Phylogeny of rhabditid nematode species used in our comparative analysis. (A) Neuronal connectivity of the polymodal ASH sensory neuron modified from [27, 41]. Red arrows indicate environmental stimuli perceived by the ASH neuron. The FLP and OLQ neurons play a minor role in mediating mechanosensory responses in Caenorhabditis elegans. Black lines indicate synaptic connections to the command interneurons that generate a backward movement in response to the stimulus. (B) Portion of the rhabditid phylogenetic tree adapted from Kiontke and Fitch  with species shown in red used in our analysis. Strain numbers are indicated in parentheses. The genus Caenorhabditis consists of different Caenorhabditis species including Caenorhabditis elegans and Caenorhabditis briggsae and the less closely related species Caenorhabditis sp. 3. Caenorhabditis tripartitum belongs to a different branch than the genus Caenorhabditis within the rhabditids. Pristionchus pacificus belongs to the diplogastrids and Panagrellus redivivus represents an outgroup to the entire group of rhabditids.