Ephemera strigata (Insecta: Ephemeroptera: Ephemeridae) is the intermediate host of the nematodes Rhabdochona denudata honshuensis and Rhabdochona coronacauda in Japan

Juvenile freshwater parasitic nematodes Rhabdochona denudata honshuensis Moravec and Nagasawa, 1989 and Rhabdochona coronacauda Belouss, 1965 (Spirurida: Thelazioidea: Rhabdochonidae) were found in mayfly nymphs collected in a mountain stream in Japan. Considering the relative density of mayfly nymphs, nematode prevalence, and intensity of parasitism, Ephemera strigata Eaton and Potamanthus formosus Ulmer (Ephemeroptera: Ephemeridae) are frequent natural intermediate hosts for R. d. honshuensis in this locality. The intermediate host of R. coronacauda also is the E. strigata nymph.     

Larval nematodes (Spiruroidea: Cystidicolidae) in Octopus vulgaris (Mollusca: Cephalopoda: Octopodidae) from the northeastern Atlantic Ocean.

Larval nematode parasites (Spiruroidea: Cystidicolidae) are recorded for the first time in Octopus vulgaris Cuvier, 1797 in the northeastern Atlantic Ocean. Prevalence was 16% and mean intensity was 1.46 worms/host. Body length of larval nematodes ranges from 8.3 to 9.3 mm, with a distance from the anterior end to nerve ring from 187.5 to 200 microm, and to excretory pore 194.6-350 microm. Anatomical characteristics, such as deirid, nerve ring, cephalic alae, excretory pore, pseudolabia amphids, sclerotized protuberance, and anus, examined using light microscopy (LM) or scanning electron microscopy (SEM), are illustrated. The nematode was designed as a cystidicolid "Type A" larva. The hemocytic infiltration present in the host tissue around the nematode capsule and the mechanical compression in the infected organs denote the pathogenicity of this nematode. In the study area, O. vulgaris may play the role of an intermediate or paratenic host in the nematode life cycle.     

Helminths of the exotic lizard Hemidactylus mabouia from a rock outcrop area in southeastern Brazil

The helminth fauna of 291 Hemidactylus mabouia (Lacertilia: Gekkonidae) from a rock outcrop area in the state of S?o Paulo, Southeastern Brazil, was studied. Five species were recovered, namely one unidentified species of centrorhynchid acanthocephalan (present only as cystacanths) and the nematodes Parapharyngodon sceleratus, P. largitor (Oxyuroidea: Pharingodonidae), Physaloptera sp. (Spiruroidea: Physalopteridae) and one indeterminate species of Acuariidae (Acuaroidea), with the latter two forms present only as larvae. Infection rates tended to increase with host size, but appeared to be unaffected by season. Hemidactylus mabouia shared most of its helminth fauna with two other sympatric lizard hosts, Mabuya frenata and Tropidurus itambere. The helminth assemblage of the H. mabouia population appears to have been entirely acquired by this exotic gecko from the local helminth species pool, rather than possessing any species from the parasite faunas of the original African populations.     

Co-evolutionary relationships between the nematode subfamily Cloacininae and its macropodid marsupial hosts

Morphologically based phylogenies of the cloacinine genera Cyclostrongylus, Macropostrongylus, Pharyngostrongylus, Popovastrongylus, Rugopharynx, Thallostonema, Wallabinema, and Zoniolaimus were constructed and compared with the phylogeny of their respective macropodid hosts. These comparisons show some evidence of co-speciation. However, there was little consistency among trees of different nematode genera, parasite species were scattered amongst hosts and basal parasite taxa were, in some instances, parasitic in hosts belonging to derived clades. A cladistic analysis, using as characters 208 cloacinine nematode species found in 23 species of host, produced a tree largely resembling that of the host tree but with significant differences explainable by host switching among macropodids occupying similar habitat. Nematodes were moderately host-specific, but some species occurred in three or more distantly related host species indicating a degree of host switching. The results are more consistent with the hypothesis of a colonisation of macropodid hosts by cloacinine nematodes rather than a prolonged period of co-speciation although alternative interpretations of the data are also considered.     

Nematodes surfing the waves: long‐distance dispersal of soil‐borne microfauna via sea swept rhizomes

Dispersal mechanisms of soil‐borne microfauna have hitherto received little attention. Understanding dispersal mechanisms of these species is important to unravel their basic life history traits, biogeography, exchange of individuals between populations, and local adaptation. Soil‐borne nematodes and root‐feeding nematodes in particular occupy a key position in soil‐food webs and can be determinants for plant growth and vegetation structure and succession. However, their dispersal abilities have been scarcely addressed, predominantly focusing on species of agricultural importance. Still, root‐feeding nematodes are usually considered as being extremely limited and bound to the rhizosphere of plants. We investigated a mechanism for long distance dispersal of root‐feeding nematodes associated to two widespread coastal dune grasses. The nematodes are known to be crucial for the functioning of these grasses. We experimentally tested the hypothesis that root‐feeding nematodes are able to move across long distances inside rhizome fragments that are dispersed by seawater. We also tested the survival capacities of the host plants in seawater. Our study demonstrates that root‐feeding nematodes and plants are able to survive immersion in seawater, providing a mechanism for long distance dispersal of root feeding nematodes together with their host plant. Drifting rhizome fragments enable the exchange of plant material and animals between dune systems. These results provide new insights to understand the ecology of dune vegetation, the interaction with soil‐borne organisms and more importantly, re‐set the scale of spatial dynamics of a group of organisms considered extremely constrained in its dispersal capacities.     

Phenotypic Adaptations in Pasteuria spp. Nematode Parasites

The endospore and central core diameters of 69 isolates of Pasteuria spp. showed a relationship with the body wall thickness of their corresponding host nematodes. A relationship was also observed when cuticle and hypodermis layer data were derived from transmission electron microscopy micrographs. Principal component analysis and hierarchical cluster analysis based on endospore and central core diameters and host nematode body wall thickness delineated six distinct groups. Five groups included nematode species of distinct taxa. Endospore morphometric diversity appears to be the result of an evolutionary adaptation that occurred during host nematode speciation related to the forces acting on adhering endospores and(or) to the host cuticle penetration phase. On this basis, the validity of endospore morphometrics and host taxonomy as significant parameters in discriminating Pasteuria species is questioned.     

Associations between mycophagous Drosophila and their Howardula nematode parasites: a worldwide phylogenetic shuffle

Little is known about what determines patterns of host association of horizontally transmitted parasites over evolutionary timescales. We examine the evolution of associations between mushroom-feeding Drosophila flies (Diptera: Drosophilidae), particularly in the quinaria and testacea species groups, and their horizontally transmitted Howardula nematode parasites (Tylenchida: Allantonematidae). Howardula species were identified by molecular characterization of nematodes collected from wild-caught flies. In addition, DNA sequence data is used to infer the phylogenetic relationships of both host Drosophila (mtDNA: COI, II, III) and their Howardula parasites (rDNA: 18S, ITS1; mtDNA: COI). Host and parasite phylogenies are not congruent, with patterns of host association resulting from frequent and sometimes rapid host colonizations. Drosophila-parasitic Howardula are not monophyletic, and host switches have occurred between Drosophila and distantly related mycophagous sphaerocerid flies. There is evidence for some phylogenetic association between parasites and hosts, with some nematode clades associated with certain host lineages. Overall, these host associations are highly dynamic, and appear to be driven by a combination of repeated opportunities for host colonization due to shared breeding sites and large potential host ranges of the nematodes.     

Developmental Nutrition of Nematodes: the Biochemical Role of Sterols,Heme Compounds,and Lysosomal Enzymes

Attempts to develop defined in vitro culture systems for the growth, reproduction and development of free-living nematodes have yielded much basic information about their nutritional requirements and biochemistry. Requirements for sterol and heme have been identified suggesting that some nematodes lack de novo synthesis of these molecules. Possible pathways of metabolism of these nutritional requirements can be derived from in vitro experiments that use a variety of sterol and heine sources as supplements to the culture mediuin. These pathways are reviewed as well as the possible role of sterol and heme in the biology of free-living and parasitic nematodes, Since these molecules must be acquired dietarily, the possible involvement of lysosomal enzymes in digestion is discussed. Also considered is the possibility that lysosomal enzymes change when nematodes are fed on a heine protein source.     

Molecular and Morphological Characterization and Biological Control Capabilities of a Pasteuria ssp. Parasitizing Rotylenchulus reniformis, the Reniform Nematode

Rotylenchulus reniformis is one of 10 described species of reniform nematodes and is considered the most economically significant pest within the genus, parasitizing a variety of important agricultural crops. Rotylenchulus reniformis collected from cotton fields in the Southeastern US were observed to have the nematode parasitic bacterium Pasteuria attached to their cuticles. Challenge with a Pasteuria-specific monoclonal antibody in live immuno-fluorescent assay (IFA) confirmed the discovery of Pasteuria infecting R. reniformis. Scanning and transmission electron microscopy were employed to observe endospore ultrastructure and sporogenesis within the host. Pasteuria were observed to infect and complete their life-cycle in juvenile, male and female R. reniformis. Molecular analysis using Pasteuria species-specific and degenerate primers for 16s rRNA and spoII, and subsequent phylogenetic assessment, placed the Pasteuria associated with R. reniformis in a distinct clade within established assemblages for the Pasteuria infecting phytopathogenic nematodes. A global phylogenetic assessment of Pasteuria 16s rDNA using the Neighbor-Joining method resulted in a clear branch with 100% boot-strap support that effectively partitioned the Pasteuria infecting phytopathogenic nematodes from the Pasteuria associated with bacterivorous nematodes. Phylogenetic analysis of the R. reniformis Pasteuria and Pasteuria spp. parasitizing a number of economically important plant parasitic nematodes revealed that Pasteuria with different host specificities are closely related and likely constitute biotypes of the same species. This suggests host preference, and thus effective differentiation and classification are most likely predicated by an influential virulence determinant(s) that has yet to be elucidated. Pasteuria Pr3 endospores produced by in vitro fermentation demonstrated efficacy as a commercial bionematicide to control R. reniformis on cotton in pot tests, when applied as a seed treatment and in a granular formulation. Population control was comparable to a seed-applied nematicide/insecticide (thiodicarb/imidacloprid) at a seed coating application rate of 1.0 x 10(8) spores/seed.     

Molecular data support a rapid radiation of aphids in the Cretaceous and multiple origins of host alternation

Many aphids display a remarkably complex life cycle of host alternation, in which cyclical parthenogenesis is combined with the obligate use of two unrelated host plants. We used mitochondrial ribosomal DNA (partial 12S and 16S) sequences to reconstruct the phylogeny of aphids, to determine how many origins of host alternation and correlated major host-plant shifts have occurred. Our results agreed with previous morphological studies in that species clustered with good support at the level of tribes. There was little well-supported phylogenetic structure at levels deeper than tribes, however, except for the monophyly of two subfamilies, Aphidinae and Lachninae. We argue that aphids experienced a rapid radiation at the tribal level, after host shifting from gymnosperms to angiosperms. A rapid radiation is consistent with aphid fossils, which record the presence of few subfamilies in the late Cretaceous, but most extant tribes by the early Tertiary. Plant fossils also record host plants of aphid tribes diversifying during this time. A hypothesized mechanism by which host alternation has evolved (fundatrix specialization), coupled with the rapid radiation, implies that this life cycle may have originated as often as in the ancestor of each tribe that displays it. We also consider, however, an alternative hypothesis of fewer origins. The basal radiation of Aphididae was dated from molecular sequences to have occurred at approximately 80–150 Mya.     

Interactions between bacteria and plant-parasitic nematodes: now and then

Based on genome-to-genome analyses of gene sequences obtained from plant-parasitic, root-knot nematodes (Meloidogyne spp.), it seems likely that certain genes have been derived from bacteria by horizontal gene transfer. Strikingly, a common theme underpinning the function of these genes is their apparent direct relationship to the nematodes' parasitic lifestyle. Phylogenetic analyses implicate rhizobacteria as the predominant group of 'gene donor' bacteria. Root-knot nematodes and rhizobia occupy similar niches in the soil and in roots, and thus the opportunity for genetic exchange may be omnipresent. Further, both organisms establish intimate developmental interactions with host plants, and mounting evidence suggests that the mechanisms for these interactions are shared too. We propose that the origin of parasitism in Meloidogyne may have been facilitated by acquisition of genetic material from soil bacteria through horizontal transfer, and that such events represented key steps in speciation of plant-parasitic nematodes. To further understand the mechanisms of horizontal gene transfer, and also to provide experimental tools to manipulate this promising bio-control agent, we have initiated a genomic sequence of the bacterial hyper-parasite of plant parasitic nematodes, Pasteuria penetrans. Initial data have established that P. penetrans is closely related to Bacillus spp., to the extent that considerable genome synteny is apparent. Hence, Bacillus serves as a model for Pasteuria, and vice versa.     

Parasitism genes and host range disparities in biotrophic nematodes: the conundrum of polyphagy versus specialisation

This essay considers biotrophic cyst and root-knot nematodes in relation to their biology, host-parasite interactions and molecular genetics. These nematodes have to face the biological consequences of the physical constraints imposed by the soil environment in which they live while their hosts inhabit both above and below ground environments. The two groups of nematodes appear to have adopted radically different solutions to these problems with the result that one group is a host specialist and reproduces sexually while the other has an enormous host range and reproduces by mitotic parthenogenesis. We consider what is known about the modes of parasitism used by these nematodes and how it relates to their host range, including the surprising finding that parasitism genes in both nematode groups have been recruited from bacteria. The nuclear and mitochondrial genomes of these two nematode groups are very different and we consider how these findings relate to the biology of the organisms.     

Host specificity of entomophilic nematodes—A review

Entomophilic nematodes can be biologically manipulated either as biological control agents or as biological insecticide agents. The characteristics, mode of application, and degree of specificity for each of these is considered. The importance of host specificity information for nematode parasites potentially useful in controlling insect pests is emphasized. A general discussion of host specificity and the factors influencing host specificity of entomophilic nematodes is presented.Characteristics of nematodes of the genus Heterotylenchus are discussed while particular emphasis is placed on H. autumnalis, a potentially useful biological control agent of the face fly, Musca autumnalis. Greater detail of the bionomics of this nematode, its attributes and disadvantages as a successful control agent are considered. The factors resulting in host specificity of this parasite, especially host resistance, in Musca domestica, Orthellia caesarion, and Ravinia l'herminieri, are encapsulation and melanization.It is emphasized that biological control workers are working with a dynamic, evolving host-parasite system and that really they are faced with the same problems (resistance of the host and target specificity of the applied material) originally and still confronting the toxicologist and economic entomologist.     

Mutualistic nematode-bacteria complexes associated with insects

In the review, the life cycles and mutualistic relations within the nematode-bacteria associations are analyzed: nematodes Bursaphelenchus xylophilus (PWN) with bacteria Pseudomonas fluorescens, Bacillus spp., Burkholderia arboris; entomopathogenic nematodes (EPN) of the genera Steinernema and Heterorhabditis with bacteria of the genera Xenorhabdus and Photorhabdus. The life cycles of PWN and EPN show traits of the primary detrital trophism. Both cycles include invasion of the living host and are completed with death of the host, which is an obligate condition for dispersal of the nematodes and their associated bacteria. Nematodes and bacteria stimulate each other to reproduce fast; the diverse forms of their interactions are considered, including direct and indirect ones (via the plant or insect host). Bacteria of both mutualistic associations produce siderophores and antibiotics that prevent reproduction of other pathogenic and putrefactive microorganisms. Ectosymbiotic bacteria of PWN may be recruited into the association from among the inhabitants of the mucous cover of the nematode body, as well as from the pathogenic bacterial biota of local conifers; thus the PWN and bacteria are facultative synergists in the phytopathogenic process. Endosymbiotic bacteria of EPN are not capable of independent life; they have developed obligate associations with highly specific nematode hosts.     

Arrested larval development in cattle nematodes

Most economically important cattle nematodes are able to arrest their larval development within the host - entering a period of dormancy or hypobiosis. Arrested larvae have a low death rate, and large numbers can accumulate in infected cattle during the grazing season. Because of this, outbreaks of disease caused by such nematodes can occur at times when recent infection with the parasites could not have occurred, for example during winter in temperature northern climates when cattle are normally housed. The capacity to arrest is a heritable trait. It is seen as an adaptation by the parasite to avoid further development to its free-living stages during times when the climate is unsuitable for free-living survival. But levels of arrestment can vary markedly in different regions, in different cattle, and under different management regimes. Climatic factors, previous conditioning, host immune status, and farm management all seem to affect arrestment levels. In this article, James Armour and Mary Duncan review the biological basis of the phenomenon, and discuss the apparently conflicting views on how it is controlled.     

Multiple-strand displacement and identification of single nucleotide polymorphisms as markers of genotypic variation of Pasteuria penetrans biotypes infecting root-knot nematodes

Pasteuria species are endospore-forming obligate bacterial parasites of soil-inhabiting nematodes and water-inhabiting cladocerans, e.g. water fleas, and are closely related to Bacillus spp. by 16S rRNA gene sequence. As naturally occurring bacteria, biotypes of Pasteuria penetrans are attractive candidates for the biocontrol of various Meloidogyne spp. (root-knot nematodes). Failure to culture these bacteria outside their hosts has prevented isolation of genomic DNA in quantities sufficient for identification of genes associated with host recognition and virulence. We have applied multiple-strand displacement amplification (MDA) to generate DNA for comparative genomics of biotypes exhibiting different host preferences. Using the genome of Bacillus subtilis as a paradigm, MDA allowed quantitative detection and sequencing of 12 marker genes from 2000 cells. Meloidogyne spp. infected with P. penetrans P20 or B4 contained single nucleotide polymorphisms (SNPs) in the spoIIAB gene that did not change the amino acid sequence, or that substituted amino acids with similar chemical properties. Individual nematodes infected with P. penetrans P20 or B4 contained SNPs in the spoIIAB gene sequenced in MDA-generated products. Detection of SNPs in the spoIIAB gene in a nematode indicates infection by more than one genotype, supporting the need to sequence genomes of Pasteuria spp. derived from single spore isolates.     

Ancient gene transfer from algae to animals: Mechanisms and evolutionary significance

ABSTRACT: BACKGROUND: Horizontal gene transfer (HGT) is traditionally considered to be rare in multicellular eukaryotes such as animals. Recently, many genes of miscellaneous algal origins were discovered in choanoflagellates. Considering that choanoflagellates are the existing closest relatives of animals, we speculated that ancient HGT might have occurred in the unicellular ancestor of animals and affected the long-term evolution of animals. RESULTS: Through genome screening, phylogenetic and domain analyses, we identified 14 gene families, including 92 genes, in the tunicate Ciona intestinalis that are likely derived from miscellaneous photosynthetic eukaryotes. Almost all of these gene families are distributed in diverse animals, suggesting that they were mostly acquired by the common ancestor of animals. Their miscellaneous origins also suggest that these genes are not derived from a particular algal endosymbiont. In addition, most genes identified in our analyses are functionally related to molecule transport, cellular regulation and methylation signaling, suggesting that the acquisition of these genes might have facilitated the intercellular communication in the ancestral animal. CONCLUSIONS: Our findings provide additional evidence that algal genes in aplastidic eukaryotes are not exclusively derived from historical plastids and thus important for interpreting the evolution of eukaryotic photosynthesis. Most importantly, our data represent the first evidence that more anciently acquired genes might exist in animals and that ancient HGT events have played an important role in animal evolution.     

Tripius gyraloura n. sp. (Aphelenchoidea: Sphaerulariidae) parasitic in the gall midge Lasioptera donacis Coutin (Diptera: Cecidomyiidae)

A new nematode, Tripius gyraloura n. sp., is described from the arundo gall midge, Lasioptera donacis Coutin (Diptera: Cecidomyiidae). This gall midge is being considered as a biological control agent for use in North America against the introduced giant reed Arundo donax (L.) (Poaceae: Cyperales). Thus the present study was initiated to investigate a nematode parasite that was unknown at the time studies with L. donacis were initiated. The new species has a rapid development in the fly host and the mature parasitic female nematodes evert their uterine cells in the hosts’ hemolymph. Because large numbers of nematodes sterilise the host, eradication of the parasite from laboratory colonies of the midge may be necessary before populations of the fly are released.     

Mermithid Nematodes: Physiological Relationships with their Insect Hosts

This paper assesses our state of knowledge of physiological processes involved in the relationships between insects and their mermithid nematode parasites. Three major components of the host-parasite relationship(s) are reviewed: effects of mermithids on host physiology, effects of host physiology on mermithids, and the physiology of the nematodes themselves. Mermithids induce an array of changes in host physiology, and the effects on host metabolism and endocrinology are discussed at some length. Few studies have been done to ascertain the effects of the host on the parasites from a physiological standpoint. Whereas host immunity mechanisms against mermithids have been described at the ultrastructural level, the physiological basis of such responses is not known. Mermithids are atypical nematodes, both structurally and physiologically. In the absence of a functional gut, nutrients are absorbed across the outer cuticle and stored in a trophosome. The transcuticular mode of feeding, storage within the trophosome, and metabolism of storage products are discussed. The usefulness of physiological information toward expediting in vitro culture of these nematodes is discussed, and problems that need to be addressed are defined.     

Biological Control Potential of Neoaplectanid Nematodes

The neoaplectanids are among the most studied of all entomogenous nematodes. Because these nematodes kill their insect hosts, they are regarded as having excellent potential as biological control agents. While the host specificity of most entontogenous nematodes tends to limit their potential usefulness, the broad host range and high virulence of neoaplectanids make them attractive candidates for industrial development. Also, recent development of economical mass rearing procedures appears to make production on a commercial basis feasible. Infective stages may be stored for years trader various laboratory conditions. Although entomogenous nematodes, as parasites, are exempt from govermnent registration requirements, the mutualistic association of neoaplectanid nematodes with a bacterium will likely necessitate a detailed safety evaluation. Studies conducted to date indicate a lack of pathogenicity to mammals. Field trial success has been limited by the intolerance of infective stages to mffavorable environmental conditions, particularly low moisture. Applications against pests on exposed plant foliage have been especially disappointing. More encouraging anti consistent results have been obtained in more favorable environments, including soil and aquatic habitats, but the most promising treatment sites ntay be cryptic habitats where infective stages are shehered from environmental extremes. Cryptic habitats also exploit the ability of neoaplectanids to actively seek out hosts in recessed places where conventional insecticide applications are intpractical.