Evolution of Neural Circuits: A Comparative Study of the Visual System across Diptera Species

The central nervous system is generally conserved across insects, yet the underlying mechanisms driving distinct behaviors remain unknown. The evolution of brain wiring and its relation to diversity across species represent a fundamental question in neurobiology. In this study, we investigate the evolution of the visual systems across three Diptera species, focusing on neuronal cell types that are conserved throughout evolution. We hypothesize that variations in molecular profiles of homologous neurons can affect the wiring of circuits and thus lead to distinct behaviors. Employing single-cell RNA sequencing (ScRNA-seq), we generated transcriptional atlases of the visual systems for two mosquito species, Aedes aegypti and Anopheles gambiae. We compared these data with the existing atlas of Drosophila melanogaster and identified conserved cell types in motion detection and other circuits. Comparison across species revealed conserved and divergent features of homologous cell types. For example, we found that Mi1 (medulla intrinsic) neurons were twice as abundant in both mosquito species as in fruit flies. To validate our findings based on transcriptome analysis, we have tested the feasibility of several protocols for in vivo labeling of specific cell types in mosquito species. Our results show that although immunohistochemistry, hybridization chain reaction FISH, and transgenic strains can be used across different species, the existing protocols and reagents require further optimization.