# Evolution of sensory systems underlies the emergence of predatory feeding behaviors in nematodes

## TL;DR

This paper shows how the nematode Pristionchus pacificus evolved to use both touch and chemical senses to hunt prey, revealing how new behaviors can emerge through changes in sensory systems and neural circuits.

## Contribution

The study identifies a mechanosensory module linked to predatory behavior in P. pacificus, revealing a novel circuit-level mechanism for behavioral evolution.

## Key findings

- P. pacificus uses mechanosensory and chemosensory systems together to detect prey.
- Ppa-mec-6 is a key mechanosensory gene expressed in IL2 neurons crucial for predation.
- Disrupting mechanosensation and chemosensation together has a synergistic effect on prey detection.

## Abstract

Understanding how new behaviors evolve is a major challenge in biology. In this study, we show the nematode Pristionchus pacificus has evolved to use both mechanical and chemical sensory modalities to detect and attack prey. By screening sensory genes and analyzing behavior with machine learning, we identified a mechanosensory module associated with the evolution of predation. Furthermore, these pathways are integrated within a specific set of neurons required for prey detection, revealing a circuit-level mechanism for predatory behavior that is distinct from the function of homologous neurons in Caenorhabditis elegans. These findings reveal how evolution can modify sensory modalities and reconfigure neural pathways to generate new behaviors, shedding light on the mechanisms that drive behavioral innovation.

Understanding how animal behavior evolves remains a major challenge, with few studies linking genetic changes to differences in neural function and behavior across species. Here, we identify specific sensory adaptations associated with the emergence of predatory feeding behaviors in the nematode Pristionchus pacificus. While Caenorhabditis elegans uses contact-dependent sensing primarily to avoid threats, P. pacificus has co-opted this modality to support both avoidance and prey detection, enabling context-dependent predatory behavior. To uncover a potential mechanism underlying the evolution of P. pacificus prey perception, we mutated 27 canonical mechanosensory genes and assessed their function using behavioral assays, automated behavioral tracking, and a machine learning analysis of behavioral states. While several mutants showed mechanosensory defects, Ppa-mec-6 mutants specifically also impaired prey detection, indicating the emergence of a mechanosensory module linked to predatory behavior. Furthermore, disrupting both mechanosensation alongside chemosensation revealed a synergistic influence for these modalities. Crucially, Ppa-mec-6 is expressed in the environmentally exposed IL2 neurons that represent the first point of predator–prey contact. Moreover, silencing Ppa-mec-6 expressing cells induced severe predation defects validating their importance for prey sensing. Thus, predation evolved through the co-option of mechanosensory and chemosensory systems that act together to shape the evolution of complex behavioral traits.