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自然选择的调控。此前学界认为，黑化型个体相较于浅色型个体具有更高的适合度，原因是在被煤烟熏黑的深色树皮上，黑化型个体在日间栖息时的被捕食率更低。工业革命期间，黑化型桦尺蛾逐渐成为优势类群；但自1970年起，其种群比例出现快速逆转，学界普遍认为这是由于当前树皮的煤污程度大幅降低，捕食者对栖息于此的黑化型个体产生了负选择压力。 近年来，上述关于黑化现象的经典解释受到了广泛质疑，学界对鸟类作为选择因子的作用普遍持怀疑态度。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，本文作者对其实验结果进行了分析与呈现。 在这项为期六年的实验中，马耶鲁斯共释放了4864只桦尺蛾，这是同类研究中规模最大的一次。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。针对黑化型个体的每日选择强度（选择系数s≈0.1）在幅度与方向上均足以解释后工业时代英国黑化型桦尺蛾比例的快速下降。本研究数据为“伪装与鸟类捕食是蛾类黑化现象兴衰的核心解释”提供了迄今为止最为直接的实证证据。