Sommer, Ralf, Riebesell, Metta, Carstensen, Heather, Bumbarger, Dan, Sarpolaki, Tahmineh, Hobert, Oliver, Moreno, Eduardo, Siebriebriennikov, Bogdan, Castrejon, Jessica, Hong, Ray, Cook, Steven, Cochella, Luisa
[
International Worm Meeting,
2019]
The ability of an organism to process sensory information is dependent upon the structure and connectivity of its neurons. The nematodes P. pacificus and C. elegans have a repertoire of different behaviors and sensory preferences, yet the neural substrate for these differences is unknown. To understand structural differences of the pharyngeal nervous system related to predatory feeding behavior, serial section EM series were generated of P. pacificus. Through a volumetric reconstruction and subsequent analysis, it was shown that an identical set of pharyngeal neurons with similar morphology generated many different synaptic patterns (Bumbarger et al 2013). Toward the goal of better understanding differences in olfactory behavior between P. pacificus and C. elegans we further analyzed these EMs and identified homologous amphid sensory and interneurons between P. pacificus and C. elegans based upon cell body position, dendritic morphology, dye staining, and reporter gene expression (see abstract by R.L. Hong et al). We determined the set of chemical and gap junction connections for the amphid circuit and compared the resultant network to C. elegans. We observed that neurons with the most similar morphology (AFD and AUA) have the most similar connectivity across species, while neurons with different dendritic structure (AWA, AWB, AWC) show a greater number of species-specific connections. Overall, we found that 60% of strong chemical connections and 40% of gap junctions are conserved across species. We next asked whether differences in connectivity are due to changes in neuronal neighborhoods, or synaptic partner choice. We found that in each instance of a discrepant synapse, the pair of neurons in questions are adjacent in both species. We are actively extending our analysis to determine whether sensory neurons are more divergent in their structure and connectivity compared to downstream inter- and motorneurons. Our results suggest evolutionary pressure has kept the overall nervous system plan of nematodes very similar, but has allowed for different synaptic configurations to permit species-specific behavioral differences.