Pristionchus pacificus

  

Contents

  

Rev: 11/02/2026

Shark-tooth Nematode Classification Biology and Ecology
Morphology and Anatomy Life Cycle
Return to Pristionchus Menu Ecosystem Functions and Services
Distribution Management
Return to Diplogastridae Menu Feeding  References
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Classification:

Chromadorea
Chromadoria
Rhabditina
            Diplogastroidea
Diplogastridae
(formerly Neodiplogastridae
             Mononchoidinae)
        Pristionchus pacificus Sommer, Carta, Kim & Sternberg, 1996
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    •     Synonyms:
     

    Extensive research conducted in the laboratory of  Ralf Sommer, Max Planck Institute for Developmental Biology, Tubingen, Germany.
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    Morphology and Anatomy:

     

     

    		 Females:

      

    Pristionchus pacificus — genome completed by NIH.

    The Pristionchus genome is 169 Mb with >23,500 genes. (Caenorhabditis elegans genome is 100 Mb with 20,170 protein-coding genes).


     
    Males:  

    Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:

     
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    Distribution:

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    Feeding:

    Pristionchus spp. have cellulases, presumably through horizontal transfer from microbes (Smant, 1998).

    Unlike the rhabditids, Pristionchus and other diplogasterids do not have a grinder in the basal bulb of the esophagus, so there are living bacteria in the intestine. 

    The mouth also differs from the tubular stoma of the rhabditids and has two forms, with teeth (eurystomatous) or without teeth (stenostomatous).  Tooth formation is triggered by starvation, similar to the dauer trigger in C. elegans.  Eurystomatous forms are able to feed on fungi.

    P. pacificus larvae develop into adults of one of two distinct feeding morphs ("eurystomatous" and "stenostomatous"). The stenostomatous morph grows rapidly on a diet of bacteria, whereas the eurystomatous morph, which is more complex in form, has higher fitness than the stenostomatous morph when fed nematode prey (Serobyan et al., 2014)

    Prey finding by P. pacificus is through the ambushing behavior of nictation by dauer juveniles  Nictation involves the nematde elevatiing itself from the tail in a soil pore or other space. Generally the elevated body waves in the pore space which increases the probability of contacting a prey individual.Studies show a positive correlation between nictation frequencies and host attachment (Brown et al., 2011)

       
       
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    Biology and Ecology:

    Pristionchus pacificus has developed into a very useful model system under the direction of Dr. Ralf Sommer of the Max Plank Institute.  It has many similar advantages to those provided by Caenorhabditis elegans as a model system:

    1.Small and Easy to Culture

    oCultured on agar and will feed on bacteria or defined nutrient media.

    oLarge populations can be maintained at very low cost

    oBoth have a non-feeding dauer stage and can be cryopreserved

    2.Short Life Cycle

    oDevelopment from egg to reproductive adult takes about 3 -5 days.

    oThe entire lifespan is only about 2 to 3 weeks.

    oGenetic and aging experiments can be conducted in a short interval of time

    3.Transparent Body

    oDirect microscopic observation of cells, organs, and developmental processes in living animals.

    oFluorescent markers can be used to track gene expression and cell behavior.

    4.Evolutionary and Developmental Biology

    oGenome completely sequenced, the fate of every somatic cell has been mapped. Structures comparable but life histories differ

    oNeuronal system mapped allowing detailed studies of neural function and behavior.

    oAdult hermaphrodites have a fixed number of somatic cells, making developmental studies highly reproducible and comparable.

    oMales can be induced for mating, allowing mating experiments and genetic recombination.

    oMany mutants and strains exist for each species

    oPhenotypic plasticity in development, morphology and evolution of feeding strategies

    5.Powerful Genetics

    oMutations, RNA interference  and CRISPR gene editing can be used easily.

    oMany genes have counterparts in humans.

     

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    Life Cycle:

    The mouth differs from the tubular stoma of the rhabditids and has two forms, with teeth (eurystomatous) or without teeth (stenostomatous).  Tooth formation is triggered by starvation, similar to the dauer trigger in C. elegans. 

    P. pacificus larvae develop into adults of one of two distinct feeding morphs ("eurystomatous" and "stenostomatous"). The stenostomatous morph grows rapidly on a diet of bacteria, whereas the eurystomatous morph, which is more complex in form, has higher fitness than the stenostomatous morph when fed nematode prey (Serobyan et al., 2014).

    Nematode prey killed by the eurystomatous morph undergo bacterial decomposition which also provides recources for the nematode.

    Ecophysiological Parameters:

    For Ecophysiological Parameters for this species, click If species level data are not available, click for genus level parameters

     

    Generation time is 4 days.

    Dauerlarva formation occurs under conditions of high nematode density and low food availability, similar to C. elegans.

    Oriental beetle (Japan) is the main host for P. pacificus.  The dauerlarva invades the insect, waits for insect death and then feeds on decomposing microbes — a necromeny association.  Each nematode species is able to detect its corresponding beetle by olfactory signals and the nematodes are attracted to the sex pheromones of the beetles.

    Pristionchus. pacificus is androdioecious; there are both self-fertile hermaphrodites (XX) and occasional males (XO) that fertilize hermaphrodites. Males are usually less than 1% of the population; however, this fraction varies among P. pacificus isolates and environmental conditions The androdioecious system is valuable for genetic studies as selfing by hermaphrodites leads to genetically identical offspring, while the presence of males allows for crosses between distinct genotypes (Schroeder, 20210..

     
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    Ecosystem Functions and Services:

    Regulation of prey species.

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    Management:

     
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    References:

    Brown, F.D., D'Anna, I. and Sommer, R. 2011. Host-finding behaviour in the nematode Pristionchus pacificus. Proc. R. Soc. B doi:10.1098/rspb.2011.0129.

    Schroeder, N.E. 2021.Introduction to Pristionschus pacificus anatomy. J. Nematology 53:  doi: 10.21307/jofnem-2021-091

    Serobyan, V., Ragsdale, E.J., Sommer, R.J. 2014. Adaptive value of a predatory mouth form in a dimorphic nematode. Proc. R. Soc. B 281: 20141334. http://dx.doi.org/10.1098/rspb.2014.1334

    Sommer, R. 2008. Genetic and transgenic approaches in the nematode model Pristionchus pacificus. Fifth International Congress of Nematology, Brisbane, Australia, July 2008.     

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    Revised by Howard Ferris: November 02, 2026.