Data from: Costs and constraints conspire to produce honest signalling: insights from an ant queen pheromone

Signal costs and evolutionary constraints have both been proposed as ultimate explanations for the ubiquity of honest signalling, but the interface between these two factors is unclear. Here, I propose a pluralistic interpretation, and use game theory to demonstrate that evolutionary constraints determine whether signals evolve to be costly or cheap. Specifically, when the costs or benefits of signalling are strongly influenced by the sender’s quality, low-cost signals evolve. The model reaffirms that cheap and costly signals can both be honest, and predicts that expensive signals should have more positive allometric slopes than cheap ones. The new framework is applied to an experimental study of an ant queen pheromone that honestly signals fecundity. Juvenile hormone was found to have opposing, dose-dependent effects on pheromone production and fecundity and was fatal at high doses, indicating that endocrine-mediated trade-offs preclude dishonesty. Several lines of evidence suggest that the realised cost of pheromone production may be non-trivial, and the antagonistic effects of juvenile hormone indicate the presence of significant evolutionary constraints. I conclude that the honesty of queen pheromones and other signals is likely enforced by both the cost of dishonesty and a suite of evolutionary constraints.信号成本与进化约束，二者均被提出作为诚实信号（honest signalling）普遍存在的终极解释，但这两类因素间的交互机制仍未明晰。本文提出一种多元诠释框架，并借助博弈论论证：进化约束决定了信号将演化至高成本还是低成本状态。具体而言，当信号的成本或收益强烈受信号发送者的个体品质影响时，便会演化出低成本信号。本模型证实，低成本与高成本信号均可为诚实信号，并预测昂贵信号的异速生长斜率（allometric slopes）应较低成本信号更为正向。本文将这一新框架应用于一项针对蚁后信息素（ant queen pheromone）诚实传递繁殖力的实验研究。研究发现，保幼激素（juvenile hormone）对信息素合成与繁殖力具有相反的剂量依赖性效应，且高剂量下可引发致命反应，这表明内分泌介导的权衡（endocrine-mediated trade-offs）从根源上杜绝了欺骗行为。多项证据显示，信息素合成的实际成本或不容小觑，而保幼激素的拮抗效应则表明存在显著的进化约束。本文最终认为，蚁后信息素及其他信号的诚实性，很可能同时由欺骗行为的成本与一系列进化约束共同维持。