Low levels of genetic differentiation with isolation by geography and environment in populations of Drosophila melanogaster from across China

The fruit fly, Drosophila melanogaster, is a model species in evolutionary studies. However, population processes of this species in East Asia are poorly studied. Here we examined the population genetic structure of D. melanogaster across China. There were 14 mitochondrial haplotypes with 10 unique ones out of 23 known from around the globe. Pairwise F(ST) values estimated from 15 novel microsatellites ranged from 0 to 0.11, with geographically isolated populations showing the highest level of genetic uniqueness. STRUCTURE analysis identified high levels of admixture at both the individual and population levels. Mantel tests indicated a strong association between genetic distance and geographical distance as well as environmental distance. Full redundancy analysis (RDA) showed that independent effects of environmental conditions and geography accounted for 62.10% and 31.58% of the total explained genetic variance, respectively. When geographic variables were constrained in a partial RDA analysis, the environmental variables bio2 (mean diurnal air temperature range), bio13 (precipitation of the wettest month), and bio15 (precipitation seasonality) were correlated with genetic distance. Our study suggests that demographic history, geographical isolation, and environmental factors have together shaped the population genetic structure of D. melanogaster after its introduction into China.