Effects Of Landscape Variables On The Genetic Structure And Gene Flow Among Plutella Xylostella Populations

In this study, we investigated the influence of fine-scale landscape features on the population genetic structure of Plutella xylostella (Linnaeus) (Lepidoptera, Plutellidae). Nineteen populations including 626 individuals were collected at the junctions of Yongtai county, Minhou county and Fuqing city, in the Fujian Province. Eight polymorphic microsatellite loci were used to assay genetic variation, population genetic structure and gene flow. We analysed the genetic data by using different methods including analysis of molecular variance (AMOVA), STURCTURE cluster analysis, Principal Coordinates Analysis (PCoA). We also tested the influence of certain landscape features such as river, mountains and roads on population genetic structure and gene flow. The principal results and conclusions of the study were as follows:1. Genetic diversity ofthe Plutella xylostella populationsMost of the 19 populations deviated from Hardy-Weinberg equilibrium (p< 0.05). All of the 19 Plutella xylostella populations showed high genetic diversity. Expected heterozygosity ranged from 0.520 to 0.606 (mean 0.562), observed heterozygosity ranged from 0.429 to 0.557 (mean 0.499) and allelic richness from 4.000 to 5.536 (mean 4.940). The TQ population and the populations on the east of major mountains have higher genetic diversity compared with the populations on the west of major mountains. A road connects the TQ population and the P. xylostella populations on the east of major mountains by transportation of cruciferous vegetables, which promotes gene exchange among them and increase genetic diversity of population TQ.2. Genetic structure and levels of gene flow of the Plutella xylostella populationsPairwise Fst values among the 19 population were below 0.15 and showed medium to lower genetic differentiation among the sampled populations. Gene flow (Nm) showed that 84% of Nm values were above 0.04, indicating high gene flow among populations. Both pairwise Fst values and gene flow analyses indicated higher genetic differentiation between the SL population and the other populations. Most individuals in population SL were collected in small vegetable isolated fields with little connection with other sites. In this study, no correlation between genetic and geographical distance was found, suggesting that geographical distance is not a factor to explain the genetic differentiation among populations. Using STRUCTURE cluster analysis, analysis of molecular variance (AMOVA) and Principal Coordinates Analysis (PCoA) methods, we found that the Dazhangxi River, major mountains and roads (G15 and G324) had no significant effects on shaping genetic structure and gene flow of these populations. However, when a subset of 10 populations on the east of major mountains were selected based on the distribution of genetic diversity and geographic location, XT and DT populations located in a valley were differentiated from other populations out of the valley. This indicated possible mountain barrier to gene flow in a finer spatial scale. The results suggested that the selection of the spatial scale for landscape genetic studies is important and may influence the results. In the case of P. xylostella, it may be that most differentiation is at either a small scale due to isolation or large scale if gene flow is limited.