Data and code from: Beyond masking: Cognitive limits on mate choice

Mate choice poses a demanding and high-stakes information-processing challenge: receivers must detect, remember, and compare mating signals across multiple potential mates. Strong preferences in simple contexts often weaken when receivers encounter numerous signalers, reshaping sexual selection. A potential mechanism driving this is energetic masking, when overlapping signals saturate sensory channels, hindering receivers’ ability to detect and discriminate among mates. Alternatively, choice overload, when the cognitive demands of evaluating too many options exceed an individual’s processing capacity, could reduce decision performance. Although energetic masking is well documented, we know little about choice overload in nonhumans. Here, we investigated both mechanisms in Cope’s gray treefrogs (Hyla chrysoscelis) using playback experiments that independently manipulated the number of calling males and the presence of background chorus noise. Females chose between a longer “target” call and one, three, or seven shorter “distractor” calls in the presence and absence of background noise. As the number of non-overlapping calls increased, females were substantially less accurate in selecting the target, took longer to decide, and more frequently deferred choice altogether. Noise only modestly affected discrimination, although in the opposite direction than expected. These results demonstrate that cognitive limits on information processing can subvert mate choice, even in the absence of sensory interference. Our findings highlight choice overload as a novel and underappreciated constraint on sexual selection. Accounting for cognitive limitations may help explain persistent variation in sexual traits despite apparently strong directional selection (“paradox of the lek”) and help refine models of selection dynamics in complex social and acoustic environments.择偶行为是一项严苛且高风险的信息处理难题：信号接收者需要在多个潜在配偶间检测、记忆并比对交配信号。在简单情境下表现出的强烈择偶偏好，常会在信号接收者面对大量信号发送者时减弱，进而重塑性选择。背后潜在的驱动机制之一是能量掩蔽（energetic masking）：当重叠信号充斥感官通道时，会阻碍信号接收者检测并区分配偶的能力。另一种可能的机制是选择超载（choice overload）：当评估过多选项所需的认知负荷超出个体的信息处理能力时，会降低决策表现。尽管能量掩蔽已有大量研究佐证，但我们对非人类动物中的选择超载现象仍知之甚少。本研究以科普氏灰树蛙（Cope’s gray treefrogs，*Hyla chrysoscelis*）为研究对象，通过回放实验独立操控鸣叫雄性的数量以及背景合唱噪声的有无。实验中，雌性树蛙需在存在或不存在背景噪声的条件下，在一段更长的‘target’鸣叫与1段、3段或7段更短的‘distractor’鸣叫之间做出选择。随着非重叠鸣叫数量的增加，雌性选择目标鸣叫的准确率显著降低，决策耗时更长，且更频繁地完全推迟选择。背景噪声仅对辨别能力产生了小幅影响，且影响方向与预期相反。上述结果表明，即便不存在感官干扰，信息处理的认知局限也会破坏择偶行为。本研究结果凸显出选择超载作为一种被忽视的新型性选择约束因素的重要性。纳入认知局限的考量，或有助于解释尽管存在显著的定向选择，性征仍持续存在变异的“paradox of the lek”（求偶场悖论），同时也能帮助完善复杂社会与声学环境下的选择动力学模型。