly of the subfamily Mesorhabditinae and identifies the unnamed strain PS1010 as a sister taxon of C. elegans despite its morphologically divergent buccal capsule. On the basis of the inferred framework, we can begin to interpret the evolution of vulval development and of morphological differences among these nematode species.

Genetic Variation in Nacobbus aberrans: An Approach toward Taxonomic Resolution

Biochemical and molecular analyses of genetic variation were evaluated to address the taxonomic status of Nacobbus aberrans. Isolates from Mexico, Peru, and Argentina, cultured on tomato in the greenhouse, were analyzed with respect to isozyme and DNA marker variation. Although acid phosphatase and malate dehydrogenase revealed distinct profiles for each isolate, non-specific esterases revealed possible affinities between the Peruvian isolates and between the isolates from Mexico and Peru. Two of l 0 RAPD primers revealed affinities suggested by esterase profiles. RFLP analysis of the rDNA repeating unit with six restriction enzymes revealed identical cleavage patterns between the Peru isolates and a distinct profile shared by isolates from Mexico and Argentina. Nucleotide sequence analysis of the 5.8S rRNA coding region revealed differences among the four isolates at eight of 157 positions; sequences of the Peruvian isolates differed from each other at only one position, whereas the Mexican and Argentine isolates were identical and could be distinguished from the Peruvian isolates. A distance matrix from unweighted pairwise comparisons of the 5.8S rDNA revealed apparent elevated intraspecific divergence in N. aberrans comparable to intergeneric divergence between Heterodera and Globodera. Analysis of additional N. aberrans isolates from throughout the distribution range should help determine the full extent of intraspecific genetic variation that underlies the phenotypic and morphologic diversity of the genus.

DNA sequences from formalin-fixed nematodes: integrating molecular and morphological approaches to taxonomy

To effectively integrate DNA sequence analysis and classical nematode taxonomy, we must be able to obtain DNA sequences from formalin-fixed specimens. Microdissected sections of nematodes were removed from specimens fixed in formalin, using standard protocols and without destroying morphological features. The fixed sections provided sufficient template for multiple polymerase chain reaction-based DNA sequence analyses.

Meloidogyne partityla on Pecan Isozyme Phenotypes and Other Host

Meloidogyne sp. from five pecan (Carya illinoensis) orchards in Texas were distinctive in host range and iszoyme profiles from common species of Meloidogyne but were morphologically congruent with Meloidogyne partityla Kleynhans, a species previously known only in South Africa. In addition to pecan, species of walnut (Juglans hindsii and J. regia) and hickory (C. ovata) also were hosts. No reproduction was observed on 15 other plant species from nine families, including several common hosts of other Meloidogyne spp. Three esterase phenotypes and two malate dehydrogenase phenotypes of M. partityla were identified by polyacrylamide gel electrophoresis. Each of these isozyme phenotypes was distinct from those of the more common species M. arenaria, M. hapla, M. incognita, and M. javanica.

Description of Tylenchorhynchus thermophilus n. sp. (Nematoda: Tylenchina) from Saltgrass in Death Valley, California

A stunt nematode, Tylenchorhynchus thermophilus n. sp., is described and illustrated from soil collected around roots of saltgrass (Distichlis spicata) in Death Valley, California. It is distinguished from the similar species, T. ewingi, T. mexicanus, and T. mashoodi, in having a longer female body, longer tail with more annules, and larger phasmids. Physical and chemical analysis of soil from saltgrass roots showed it to consist of 71% sand and possess high salinity (salt content of 0.51%) and a pH of 9.3.

Fine Structure of Sperm of Ekphymatodera thomasoni (Heteroderinae, Nemata)

Fine structure of developing sperm of the monospecific genus, Ekphymatodera, was compared with other Heteroderinae as part of a study to recognize diversity and phylogenetically informative characters within the subfamily. Sperm of Ekphymatodera originate from germ cells connected to a central rachis, a character which is shared with Globodera, but not with other Heteoderinae. In Ekphymatodera, and cyst-forming genera, a layer of cortical microtubules lies just beneath the surface of the plasma membrane. Sperm of Ekphymatodera are unique among Heteroderinae examined by the presence of spiral surface elevations on the filopodia, a character that may prove to be a synapomorphy for Sarisoderini. Fibrous bodies are abundant in spermatids; however, they do not persist in sperm of Ekphymatodera as they do in Meloidodera and Verutus. The male gonad of Ekphymatodera is lined by epithelial cells, which are greatly enlarged near the ejaculatory canal. These enlarged cells contain vesicles with concentric lamellar inclusions, not observed in other genera of the subfamily. Sperm of Heteroderinae are rich in diversity, and examination of additional representative species may indicate new phylogenetically informative characters.

Morphology of Nurse Cell Nuclei Induced by Meloidodera floridensis: A Graphics Application

The highly irregular distribution of nuclear material in the host nurse cell induced by Meloidodera floridensis has made it difficult to interpret the number of nuclei from two-dimensional micrographs alone. The primary goal of this investigation was to determine the distribution of nuclear material from a three-dimensional solid surface model of the nurse cell nucleus. This model demonstrated the continuity of nuclear material as a single highly irregular nucleus. Custom computer graphics programs were written to accept digitized tracings of nuclear material. From these digitized tracings, a wireframe or polygonalized mesh model was generated. The model was shaded, colored, rotated, and analyzed. This technique provides controlled transparency of the model to display nucleoli within the nucleus. Photographs of the computer screen, color printouts, and video recordings were used to record final results. These refined computer graphic tools have a range of applications in nematode host-parasite relationships, ontogeny, and morphology.

Description of Bursaphelenchus abruptus n. sp. (Nemata: Aphelenchoididae), an Associate of a Digger Bee

Bursaphelenchus abruptus n. sp., an associate of the digger bee, Anthophora abrupta (Hymenoptera: Anthophoridae), is described and illustrated. Bursaphelenchus abruptus n. sp. can be differentiated from other species of Bursaphelenchus by the absence of head annules, stylet length, length of the postuterine sac, shape of female tail, spicule morphology, and male caudal papillae arrangement. Two plant-pathogenic fungi, Monilinia fructicola and Botrytis cinerea, and a Monilia sp. isolated from an adult bee from Prince Georges County, Maryland, were good hosts for B. abruptus n. sp. Dauer juveniles (JIII) of B. abruptus n. sp. were isolated from the reproductive tracts of A. abrupta from Montgomery County, Alabama, for measurements and comparison with J2 -JIII inter-molts from a 4-week-old monoxenic culture on Monilia sp. Gonad lengths in dauer juveniles isolated from A. abrupta were highly variable (49 +/- 23 mum SD; range 21-93 mum; n = 29) compared with J2-JIII intermolts from culture (28 +/- 7 mum SD; range = 16-42 mum; n = 16), suggesting that postembryonic gonad development may continue while dauers are in the bee host. Adult males and females of B. abruptus n. sp. were examined with scanning electron microscopy (SEM) for ultrastructural comparisons with other members of the genus Bursaphelenchus.

Fine Structure of the Cone of Heterodera schachtii with Emphasis on Musculature and Fenestration

Fine structure of the posterior cone of monoxenically cultured Heterodera schachtii is examined. The cone is not evident at the end of the fourth molt, but as the female matures the cone elongates, vulval lips enlarge, and cuticular patterns on the lips are modified. Body wall cuticle (BW) of the cone includes layers A and B, but C is modified or replaced by a network of fibers which correspond to the semifenestrae. Vaginal lining is continuous with the BW and terminates at the cuticular underbridge near the uterus. Vaginal musculature includes 48 dilatores vaginae (DV) as well as a sphincter vaginae (SV). The DV include a contractile and noncontractile region with abundant actin and glycogen. A distinct anal depressor muscle is present. In the cyst, only bullae, the underbridge, vagina lining, and traces of the SV muscle persist. Detailed morphology of the cone of H. schachtii provides insight into characters which, when compared with other heteroderines, will be useful in phylogenetic analysis of Heteroderinae.