Data from: Number sense and state-dependent valuation in cuttlefish

Identifying the amount of prey available is an important part of an animal's foraging behaviour. The risk-sensitive foraging theory predicts that an organism's foraging decisions with regard to food rewards depending upon its satiation level. However, the precise interaction between optimal risk-tolerance and satiation level remains unclear. In this study, we examined, firstly, whether cuttlefish, with one of the most highly evolved nervous system among the invertebrates, have number sense, and secondly, whether their valuation of food reward is satiation state dependent. When food such as live shrimps is present, without training, cuttlefish turn toward the prey and initiate seizure behaviour. Using this visual attack behaviour as a measure, cuttlefish showed a preference for a larger quantity when faced with two-alternative forced choice tasks (1 versus 2, 2 versus 3, 3 versus 4 and 4 versus 5). However, cuttlefish preferred the small quantity when the choice was between one live and two dead shrimps. More importantly, when the choice was between one large live shrimp and two small live shrimps (a prey size and quantity trade-off), the cuttlefish chose the large single shrimp when they felt hunger, but chose the two smaller prey when they were satiated. These results demonstrate that cuttlefish are capable of number discrimination and that their choice of prey number depends on the quality of the prey and on their appetite state. The findings also suggest that cuttlefish integrate both internal and external information when making a foraging decision and that the cost of obtaining food is inversely correlated with their satiation level, a phenomenon similar to the observation that metabolic state alters economic decision making under risk among humans.评估可获取猎物的数量，是动物觅食行为的核心组成环节之一。风险敏感觅食理论（risk-sensitive foraging theory）预测，生物体针对食物奖励的觅食决策由其自身饱足状态决定。然而，最优风险耐受性与饱足状态之间的确切互作机制仍未阐明。本研究首先探究了：作为无脊椎动物中神经系统演化程度最高的类群之一的乌贼（cuttlefish）是否具备数量认知能力；其次探究了其对食物奖励的价值评估是否依赖于饱足状态。当存在活虾等活体猎物时，未经任何训练的乌贼会自动转向猎物并启动攫取捕食动作。以该视觉攻击行为作为行为学评估指标，乌贼在二择一强制选择任务（two-alternative forced choice tasks）中，面对1对2、2对3、3对4及4对5的数量对比时，均表现出对更大数量猎物的偏好。但当选择为1只活体虾与2只死虾时，乌贼则更倾向于选择数量更少的选项。更为关键的是，当处于猎物大小与数量的权衡情境中时（即选择1只大型活体虾与2只小型活体虾），乌贼会在饥饿状态下选择单只大型猎物，而在饱足状态下选择两只小型猎物。上述实验结果表明，乌贼具备数量辨别能力，且其对猎物数量的选择同时依赖于猎物品质与自身食欲状态。本研究还发现，乌贼在做出觅食决策时会整合内部生理状态与外部环境信息，且获取食物的成本与其饱足状态呈负相关——这一现象与人类中代谢状态改变风险下经济决策的相关研究结果高度相似。