Data from: Selective bird predation on the peppered moth: the last experiment of Michael Majerus

Colour variation in the peppered moth Biston betularia was long accepted to be under strong natural selection. Melanics were believed to be fitter than pale morphs because of lower predation at daytime resting sites on dark, sooty bark. Melanics became common during the industrial revolution, but since 1970 there has been a rapid reversal, assumed to have been caused by predators selecting against melanics resting on today's less sooty bark. Recently, these classical explanations of melanism were attacked, and there has been general scepticism about birds as selective agents. Experiments and observations were accordingly carried out by Michael Majerus to address perceived weaknesses of earlier work. Unfortunately, he did not live to publish the results, which are analysed and presented here by the authors. Majerus released 4864 moths in his six-year experiment, the largest ever attempted for any similar study. There was strong differential bird predation against melanic peppered moths. Daily selection against melanics (s ≃ 0.1) was sufficient in magnitude and direction to explain the recent rapid decline of melanism in post-industrial Britain. These data provide the most direct evidence yet to implicate camouflage and bird predation as the overriding explanation for the rise and fall of melanism in moths.

长期以来，学界普遍认为桦尺蛾（peppered moth，*Biston betularia*）的体色变异受到强烈的自然选择作用。此前学界认为，黑化型个体（melanics）比浅色型（pale morphs）更具适合度，原因是它们在被煤烟熏黑的树皮这类日间栖息位点上的被捕食概率更低。工业革命期间，黑化型桦尺蛾的种群比例逐渐升高；但自1970年以来，该比例出现了快速逆转，学界普遍认为这是由于捕食者对栖息在如今煤烟污染减轻的树皮上的黑化型个体进行选择所致。近年来，这些关于黑化现象（melanism）的经典解释受到了质疑，学界普遍对鸟类作为选择因子的作用提出了质疑。为此，迈克尔·马耶鲁斯（Michael Majerus）开展了一系列实验与观测，以弥补此前研究中存在的已知缺陷。遗憾的是，他未能在生前完成研究成果的发表，本文作者对其未竟的实验结果进行了分析与呈现。在这项耗时六年的实验中，马耶鲁斯共计放飞了4864只桦尺蛾，这是同类研究中迄今为止规模最大的实验。实验结果显示，鸟类对黑化型桦尺蛾存在显著的差异性捕食。对黑化型个体的每日选择系数（s ≈ 0.1）在强度与方向上，足以解释后工业时代英国境内黑化型桦尺蛾比例的快速下降。本研究数据为"伪装作用与鸟类捕食是桦尺蛾黑化现象兴衰的主导性解释"这一观点提供了迄今为止最为直接的证据。