Consistent inter-individual differences in daily activity rhythms (i.e., chronotypes) can have ecological consequences in determining access to food resources and avoidance of predators. The most common measure to characterize chronotypes in animals as well as humans is the onset of activity (i.e., early or late chronotypes). However, daily activity rhythms may also differ in the relative amount of activity displayed at particular time periods. Moreover, chronotypes may also be linked to other consistent inter-individual differences in behavior (i.e., personality), such as the propensity to take risks. Here, we used the signal crayfish Pacifastacus leniusculus to test the presence of chronotypes and risk-taking personality traits and a potential behavioral syndrome between these traits. We first exposed crayfish to 5 days of light–darkness to measure daily activity rhythms and then we applied a visual predator-simulating stimulus in 2 different contexts (neutral and food). Our results showed consistent (i.e., across 5 days) inter-individual differences in the relative nocturnal activity displayed in the early and middle, but not in the late part of darkness hours. Moreover, while crayfish displayed inter-individual differences in risk-taking behavior, these were not found to be consistent across 2 contexts. Therefore, we were not able to formally test a behavioral syndrome between these 2 traits. In conclusion, our study provides the first evidence of chronotypes in the relative amount of activity displayed at particular time periods. This could be a valuable information for applied ecological aspects related to the signal crayfish, which is a major invasive species of freshwater ecosystems.

中文翻译：

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信号小龙虾的日常活动节奏、时间表和冒险行为

日常活动节律（即时间类型）的一致的个体间差异可能在决定获取食物资源和避免捕食者方面产生生态后果。表征动物和人类表型的最常见测量是活动的开始（即早期或晚期表型）。然而，日常活动节奏也可能在特定时间段显示的相对活动量方面有所不同。此外，时间型也可能与其他一致的个体间行为（即个性）差异有关，例如冒险倾向。在这里，我们使用信号小龙虾 Pacifastacus leniusculus 来测试时间型和冒险人格特征的存在以及这些特征之间的潜在行为综合征。我们首先将小龙虾暴露在 5 天的明暗环境中以测量日常活动节律，然后我们在 2 种不同的环境（中性和食物）中应用视觉捕食者模拟刺激。我们的结果表明，在早期和中期显示的相对夜间活动的个体间差异是一致的（即，跨越 5 天），但在黑暗时间的后期却没有。此外，虽然小龙虾在冒险行为方面表现出个体间差异，但在两种情况下并未发现这些差异。因此，我们无法正式测试这两个特征之间的行为综合征。总之，我们的研究提供了在特定时间段显示的相对活动量中表型的第一个证据。