Synchrony can be defined as the precise coordination between independent individuals, and this behaviour is more enigmatic when it is imperfect. The traditional theoretical explanation for imperfect synchronous courtship is that it arises as a by-product of the competition between males to broadcast leading signals to attract female attention. This competition is considered an evolutionary stable strategy maintained through sexual selection. However, previous studies have revealed that leading signals are not honest indicators of male quality. We studied imperfect courtship synchrony in fiddler crabs to mainly test whether (i) signal leadership and rate are defined by male quality and (ii) signal leadership generates synchrony. Fiddler crab males wave their enlarged claws during courtship, and females prefer leading males—displaying ahead of their neighbour(s). We filmed groups of waving males in the field to detect how often individuals were leaders and if they engaged in synchrony. Overall, we found that courtship effort is not directly related to male size, a general proxy for quality. Contrary to the long-standing assumption, we also revealed that leadership is not directly related to group synchrony, but faster wave rate correlates with both leadership and synchrony.

This article is part of the theme issue ‘Synchrony and rhythm interaction: from the brain to behavioural ecology’.

同步性可以定义为独立个体之间的精确协调，当这种行为不完美时就更加神秘。对不完美同步求爱的传统理论解释是，它是雄性之间为了吸引雌性注意力而传播领先信号的竞争的副产品。这种竞争被认为是通过性选择维持的进化稳定策略。然而，之前的研究表明，领先信号并不是男性素质的诚实指标。我们研究了招潮蟹的不完美求爱同步性，主要测试（i）信号领导力和速率是否由雄性质量定义以及（ii）信号领导力是否产生同步性。雄性招潮蟹在求爱时会挥动它们肥大的爪子，而雌性招潮蟹更喜欢领头的雄性——在邻居面前展示自己。我们拍摄了一群在野外挥手的男性，以检测个体担任领导者的频率以及他们是否同步。总体而言，我们发现求偶努力与雄性体型（质量的一般指标）没有直接关系。与长期以来的假设相反，我们还发现领导力与群体同步性没有直接关系，但更快的波速与领导力和同步性都相关。

本文是主题“同步与节奏互动：从大脑到行为生态学”的一部分。