Amplitude of circadian rhythms becomes weaken in the north, but there is no cline in the period of rhythm in a beetle

Many species show rhythmicity in activity, from the timing of flowering plants to that foraging behavior animals. The free-running periods and amplitude (sometimes called strength or power) circadian rhythms are often used as indicators biological clocks. reports have shown these traits highly geographically variable, interestingly, they latitudinal longitudinal clines. In many cases, higher latitude is, longer period (i.e., rhythm) insects plants. However, positive correlations between longitude rhythm traits, including periods, power locomotor limited certain taxonomic groups. Therefore, we collected a cosmopolitan stored-product pest species, red flour beetle Tribolium castaneum , various parts Japan examined its rhythm, which were calculated activity. analysis revealed was significantly lower for beetles northern areas than southern Japan. it is worth noting did not any clines; specifically, vary among sampling sites, despite very large sample size (n = 1585). We discuss why cline trends observed T .