Data from: Real-time social selection maintains honesty of a dynamic visual signal in cooperative fish

Our understanding of animal communication has been largely driven by advances in theory since empirical evidence has been difficult to obtain. Costly signaling theory became the dominant paradigm explaining the evolution of honest signals, according to which communication reliability relies on differential costs imposed on signalers to distinguish animals of different quality. On the other hand, mathematical models disagree on the source of costs at the communication equilibrium. Here we present an empirical framework to study the evolution of honest signals that generates predictions on the form, function and sources of reliability of visual signals. We test these predictions on the facial color patterns of the cooperatively breeding Princess of Burundi cichlid, Neolamprologus brichardi. Using theoretical visual models and behavioral experiments we show that these patterns possess stable chromatic properties for efficient transmission in the aquatic environment, while dynamic changes in signal luminance are used by the fish to communicate switches in aggressive intent. By manipulating signal into out-of-equilibrium expression and simulating a cheater invasion, we demonstrate that social costs (receiver retaliation) promote the honesty of this dynamic conventional signal. By directly probing the sender of a signal in real time, social selection is likely to be the mechanism of choice shaping the evolution of inexpensive, yet reliable context-dependent social signals in general.

长期以来，受限于实证证据的获取难度，动物通讯领域的认知突破大多源自理论研究的进步。代价信号理论（Costly signaling theory）成为解释诚实信号（honest signals）演化的主流范式，该理论提出，通讯可靠性依赖于对信号发出者施加的差异化成本，以此区分不同质量等级的动物个体。但另一方面，针对通讯均衡（communication equilibrium）下成本的来源，不同数学模型的结论存在分歧。本研究提出了一套用于研究诚实信号演化的实证框架（empirical framework），该框架可针对视觉信号（visual signals）的形式、功能及可靠性来源作出预测。我们以合作繁殖（cooperatively breeding）的布隆迪公主丽体鱼（Princess of Burundi cichlid，*Neolamprologus brichardi*）的面部色斑为研究对象，对上述预测进行了验证。通过理论视觉模型（theoretical visual models）与行为实验（behavioral experiments），我们发现这些色斑具备稳定的色度特性（chromatic properties），可在水生环境（aquatic environment）中实现高效信号传递；同时，鱼类通过信号亮度（signal luminance）的动态变化，传递攻击意图（aggressive intent）的切换信号。通过将信号操控至非均衡表达（out-of-equilibrium expression）状态并模拟骗子入侵（cheater invasion）场景，我们证实社会成本（social costs，接收者的报复行为）可维持该动态常规信号的诚实性。通过实时直接探测信号发出者的方式，本研究表明，社会选择（social selection）极有可能是塑造一类普遍存在的低成本、可靠且依赖情境的社会信号演化的首选机制。