Bilateral Neuron Pairs Share Redundant Network Roles Despite Incomplete Connection Symmetry in Caenorhabditis elegans.

Bilateral organization is a prominent feature of the C. elegans nervous system, yet bilateral neuron pairs differ substantially in their individual left-right connections. Whether, and how, such pairs nonetheless come to occupy similar roles in the network is not fully understood. Here we analyze the adult hermaphrodite and male C. elegans connectomes to examine bilateral redundancy using three complementary graph-theoretic measures: connectivity similarity, which captures overlap in shared in- and out-neighbours; motif-fingerprint difference, which captures the difference in local motif participation (with lower differences indicating greater overlap); and path compensation, which quantifies the extent to which paired neurons make overlapping contributions to global communication. Across measures, bilateral pairs showed elevated redundancy relative to other neuron pairs. Null-model comparisons further supported this finding, demonstrating that these patterns cannot arise from preserving symmetry alone: e.g., for connectivity similarity, randomizing the asymmetric edges while holding the symmetric ones reduced bilateral similarity, suggesting that bilateral asymmetry is itself what enables paired neurons to share neighbours and converge on similar network roles. Redundancy was not uniform across the nervous system: in the hermaphrodite it was more pronounced among interneurons than among sensory neurons across all three measures, while in the male this gradient was only significant for path compensation. Together, these results show that bilateral redundancy is a systematic multiscale principle of the C. elegans connectome, one that cannot be explained by bilateral symmetry alone.