Evolution and Development of Phototaxis: A Comparative Study of ipRGC Function in Fish

• Applicant: Dr. Cesar Bertinetti Cerrato, Ph.D.
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Sensory and Behavioural Biology ; Evolutionary Cell and Developmental Biology (Zoology)
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 584459308

Light strongly influences animal behavior. One common light-driven behavior is phototaxis, the tendency to move toward or away from light. Phototaxis plays an important role in navigation, foraging, and predator avoidance, yet the biological mechanisms that control it remain poorly understood. In particular, it is unclear how changes in gene expression and neural circuits during development can rapidly alter light preference. This project investigates the cellular and molecular mechanisms underlying developmental changes in phototaxis using two fish species with strikingly different behaviors. Zebrafish larvae are initially attracted to light but later become light-avoiding, whereas the shell-dwelling cichlid, Lamprologus ocellatus, shows the opposite pattern, shifting from light avoidance to light preference during early development. These opposing trajectories provide a powerful comparative system to identify conserved and flexible mechanisms that shape behavior. This project focuses on a specialized group of retinal neurons called intrinsically photosensitive retinal ganglion cells (ipRGCs). Unlike most visual neurons, ipRGCs detect light directly and connect light input to brain circuits that control behavior. Although ipRGCs are known to be essential for phototaxis in zebrafish, it is not known how different ipRGC subtypes contribute to light-seeking versus light-avoiding behavior, or how their molecular properties change during development. The first part of the project will identify distinct ipRGC subtypes in zebrafish and track how their gene expression and neurotransmitter usage change across developmental stages. The second part will test the causal role of these cells by selectively manipulating specific ipRGC subtypes and measuring their effects on phototactic behavior and neural circuits. The third and fourth parts will extend this framework to ocellatus, examining whether similar genes and cell types are involved in its opposite phototactic switch and testing their functional relevance. By combining developmental, genetic, behavioral, and comparative approaches, this project aims to explain how changes at the level of individual cell types can lead to rapid and reversible behavioral transitions. The results will advance our understanding of how sensory systems generate flexible behavior during development and how conserved neural cell types can support divergent behavioral outcomes across species.

• DFG Programme: Position