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，是动物觅食行为中的关键环节。风险敏感觅食理论（risk-sensitive foraging theory）指出，生物体针对食物奖励的觅食决策，取决于自身的饱足水平。然而，最优风险耐受度与饱足水平之间的精确相互作用机制仍未明确。
本研究首先探讨了乌贼作为无脊椎动物中神经系统高度演化的类群之一，是否具备数量感知能力（number sense），其次探究其食物奖励的价值评估是否依赖于饱足状态。当存在活虾类食物时，未经训练的乌贼会自动转向猎物并启动捕食行为。以该视觉攻击行为作为评估指标，在二选一强制选择任务（two-alternative forced choice tasks，1对2、2对3、3对4及4对5）中，乌贼表现出对更大数量猎物的偏好。但当选择为1只活虾与2只死虾时，乌贼则更倾向于选择数量更少的选项。更关键的是，当选择为1只大型活虾与2只小型活虾（存在猎物体型与数量的权衡）时，处于饥饿状态的乌贼会选择单只大型猎物，而饱足状态的乌贼则会选择两只小型猎物。
上述结果表明，乌贼具备数量辨别能力，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。本研究结果还显示，乌贼在做出觅食决策时会整合内部与外部信息，且获取食物的代价与自身饱足水平呈负相关——这一现象与人类在风险情境下代谢状态会改变经济决策的观测结果类似。