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.

确定可获取的猎物数量是动物觅食行为（foraging behaviour）的重要组成部分。风险敏感性觅食理论（risk-sensitive foraging theory）预测，生物体针对食物奖励的觅食决策取决于其饱足水平（satiation level）。然而，最优风险耐受性与饱足水平之间的确切相互作用仍不明确。本研究首先探究了无脊椎动物中神经系统高度演化的类群之一——乌贼（cuttlefish）是否具备数感（number sense），其次探究了其对食物奖励的评估是否依赖于饱足状态。当存在活虾等食物时，无需训练，乌贼便会转向猎物并启动捕食攫取行为。以该视觉攻击行为作为衡量指标，乌贼在二择一强制选择任务（two-alternative forced choice tasks）中表现出对更大数量的偏好，该任务涵盖1对2、2对3、3对4及4对5四类对比组合。但当选择为1只活虾与2只死虾时，乌贼则偏好数量更少的猎物。更为关键的是，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，乌贼在处于饥饿状态时会选择单只大型猎物，而在饱足状态下则会选择两只较小的猎物。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取决于猎物质量与自身食欲状态。该研究结果还提示，乌贼在做出觅食决策时会整合内部与外部信息，且获取食物的成本与其饱足水平呈负相关，这一现象与人类在风险情境下代谢状态改变经济决策的观测结果相似。