Table 2.
Comparison of sensory response networks in free-living nematodes
| Stimulus | Contributing cells | Species | ||
| Caenorhabditis elegans | Caenorhabditis sp. 3 | Pristionchus pacificus | ||
| Octanol | ASH | +++ | +++ | +++ |
| Nose touch | ASH | ++ | +++ | ++ |
| FLP | + | -- | ND | |
| OLQ | (+) | -- | ND | |
| Osmotic | ASH | +++ | +++ | ++ |
| stress | ADL | -- | -- | + |
Most species respond similarly to the volatile odorant 1-octanol. This response is completely mediated by the ASH neuron. However, nose touch and osmotic avoidance responses evolve: in Caenorhabditis elegans, three neurons mediate nose touch whereas in Caenorhabditis sp. 3, only ASH mediates this response. Avoidance to high osmolarity conditions is primarily mediated by the ASH neuron, but in Pristionchus pacificus, the ADL neuron also contributes to this sensory response. '+' denotes the degree of involvement of the neuron in mediating the behavior; '+++', completely mediates; '++', partially mediates; '+', weakly mediates; '(+)', mediates but only observable when other neurons are ablated; '-', not involved; ND, not tested.