Comparative analysis of hermaphrodite and male caenorhabditis elegans connectomes based on complex network theory

Abstract

C. elegans are nematodes that exist in two sexes: hermaphrodite and male. Although these two sexes share a lot of structurally similar neurons, their nervous system is strongly sexualized and functionality differs at multiple levels. For decades, hermaphrodite c. elegans has been the only organism with a complete cellular level connectome. Recently, a complete neural wiring has been constructed for male c. elegans as well. Network analysis of an organism’s neural wiring reveals the role of connection topology in the nervous system’s structure and function. In this work, we analyzed connectomes of the two sexes of c. elegans using graph theoretical tools and community detection methods to understand network level differences in their nervous system. Both networks are small-world and display heavy tailed degree distributions. However, the hermaphrodite neurons tend to have more diverse connections than male, whereas the male neurons form stronger connections with each other. In addition, the hermaphrodite connectome is disassortative while the male connectome shows positive assortativity. Clustering coefficient analysis reveals that the hermaphrodite connectome shows hierarchical organization while the male connectome does not. Both connectomes show rich club organization, however neurons that form the rich clubs are not the same for the two sexes. Both connectomes show modular structure with sex-specific neurons interacting with sex-shared neurons in separate communities. We also tested and found sex-shared, but quantitatively dimorphic neurons using various nodal features.