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First report, morphological and molecular characterization of Caenorhabditis brenneri (Nematoda: Rhabditidae) isolated from the giant African land snail Achatina fulica (Gastropoda: Achatinidae)
Abstract
Gastropods are extremely diverse taxa comprising nearly 60,000 species, of which, the giant African land snail, Achatina fulica is a well-known member. It is an invasive species, and it serves as vector and host for several free-living and parasitic nematodes. This makes studies on the diversity of nematodes isolated from gastropods be more emphasized. Studies have been conducted on other Caenorhabditis-gastropod associations such as in the model organism C. elegans, however, less attention is given to other Caenorhabditis species. Through morphological and morpho-taxometrical data, and analysis of the D2-D3 of 28S rDNA and 18S rDNA regions, nematodes found inside a dissected A. fulica cadaver from Kabacan, North Cotabato (7°6’3.076” N, 124°51’68.33” E) in Mindanao, Philippines were identified as Caenorhabditis brenneri. We herein report for the first time C. brenneri from A. fulica. Moreover, to our knowledge, this is also the first report of C. brenneri-gastropod association.
... It is presumed that the association between nematodes and terrestrial gastropods is both ancient and widespread (Morand et al., 2004). Recent studies indicated that nematodes use terrestrial gastropods as either intermediate or definitive hosts (Diano et al., 2022;Gimond et al., 2022;Schurkman et al., 2022). ...
... One gonochoristic member species is Caenorhabditis brenneri Sudhaus & Kiontke, 2007 (Nematoda: Rhabditida), which is unique among Caenorhabditis as it has the highest within-species molecular diversity (hyperdiverse) among eukaryotes (Dey et al., 2013). It has been recorded to thrive in soil detritus (Fitch et al., 1994) and was associated with the giant African land snail, Achatina fulica Bowdich, 1822 (Gastropoda: Achatinidae) from the Philippines (Diano et al., 2022). ...
... Resolution into species level using morphology based on light microscopy does not guarantee a robust identification; thus, molecular analysis limited to the use of small subunit (18S) and large subunit (D2-D3 expanded segments of 28S) rDNA was also performed. An 18S rDNA gene sequence was generated (MT130970) and was found to be 99.8% closely related to C. brenneri strain Kbcn01 (MT039632) from the Philippines (Diano et al., 2022) and was designated as C. brenneri strain IZSP; 99.88% similar with C. brenneri isolates CFB234 (OK086052), CFB135 (OK086050), CFB104 (OK086049) and CFB50 (OK086048) from Vietnam, and 99.40% similar with C. brenneri CB5161 (U13930) (formerly Caenorhabditis sp. CB5161) from Trinidad (Fitch et al., 1994). ...
Gastropod-associated nematodes have been previously studied and documented worldwide, with some species forming host-specific association as obligate parasites of molluscs while others form intermediate and temporary association. Philippinella moellendorffi from Imelda, Zamboanga Sibugay, Philippines, were collected, washed and maintained in the laboratory until death. Cadavers were placed on nutrient agar to allow nematode proliferation. Nematode pure culture was obtained using one gravid female for propagation. Morphology and molecular analyses (18S ribosomal DNA (rDNA) and D2–D3 expansion segments of 28S rDNA) were employed as diagnostic tools in identifying the nematode species isolated from P. moellendorffi. The newly isolated nematode was identified as Caenorhabditis brenneri , thus designated as C. brenneri strain IZSP from the Philippines. This is the first record of C. brenneri isolated from the terrestrial slug P. moellendorffi .
Background
Steinernema feltiae is an entomopathogenic nematode used in biological control programs with a global distribution. Populations of this species show phenotypic plasticity derived from local adaptation and vary in different traits, such as location and host penetration. The aim of this work was to describe a Chilean isolate of this nematode species, using integrative approaches.
Methods
Nematode morphological and morphometric studies were conducted along with molecular analysis of nuclear genes. The symbiotic bacterium was also identified by sequencing the 16S rRNA gene. Some ecological characteristics were described, including the temperature requirements for the nematode life cycle and the effect of soil water content for optimal reproduction.
Results
Morphometric characterization revealed a large intra-specific variability. The isolate identity was also corroborated with the analysis of nuclear genes. Based on the 16S gene, its symbiont bacteria, Xenorhabdus bovienii, was identified. The lowest, optimal and highest temperatures found to limit the infestation and reproduction on Galleria mellonella were 10, 20 and 30 °C, respectively; the emergence from the host larvae occurred approximately 10 days after inoculation. Differences were observed in offspring, and 120 infective juveniles (IJ)/larva was the most prolific dose at 20 °C. The soil water content did not affect the number of IJ invaders, penetration efficacy and IJ emergence time or offspring per larva, but it caused a delay in achieving full mortality at the permanent wilting point with respect to saturation and field capacity.
Conclusions
For the first time, a Chilean isolate of S. feltiae is described in detail considering morphological, molecular and ecological aspects. The isolate was shown to be efficient in soil containing water, with optimal temperatures ranging from 15 to 25 °C for host infestation and production of an abundant offspring; these characteristics would allow its potential use as control agents in a wide geographical area of the country.
During a survey in western Venezuela in 2011, three new populations of Heterorhabditis amazonensis (LPV081, LPV156, and LPV498) were isolated. Some differences were found in terms of morphometry compared with the original description; however, the distance from the anterior end to the excretory pore is the most variable character; significantly shorter in all infective juveniles and in other developmental stages depending on the population. According to a Principal Component Analysis, LPV498 possesses more differences in morphometric characteristics and can be separated from the other two. Those intraspecific differences could be attributed to the geographic origin of the nematode. Molecular studies of ITS regions demonstrated that the sequences of the Venezuelan strains were identical to those of the type species originally isolated in the Brazilian Amazonian forest. This is an interesting fact because in several studies on heterorhabditids, intraspecific variability has been recorded. Herein, we present the first report of H. amazonensis in Venezuela and the characterization of three populations of this species.
Aim: The aim of the study was to evaluate the utility of DNA sequencing in differentiating Root- Knot Nematodes (RKN) (Meloidogyne spp) infecting Indigenous Leafy Vegetables (ILVs) in Kisii and Transmara sub-counties in Kenya. Study Design: Cross-sectional study. Place and Distribution of Study: Nematology Laboratory, Kenyatta University and International Livestock Research Institute (ILRI) Laboratories, Nairobi, between March 2009 to September 2011. Methodology: Samples were obtained from two sites; Kisii and Trans-mara sub-counties. From each selected site; 10 farms which grew ILVs were randomly sampled. From each farm 10 plants of each ILV infected by Root knot nematodes were randomly selected. They were uprooted together with the surrounding soil and transported to the laboratory. In the laboratory female second-stage juveniles (J2) were extracted and used for genomic DNA isolation and sequencing. PCR amplifications of the extracted DNA was carried out for each isolate using primers: SSU18A (5'- AAAGATTAAAGCCATGCATG-3') and SSU26R (5'-CATTCTTGGCAAATGCTTTCG-3'). Double stranded DNA were sequenced by cycle sequencing with Big Dye 3.0 Terminator cycle sequencing kit and analysed with an ABI 310 Gene Analyser. Sequences were determined on one strand using the M13 forward primer. Sequence information was assembled using sequencer 4.1. Alignments were performed using ClustalW. Results: All the three major species identified, namely Meloidogyne arenaria, M. javanica and M. incognita amplified using SSUrRNA produced a single PCR product of 700 bp and 11 sequences obtained that were compared with nucleotide sequences in the Gene bank using the BLAST Software to determine similarities. Several sequences of Meloidogyne nematodes (5 S ribosomal RNA) were identified with regions that matched with the obtained sequences. The nearly complete 5S rDNA sequences obtained from the 11 sequences varied from 675 to 692 base pairs. Conclusion: The selected primers can be used for determining variation in the rDNA region in RKN infecting ILVs in Kenya.
Achatina fulica is a ubiquitous land snail commonly found throughout the Philippines. As a generalist feeder and being able to survive in a wide range of habitat types and conditions, the snail can easily establish itself in a new area after introduction. It also acts as host to a variety of parasites, including nematodes, which may accidentally infect humans. In this study, A. fulica individuals from 13 areas in the Philippines were sampled and analyzed for nematode infection rate and load. Of the 393 individuals sampled, 80 (20%) were found to be infected, with 5049 nematodes isolated. The infection rates and parasite load were highly variable. Overall, the parasite load ranges from 1 to 867 per snail. Representative nematodes from A. fulica from Plaridel (n=8) and Davao C i t y (n = 2 6) i n M i n d a n a o w e r e s u b j e c t e d t o D N A e x t r a c t i o n , P C R amplif ication, and sequencing of the SSU rRNA gene, which is the universal barcode for nematodes. Sequences successfully matched with the dog lungworm Oslerus osleri for the Plaridel nematodes and the rat lungworm Angiostrongylus cantonensis for the Davao City nematodes, r e s p ec t i v e l y. T h e l a t t e r i s k n ow n to i n fec t h u m a n s a n d c a n c a u s e eosinophilic meningoencephalitis. This study presents the f irst repor t of A. cantonensis in A. fulica from Mindanao and raises a public health concern.
How do very small animals with limited long-distance dispersal abilities move between locations, especially if they prefer ephemeral micro-habitats that are only available for short periods of time? The free-living model nematode Caenorhabditis elegans and several congeneric taxa appear to be common in such short-lived environments, for example decomposing fruits or other rotting plant material. Dispersal is usually assumed to depend on animal vectors, yet all current data is based on only a limited number of studies. In our project we performed three comprehensive field surveys on possible invertebrate vectors in North German locations containing populations of C. elegans and two related species, especially C. remanei, and combined these screens with an experimental analysis of persistence in one of the vector taxa.
Our field survey revealed that Caenorhabditis nematodes are commonly found in slugs, isopods, and chilopods, but are not present in the remaining taxonomic groups examined. Surprisingly, the nematodes were frequently isolated from the intestines of slugs, even if slugs were not collected in close association with suitable substrates for Caenorhabditis proliferation. This suggests that the nematodes are able to enter the slug intestines and persist for certain periods of time. Our experimental analysis confirmed the ability of C. elegans to invade slug intestines and subsequently be excreted alive with the slug feces, although only for short time periods under laboratory conditions.
We conclude that three invertebrate taxonomic groups represent potential vectors of Caenorhabditis nematodes. The nematodes appear to have evolved specific adaptations to enter and persist in the harsh environment of slug intestines, possibly indicating first steps towards a parasitic life-style.
Achatina fulica or "giant African snail" is an exotic species, considered to be one of the world's hundred most invasive species, causing serious environmental damages. In the present study we report, for the first time, the occurrence of Aelurostrongylus abstrusus infecting A.fulica in the Amazon region. This nematode is described parasitizing mainly the pulmonary system of felines, which causes "aelurostrongilose", also known as feline cardio-pulmonary strongyloidosis. New morphometric data of third stage larvae are presented herein. The present study demonstrated that 40% of all the snails were infected by A. abstrusus. Achatina fulica specimens were collected from three different areas in Manaus namely: rural; east and west areas. The east area presents the highest prevalence of 80%. The large number of A.fulica found in inhabited areas increases the chances of emergent zoonoses, which highlights the need of further studies so as to better control this disease.
Since the discovery of single gene mutations that double its lifespan, the nematode Caenorhabditis elegans has provided remarkable insights into the biology of aging. The precisely measurable lifespan of worms has proven to be an efficient tool to assess the impact of various genetic, physiological and environmental factors on organismal aging. In this article, we describe methods to set up and monitor experiments to determine worm lifespan. We include procedures used for classical, small-scale lifespan assays that are generally performed on solid media, and review recent advances in high-throughput, automated longevity experiments conducted in liquid culture and microfluidic devices. In addition, tools that help analyze this data to obtain survival statistics are summarized, and C. elegans strains that offer particular advantages for lifespan studies are listed.
Bursaphelenchus xylophilus, the pine-wood nematode (PWN), is the causal agent of pine wilt disease, one of the most damaging emerging pest problems to forests around the world. It is native to North America where it causes relatively minor damage to native conifers but is labeled an EPPO-A-2 pest and a quarantine nematode for many countries outside of the United States because of its potential for destruction to their native conifers. Exports of wood logs and commodities involving softwood packaging materials now require a lab test for the presence/absence of this regulated nematode species. We characterized the DNA sequences on the ribosomal DNA small subunit, large subunit D2/D3, internal transcribed spacer (ITS) and mitochondrial DNA cytochrome oxidase subunit one on the aphelenchid species and described the development of a real-time-PCR method for rapid and accurate identification of PWN targeting the ITS-1. A total of 97 nematode populations were used to evaluate the specificity and sensitivity of this assay, including 45 populations of B. xylophilus and 36 populations of 21 other species of Bursaphelenchus which belong to the abietinus, cocophilus, eggersi, fungivorus, hofmanni, kevini, leoni, sexdentati, and xylophilus groups and one unassigned group from a total of 13 groups in the genus Bursaphelenchus; 15 populations of Aphelenchoides besseyi, A. fragariae, Aphelenchoides species and Aphelenchus avenae; and one population of mixed nematode species from a soil sample. This assay proved to be specific to B. xylophilus only and was sensitive to a single nematode specimen regardless of the life stages present. This approach provides rapid species identification necessary to comply with the zero-tolerance export regulations.
Short surveys on the nematode fauna of terrestrial molluscs in Sofia, Bulgaria and Crimea,
Ukraine were performed. The composition of nematode fauna was compared with data from the literature
and in our records of nematode fauna from different regions of continental Europe and the British isles.
Two nematode species, Angiostoma dentiferum Mengert, 1953 and Agfa tauricus Korol & Spiridonov,
1991 were found parasitising three and four, respectively, out of a total of 23 host species. The
composition of nematode fauna was similar in both surveys, though the dominant nematode species in
each region were different, with A. dentiferum in Bulgaria and A. tauricus in Crimea. Both morphological
and molecular methods have demonstrated the complete identity of material from the two regions. The reexamination
of our own material of A. dentiferum from Belgium has confirmed its similarity to that from
Bulgaria and Crimea by molecular characteristics, and slightest morphological differences.
Morphologically, A. dentiferum from Bulgaria, Crimea and Belgium corresponds well with its original
description from Germany (Mengert, 1953). We assume that the re-description of A. dentiferum by
Morand & Spiridonov, 1989, based on the material from France, is that of a closely related but different
species, which is distinguished by presence vs absence of lateral alae and shorter spicules. Although the
data on the distribution of parasitic nematodes of terrestrial molluscs in Europe are inconsistent, it seems
that A. tauricus tends to be present in the south-east of Europe and absent from more northern territories
where it is replaced by A. flexilis though the host range for both species is similar.
Rhabditis stammeri is a carrion-dwelling nematode specifically associated with the burying beetle Nicrophorus vespilloides. The dauerjuveniles of the nematode utilize the beetle for transport to the carrion. Both imagines and larvae of the beetles are infested. This can be understood in the context of the complex brood care behaviour of Nicrophorus. In the beetle larvae, the dauerjuvenile: use the gut for transportation to the pupal chamber. After pupation the dauerjuveniles are founc in the pupal chamber at protected places such as the exuviae of the larvae or underneath the hindwing-anlagen of the pupae. Upon eclosion the dauerjuveniles migrate to the genitalia and gul of the young imagines. Rhabditis stammeri is also transmitted by imagines via copulation.
The new gonochoristic member of the Caenorhabditis Elegans group, C. brenneri sp. n., is described. This species is reproductively isolated at the postmating level from its sibling species, C. remanei. Between these species, only minute morphological differences are found, but there are substantial genetic differences. The stem species pattern of the Ele-gans group is reconstructed. C. brenneri sp. n. deviates from this character pattern only in small diagnostic characters. In mating tests of C. brenneri sp. n. females with C. remanei males, fertilization takes place and juveniles occasionally hatch. In the reverse combination, no offspring were observed. Individuals from widely separated populations of each species can be crossed successfully (e.g. C. brenneri sp. n. populations from Guadeloupe and Sumatra, or C. remanei populations from Japan and Germany). Both species have been isolated only from anthropogenic habitats, rich in decom-posing organic material. C. brenneri sp. n. is distributed circumtropically, C. remanei is only found in northern temperate regions. To date, no overlap of the ranges was found. Hypotheses to explain the allopatric distribution of the two species are discussed. One suggests that the speciation center for the Elegans group was in East Asia, and globally distributed members dispersed from there.
A b s t r a c t The highly diverse Nematoda are free-living in all marine, freshwater and terrestrial habitats and parasitic in plants or animals from Foraminifera to Vertebrata. At present about 10 % of the estimated existing species might be scientifi cally known. About 30 parasitic lineages originated independently in different geological periods since Sil-urian times, most of them in the terrestrial Secernentea and several of them in the "Rhabditidae". Descendants from these lineages also invaded aquatic hosts. Within the primarily marine "Adenophorea" only the rare invertebrate-parasitic Benthimermithida and Marimermithida originated in the marine environment. Nearly all marine animals are free from parasitic "Adenophorea". This ecological "void in the sea" (OSCHE 1966) with respect to parasitic "Ade-nophorea" and the multiple parasitic lineages of Secernentea can be elucidated by the preadaptation concept, which is illustrated here in detail. This concept implies that crucial problems for life as a parasitic worm are "pre-solved" by manifold physiological and reproductive adaptations as bacterial feeding inhabitants of patchily distributed, rap-idly changing and short-lived (ephemeral) saprobious habitats on land. Such saprobiontic nematodes ultimately must contact a larger animal for transport (phoresy) and its dauer larva (evolved in the ancestral lineage of Secernentea) respond to cues of the carrier. A transformed dauer larva initiated special associations like endophoresy, entoecy, necromeny, larval parasitism, accidental, facultative and obligate parasitism in terrestrial gastropods, annelids, ar-thropods and vertebrates. Some examples for these associations are reported, and the gradual evolutionary transi-tions are depicted in a diagram. The intergradation from preadapted saprobiontic rhabditids is not only evidenced in parasites retaining a free-living saprobiontic phase like Strongylida and Rhabdiasidae, but is also plausible for the exclusively parasitic Spiroascarida originating at the base of Secernentea encompassing most parasitic nematodes in vertebrates. The evolution of life cycles of clades within the Spiroascarida (Ascaridida, Gnathostomatida, Oxy-urida, Rhigonematida, Spirurida) are explored in a phylogenetic context starting with the suggestion that the stem-species of Spiroascarida lived endo-saprobiontically in the hindgut of a terrestrial, saprophagous arthropod. Thus, an arthropod-parasitic state preceded vertebrate parasitism in Ascaridida, Gnathostomatida, Spirurida and part of the Oxyurida. Cutaneous penetration by the infective larva and a lung route of migration via the circulatory system are conspicuous convergences in the life cycles of different parasites in tetrapods. K e y w o r d s : Parasitic "Adenophorea", preadaptation concept, life cycles of stemspecies, Ascaridida, Gnath-ostomatida, Oxyurida, Rhigonematida, Spirurida. Z u s a m m e n f a s s u n g Nematoden zeigen eine große Mannigfaltigkeit, freilebend in sämtlichen Lebensstätten im marinen, limnischen und terrestrischen Bereich und parasitisch an Pfl anzen und in Tieren von Foraminiferen bis zu Wirbeltieren. Der-zeit dürften erst ca. 10 % der geschätzten Arten wissenschaftlich bekannt sein. Aus freilebenden Formen entstanden seit dem Silur unabhängig und zu verschiedenen Zeiten der Erdgeschichte etwa 30 parasitische Linien, die meisten von ihnen innerhalb der terrestrischen Secernentea und etliche davon innerhalb der "Rhabditidae". Abkömmlinge dieser Parasitenlinien erschlossen auch wasserlebende Wirte. Im marinen Bereich entstanden innerhalb der "Ade-nophorea" als Parasiten nur die seltenen Benthimermithida und Marimermithida. Parasitische "Adenophorea" in Meerestieren gibt es sonst fast nicht. Diese "Lücke im Meer" (OSCHE 1966) sowie der Tatbestand vielfacher Parasit-werdung innerhalb der Secernentea kann durch das näher erläuterte Präadaptations-Konzept erklärt werden. Dieses Konzept beinhaltet, dass entscheidende Probleme für ein Leben als Parasit bereits gelöst sind durch verschiedene physiologische und reproduktive Anpassungen an eine Lebenssituation als Bakterienfresser in saproben terrestri-schen Lebensstätten, die disjunkt verteilt sowie kurzlebig (ephemer) sind und rascher Zersetzung unterliegen. Sa-probionte Nematoden müssen durch größere Bewohner dieser Lebensstätten transportiert werden, wobei die in der Ahnenlinie der Secernentea evolvierte Dauerlarve als phoretisches Stadium auf verschiedene Signale reagieren muss. Eine Abänderung der Dauerlarve ermöglichte spezielle Assoziationen wie Endophoresie, Entoecie, Necrome-nie, Larvalparasitismus, zufälligen, fakultativen und obligaten Parasitismus in terrestrischen Gastropoden, Anneli-den, Arthropoden und Wirbeltieren. Diese werden beispielhaft und in einem Diagramm als graduelle evolutionäre Übergänge dargestellt. Überzeugend ist der allmähliche Übergang präadaptierter saprobionter "Rhabditidae" für Parasitenlinien wie Strongylida und Rhabdiasidae, die eine freilebende saprobiontische Phase beibehalten haben.
The program MRBAYES performs Bayesian inference of
phylogeny using a variant of Markov chain Monte Carlo.
Availability: MRBAYES, including the source code, documentation,
sample data files, and an executable, is available at http://brahms.biology.rochester.edu/software.html.
Contact: johnh{at}brahms.biology.rochester.edu
The nematode Caenorhabditis elegans is a major laboratory model in biology. Only ten Caenorhabditis species were available in culture at the onset of this study. Many of them, like C. elegans, were mostly isolated from artificial compost heaps, and their more natural habitat was unknown.
Caenorhabditis nematodes were found to be proliferating in rotten fruits, flowers and stems. By collecting a large worldwide set of such samples, 16 new Caenorhabditis species were discovered. We performed mating tests to establish biological species status and found some instances of semi-fertile or sterile hybrid progeny. We established barcodes for all species using ITS2 rDNA sequences. By obtaining sequence data for two rRNA and nine protein-coding genes, we determined the likely phylogenetic relationships among the 26 species in culture. The new species are part of two well-resolved sister clades that we call the Elegans super-group and the Drosophilae super-group. We further scored phenotypic characters such as reproductive mode, mating behavior and male tail morphology, and discuss their congruence with the phylogeny. A small space between rays 2 and 3 evolved once in the stem species of the Elegans super-group; a narrow fan and spiral copulation evolved once in the stem species of C. angaria, C. sp. 8 and C. sp. 12. Several other character changes occurred convergently. For example, hermaphroditism evolved three times independently in C. elegans, C. briggsae and C. sp. 11. Several species can co-occur in the same location or even the same fruit. At the global level, some species have a cosmopolitan distribution: C. briggsae is particularly widespread, while C. elegans and C. remanei are found mostly or exclusively in temperate regions, and C. brenneri and C. sp. 11 exclusively in tropical zones. Other species have limited distributions, for example C. sp. 5 appears to be restricted to China, C. sp. 7 to West Africa and C. sp. 8 to the Eastern United States.
Caenorhabditis are "fruit worms", not soil nematodes. The 16 new species provide a resource and their phylogeny offers a framework for further studies into the evolution of genomic and phenotypic characters.
Although there are no confirmed fossil records of mollusc parasitic nematodes, diverse associations of more than 108 described nematode species with slugs and snails provide a fertile ground for speculation of how mollusc parasitism evolved in nematodes. Current phylogenic resolution suggests that molluscs have been independently acquired as hosts on a number of occasions. However, molluscs are significant as hosts for only two major groups of nematodes: as intermediate hosts for metastrongyloids and as definitive hosts for a number of rhabditids. Of the 61 species of nematodes known to use molluscs as intermediate hosts, 49 belong to Metastrongyloidea (Order Strongylida); of the 47 species of nematodes that use molluscs as definitive hosts, 33 belong to the Order Rhabditida. Recent phylogenetic hypotheses have been unable to resolve whether metastrongyloids are sister taxa to those rhabditids that use molluscs as definitive hosts. Although most rhabditid nematodes have been reported not to kill their mollusc hosts prior to their reproduction, some species are pathogenic. In fact, infective juveniles of Phasmarhabditis hermaphrodita vector a lethal bacterium into the slug host in which they reproduce. This life cycle is remarkably similar to the entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae. Also, the discoveries of Alloionema and Pellioditis in slugs are interesting, as these species have been speculated to represent the ancestral forms of the entomopathogenic nematodes. Development of the infective stage appears to be an important step toward the acquisition of molluscs as definitive hosts, and the association with specific bacteria may have arisen in conjunction with the evolution of necromeny.
A new strain of Steinernema feltiae (Rhabditida: Steinernematidae) was isolated in La Rioja (Spain) from larvae of Bibio hortulanus (Diptera: Bibionidae). A comparative morphometric analysis of this new strain and four additional S. feltiae isolates was performed. Although significant differences in morphometric measurements were observed, PCR-RFLP profiles and sequence analysis of the ITS region of rDNA confirmed the identity of the new strain as A2 RFLP type of S. feltiae. A comparative morphometric study among nematodes from three hosts, Galleria mellonella (Lepidoptera: Pyralidae), Spodoptera littoralis (Lepidoptera: Noctuidae) and B. hortulanus, was conducted. Ecological characterization of the Rioja isolate was performed in G. mellonella larvae. Larval mortality was 75.3 and 78.12% in penetration and sand column assays, respectively, and the percentage of penetrating infective juveniles was 12.0 and 2.8% in these assays. Larval mortality in the one-on-one bioassay was 4.2%, and in exposure-time bioassays, it was 50% at 11.25 hours. Relationships between morphometric characteristics and host mortality are discussed for this new strain of entomopathogenic nematode.
The majority of nematodes are gonochoristic (dioecious) with distinct male and female sexes, but the best-studied species, Caenorhabditis elegans, is a self-fertile hermaphrodite. The sequencing of the genomes of C. elegans and a second hermaphrodite, C. briggsae, was facilitated in part by the low amount of natural heterozygosity, which typifies selfing species. Ongoing genome projects for gonochoristic Caenorhabditis species seek to approximate this condition by intense inbreeding prior to sequencing. Here we show that despite this inbreeding, the heterozygous fraction of the whole genome shotgun assemblies of three gonochoristic Caenorhabditis species, C. brenneri, C. remanei, and C. japonica, is considerable. We first demonstrate experimentally that independently assembled sequence variants in C. remanei and C. brenneri are allelic. We then present gene-based approaches for recognizing heterozygous regions of WGS assemblies. We also develop a simple method for quantifying heterozygosity that can be applied to assemblies lacking gene annotations. Consistently we find that approximately 10% and 30% of the C. remanei and C. brenneri genomes, respectively, are represented by two alleles in the assemblies. Heterozygosity is restricted to autosomes and its retention is accompanied by substantial inbreeding depression, suggesting that it is caused by multiple recessive deleterious alleles and not merely by chance. Both the overall amount and chromosomal distribution of heterozygous DNA is highly variable between assemblies of close relatives produced by identical methodologies, and allele frequencies have continued to change after strains were sequenced. Our results highlight the impact of mating systems on genome sequencing projects.
Free-living nematodes may harbor, protect, and disperse bacteria, including those ingested and passed in viable form in feces. These nematodes are potential vectors for human pathogens and may play a role in foodborne diseases associated with fruits and vegetables eaten raw. In this study, we evaluated the associations between a free-living soil nematode, Caenorhabditis elegans, and Escherichia coli, an avirulent strain of Salmonella Typhimurium, Listeria welshimeri, and Bacillus cereus. On an agar medium, young adult worms quickly moved toward colonies of all four bacteria; over 90% of 3-day-old adult worms entered colonies within 16 min after inoculation. After 48 h, worms moved in and out of colonies of L. welshimeri and B. cereus but remained associated with E. coli and Salmonella Typhimurium colonies for at least 96 h. Young adult worms fed on cells of the four bacteria suspended in K medium. Worms survived and reproduced with the use of nutrients derived from all test bacteria, as determined for eggs laid by second-generation worms after culturing for 96 h. Development was slightly slower for worms fed gram-positive bacteria than for worms fed gram-negative bacteria. Worms that fed for 24 h on bacterial lawns formed on tryptic soy agar dispersed bacteria over a 3-h period when they were transferred to a bacteria-free agar surface. The results of this study suggest that C. elegans and perhaps other free-living nematodes are potential vectors for both gram-positive and gram-negative bacteria, including foodborne pathogens in soil.
Here, we consider that most of the research concerning Caenorhabditis elegans has been laboratory focused and that only limited research has directly considered the worm's biology relative to its natural history in the wild. We describe that, although the worm has traditionally been considered a soil nematode, we could not find it in soil but frequently recovered it from snails. Finally, we discuss how a better understanding of the natural history of C. elegans may enhance its usefulness as a model organism for studying aging and other phenomena.
The nematode Pristionchus pacificus has originally been developed as a satellite organism for comparison to Caenorhabditis elegans. A 10X coverage of the whole genome of P. pacificus is available, making P. pacificus the first non-Caenorhabditis nematode with a fully sequenced genome. The macroevolutionary comparison between P. pacificus and C. elegans has been complemented by microevolutionary studies of closely related strains and species within the genus Pristionchus. In addition, new understanding of the biology of Pristionchus from field studies, demonstrating a close association with various scarab beetles and the Colorado potato beetle, supports consideration of this nematode in studies of ecosystems. In the course of field studies on four continents more than 1,200 isolates were established from 15,000 beetle specimens representing 18 Pristionchus species. Two remarkable features of the Pristionchus-beetle association are the high species specificity of the interaction and the interception of the beetle's sex communication system for host recognition by the nematodes, as suggested by chemotaxis studies. Evolutionary interpretations of differences in developmental, behavioral and ecological patterns require a phylogenetic framework of the genus Pristionchus.
Here, we provide a robust phylogeny of all 18 available Pristionchus species based on a set of 27 ribosomal protein genes encompassing a total of 10,971 bp. The phylogenetic tree provides evidence for North American and European clades, which are embedded in a deeper clade that includes Asian species. It also indicates putative invasion events. Of the 18 Pristionchus species, 13 are gonochoristic and five are hermaphroditic. The phylogeny indicates that all hermaphroditic species have arisen independently within the genus Pristionchus.
Combined ribosomal protein cDNA data can provide the basis for reconstruction of a robust phylogenetic framework for microevolutionary and biogeographic analyses. An additional major implication of our studies is the use of Pristionchus for nematode biodiversity assessments. While some species are represented by more than 100 isolates, others were found less than four times. Such patterns were observed on all continents and in all phylogenetic clades indicating that species asymmetry is a widespread phenomenon, which can now be further investigated by molecular tools.
Although several Caenorhabditis species are now studied in laboratories in great detail, the knowledge of the ecology of most Caenorhabditis species is scarce. In this chapter we present data on the habitat, animal associations, and geographical distribution of the eighteen described and five undescribed Caenorhabditis species currently known to science. The habitats of these species are very diverse, ranging from rotting cactus tissue to inflamed auditory canals of zebu cattle. Some species, including C. elegans, have only been isolated from anthropogenic habitats. Consequently, their natural habitat is unknown. All Caenorhabditis species are colonizers of nutrient- and bacteria-rich substrates and none of them is a true soil nematode. Dauer juveniles of many Caenorhabditis species were shown to be associated with terrestrial arthropods or gastropods. An association with invertebrates is also likely for the remaining species. The type of association is either phoresy (for transport to a new habitat) or necromeny (to secure the body of the associated animal as a future food source). There are also some records of Caenorhabditis species associated with vertebrates. The Caenorhabditis stem species was probably a colonizer of nutrient-rich substrates and was phoretic on arthropods. Some evolutionary trends within the taxon are discussed.
This 19-chapter book discusses the biology (including reproduction, life history, feeding preferences and sexual behaviour) of molluscs as pests of horticultural, field and fodder crops, and outlines the development of appropriate mechanisms for the control of these pests (mainly biological, cultural and chemical). Two chapters review progress towards the development of chemical control strategies, one addressing the toxicology of chemicals, the other the deployment of molluscicides in baits. These chapters also highlight the statistical and biological procedures for screening and evaluating molluscicides which are not a component of the standard procedure of mollusc control. A series of chapters focus on specific crop situations, providing a synopsis of the current pest status of gastropod species or species groups.
This 19-chapter book discusses the biology (including reproduction, life history, feeding preferences and sexual behaviour) of molluscs as pests of horticultural, field and fodder crops, and outlines the development of appropriate mechanisms for the control of these pests (mainly biological, cultural and chemical). Two chapters review progress towards the development of chemical control strategies, one addressing the toxicology of chemicals, the other the deployment of molluscicides in baits. These chapters also highlight the statistical and biological procedures for screening and evaluating molluscicides which are not a component of the standard procedure of mollusc control. A series of chapters focus on specific crop situations, providing a synopsis of the current pest status of gastropod species or species groups.
This book, the first of two volumes, covers recent advances and future perspectives in the research on nematode morphology, physiology and ecology, particularly those relating to free-living, plant-parasitic and entomopathogenic nematodes. It is intended for researchers and students with an interest in nematology.
We have attempted interspecific hybridizations among six species of rhabditid nematodes: Caenorhabditis elegans, Caenorhabditis briggsae, Caenorhabditis remanei, Caenorhabditis sp. v, Rhabditis sp., and Pelodera teres. Copulation was observed in all crosses between Caenorhabditis species; however, none resulted in the generation of stable hybrid populations. No copulation was observed in crosses between Caenorhabditis males and Rhabditis or Pelodera females, even when congeneric females were present, suggesting that Caenorhabditis males are able to selectively recognize congeneric females by a short-range stimulus. All pairwise combinations of Caenorhabditis species were isolated to some degree by gametic mechanisms; 7 of 12 combinations were cross infertile and 5 of 12 were cross-fertile but had low brood sizes. In cross-fertile combinations, most hybrid embryos were inviable and arrested prior to gastrulation. Only in crosses of C. briggsae males to C. sp. v females did any hybrids survive embryogenesis. Most of these C. briggsae/C. sp. v hybrids arrested during larval development, and the few that reached adulthood invariably were female. These results are consistent with the presence of at least two lethal factors in the C. briggsae-C. sp. v combination: a maternal lethal factor in the cytoplasm of C. briggsae and a recessive lethal factor on the X chromosome of C. sp. v.
Terrestrial molluscs (Mollusca: Gastropoda) are important economic pests worldwide, causing extensive damage to a variety of crop types, and posing a health risk to both humans and wildlife. Current knowledge indicates that there are eight nematode families that associate with molluscs as definitive hosts, including Agfidae, Alaninematidae, Alloionematidae, Angiostomatidae, Cosmocercidae, Diplogastridae, Mermithidae and Rhabditidae. To date, Phasmarhabditis hermaphrodita (Schneider, 1859) Andrássy, 1983 (Rhabditida: Rhabditidae) is the only nematode that has been developed as a biological molluscicide. The nematode, which was commercially released in 1994 by MicroBio Ltd, Littlehampton, UK (formally Becker Underwood, now BASF) under the tradename Nemaslug ® , is now sold in 15 different European countries. This paper reviews nematodes isolated from molluscs, with specially detailed information on the life cycle, host range, commercialization, natural distribution, mass production and field application of P. hermaphrodita .
Although molecular techniques are revolutionising nematode taxonomy, morphological data still form the basis of nematode species descriptions. However, morphological characters show a natural variability that should be taken into account before describing new species. The current study presents the results of an elaborate morphometric study of Halicephalobus cf. gingivalis, including 15 measurements and 13 indices of 540 specimens, the progeny of a single parthenogenetic female and cultured under different temperature and food conditions and measured in different adult age groups, i.e., young adults with a developed vulva but before the onset of oviposition, adults laying eggs, and old, post-reproductive adults near the end of their life cycle. The morphometric characters were analysed using both univariate (analysis of variance) and multivariate (principal components and canonical discriminant analysis) techniques. The main results reveal that the morphometric characters most used in Halicephalobus identification keys have a huge variability within a single progeny, e.g., body length 1.9 times longer than the shortest or ratio VA/tail length 3.9 times larger than the smallest. This variability has a magnitude that has not been observed in nematodes before. Further, by changing the environmental factors, the morphometric characters are influenced to an extent that one could assign - with seemingly 'statistical support' - different 'species' of the genus to different subpopulations. With this experimental study we provide convincing elements to advocate an integrative taxonomic approach and to discourage the description of new species based only on morphometric differences.
We have attempted interspecific hybridizations among six species of rhabditid nematodes: Caenorhabditis elegans, Caenorhabditis briggsae, Caenorhabditis remanei, Caenorhabditis sp. v, Rhabditis sp., and Peloderateres. Copulation was observed in all crosses between Caenorhabditis species; however, none resulted in the generation of stable hybrid populations. No copulation was observed in crosses between Caenorhabditis males and Rhabditis or Pelodera females, even when congeneric females were present, suggesting that Caenorhabditis males are able to selectively recognize congeneric females by a short-range stimulus. All pairwise combinations of Caenorhabditis species were isolated to some degree by gametic mechanisms; 7 of 12 combinations were cross infertile and 5 of 12 were cross-fertile but had low brood sizes. In cross-fertile combinations, most hybrid embryos were inviable and arrested prior to gastrulation. Only in crosses of C. briggsae males to C. sp. v females did any hybrids survive embryogenesis. Most of these C. briggsae/C. sp. v hybrids arrested during larval development, and the few that reached adulthood invariably were female. These results are consistent with the presence of at least two lethal factors in the C. briggsae- C. sp. v combination: a maternal lethal factor in the cytoplasm of C. briggsae and a recessive lethal factor on the X chromosome of C. sp. v.
Eine Methode wird beschrieben bei der Nematoden innerhalb 24 Stunden von der Fixierungsflüssigkeit in wasserfreies Glyzerin überführt werden. Die Nematoden werden nach Fixierung in ein Gemisch von 20 Teilen Aethanol 96%, I Teil Glyzerin und 79 Teilen Wasser gebracht. Das Aethanol in diesem Gemisch wird durch Wasserentzug im Exsiccator mit Aethanol 96% bei 35°-40°C in nicht weniger als 12 Stunden bis zu etwa 95% konzentriert. Danach wird ein Gemisch von 5 Teilen Glyzerin in 95 Teilen Aethanol 96% hinzugefügt. Dieser wird bei 40°C in wenigstens 3 Stunden zu reines Glyzerin konzentriert.
Caenorhabditis vulgaris sp.n. (Nematoda: Rhabditidae), a necromenic associate of pill bugs (Armadillidium vulgare and Armadillidium nasatum) and snails (Oxychilus sp.), is described. C. vulgaris is known from two locations, both in the northeastern United States. It is gonochoristic, with males & females equally abundant. Its associations with pill bugs and snails are as dauer juveniles and appear not to be deleterious to the host animal. These associations are not a requisite part of the C. vulgaris life-cycle; cultures of C. vulgaris can be maintained indefinitely if grown on a bacterial lawn. C. vulgaris can be distinguished from other species of Caenorhabditis based on reproductive, molecular and morphological criteria.
Morphometrics of four Canadian, three US and two European isolates representing distinct geographic populations of Steinernema kraussei (Steiner, 1923) were compared and analysed by multivariate analysis. A total of 540 individuals (270 males and 270 third-stage infective juveniles) representing the nine populations was measured. Fourteen morphometric variables were selected and subjected to principal component and canonical analyses. Results from both analyses indicate that there are morphological differences among the studied isolates, and that these differences are congruent with their geographic origin. The European isolates were shown to be distinctly different from the North American isolates. Within the North American isolates, the western isolates were distinguished from the eastern one (Parishville). No significant differences were observed between the two European isolates studied. Ont été comparées et étudiées par analyse multivariable les caractéristiques morphométriques de quatre isolats canadiens, trois isolats américains et deux isolats européens représentant des populations géographiques distinctes de Steinernema kraussei. Un total de 540 individus (270 mâles et 270 juvéniles infestants de troisième stade) représentant les neuf populations a été mesuré. Quatorze variables morphométriques ont été sélectionnées et soumises à des analyses en composantes principales et canonique. Les résultats des deux analyses montrent quil existe des différences morphologiques entre les isolats étudiés et que ces différences sont congruentes avec leur origine géographique. Les isolats européens sont apparus comme étant nettement différents des isolats nordaméricains. Dans le groupe des isolats nord-américains, les isolats de louest ont été différenciés de celui de lest (Parishville). Aucune différence significative na été observé entre les deux isolats européens étudiés.
A phylogenetic analysis was conducted using morphological characters. Eleven of the 18 Caenorhabditis-species described were investigated. The polarity for character transformations was established and a cladogram and the character set of the stem species reconstructed. There are two possible positions for R. plicata. It was not possible to resolve the phylogenetic relationship of the Elegans-group, which consists of seven species, including the four best-known Caenorhabditis-species. Transformation series of characters, e.g. the structure of the precloacal lip, are presented. The evolution of a pharyngeal sleeve is discussed. For the terms caudal papilla, bursal papilla and ray are given precise definitions. Two individual rays are specified as ‘anterior dorsal’ and ‘posterior dorsal’. We present here a new case of a Rhabditis with 10 pairs of bursal papillae where one pair (no. 10) is the phasmids. Information on the geographical distribution and the ecology of the Caenorhabditis-species is given. The markedly different ecological niches of these species must be derived from a way of life in the stem species in patchily distributed decomposing organic material which necessitated a phoretic phase with waving behaviour of the dauer juveniles.
Fourteen 7-alkoxy-2,2-dimethylchromenes were synthetized and studied in JH competition experiments: precocenes (Ps) PI and PII, and synthetic analogs (PAs) including (i) three with both antiallatal and P-like activities: 7-ethoxy-PII (7-EPII); 7-(prop-2-ynyloxy)-2,-2-dimethylchromene (PPI); and 6-methoxy-7-(prop-2-ynyloxy)-2,2-dimethylchromene (PPIII); (ii) six without antiallatal activity, exerting P-like activity in nematodes; and (iii) three without either antiallatal or P-like activity, but with a strong nematocidal effect. Within the dose range 8–1000 μg/ml, different concentrations of each PA were applied to nematode growth medium which did or did not contain 1000 μg methoprene (a juvenile hormone analog JHA)/ml. Plates inoculated with Caenorhabditis embryos were incubated and scored for developmentally affected survivors. The JHA did not compete with any PA mentioned as (iii). It competed moderately with some nonantiallatal PAs (8-Me-PPI, 8-MeO-PPI, and 3,4-diCl-PPI) with strong P-like and nematocidal activities. The JHA competed most efficiently with all Ps, antiallatal PAs, and two nonantiallatal PAs (PPII and thio-PI) which exerted severe P-like activities in nematodes. Parameters assumed to be indicators of the P-like (rather than nematocidal) activity of the PAs proved more sensitive to the JHA than those of nematocidal activity. Whether the JH-compensable P-like activity of some PAs can be regarded as a real anti-JH action needs further clarification.
The effect of infection by Angiostrongylus cantonensis on the activity of the enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and the concentration of total proteins, uric acid and urea in the hemolymph of Biomphalaria glabrata were investigated. The snails were dissected after 1, 2 and 3 weeks of infection to collect the hemolymph. The infection by A. cantonensis induced severe changes in the host snail's metabolism, triggering physiological mechanisms to minimize the deleterious effects caused by the larvae. There was a significant decrease in the concentration of total proteins in the infected snails, which occurred gradually as the infection advanced. This change was accompanied by an increase in the concentrations of urea and a decrease in the levels of uric acid in the hemolymph, suggesting that in this model the infection induces proteolysis and inversion of the excretion pattern of the infected snails. Besides this, variations in the activities of the aminotransferases were observed, with significantly higher levels in the infected groups than in the control group. These results indicate an increase in the protein metabolism of the infected snails, since there was an increase in nitrogen catabolites such as urea.
Many nematodes show a stage-specific behavior called nictation in which a worm stands on its tail and waves its head in three dimensions. Here we show that nictation is a dispersal behavior regulated by a specific set of neurons, the IL2 cells, in C. elegans. We established assays for nictation and showed that cholinergic transmission was required for nictation. Cell type-specific rescue experiments and genetic ablation experiments revealed that the IL2 ciliated head neurons were essential for nictation. Intact cilia in IL2 neurons, but not in other ciliated head neurons, were essential, as the restoration of the corresponding wild-type gene activity in IL2 neurons alone in cilia-defective mutants was sufficient to restore nictation. Optogenetic activation of IL2 neurons induced nictation, suggesting that signals from IL2 neurons are sufficient for nictation. Finally, we demonstrated that nictation is required for transmission of C. elegans to a new niche using flies as artificial carriers, suggesting a role of nictation as a dispersal and survival strategy under harsh conditions.
In the laboratory, the nematode Caenorhabditis elegans lives on the surface of nutrient agar in Petri dishes, feeding on a lawn of the uracil auxotroph strain OP50, an Escherichia coli mutant strain. This sentence sums up the fundamentals of C. elegans ecology, as most of us know it. While over 15,000 articles on diverse biological aspects of C. elegans attest to the worm's undisputable virtues as a major model organism, its biology in the wild remains mysterious. To properly interpret and fully understand the available wealth of genetic, molecular and other biological observations made in the laboratory, it will be important to know its natural history and to place the species in its ecological and evolutionary context. With the aim of connecting the discoveries that have been made about C. elegans biology to its 'real life', we shall discuss recent studies on the worm's natural habitat and population biology, and outline key issues in attaining a modern natural history of C. elegans.
Whether phenotypic evolution proceeds predominantly through changes in regulatory sequences is a controversial issue in evolutionary
genetics. Ample evidence indicates that the evolution of gene regulatory networks via changes in cis-regulatory sequences is an important determinant of phenotypic diversity. However, recent experimental work suggests that
the role of transcription factor (TF) divergence in developmental evolution may be underestimated. In order to help understand
what levels of constraints are acting on the coding sequence of developmental regulatory genes, evolutionary rates were investigated
among 48 TFs required for neuronal development in Caenorhabditis elegans. Allelic variation was then sampled for 28 of these genes within a population of the related species Caenorhabditis remanei. Neuronal TFs are more divergent, both within and between species, than structural genes. TFs affecting different neuronal
classes are under different levels of selective constraints. The regulatory genes controlling the differentiation of chemosensory
neurons evolve particularly fast and exhibit higher levels of within- and between-species nucleotide variation than TFs required
for the development of several neuronal classes and TFs required for motorneuron differentiation. The TFs affecting chemosensory
neuron development are also more divergent than chemosensory genes expressed in the neurons they differentiate. These results
illustrate that TFs are not as highly constrained as commonly thought and suggest that the role of divergence in developmental
regulatory genes during the evolution of gene regulatory networks requires further attention.
Precocenes (PI and PII) and 114 of their analogs (PAs) were synthetized and tested on C. remanei embryos for their precocene-like (P-like) activities resulting in unusual development at sublethal doses. The P-like activity was quantitated by plotting the probit of the percentage of the developmentally affected survivors against the (log) dose to obtain the EC plot and the half effective concentration (EC50). All five PAs (PI, PII, 7-ethoxy-PII, 7-(prop-2-ynyloxy)-PI, and 6-methoxy-7-(prop-2-ynyloxy)-PII) which exert both antiallatal activity in insects and P-like activity in nematodes are 7-alkoxy-substituted 2,2-dimethylchromenes. Both activities can be enhanced by an additional 6-MeO-substitution or by an asymmetric 6,7-dialkoxy-substitution, on condition that R-7 is longer than R-6. There are many more similarities than dissimilarities in the structural requirements needed for antiallatal and P-like activities. All but three nonantiallatal PAs effective in nematodes are 7-prop-2-ynyloxy-subsituted; two are symmetrically 6,7-disubstituted, and one is heterosubstituted (thio-PI). All PAs with antiallatal but without P-like activity are 7-monosubstituted with a relatively long alkoxy group. Certain substitutions favor antiallatal activity and others P-like activity. The severe nematocidal effect of 6,7-methylenedioxy-2,2-dimethylchromene (inert in insects) is not accompanied by P-like activity. The present findings lend some indirect support to the supposition that JH-producing cells and/or JH-dependent function(s) might exist in the nematodes.
We have investigated the molecular evolution of the nucleotide sequences of 18S ribosomal RNA genes (18S rDNA) from a set of nematodes in the family Rhabditidae (Nematoda: Secernentea). Our aim was to evaluate the usefulness of this gene for molecular systematics of this family, as well as to establish phylogenetic relationships within a group that has potential for comparative studies of the relationship between development and evolution. We determined the 18S rDNA sequences of nine species of nematodes representing six genera within this family (Caenorhabditis briggsae, C. vulgaris, C. remanei, Rhabditis blumi, Rhabditis sp. br, Rhabditella axei, Pellioditis typica. Teratorhabditis palmarum, and Pelodera strongyloides dermatitica). Using hypothetical models for secondary structure as well as nucleotide similarity, these sequences were aligned with the 18S rDNA sequence published by Ellis et al. for C. elegans and with the partial sequences published by Nadler for eight ascaridoid species. We find that 18S rDNA is likely to be a useful tool to resolve relationships at the intrafamilial level. However, 18S rDNA sequences cannot be used to resolve relationships between taxa as closely related as the Caenorhabditis species. Parsimony, minimum-evolution, and maximum-likelihood methods strongly reject Andrássy's proposed phylogenetic classification based on adult morphological characters but support that of Sudhaus as one alternative of a few possible phylogenies. Distances between genera in this family are about eight times as great as distances between tetrapod classes, suggesting rapid rates of substitution, ancient divergence, or both.
Since introns were discovered 26 years ago, people have wondered how changes in intron/exon structure occur, and what role these changes play in evolution. To answer these questions, we have begun studying gene structure in nematodes related to Caenorhabditis elegans. As a first step, we cloned a set of five genes from six different Caenorhabditis species, and used their amino acid sequences to construct the first detailed phylogeny of this genus. Our data indicate that nematode introns are lost at a very high rate during evolution, almost 400-fold higher than in mammals. These losses do not occur randomly, but instead, favor some introns and do not affect others. In contrast, intron gains are far less common than losses in these genes. On the basis of the sequences at each intron site, we suggest that several distinct mechanisms can cause introns to be lost. The small size of C. elegans introns should increase the rate at which each of these types of loss can occur, and might account for the dramatic difference in loss rate between nematodes and mammals.
The most common cause of eosinophilic meningitis is the rat lungworm Angiostrongylus cantonensis a parasite that is endemic in the southeast Asian and Pacific regions. Outbreaks of eosinophilic meningitis associated with drinking raw vegetable juice are rarely reported, even in regions of endemic infection. We performed a cohort study among Taiwanese with eosinophilic meningitis who drank raw vegetable juice within three months of the onset of the outbreak. Clinical manifestations, laboratory examinations, and outcomes were prospectively followed. Five native Taiwanese met the case definition of eosinophilic meningitis. Specific antibodies to A. cantonensis were detected in the serum of five of the patients and in the cerebrospinal fluid (CSF) of four of the patients. Central nervous system manifestations included headache (n = 5 [100%]), Brudzinski's sign/stiff neck (n = 5 [100%]), hyperesthesia/paresthesias (n = 5 [100%]), and cranial nerve palsy (n = 1 [20%]). Laboratory findings included peripheral (n = 5 [100%]) and CSF eosinophilia (n = 4 [80%]), transient increases in the white blood cell count (n = 1 [20%]), and in serum levels of creatine kinase (n = 1 [20%]). Meningeal enhancement, as well as high signal intensity, at the subcortical white matter on T2 weighted and fluid attenuated inversion recovery images were observed on magnetic resonance imaging in four patients. There were three episodes of relapse during treatment and all resolved with after a lumbar puncture and/or administration of steroids. At the 12-month follow up, all five patients had recovered without neurologic sequelae. Risk factors identification showed that consumption of raw vegetable juice was associated with illness (Pearson correlation test r = 0.867, P = 0.01). There was association between the presence of raw vegetable juice and CSF eosinophilia (Spearman's correlation test r = 0.816, P = 0.004).
Caenorhabditis elegans is a major model system in biology, yet very little is known about its biology outside the laboratory. In particular, its unusual mode of reproduction with self-fertile hermaphrodites and facultative males raises the question of its frequency of outcrossing in natural populations.
We describe the first analysis of C. elegans individuals sampled directly from natural populations. C. elegans is found predominantly in the dauer stage and with a very low frequency of males versus hermaphrodites. Whereas C. elegans was previously shown to display a low worldwide genetic diversity, we find by comparison a surprisingly high local genetic diversity of C. elegans populations; this local diversity is contributed in great part by immigration of new alleles rather than by mutation. Our results on heterozygote frequency, male frequency, and linkage disequilibrium furthermore show that selfing is the predominant mode of reproduction in C. elegans natural populations but that infrequent outcrossing events occur, at a rate of approximately 1%.
Our results give a first insight in the biology of C. elegans in the natural populations. They demonstrate that local populations of C. elegans are genetically diverse and that a low frequency of outcrossing allows for the recombination of these locally diverse genotypes.
Vulva formation is a paradigm for evolutionary developmental biology in nematodes. Not only do the number of vulval precursor cells (VPCs) differ between members in the Rhabditidae and Diplogastridae, they are also sculpted via different developmental mechanisms, either by cell fusion in most Rhabditidae or by programmed cell death in the Diplogastridae. In this context, the species Poikilolaimus oxycercus is the only known species in the family Rhabditidae to have a subset of the Pn.p cells commit programmed cell death during the patterning of the VPCs. Our current study introduces P. oxycercus as a new laboratory organism. There are discrete laboratory strains that are genetically polymorphic from each other as well as heterogeneous within each strain. In order to cultivate this gonochoristic nematode into an experimental model with a tractable genetic system, we produced two inbreeding tolerant, near-isogenic strains capable of producing viable progeny with each other. We also described P. oxycera's morphology by scanning electron microscopy (SEM), basic life history traits, hybrid viability, and mating behavior. P. oxycercus females have no preference for inter- or intra-strain matings, and can mate with multiple males in a relatively short time period, suggesting a propensity for maintaining heterozygosity through promiscuity. Interestingly, all sexes from three species in the genus Poikilolaimus show five 4',6-diamidino-2-phenylindole (DAPI) staining bodies in their germ line cells. This could indicate that Poikilolaimus species possess five bivalent chromosomes in their germ lines, in contrast to the hermaphroditic Caenorhabditis elegans or Pristionchus pacificus, which have six chromosomes.
Nematode molecular evolution
- G B Nunn
Nunn GB (1992) Nematode molecular evolution. PhD dissertation,
University of Nottingham, Nottingham, UK
Biological and systematic implications of a phylum-wide phylogenetic analyses of ~ 2,800 nearly full length small subunit ribosomal DNA sequences from nematodes. NCBI GenBank
- H Van Megen
- S Van Den Elsen
- P Mooijman
- F Bakker
- J Bakker
- J Helder
van Megen H, van den Elsen S, Mooijman P, Bakker F, Bakker J,
Helder J (2004) Biological and systematic implications of a
phylum-wide phylogenetic analyses of ~ 2,800 nearly full length
small subunit ribosomal DNA sequences from nematodes. NCBI
GenBank. https:// www. ncbi. nlm. nih. gov/ nucco re/ KJ636 315.
Accessed 31 Jan 2021