Appropriate evaluation of rapid evolutionary responses to seasonal environmental variability in a wild Drosophila population

Abstract Seasonal environmental change is one of the most rapid and striking environmental variables. Although relatively rapid adaptation to environmental changes over several years or several decades has been described in many taxa, rapid responses to seasonal environments are delicate, and therefore, the detection of the evolutionary responses requires sensitive methods. Here, we examined the evolutionary response to seasonal environmental changes in terms of thermal tolerance and morphological traits using Drosophila lutescens collected at the spring and autumn periods in a single location. We first demonstrated that flies in the two seasonal periods were almost genetically identical using double-digest restriction site-associated DNA sequencing and analysis. With an experimental design that eliminated the effect of possible confounding environmental factors that influence thermal tolerance, we showed that the heat tolerance of D. lutescens was significantly higher in the autumn than in the spring. Furthermore, cold tolerance was slightly higher in the spring than in the autumn. Although wing length and thorax length did not change significantly between seasons, the ratio of wing length to thorax length changed significantly between them. These results indicate that seasonal environmental heterogeneity can induce evolution within a year. The present study demonstrates rapid evolutionary responses to environmental fluctuations.