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, the population processes of this species in East Asia
are poorly studied, even though this area was one of the first regions
colonized outside of its native distribution range. Here we examined the
population genetic structure of D. melanogaster across China. There were
14 mitochondrial haplotypes with ten unique ones out of 23 known from
around the globe. Pairwise FST 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 RDA analysis 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, three environmental
variables of 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 a high level of gene flow, geographical isolation, and environmental
factors have together shaped the population genetic structure of D.
melanogaster after its introduction into China.