Roaming Romeos: male crickets evolving in silence show increased locomotor behaviours

Loss of sexual signals should be strongly selected against when these signals are necessary for mate attraction or acquisition. Male Teleogryllus oceanicus field crickets produce a long-distance calling song to attract females. Separate genetic mutations recently evolved on the Hawaiian Islands of Kauai and Oahu, rendering approximately 90% and 50% of males, respectively, incapable of calling. We examined whether males from three populations, each with a distinct prevalence of this silent ‘flatwing’ phenotype, show behavioural plasticity in response to being reared in a call-less environment. Crickets from Kauai, Oahu and Mangaia, a Cook Islands population without the flatwing phenotype, either were or were not exposed to calling song during late juvenile and early adult development. Movement assays showed that when males originating from Kauai were reared in silence, they moved sooner, moved more and spent more time walking during silent behaviour trials than did their counterparts reared with calling song. Males from Oahu and Mangaia, however, showed no such effect of acoustic rearing environment on these behaviours. This suggests that there has been directional selection on Kauai for males to respond to a silent environment by increasing their mobility, thus compensating for their lack of song and increasing their chance of encountering receptive females.

当性信号对于配偶吸引或获取不可或缺时，性信号的丢失理应受到强烈的负向选择。雄性海洋蟋蟀（Teleogryllus oceanicus）会通过发出远距离召唤鸣曲以吸引雌性。近期，夏威夷群岛考爱岛与瓦胡岛的种群分别演化出独立的遗传突变，分别导致约90%和50%的雄性个体无法发出召唤鸣曲。本研究针对三种种群的雄性个体展开实验，这三种种群各自的沉默“平翅”表型发生率各不相同：我们将来自考爱岛、瓦胡岛以及无平翅表型的库克群岛曼加伊阿种群的蟋蟀分为两组，分别在幼龄晚期至成虫早期的发育阶段中，暴露于召唤鸣曲环境或处于无鸣曲的静默环境。运动行为实验结果显示，相较于在有鸣曲环境中饲养的考爱岛雄性个体，在无声环境中饲养的考爱岛雄性个体在静默行为测试中启动运动更早、移动距离更长且步行时长占比更高。然而，瓦胡岛与曼加伊阿种群的雄性个体并未表现出声学饲养环境对上述行为的此类影响。上述结果表明，考爱岛种群的雄性个体已受到定向选择，使其能够通过提升运动能力来响应无声环境，从而弥补自身无法鸣唱的缺陷，提高邂逅接受性雌性个体的概率。