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First report of Caenorhabditis brenneri (Nematoda: Rhabditida) isolated from the cadaver of Philippinella moellendorffi (Stylommatophora: Ariophantidae), a terrestrial slug in the Philippines
Abstract
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 .
... Despite this crucial role in the ecosystem, the life history of soil fauna such as nematodes has remained understudied (Bardgett and van der Putten 2014). Sudhaus and Kiontke (2007) reported that Caenorhabditis brenneri Sudhaus and Kiontke 2007 is a gonochoristic member species of the Elegans group; it is found mainly in different habitats, such as in decaying plant matter and soil, and often forms an association with invertebrates such as terrestrial gastropods with pantropical distribution (Sudhaus and Kiontke 2007;Dalan et al. 2022;. Interestingly, C. brenneri has the most molecular polymorphic synonymous sites between individuals (14.1%), making them the most hyper-diverse eukaryote comparable to hyper-diverse bacteria (Dey et al. 2013). ...
Dalan L, Tañan V, Diano MA, Demayo C, Tabelin M, Sumaya NH. 2024. Life history traits of the gastropod-associated bacterivorous nematode Caenorhabditis brenneri (Nematoda: Rhabditida). Biodiversitas 25: 3106-3113. Caenorhabditis species are associated with decaying plant materials and invertebrates such as terrestrial gastropods. Few Caenorhabditis species have been studied regarding their ecology, genetics, development, and essential life history traits (LHT). In this study, we describe the life cycle of a free-living, wild-type, bacterivorous nematode, Caenorhabditis brenneri Sudhaus and Kiontke 2007, associated with the terrestrial slug Philippinella moellendorffi Collinge 1899 and account for the effects of food density and temperature on its population dynamics by employing the hanging drop technique. The bacterial food supply was sourced from the slug cadaver and identified as Alcaligenes faecalis (MT012081). C. brenneri was fed with varying bacterial densities (109 and 5×109 cells mL-1) and incubated at 20 and 25°C. The bacterial food density-temperature interaction was found to have no significant influence on the offspring production of C. brenneri. Moreover, the total fertility rate (TFR) and net reproductive rate (Ro) are higher in 109 cells mL-1 in both temperatures (TFR at 20°C: 139; 25°C: 169 and Ro at 20°C: 134; 25°C: 156). Whereas the alternative generation time (To, T1, T) and population doubling time (PDT) are faster at 25°C in both bacterial densities, the intrinsic rate of natural increase (rm) is faster at lower temperatures (20°C) in both bacterial densities. The average lifespan of C. brenneri is seven days when fed with A. faecalis. Offspring somatic growth (body length and width) was influenced by bacterial food density-temperature interaction with increased length and girth observed in higher bacterial density and temperature in our knowledge. This study is the first attempt to use A. faecalis, a wild-type bacterium from the terrestrial slug P. moellendorffi cadaver, as the bacterial food source for a Caenorhabditis LHT analysis.
The grey field slug, Deroceras reticulatum, is an agricultural pest causing damage to a wide variety of crops each year. The nematode Phasmarhabditis hermaphrodita has been shown to effectively kill this slug in field-simulated conditions, leading to its widespread use as a biological control agent in Europe. However, recently discovered isolates of Phasmarhabditis from California have not been tested in a field-simulated environment. The lethality of three local isolates of Phasmarhabditis (P. hermaphrodita, P. californica, & P. papillosa) as well as the molluscicide Sluggo Plus® was assessed on D. reticulatum in a lath house. Remaining leaf area on Canna lilies and slug mortality were recorded after 3 weeks of exposure to treatments. Local isolates efficiently killed D. reticulatum and protection from leaf damage was attained by treatment with P. papillosa. Further experimentation is required to assess plant protection afforded by Phasmarhabditis as plants in some trials may have been in poor health. The three tested Phasmarhabditis isolates are reasonable candidates for biological control within the United States but additional information, particularly on the lethality to non-target gastropods, is needed before an informed decision on their use can be made.
This book, which contains 15 chapters, draws together the available information on the diversity of organisms that constitute the natural enemies of terrestrial gastropods. In a series of review chapters, it provides an authoritative synthesis of current knowledge and research for predators, parasites and pathogens. This book is for both students and professionals concerned with the conservation of gastropod communities in natural habitats and management of pestiferous species.
The Molecular Evolutionary Genetics Analysis (MEGA) software has matured to contain a large collection of methods and tools of computational molecular evolution. Here, we describe new additions that make MEGA a more comprehensive tool for building timetrees of species, pathogens, and gene families using rapid relaxed-clock methods. Methods for estimating divergence times and confidence intervals are implemented to use probability densities for calibration constraints for node-dating and sequence sampling dates for tip-dating analyses, which will be supported by new options for tagging sequences with spatiotemporal sampling information, an expanded interactive Node Calibrations Editor, and an extended Tree Explorer to display timetrees. We have now added a Bayesian method for estimating neutral evolutionary probabilities of alleles in a species using multispecies sequence alignments and a machine learning method to test for the autocorrelation of evolutionary rates in phylogenies. The computer memory requirements for the maximum likelihood analysis are reduced significantly through reprogramming, and the graphical user interface (GUI) has been made more responsive and interactive for very big datasets. These enhancements will improve the user experience, quality of results, and the pace of biological discovery. Natively compiled GUI and command-line versions of MEGA11 are available for Microsoft Windows, Linux, and macOS from www.megasoftware.net.
Parasites and parasitic lifestyles have evolved from free-living organisms multiple times. How such a key evolutionary transition occurred remains puzzling. Facultative parasites represent potential transitional states between free-living and fully parasitic lifestyles because they can be either free-living or parasitic depending on environmental conditions. We suggest that facultative parasites with phenotypically plastic life-history strategies may serve as evolutionary stepping-stones towards obligate parasitism. Pre-adaptations provide a starting point for the transition towards opportunistic or facultative parasitism, but what evolutionary mechanism underlies the transition from facultative to obligate parasitism? In this Opinion Piece, we outline how facultative parasites could evolve towards obligate parasites via genetic assimilation, either alone or in combination with the Baldwin effect. We further describe the key predictions stemming from each of these evolutionary pathways. The importance of genetic assimilation in evolution has been hotly debated. Studies on facultative parasites may not only provide key insights regarding the evolution of parasitism, but also provide ideal systems in which to test evolutionary theory on genetic accommodation.
Specimens of the African snail Achatina fulica, collected in Bucaramanga, Colombia, were examined for parasites. Numerous specimens of Caenorhabditis briggsae were collected from the digestive tract of the snails and identified by the structure of male spiculum, caudal bursa, gubernaculum and precloacal lip in males, triangular tooth in metarhabdion, and protandrous hermaphrodites with a female:male ratio of 15:1 and with morphometry. DNA sequences of the ITS2 region of the ribosomal gene array from worms in this study matched with 99% similarity to published sequences of C. briggsae. A redescription of the species is provided. This is the first record of the species in South America.
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.
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.
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.
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.
The nematode Caenorhabditis elegans is a major model organism in laboratory biology. Very little is known, however, about its ecology, including where it proliferates. In the past, C. elegans was mainly isolated from human-made compost heaps, where it was overwhelmingly found in the non-feeding dauer diapause stage.
C. elegans and C. briggsae were found in large, proliferating populations in rotting plant material (fruits and stems) in several locations in mainland France. Both species were found to co-occur in samples isolated from a given plant species. Population counts spanned a range from one to more than 10,000 Caenorhabditis individuals on a single fruit or stem. Some populations with an intermediate census size (10 to 1,000) contained no dauer larvae at all, whereas larger populations always included some larvae in the pre-dauer or dauer stages. We report on associated micro-organisms, including pathogens. We systematically sampled a spatio-temporally structured set of rotting apples in an apple orchard in Orsay over four years. C. elegans and C. briggsae were abundantly found every year, but their temporal distributions did not coincide. C. briggsae was found alone in summer, whereas both species co-occurred in early fall and C. elegans was found alone in late fall. Competition experiments in the laboratory at different temperatures show that C. briggsae out-competes C. elegans at high temperatures, whereas C. elegans out-competes C. briggsae at lower temperatures.
C. elegans and C. briggsae proliferate in the same rotting vegetal substrates. In contrast to previous surveys of populations in compost heaps, we found fully proliferating populations with no dauer larvae. The temporal sharing of the habitat by the two species coincides with their temperature preference in the laboratory, with C. briggsae populations growing faster than C. elegans at higher temperatures, and vice at lower temperatures.
Caenorhabditis elegans is a preeminent model organism, but the natural ecology of this nematode has been elusive. A four-year survey of French orchards published in BMC Biology reveals thriving populations of C. elegans (and Caenorhabditis briggsae) in rotting fruit and plant stems. Rather than being simply a 'soil nematode', C. elegans appears to be a 'plant-rot nematode'. These studies signal a growing interest in the integrated genomics and ecology of these tractable animals.
See research article http://www.biomedcentral.com/1741-7007/10/59
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
A new approach to rapid sequence comparison, basic local alignment search tool (BLAST), directly approximates alignments that optimize a measure of local similarity, the maximal segment pair (MSP) score. Recent mathematical results on the stochastic properties of MSP scores allow an analysis of the performance of this method as well as the statistical significance of alignments it generates. The basic algorithm is simple and robust; it can be implemented in a number of ways and applied in a variety of contexts including straightforward DNA and protein sequence database searches, motif searches, gene identification searches, and in the analysis of multiple regions of similarity in long DNA sequences. In addition to its flexibility and tractability to mathematical analysis, BLAST is an order of magnitude faster than existing sequence comparison tools of comparable sensitivity.
Wild populations of the model organism C. elegans represent a valuable resource, allowing for genetic characterization underlying natural phenotypic variation. Here we provide a simple protocol on how to sample and rapidly identify C. elegans wild isolates. We outline how to find suitable habitats and organic substrates, followed by describing isolation and identification of C. elegans live cultures based on easily recognizable morphological characteristics, molecular barcodes, and mating tests. This protocol uses standard laboratory equipment and requires little prior knowledge of C. elegans biology.Key words
Caenorhabditis elegans
Natural genetic variationNatural populationsWild isolatesNatural habitatEcology
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.
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.
As we learn more and more about the classes of organisms that infect humans, we are discovering that many organisms, including pathogenic organisms, may have a complex relationship with humans in which infection seldom results in the production disease. In some cases, infection may be just one biological event that occurs during a multievent process that develops sequentially, over time, and involves genetic and environmental factors that may vary among individuals. Consequently, the role of infectious organisms in the development of human disease may not meet all of the criteria normally required to determine when an organism can be called the cause of a disease. This chapter reviews the expanding role of infections in the development of human disease. We discuss prion diseases of humans, a fascinating example of an infectious disease-causing agent that is not a living organism. We also discuss the diseases of unknown etiology for which infectious organisms may play a role. In addition, this chapter reviews some of the misconceptions and recurring errors associated with the classification of infectious diseases that have led to misdiagnoses and have impeded our understanding of the role of organisms in the development of human diseases.
Phasmarhabditis hermaphrodita is reported for the first time in North America from cadavers of the invasive slug species Deroceras reticulatum, D. laeve and Lehmannia valentiana collected from three different locations in California, USA. Four isolates were identified using combined morphology, morphometrics and molecular sequence data for complete internal transcribed spacer (ITS-1, 5.8S, ITS-2), D2-D3 expansion segments of the large subunit (LSU or 28S) and nearly complete small subunit (SSU or 18S) ribosomal DNA. Extremely low sequence variations in the COI gene of the mitochondria were observed among US isolates as well as between US isolates and the two UK sequences. The occurrence of P. hermaphrodita in North America has regulatory implications for potential biological control strategies against non-native gastropod species that are pests in ornamental and agricultural cultivation on this continent. The D2-D3 sequence of the LSU rDNA is new for the species. Phasmarhabditis hermaphrodita (Schneider, 1859) An-drássy, 1983 was first described as Pelodytes herma-phroditus Schneider, 1859 from Arion sp. in Germany (Schneider, 1859) and was rediscovered in 1988 from De-roceras reticulatum O.F. Müller during a search for bio-logical control agents in the UK (Wilson et al., 1993; Glen et al., 1996). Bacterial associates were identified and viru-lence tested in monoxenic combinations with D. reticula-tum. Of these bacteria, Moraxella osloensis supported the highest production of the nematode (Wilson et al., 1995) and together both have been used in a commercial prepa-ration marketed as 'Nemaslug ® ' (BASF Agricultural Spe-cialties, formerly by Becker Underwood, Littlehampton, UK) for home gardeners since spring of 1994. This prod-uct has been approved for application on vegetables, high-value crops (Rae et al., 2007) and field crops (Brown et al., 2011) and is available in the UK, Switzerland (Rae et al., 2007); however, it has not been
The biology of Sydney Brenner's eponymous species of nematode, Caenorhabditis brenneri, is little known to science, despite its famous sibling Caenorhabditis elegans. Here we demonstrate that C. brenneri harbors the most molecular diversity of any eukaryote, with its 14.1% of polymorphic synonymous sites between individuals being 150-fold greater than humans and most comparable to hyperdiverse bacteria. This diversity is not an artifact of cryptic species divergence but reflects an enormous pan-tropical population, confirmed by fully viable genetic crosses between continents, extensive intralocus recombination, selection on codon use, and only weak geographic genetic structure. These findings in an animal galvanize tests of theory about the evolution of complexity in genomes and phenotypes and enable molecular population genetics methods to finely resolve uncharacterized functional noncoding elements.
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.
Caenorhabditis remanei was found in association with the terrestrial isopod Trachelipus rathkii at several wooded locations in southwestern Ohio. These associations were as developmentally arrested dauer larvae. The sites of association were the inner surfaces of the dorsal plates and ventral appendages. C. remanei associations also were observed with Armadillidium nasatum, Cylisticus convexus, and Porcellio scaber. They were not observed with Porcellio spinicornis even though Fl spinicornis populations were intermingled with infested populations of T. rathkii. Consistent with the observed natural associations, C. remanei dauers were experimentally able to infest T. rathkii and P. scaber. Dauer larvae responded to confinement with isopods by nictating and by climbing upon these potential hosts. Experimental infestations were able to persist for at least five days. Long-term infestations were not attempted.
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.
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.
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