''Pristionchus pacificus'' is a species of free-living

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

s (roundworms) in the family

Diplogastridae Diplogastridae, formerly Diplogasteridae, are a family of nematodes (roundworms) known from a wide range of habitats, often in commensal or parasitic associations with insects. Description Diplogastrid nematodes are characterized by a distinct ...

. The species has been established as a satellite

model organism A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Mo ...

to ''

Caenorhabditis elegans ''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a Hybrid word, blend of the Greek ''caeno-'' (recent), ''r ...

'', with which it shared a common ancestor 200–300 million years ago. The

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

of ''P. pacificus'' has been fully sequenced, which in combination with other tools for genetic analysis make this species a tractable model in the laboratory, especially for studies of

developmental biology Developmental biology is the study of the process by which animals and plants grow and develop. Developmental biology also encompasses the biology of Regeneration (biology), regeneration, asexual reproduction, metamorphosis, and the growth and di ...

Mouth dimorphism

Like other species of '' Pristionchus'' and many other free-living nematodes, ''P. pacificus'' exhibits a

polyphenism A polyphenic trait is a trait for which multiple, discrete phenotypes can arise from a single genotype as a result of differing environmental conditions. It is therefore a special case of phenotypic plasticity. There are several types of polyphen ...

in its mouthparts that allows individual nematodes to specialize on different food sources, which has made the species a case study in

phenotypic plasticity Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompa ...

. The polyphenism has two forms (morphs). The most common type, at least in

wild-type The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, " ...

lab strains, is the "eurystomatous" morph, which can feed on both bacteria and other nematode species. The "stenostomatous" morph, on the other hand, is specialised for feeding on bacteria exclusively. Differentiation into one or the other morph depends on a combination of environmental conditions and

stochasticity Stochastic (; ) is the property of being well-described by a random probability distribution. ''Stochasticity'' and ''randomness'' are technically distinct concepts: the former refers to a modeling approach, while the latter describes phenomena; in ...

. The main morphological differences can be seen in the mouthparts. The eurystomatous morph has a secondary tooth and a wider buccal cavity. The secondary tooth allows the eurystomatous morph to feed on other nematode worms. The two feeding morphs, which allow the nematodes to respond quickly to changing environments, are specified by a hormonal and genetic cascade during

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

l development.

Self-recognition

As a predatory species that feeds on related species, it is likely that there is a

selective pressure Evolutionary pressure, selective pressure or selection pressure is exerted by factors that reduce or increase reproductive success in a portion of a population, driving natural selection. It is a quantitative description of the amount of change oc ...

for

self-recognition In philosophy, self-awareness is the awareness and reflection of one's own personality or individuality, including traits, feelings, and behaviors. It is not to be confused with consciousness in the sense of qualia. While consciousness is be ...

, i.e. recognition of conspecifics. ''P. pacificus'' does not feed on conspecifics and therefore must be capable of distinguishing them from other nematode species. Self-recognition is not

cilia The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...

-dependent, unlike prey recognition.

Genomics

The ''Pristionchus pacificus'' genome was sequenced in 2005 and 2006. The analysis of ''P. pacificus'' has provided ecological information about this organism. It was determined that the genome of ''P. pacificus'' is larger than that of the widely studied nematode ''C. elegans'', and was predicted that the genome of ''P. pacificus'' contains more than 26,000 protein-coding genes.

Ecology

It has been indicated that ''Pristionchus'' nematodes live in a necromenic association with

scarab beetle The family Scarabaeidae, as currently defined, consists of over 35,000 species of beetles worldwide; they are often called scarabs or scarab beetles. The classification of this family has undergone significant change. Several groups formerly tre ...

s. "After the beetle dies, the nematode continues to develop and feed on microbes growing inside the dead beetle. The collection of bacteria, fungi and the nematodes work hand in hand to decompose the beetle carcass". Thus, ''Pristionchus'' is an

omnivore An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize t ...

that can utilize bacteria, protozoa and fungi as food sources, all of which grow on the carcasses of scarab beetles.

References

External links

* {{Authority control Rhabditida Nematodes described in 1996 Animal models