Test of the prey-attraction hypothesis for the scorpion fluorescence

A striking feature of most scorpion species is fluorescence under ultraviolet light, but few studies have investigated the adaptive benefit of this trait. A hypothesis is that fluorescence may lure prey towards the scorpion improving foraging success. In this study, we investigated whether the fluorescence of the scorpion Centruroides granosus Thorell, 1876 lures the house cricket Acheta domesticus Linnaeus, 1758. We performed two experiments: 1) an arena in which crickets were exposed to both fluorescing and black-painted non-fluorescing scorpions and 2) a tunnel in which crickets could walk out through one of the two exits, each with a scorpion treatment. None of the experiments provided evidence that the scorpion fluorescence is attractive to house crickets since they did not show preference for any of the two scorpion types. Variables such as cricket sex or scorpion sex did not influence their response towards the fluorescence; however, crickets were on average closer to male scorpions in the outdoor arena and closer to female scorpions in the laboratory arenas. Moreover, male crickets were more active than females in the tunnel experiment, in line with the results of the arena experiment showing that male crickets were on average closer to the scorpions in the laboratory. We discuss potential implications and suggest that more experimental work is required to investigate potential adaptive benefits of the scorpion fluorescence under various biotic and abiotic factors.多数蝎子物种的一个显著特征是在紫外线（ultraviolet light）照射下会发出荧光（fluorescence），但目前鲜有研究探讨这一性状的适应性优势。有假说提出，蝎子的荧光或许能引诱猎物靠近自身，从而提升觅食成功率。本研究以Centruroides granosus Thorell, 1876的荧光特性与家蟋蟀Acheta domesticus Linnaeus, 1758为研究对象，探究其荧光是否具备引诱作用。我们开展了两项实验：1）行为竞技场（arena）实验：将家蟋蟀同时暴露于发出荧光的蝎子与经黑色涂装的非荧光蝎子环境中；2）隧道实验：家蟋蟀可通过两个出口之一离开隧道，每个出口分别设置不同处理的蝎子。两项实验均未发现蝎子荧光对家蟋蟀具有吸引力的证据，家蟋蟀并未表现出对两种蝎子处理组的偏好。家蟋蟀的性别、蝎子的性别均未对其针对荧光的反应产生影响；但在野外行为竞技场实验中，家蟋蟀平均更接近雄性蝎子，而在实验室行为竞技场实验中则更接近雌性蝎子。此外，隧道实验中雄性家蟋蟀的活动性强于雌性，这与实验室行为竞技场实验的结果一致——后者显示雄性家蟋蟀平均更接近蝎子。我们讨论了本研究的潜在意义，并提出未来需开展更多实验，以探究蝎子荧光在各类生物与非生物因子下的适应性优势。