TESTING BMAL FUNCTION IN CIRCADIAN AND CIRCALUNAR CLOCKS OF <EM>PLATYNEREIS DUMERILII</EM>

Biological clocks are genetically encoded, endogenous oscillators that confer adaptive advantages by synchronizing physiology and behavior with predictable environmental cycles. Increasing evidence suggests that multiple biological clocks can coexist and interact within a single organism. The marine annelid Platynereis dumerilii represents an optimalmodel to study such interactions, as it possesses two endogenous timing systems coordinating reproduction at the population level. A circalunar clock (~29.5 days) aligns reproductive maturation with specific lunar days, while a circadian clock restricts spawning to the darkest phase of the night. It remains unknown whether these oscillators share molecular components. In crustaceans, the circadian core clock component BMAL is required for circatidal timekeeping, suggesting it as a shared element across distinct biological oscillators in this species. To test whether BMAL geneticallylinks circadian and circalunar clocks in Platynereis dumerilii, we generated bmal mutants.Immunohistochemistry revealed predominant localization of BMAL in the posterior oval-shaped domain in the brain of wild-type animals, along with circadian oscillations in signal intensity consistent with transcript localization and dynamics. In bmal mutants, BMAL protein levels and dynamics were severely altered. Locomotor behaviors are currently being analysed. Spawning behavior and maturation across consecutive lunar months showed comparable circalunar rhythmicity in wild-type and bmal -/-animals, indicating that BMAL is dispensable for circalunar timekeeping.