Variation in Social Feeding Behaviors and Interactions Among Caenorhabditis Nematodes.

The ability to respond to stimuli and environmental cues is essential for higher order organisms to survive and reproduce and 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 12 members of the Caenorhabditis clade, including members of both the elegans and japonica a subgroups, and the basal taxon C. monodelphis. For each species, we analyzed social feeding and food 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 with 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 the evolutionary relatedness of the species. The addition of male animals with female or hermaphrodite animals of the same species increased the aggregation behavior of a subset of species, but not other species. The combination of a second species with C. elegans significantly reduced the aggregate feeding behavior of C. elegans, but not the other species, suggesting intraspecies and interspecies interactions modify behaviors. 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 contextual sensory cues. The Caenorhabditis clade represents a compelling model to dissect the evolution of behavior across diverse environments and a large timescale.