Can behaviour impede evolution? persistence of singing effort after morphological song loss in crickets

Evolutionary loss of sexual signals is widespread. Examining the consequences for behaviours associated with such signals can provide insight into factors promoting or inhibiting trait loss. We tested whether a behavioural component of a sexual trait, male calling effort, has been evolutionary reduced in silent populations of Hawaiian field crickets (Teleogryllus oceanicus). Cricket song requires energetically costly wing movements, but ‘flatwing’ males have feminised wings that preclude song and protect against a lethal, eavesdropping parasitoid. Flatwing males express wing movement patterns associated with singing but, in contrast to normal-wing males, sustained periods of wing movement cannot confer sexual selection benefits and should be subject to strong negative selection. We developed an automated technique to quantify how long males spend expressing wing movements associated with song. We compared calling effort among populations of Hawaiian crickets with differing proportions of silent males, and between male morphs. Contrary to expectation, silent populations invested as much in calling effort as non-silent populations. Additionally, flatwing and normal-wing males did not differ in calling effort. The lack of evolved behavioural adjustment following morphological change in silent Hawaiian crickets illustrates how behaviour might sometimes impede, rather than facilitate, evolution.

Methods
Sining effort data was produced by automatic video tracking of adult male crickets with reflectors on their wings. The csv files were produced by MATLAB using custom scripts. Two files are provided, clearly labelled: one in which singing bouts are defined by 10-second intervals, the other by 5-second intervals. The variable canSing refers to whether each individual was able to sing, and 'pl' refers to pronotum length in mm.

性信号的进化丢失现象广泛存在。探究此类信号相关行为的演化后果，有助于揭示推动或抑制性状丢失的潜在因素。我们针对夏威夷田野蟋蟀（Teleogryllus oceanicus）的无声种群，检验了性性状的行为组分——雄性求偶鸣叫投入（male calling effort）是否已发生进化性降低。蟋蟀鸣曲需要消耗大量能量的翅部运动，但平翅型（flatwing）雄性的翅部已雌性化，无法产生鸣曲，同时可免受一种通过窃听鸣曲定位寄主的致命寄生蜂的侵害。平翅型雄性会表现出与鸣唱相关的翅部运动模式，但与正常翅型雄性相比，持续的翅部运动无法为其带来性选择优势，因此应受到强烈的负选择作用。我们开发了一种自动化技术，用于量化雄性展现鸣唱相关翅部运动的时长。我们比较了不同无声雄性比例的夏威夷蟋蟀种群间，以及不同雄性形态间的求偶鸣叫投入。结果与预期相悖：无声种群的鸣叫投入与非无声种群并无差异；此外，平翅型与正常翅型雄性的鸣叫投入也无显著差别。夏威夷无声蟋蟀在形态发生改变后未出现进化性的行为调整，这一现象揭示了行为有时可能会阻碍而非推动演化进程。

研究方法
鸣曲投入数据通过对翅部粘贴反光标记的成年雄性蟋蟀进行自动视频追踪获得。相关CSV文件由MATLAB通过自定义脚本生成。本次提供了两个已清晰标注的文件：一个以10秒间隔定义鸣唱时段，另一个以5秒间隔定义鸣唱时段。变量canSing代表每只个体是否能够鸣唱，'pl'代表以毫米为单位的前胸背板长度。