Abstract While many intertidal animals exhibit circatidal rhythms, the nature of the underlying endogenous clocks that control these rhythms has been controversial. In this study American horseshoe crabs, Limulus polyphemus, were used to test the circalunidian hypothesis by exposing them to four different tidal regimes. Overall, the results obtained support the circalunidian hypothesis: each of the twice-daily rhythms of activity appears to be controlled by a separate clock, each with an endogenous period of approximately 24.8 h. First, spontaneous “skipping” of one of the daily bouts was observed under several different conditions. Second, the presence of two bouts of activity/day, with different periods, was observed. Lastly, we were able to separately synchronize bouts of activity to two artificial tidal regimes with different periods. These results, taken together, argue in favor of two separate circalunidian clocks in Limulus, each of which controls one of the two bouts of their daily tidal activity rhythms.

中文翻译：

---

昼夜节律控制美洲鲎（鲎）运动的潮汐节律

摘要 虽然许多潮间带动物表现出昼夜节律，但控制这些节律的潜在内源生物钟的性质一直存在争议。在这项研究中，美国鲎（Limulus polyphemus）被用来测试昼夜节假说，将它们暴露在四种不同的潮汐状态中。总体而言，获得的结果支持昼夜节律假说：每个每日两次的活动节律似乎都由一个单独的时钟控制，每个时钟的内源周期约为 24.8 小时。首先，在几种不同的条件下观察到自发“跳过”每日的一场比赛。其次，观察到每天存在两次不同时期的活动。最后，我们能够分别将不同周期的活动同步到两个人工潮汐状态。综合起来，这些结果支持鲎体内存在两个独立的生物钟，每个生物钟控制着每日潮汐活动节律的两次发作中的一次。