To intake proper food, animals have developed various feeding strategies. Pristionchus pacificus is a satellite model nematode for comparative studies with Caenorhabditis elegans. P. pacificus exhibits two types of feeding behavior: bacterial feeding and predatory feeding toward other nematodes. While bacterial feeding is observed in most species of nematodes in the same taxonomical clade, predatory feeding is only seen in the family Diplogastridae. Thus, predatory feeding is considered to be an evolutionally novel behavior. Previous studies revealed that the neuromodulator serotonin is a key factor to modulate predatory feeding behavior in P. pacificus. To elucidate downstream mechanisms regulating predation, we focused on serotonin receptor orthologs that have been functionally characterized in C. elegans. Using the CRISPR/Cas9 system, we produced flame-shift mutants of five serotonin receptors in P. pacificus. We examined predatory feeding behavior in those mutants and found that
Ppa-ser-5 mutant and
Ppa-ser-1;
Ppa-ser-7 double mutant decreased predation toward C. elegans larvae. During predation, the
Ppa-ser-1;
Ppa-ser-7 mutant decreased tooth movements that are assumed to be important for predation.
Ppa-ser-1 was expressed in the anterior pharyngeal muscles including the dorsal tooth muscle and
Ppa-ser-7 was expressed in pharyngeal neurons including the M1 neuron, which is innervating onto the dorsal tooth muscles. Interestingly, the expression patterns of those serotonin receptors are partially different between C. elegans and P. pacificus, implying that changes in the expression patterns may be associated with evolution of the predatory feeding behavior in P. pacificus. To find novel genetic factors that are critical for predatory feeding behavior, we performed a forward genetic screening. Among 5150 strains, we found five mutants that are almost completely unable to kill the prey worms. We are now searching for the responsible genes and examining a new genetic mechanism and evolution of predation using those mutants.