Sporadic Feeding Regulates Robust Food Entrainable Circadian Clocks in Blind Cavefish

The circadian clock represents a key timing system entrained by various periodic signals that ensure synchronization with the environment. Many investigations have pointed to the existence of two distinct circadian oscillators: one regulated by the light-dark cycle and the other set by feeding time. Blind cavefish have evolved under extreme conditions where they completely lack light exposure and experience food deprivation. Here, we have investigated feeding regulated clocks in two cavefish species, the Somalian cavefish Phreatichthys andruzzii and the Mexican cavefish Astyanax mexicanus, in comparison with the surface-dwelling zebrafish Danio rerio. Our results reveal that feeding represents an extremely strong synchronizer for circadian locomotor rhythmicity in subterranean cavefish. Indeed, we showed that consuming just one meal every 4 days is sufficient to entrain circadian rhythmicity in both cavefish species, but not in zebrafish. These profound adaptations to an extreme environment provide insight into the connections between feeding and circadian clocks.