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起着核心作用。然而，与人工选择家养动植物的许多卓有成效的结果相比，支持自然选择作用的实地证据很少。在这项研究中，我调查了日本瓢虫甲虫，Harmonia axyridds，抒情色彩多态性的地理变化及其几十年来的变化。在本州岛、四国岛和九州岛，黑色和非黑色基因的频率存在显著的地理差异。认为4 ~ 7月的繁殖季节温度可能是产生地理差异的重要因素。在这些岛屿的大多数采样地点，在过去的几十年里，黑色基因的频率增加了，而非黑色基因的频率减少了。自然选择模式的改变作用于颜色多态性被认为是基因频率变化的主要原因。在高纬度地区，估计选择的幅度更大。在靠近采样地点的大多数气象站，观察到的基因频率的变化与繁殖季节温度的升高相一致。这些结果可能是自然选择的微观进化的现场证据，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.