Abe Hideaki, Nagao Kenji, Nakamura Akihiro, Inoue-Murayama Miho
Wildlife Research Center, Kyoto University, Sakyo, Kyoto 606-8203, Japan.
Behav Processes. 2013 Oct;99:95-9. doi: 10.1016/j.beproc.2013.07.004. Epub 2013 Jul 13.
Freezing responses to fearful stimuli are crucial for survival among all animal species within a prey-predator system. Generally, the degree of fearfulness correlates with intensity, duration, and frequency of freezing behaviours in response to fear-relevant stimuli. The present study examines innate fear responses to human handling in 144 newly hatched chicks through a tonic immobility (TI) test. Two fear responses-freezing duration and number of TI inductions-were examined. Individual variations in innate fear were investigated in chicks 1-2 days post-hatching when the restraint procedure was successively repeated 3 times within each day. Chicks showed sensitivity to fearful stimuli and considerable inter-individual variation in freezing duration and number of attempts required to induce TI. Moreover, differences were observed between breeds; White Leghorn chicks showed relatively low fear levels with gradual increases in TI duration, whereas Nagoya chicks showed extended TI duration and habituation to fearful stimuli. Our results suggest that TI reactions among newly hatched chicks are an innately determined behaviour specific to a breed or strain of chicken. Further, fearful responses among newborn chicks are not simple, but complex behaviours that involve multiple factors, such as breed-specific contextual fear learning and habituation/sensitisation processes.
在捕食者 - 猎物系统中，对恐惧刺激的冻结反应对所有动物物种的生存至关重要。一般来说，恐惧程度与对恐惧相关刺激做出反应时冻结行为的强度、持续时间和频率相关。本研究通过强直性静止（TI）试验，检测了144只新孵化雏鸡对人类操作的先天恐惧反应。研究了两种恐惧反应——冻结持续时间和TI诱导次数。在孵化后1 - 2天的雏鸡中，当每天依次重复3次约束程序时，研究了先天恐惧的个体差异。雏鸡对恐惧刺激表现出敏感性，在冻结持续时间和诱导TI所需的尝试次数上存在相当大的个体间差异。此外，不同品种之间也观察到差异；白来航雏鸡表现出相对较低的恐惧水平，TI持续时间逐渐增加，而名古屋雏鸡表现出较长的TI持续时间和对恐惧刺激的习惯化。我们的结果表明，新孵化雏鸡的TI反应是一种由品种或品系决定的先天行为。此外，新生雏鸡的恐惧反应不是简单的行为，而是涉及多种因素的复杂行为，如特定品种的情境恐惧学习和习惯化/敏感化过程。
