Terrestrial insects exhibit a state called ‘chill coma’ (CC) at around 0 ºC. In this study, we tested the hypotheses that ‘cool coma’ (COC) occurs at a far higher temperature than chill coma, and that sea skaters collected near the Kuroshio current show a higher resistance to lower temperature than those collected far from the current. The temperature at which COC occurs (cool coma temperature: COCT) was recorded on a low-temperature thermostatic water bath in which the temperature was decreased by 1 ºC every 15 min until COC occurred. After measurement of COCT, the super-cooling point (SCP) was measured. COC occurred at 19.01 ºC for adults collected at 25ºN, 160ºE and at 17.5 ºC for those collected at 24ºN, 138ºE, both of which are far higher than the CCT. The COCT and SCP (-14.8 ºC) values for those collected at 25ºN, 138ºE near the Kuroshio current were lower than the values for animals collected at 24ºN, 160ºE (COCT: p = 0.005; SCP: -14.0 ºC, p = 0.115). These results support both hypotheses.
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