Kin-recognition shapes collective behaviors in the cannibalistic nematodePristionchus pacificus

Abstract

Kin-recognition is observed across diverse species forming an important behavioral adaptation influencing organismal interactions. In most species, proximate level mechanisms are poorly characterized, but in the nematode Pristionchus pacificus molecular components regulating its kin-recognition system have been identified which determine its predatory behaviors. This ability prevents the killing of kin however, its impact on other interactions including collective behaviors is unknown. Utilizing pairwise aggregation assays between distinct strains of P. pacificus, we observed aggregation between kin but not distantly related con-specifics. In these assays, only one strain aggregates with solitary behavior induced in the rival. Abolishing predation through Ppa-nhr-40 mutations results in rival strains successfully aggregating together. Additionally, interactions between P. pacificus populations and Caenorhabditis elegans are dominated by P. pacificus which also disrupts C. elegans aggregation dynamics. Thus, aggregating strains of P. pacificus preferentially group with kin, revealing competition and nepotism as previously unknown components influencing collective behaviors in nematodes.

Genetic regulators of a resource polyphenism interact to couple predatory morphology and behaviour

“…Differences between nhr-1 and nhr-40 in their interactions with mdt-15.1 are consistent with their only partially overlapping expression levels in the Pristionchus pharynx [44], which possibly mediate different parts of morphological and behavioural polyphenism. Furthermore, because nhr-40 not only influences predation but also the willingness to aggregate through reduced aggression [33], defects in mdt-15.1 may also interfere with behaviours more complex than biting alone. Given these three polyphenism regulators’ overlapping but distinct effects on gene transcription and co-expression networks [29,45], transcriptomic comparisons including the two double-mutants can, in principle, pinpoint the observed epistasis in terms of downstream gene expression.…”

“…In the case of resource polyphenism, alternative morphs are induced by different environments and are characterized by traits that enable differential niche and resource use, highlighting the necessity to integrate behavioural traits for recognizing and acquiring different resources, morphological traits to handle different resources, and physiological traits to digest and process different resources [30]. Although the genetic basis of resource polyphenisms has generally been studied in terms of their morphology [31,32], attention to behaviour or physiology in the same polyphenisms can reveal how the response functions as a coordinated organismal phenotype [33,34]. Thus, the challenge remains to understand how different components of a resource polyphenism interact in a developmental genetic context.…”

“…In addition to their effects on morphology, polyphenism regulators also influence metabolic processes, including fat storage [29,45]. Furthermore, NHR-1 was shown to influence both predation ability and social aggregation [33], supporting the integration of morphology with behaviour. Thus, an examination of behavioural effects of mutations in polyphenism control genes, both singly and in epistasis, can test what parts of the polyphenism network regulate predatory activity and ability.…”

Surface lipids in nematodes are developmentally dependent and species-specific

“…5a) (16,(40)(41)(42)(43) as well as other P. pacificus con-specifics, resulting in highly cannibalistic interactions. However, a kin-recognition system prevents them from killing their direct progeny as well as their close relatives (44)(45)(46). Crucially, there appears to be little influence from any volatile secreted molecules on this behaviour, which is instead determined by nose contact of the predator with the cuticle surface of a potential prey (47).…”

Predatory aggression evolved through adaptations to noradrenergic circuits

“…Specifically, compared to Caenorhabditis elegans, the predatory nematode Pristionchus pacificus has evolved striking behavioral differences. This includes diversification in odorant sensitivity (8), social preference (9,10), and aggressive behaviors used to establish territory and remove competitors from their environment through intraguild predation and cannibalism (11)(12)(13)(14). Consequently, we have leveraged the behavioral diversity between these nematode species to investigate the evolutionary adaptations molding the P. pacificus aggressive traits.…”