Experimentally-seeded social cues in the wild: Costs to bearers and potential benefits to receivers

Conspecifics can provide social cues about the presence of key features of the surrounding environment, such as food or predators. Attending to social cues may therefore potentially benefit receivers, or at least be worth following. Yet, bearing social cues could also be costly, particularly if it increases the likelihood of close-range interaction with non-kin. Here, we experimentally-seeded social cues in the wild onto focal individuals of the social hermit crab (Coenobita compressus), testing (1) the 'potential benefits to receivers' hypothesis, which predicts that receivers will follow social cues to orient towards valuable resources, and (2) the 'costs to bearers' hypothesis, which predicts that bearers of social cues will experience direct (physical) costs or indirect (constrained movement) costs due to interaction with receivers. Consistent with hypothesis (1), in natural encounters, conspecifics that crossed paths frequently made antennal contact, potentially gathering social information at close range. In experiments, naïve conspecifics followed focal individuals bearing 'positive' social cues (about a valuable food resource) significantly more often than they followed individuals bearing less attractive ('neutral' or 'ambivalent') social cues, pointing to a potential benefit. Consistent with hypothesis (2), individuals bearing positive social cues incurred greater direct and indirect costs, being physically flipped more often and achieving shorter displacements compared to individuals bearing other social cues. We conclude that experimentally-seeded social cues in the wild can confer costs to bearers and potentially benefit receivers. Broadly, the costs of bearing social cues, revealed here, underscore the importance of not overlooking that social cues may be costly.

同种个体可提供关于周围环境关键特征（如食物资源或捕食者）存在的社会线索。因此，对社会线索的关注或可为接收者带来收益，至少值得遵循。然而，携带社会线索也可能产生代价，尤其当此举增加了与非亲属个体发生近距离互动的概率时。

本研究针对社会寄居蟹（Coenobita compressus）的目标个体，在野外环境中人工植入社会线索，以此检验两项假说：其一为「接收者潜在收益」假说，该假说预测接收者会遵循社会线索，以定位有价值的资源；其二为「线索携带者代价」假说，该假说预测社会线索的携带者会因与接收者的互动，遭受直接（物理）代价或间接（运动受限）代价。

研究结果与假说（1）相符：在自然相遇场景中，频繁途经彼此的同种个体常会进行触角接触，从而在近距离范围内获取社会信息。实验结果显示，无相关经验的同种个体跟随携带「正向」社会线索（指向珍贵食物资源）的目标个体的频率，显著高于跟随携带吸引力较低（「中性」或「矛盾」）社会线索的个体，这印证了接收者潜在收益的可能性。同时，结果也与假说（2）一致：与携带其他类型社会线索的个体相比，携带正向社会线索的个体承受了更高的直接与间接代价——被翻转的频率更高，且移动距离更短。

综上，本研究表明，在野外环境中人工植入的社会线索，既可能为线索携带者带来代价，也可能为接收者带来潜在收益。总体而言，本研究揭示的携带社会线索的代价，凸显了不应忽视社会线索可能存在成本这一要点的重要性。