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）研究中，动物会在获取奖励所需的时长与奖励的质量之间进行权衡，即在更早可获得的小额奖励与更晚可获得的大额奖励之间做出选择。类似的贴现效应同样存在于空间维度：当动物在距离更近但体量更小的奖励与距离更远但体量更大的奖励之间抉择时，便会产生此类权衡。 当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类型，尚不明确动物是否会以类似方式对其他偏好性刺激进行权衡。本研究以雌性孔雀鱼（Poecilia reticulata）为研究对象，设置空间贴现任务：以距离更近的小额奖励为参照，逐步提升大额奖励的获取距离，以此测量受试个体对大额奖励的偏好变化。我们通过为受试个体提供食物或同性同种个体作为奖励，检验鱼类对不同类型奖励的贴现模式是否存在差异。在正式开展贴现任务前，我们进行了偏好验证实验，以确保受试个体对本次实验中使用的等量食物与社交刺激具有同等的偏好价值。 在贴现任务中，随着大额奖励的获取距离增加，受试个体的偏好从大额奖励转向小额奖励，表现出典型的空间贴现行为；但两种奖励类型下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相似。 然而，在对游动时长的分析中发现，受试个体前往食物奖励处的游动速度显著快于前往集群同伴处的游动速度。这种游动速度的差异意味着，鱼类对社交奖励的时间贴现程度弱于食物奖励。由此可见，奖励类型会对时间贴现产生影响，这提示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（时间、距离）与收益（食物、社交同伴）的类型，调整自身的选择行为与移动速度。