Variation in social feeding behavior and interactions among Caenorhabditis nematodes

The ability to respond to complex stimuli and environmental cues is essential for organisms to survive and reproduce. Responding to a wide range of stimuli requires a neuronal network that can integrate cues and execute behavioral responses. Evolution of behaviors occurs ubiquitously in most established ecological niches, even among closely related species. To uncover the genetic and neuronal drivers of evolving behaviors, we have taken advantage of the large and relatively ancient divergence in the Caenorhabditis genus to ask how different Caenorhabditis nematodes respond to environmental stimuli and whether behavioral traits are shared or distinct. Here, we assayed foraging behaviors of twelve members of the Caenorhabditis clade, including members of both the elegans and japonica supergroup, and the basal taxon C. monodelphis. For each species, we analyzed social feeding and bordering behaviors, which are well characterized in C. elegans. These behaviors are the functional readout of complex sensory integration of multiple sensory cues including pheromones, touch, O₂/CO₂ concentration, and attractive and noxious stimuli. We hypothesized that the evolutionary divergence between species would correlate to divergence in these behaviors. We observed a wide variation in social aggregate feeding and bordering behaviors of hermaphrodite and female animals, but the variation did not correlate with evolutionary relatedness of the species. Addition of male animals with female or hermaphrodite animals of the same species increased aggregation behavior of subset of species, but not others. Combination of a second species with C. elegans significantly reduced aggregate feeding behavior of C. elegans, but not the other species. Intraspecies and interspecies interactions therefore modifies behavioral paradigms. Overall, we find that foraging and social feeding behaviors vary widely across Caenorhabditis species, likely due to species-specific responses and integration of environmental and context sensory cues. In general, the clade represents a compelling model to dissect evolution of behavior across diverse environments and a large timescale.