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

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Natural selection has played a central importance in the explanation of adaptive evolution in organism. 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 elytral colour polymorphism of the ladybird beetle,Harmonia axyrids, in Japan. In most of the sampling locations in Honsyu, Shikoku and Kyusyu islands, the frequencies of melanic genes increased, while the frequency of non-melanic gene decreased during the last several decades. The observed change in the gene frequencies coincided with the increase in the temperature in the reproductive season at most meteorological stations close to the sampling locations. These results could be a field evidence of micro-evolution by natural selection.