Self-recognition described as the capacity to discriminate between identical and foreign tissue is observed abundantly throughout nature and is exploited for a plethora of diverse biological functions. These range from the adaptive immune response in jawed vertebrates to neuronal wiring and dendrite self-avoidance in fruit flies to inducing swarming behaviour in bacteria. However, although self-recognition is observed ubiquitously in nature, relatively little is known about the mechanisms behind this phenomenon and surprisingly, despite the pre-eminence of Caernorhabditis elegans as a model organism, evidence of self-recognition has thus far never been described in nematodes. Our recent investigations explored the feeding dynamics in the predatory nematode Pristionchus pacificus and revealed P. pacificus to be voracious killers of C. elegans. We have subsequently, analysed predatory interactions in the context of self-recognition by investigating predation between P. pacificus and its self-progeny. Predation occurs interspecifically between a wide range of closely related nematode species however never on self-progeny, a mechanism that is conserved amongst other Pristionchus species. Furthermore, the ability to determine self from non-self is highly specific with even closely related strains of P. pacificus perceived as prey, while self-progeny are ignored. The identification of self-progeny is dependent on interactions with surface bound molecules, a process which is maintained despite severe starvation and additionally, not disrupted in a host of cuticle morphology mutants. Finally as even closely related P. pacificus strains predate one another while distinguishing and ignoring self-progeny, we have exploited single nucleotide polymorphisms between two strains and generated recombinant inbred lines (RILs) to isolate the genetic component of self-recognition. Each of the RILs was successfully predated by only a single parental lineage facilitating quantitative trait locus (QTL) mapping resulting in the identification of a putative candidate gene and the underlying molecular mechanism. We thus present the first evidence of self-recognition in nematodes, a phenomenon that enables P. pacificus to avoid cannibalism while also promoting the killing of larvae from potential competing nematodes.
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