Data from: Dopamine disruption increases cleanerfish cooperative investment in novel client partners

Social familiarization is a process of gaining knowledge that results from direct or indirect participation in social events. Cooperative exchanges are thought to be conditional upon familiarity with others. Indeed, individuals seem to prefer to engage with those that have previously interacted with them, which are more accurate predictors of reward than novel partners. On the other hand, highly social animals do seek novelty. Truth is that the physiological bases underlying how familiarity and novelty may affect cooperative decision-making are still rather obscure. Here, we provide the first experimental evidence that the level of the dopaminergic influence in cooperative exchanges is constrained to mechanisms of social familiarization and novelty in a cleanerfish, Labroides dimidiatus. Cleaners were tested against familiar and novel Ctenochaetus striatus surgeonfish (a common client species) in laboratorial conditions, and were found to spend more time providing physical contact (also referred to as tactile stimulation) to familiar fish clients. Cleaners use tactile stimulation as a way to reduce the risk of a non-rewarding outcome, a behavioural response that is even more pronounced when blocking dopamine (DA) D1 receptors. We discovered that the influence of DA disruption on cleaners' provision of physical contact was dependent on the level of familiarity with its partner, being highly exacerbated whenever the client is novel, and unnoticed when dealing with a familiar one. Our findings demonstrate that DA mediation influences the valuation of partner stimuli and the enhancing investment in novel partners, mechanisms that are similar to other vertebrates, including humans.

社会熟悉化（social familiarization）是指通过直接或间接参与社会活动以获取知识的过程。合作交换被认为依赖于个体对他人的熟悉程度。事实上，个体似乎更倾向于与此前存在互动经历的对象进行交往，相较于陌生伙伴，这类对象能够更精准地预测回报结果。另一方面，高度社会化的动物同样会主动寻求新奇性。然而，熟悉性与新奇性如何调控合作决策的生理学基础，目前仍不甚明晰。
本研究首次提供实验证据，证明在裂唇鱼（Labroides dimidiatus，清洁鱼的一种）中，合作交换过程中的多巴胺能调控水平受社会熟悉化与新奇性机制的约束。研究人员在实验室环境下，让清洁鱼分别与熟悉及陌生的栉齿刺尾鱼（Ctenochaetus striatus，一种常见的客户鱼）开展互动实验，结果发现清洁鱼会花费更多时间对熟悉的客户鱼提供身体接触（亦称触觉刺激）。清洁鱼通过触觉刺激来降低无回报结果的发生风险，而当多巴胺（DA）D1受体被阻断时，这种行为响应会更为显著。
本研究进一步发现，多巴胺阻断对清洁鱼提供身体接触行为的影响，取决于其与互动对象的熟悉程度：当客户鱼为陌生个体时，该影响会显著加剧；而面对熟悉个体时，则未观察到明显效应。本研究结果表明，多巴胺介导的过程会影响对互动对象刺激的评估，并提升对陌生伙伴的行为投入，这类调控机制与包括人类在内的其他脊椎动物高度相似。