Genome editing reveals no potential role of the circadian clock gene period in the circatidal rhythm of the mangrove cricket

The mangrove cricket, Apteronemobius asahinai, inhabits the mangrove floor, and adults collected from the field clearly exhibit both circatidal and circadian rhythms in their locomotor activity. Previous studies revealed that RNAi of the circadian clock genes, period (per) and Clock (Clk), that form the circadian clock disrupted the circadian rhythm, but not the circatidal rhythm, leading to the conclusion that the circatidal rhythm in this species is not controlled by circadian clock components. However, it remains possible that a small amount of mRNA of per or Clk is sufficient to maintain the expression of the circatidal rhythm. Here, we produced per-knockout mutant mangrove crickets using the CRISPR/Cas9 system and measured their locomotor activity rhythms. Singular spectrum analysis and a correlation analysis method revealed that the circatidal rhythm was observed in a per-mutant cricket. This finding suggests that per is not required for the expression of the circatidal rhythm in mangrove crickets.