Data from: Predation cost of a sexual signal in the threespine stickleback

Much evidence exists for sexually selected traits reflecting various components of mate quality, but the factors that limit signal expression and ensure honest signaling are less well known. Predation risk has been proposed to be one factor that could constrain the elaboration of visually conspicuous signals and ensure honesty, but little evidence exists because of limitations of earlier used methods. We investigated using a combination of field observations and experimental work if a conspicuous sexual signal of the threespine stickleback Gasterosteus aculeatus, the red nuptial coloration of the male, increases predation risk. We compared the proportion of colorful males in the gut of a predator in the wild, the perch Perca fluviatilis, to that in the population, and found proportionally more red-colored stickleback in the gut. This indicates that the predator selectively preys on colorful males under natural conditions. To differentiate between the effects of color and behavior on susceptibility to predation, we experimentally investigated the attack behavior of the predator towards breeding stickleback males differing in coloration. We found the predator to preferentially attack more colorful males, independent of their behavior. These results indicate that predation risk is a cost of the sexual signal that could limit expression and influence the honesty of the signal as an indicator of mate quality.

已有大量实证研究证实，性选择性状（sexually selected traits）能够反映配偶质量的多个维度，但限制信号表达、保障诚实信号传递（honest signaling）的相关机制却尚未得到充分阐明。捕食风险曾被提出是制约视觉醒目信号演化增强、维持信号诚实性的潜在因素之一，但由于早期研究方法存在局限，相关实证证据仍较为匮乏。本研究结合野外观测与实验研究，以三刺棘鱼（threespine stickleback, *Gasterosteus aculeatus*）为研究对象，探究其雄性个体标志性的红色婚色是否会提升被捕食风险。我们对比了野外捕食者河鲈（perch, *Perca fluviatilis*）胃容物中具有红色婚色的雄性棘鱼占比，与自然种群中的对应占比，结果发现胃容物内红色棘鱼的比例显著更高。该结果表明，在自然环境中该捕食者会选择性捕食体色更为鲜艳的雄性棘鱼。为区分体色与行为对棘鱼被捕食易感性的影响，我们通过实验探究了河鲈对不同体色繁殖期雄性棘鱼的攻击行为偏好。实验结果显示，河鲈会优先攻击体色更鲜艳的雄性棘鱼，且该偏好不受其行为的影响。综上结果表明，捕食风险是性选择信号的潜在生存代价，这一机制能够限制信号的过度表达，并影响其作为配偶质量指示信号的诚实性。