Department of General Psychology, University of Padova, Padova, Italy.
Animal Comparative Economics Laboratory, Department of Zoology and Evolutionary Biology, University of Regensburg, Regensburg, Germany.
Anim Cogn. 2021 Nov;24(6):1237-1245. doi: 10.1007/s10071-021-01516-1. Epub 2021 May 3.
Animals must often decide between exploiting safe options or risky options with a chance for large gains. Both proximate theories based on perceptual mechanisms, and evolutionary ones based on fitness benefits, have been proposed to explain decisions under risk. Eusocial insects represent a special case of risk sensitivity, as they must often make collective decisions based on resource evaluations from many individuals. Previously, colonies of the ant Lasius niger were found to be risk-neutral, but the risk preference of individual foragers was unknown. Here, we tested individual L. niger in a risk sensitivity paradigm. Ants were trained to associate one scent with 0.55 M sucrose solution and another with an equal chance of either 0.1 or 1.0 M sucrose. Preference was tested in a Y-maze. Ants were extremely risk-averse, with 91% choosing the safe option. Based on the psychophysical Weber-Fechner law, we predicted that ants evaluate resources depending on their logarithmic difference. To test this hypothesis, we designed 4 more experiments by varying the relative differences between the alternatives, making the risky option less, equally or more valuable than the safe one. Our results support the logarithmic origin of risk aversion in ants, and demonstrate that the behaviour of individual foragers can be a very poor predictor of colony-level behaviour.
动物在面临安全选项和风险选项（有获得大收益的机会）时，往往需要做出抉择。为了解释风险下的决策，人们提出了基于感知机制的近期理论和基于适应度收益的进化理论。群居昆虫对风险的敏感性是一个特殊情况，因为它们必须经常根据许多个体对资源的评估做出集体决策。先前的研究发现，黑蚁（Lasius niger）的蚁群是风险中立的，但单个觅食者的风险偏好尚不清楚。在这里，我们在风险敏感性范式中测试了单个黑蚁。蚂蚁被训练将一种气味与 0.55 M 蔗糖溶液相关联，另一种气味与 0.1 或 1.0 M 蔗糖的机会相等。在 Y 型迷宫中测试偏好。蚂蚁非常厌恶风险，有 91%的蚂蚁选择安全选项。根据心理物理学韦伯-费希纳定律，我们预测蚂蚁会根据资源的对数差异来评估资源。为了验证这一假设，我们设计了另外 4 个实验，通过改变选项之间的相对差异，使风险选项的价值小于、等于或大于安全选项。我们的结果支持了蚂蚁回避风险的对数起源，并表明单个觅食者的行为可能是蚁群行为的一个很差的预测指标。
