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Abstract

Pristionchus pacificus and its relatives are omnivores and are capable of consuming both bacteria and also predating other nematodes including the larvae of Caernorhabditis elegans. To this end Pristionchus species show specific predatory adaptations in the form of teeth-like denticles for lacerating open the cuticle of their prey. Accompanying these teeth structures, the variation in diet induces distinct feeding modes with predation characterised by slowed pharyngeal pumping rates and stimulation of tooth activity, while during bacterial feeding, pumping rates are higher and the tooth remains static. The switch between these distinct feeding modes is rapid, highly dynamic, and dependent on their immediate diet however little is known of the neurological bases regulating the feeding mode switch. Therefore, to elucidate the neurobiological basis underlying the regulation of the predatory feeding behaviour, we conducted pharmacological experiments analysing the effects of several neurotransmitters on pharyngeal pumping and tooth movement rate. Only the addition of serotonin recapitulated the feeding kinetics observed during predatory feeding indicating a previously uncharacterised role for this neurotransmitter. Immunostaining against serotonin revealed an additional serotonergic neuronal pair in the pharynx of P. pacificus compared to C. elegans. These likely correspond to P. pacificus NSM and the interneurons I1. We have subsequently identified the P. pacificus homologues of the serotonin synthesis enzyme (ppa-tph-1) and serotonin transporter (ppa-mod-5) for targeting by CRISPR/Cas9 in order to further investigate the neuronal networks regulating the behavioural switch and for understanding the evolution of these complex behaviours.