Influence of global warming on geographical cline of elytral color polymorphism in the ladybird beetle Harmonia axyrids

自然选择在解释生物体的适应性进化中发挥了核心作用。然而，与家养动植物的人工选择的许多丰硕成果相比，支持自然选择作用的实地证据很少。在这项研究中，我调查了地理渐变和它的变化，几十年来的lytral颜色多态性的瓢虫，异色瓢虫，在日本。在本州岛、四国岛和九州岛上观察到显黑和非显黑基因频率的地理渐变。认为生殖季节（4 - 7月）的温度是产生地理渐变群的重要因子。在这些岛屿的大多数采样点，在过去的几十年中，黑素基因的频率增加，而非黑素基因的频率下降。自然选择作用于颜色多态性的模式变化被认为是基因频率变化的主要原因。在较高的纬度，选择的幅度估计更大。观察到的基因频率的变化与生殖季节的温度在大多数气象站接近采样点的增加。这些结果可能是自然选择导致的微进化的现场证据，并表明全球变暖可以影响物种的遗传构成。

Natural selection has played a central role in the explanation of adaptive evolution in organisms. There have been, however, very few field evidences supporting the action of natural selection, compared to many fruitful results in artificial selection of domestic plants and animals. In this study, I investigated the geographical cline and its change over decades in the lytral colour polymorphism of the ladybird beetle, Harmonia axyrids, in Japan. Geographical cline in the frequencies of melanic and non-melanic genes was remarkably observed over Honsyu, Shikoku and Kyusyu islands. It was considered that temperature in reproductive season of this beetle (April-July) could be an important factor for generating the geographical cline. In most of the sampling locations of these islands, the frequencies of melanic genes increased, while the frequency of the non-melanic gene decreased during the last several decades. Change of pattern in natural selection acting on colour polymorphism was considered to be a major cause of the change in gene frequencies. At the higher latitude, the magnitude of selection was estimated to be larger. The observed change in the gene frequencies coincided with an increase in the temperature in reproductive season at most meteorological stations close to the sampling locations. These results could be a field evidence of micro-evolution by natural selection, and suggest that global warming can affect the genetic constitution of species.