Data from: Spatial discounting of food and social rewards in guppies (Poecilia reticulata).

In temporal discounting, animals trade off the time to obtain a reward against the quality of a reward, choosing between a smaller reward available sooner versus a larger reward available later. Similar discounting can apply over space, when animals choose between smaller and closer versus larger and more distant rewards. Most studies of temporal and spatial discounting in nonhuman animals use food as the reward, and it is not established whether animals trade off other preferred stimuli in similar ways. Here, we offered female guppies (Poecilia reticulata) a spatial discounting task in which we measured preferences for a larger reward as the distance to it increased relative to a closer but smaller reward. We tested whether the fish discounted reward types differently by offering subjects either food items or same-sex conspecifics as rewards. Before beginning the discounting tasks, we conducted validation tests to ensure that subjects equally valued the food and social stimuli in the quantities provided. In the discounting task, subjects switched their preferences from the larger to the smaller reward as the distance to the larger reward increased (spatial discounting), but the pattern and magnitude of discounting did not differ across the two reward types. These findings indicate that guppies show similar patterns of discounting food and social rewards in a spatial task. In an analysis of travel times, however, the fish swam faster to food rewards than to shoaling partners. This difference in travel times implies that fish temporally discounted social rewards less steeply than food rewards. Thus, reward type influences temporal discounting, suggesting a dissociation between temporal and spatial discounting. Our results illustrate how animals adjust choices and travel times depending on both the type of cost (time, distance) and benefits (food, social partners).在时间贴现（temporal discounting）范式中，动物会在获得奖励的时长与奖励质量之间进行权衡，即在更快获取的较小奖励与更晚获得的较大奖励之间做出选择。类似的权衡机制也可应用于空间维度，即动物在距离更近的较小奖励与距离更远的较大奖励之间做出选择，此即为空间贴现（spatial discounting）。目前针对非人类动物的时间与空间贴现研究大多以食物作为奖励物，但尚不明确动物是否会以类似方式权衡其他偏好性刺激。本研究以雌性孔雀鱼（Poecilia reticulata）为实验对象，设置空间贴现任务，当较大奖励的获取距离相对于更近但更小的奖励逐渐增加时，测定实验对象的偏好变化。我们为实验对象分别提供食物或同性同种个体作为奖励，以此检验鱼类对不同类型奖励的贴现程度是否存在差异。在正式开展贴现任务前，我们先进行了有效性验证实验，以确保实验对象对给定数量的食物与社交刺激具有同等的偏好价值。在贴现任务中，随着较大奖励的获取距离增加，实验对象的偏好会从较大奖励转向较小奖励（即表现出空间贴现行为），但两种奖励类型的贴现模式与贴现幅度均无显著差异。上述结果表明，孔雀鱼在空间任务中对食物奖励与社交奖励的贴现模式并无二致。但在游动时长的分析中，鱼类前往食物奖励的游动速度显著快于前往集群同伴的速度。游动时长的差异意味着，鱼类对社交奖励的时间贴现程度弱于食物奖励。由此可见，奖励类型会影响时间贴现行为，这表明时间贴现与空间贴现之间存在分离效应。本研究结果揭示了动物如何根据成本类型（时间、距离）与收益类型（食物、社交同伴）调整自身的选择行为与游动时长。