| In this paper, landscape genetics studies on Chilo suppressalis (Walker)(Lepidoptera:Crambidae) were conducted at two different spatial scales using16microsatellite markers. The fine spatial scale experiment was conducted in the approximately154km2rice-growing area around the Huangcun national agriculture-developed project area in Wuyishan, China. The large spatial scale experiment was conducted in the entire area of Fujian province, which is approximately120,000km2. The principal findings of this study are as follows.1. The effects of agricultural landscape characteristics on patterns of genetic variation within and among populations of C. suppressalis at the fine spatial scale of WuyishanGenetic diversity and patterns of differentiation among sitesIn this study, a total of140individuals from15sites were considered for analysis. The16microsatellite primers were used to amplify a total of299loci, all of which showed high levels of variability. The total number of alleles per locus ranged from six alleles at CS20to48alleles at CS248. The total number of alleles per site ranged from60alleles at site LD-b to104alleles at site LE-b. The total number of alleles at site LB-a was68, which is lower number than other sites. The average expected heterozygosity ranged from0.568at site LB-a to0.754at site LE-c. The average allelic richness ranged from3.396at site LB-a to4.848at site LE-a. By linking the analysis of agricultural landscape characteristics in the area, we found that the population at site LB-a, which is located at the highest elevation among the research sites, showed the lowest level of genetic diversity and a more homogenous genetic background. The populations at the sites near the Huangcun national agriculture-developed project area (such as LE-c and LG-b) were located at lower elevations and had a high level of genetic diversity and gene flow than other populations. Therefore, the effects of elevation on gene flow and the genetic structure of C. suppressalis are evident here.Identification of population units and environmental factorsUsing analysis of molecular variance (AMOVA), analysis of pairwise FSTS, STRUCTURE clustering analysis and CAUSAL MODELING analysis, we found that mountain ridges and geographical distance were factors that were significantly associated with genetic divergence among sites at the fine spatial scale of Wuyishan. The other two factors (elevation and land cover) were also effective in shaping genetic structure in the area. Moreover, compared with mountain ridges and geographical distance, the effects of elevation and land cover were of minor importance. The Jiuqu River had no significant influence on gene flow or genetic structure between populations at different sites of the river.2. The effects of agricultural landscape characteristics on patterns of genetic variation within and among populations of C. suppressalis at the large spatial scale of FujianGenetic diversity and patterns of differentiation among sitesIn this study, a total of215individuals from21sites were considered for analysis. The16microsatellite primers were used to amplify a total of386loci, all of which showed high levels of variation. The total number of alleles per locus ranged from five alleles at CS20to53alleles at CS248. The total number of alleles per site ranged from53alleles at site Shaowu (SW) to124alleles at site Wuyishan (WY). The total number of alleles at site Xiapu (XP) was67, which was lower number than the other sites. The average expected heterozygosity ranged from0.521at site SW to0.703at site Hanjiang (HJ). The average allelic richness ranged from3.313at site SW to6.526at site WY. By linking the analysis of the agricultural landscape characteristics in the area, we found that the populations at sites SW, Taining (TN), Ninghua (NH), Yunxiao (YX), Dongshan (DS), and XP (which are located in areas with extreme temperatures--i.e., sites SW, TN, and NH are located in areas with low temperatures and sites YX and DS are in areas with high temperatures) showed low levels of genetic divergence and a more homogenous genetic background. Moreover, the populations at sites WY, Jianou (JO), Hanjiang (HJ), Jinjiang (JJ), and Changting (CT)(which are located in areas with intermediate temperatures) showed high levels of genetic divergence and more complicated genetic backgrounds. Therefore, the effects of climatic differences on gene flow and the genetic structure of C. suppressalis are evident here.Identification of population units and environmental factorsBy using the analysis of molecular variance (AMOVA), analysis of pairwise FsTS, STRUCTURE clustering analysis and CAUSAL MODELING analysis, we found that climatic and geomorphic differences are factors that were associated with genetic divergence among sites at the large spatial scale of Fujian. Moreover, further analyses revealed that for the climatic factor, the annual average temperature, annual average date of frost, and relative humidity were responsible for the effect of climatic differences in shaping genetic structure among the sites. For the geomorphic factor, there were two factors (elevation difference and land cover) that were responsible for the effect of geomorphic differences in shaping genetic structure among the sites.Apart from the observed results that were obtained from the fine scale of Wuyishan, at the large spatial scale of Fujian Mountain, ridges tended to have slight but non-significant effects on gene flow and genetic structure between populations at the different sites of the ridges, whereas geographic distance was without effect. Differences in the physical geography characteristics and population density also had no effect on gene flow or genetic structure of C. suppressalis between sites.In conclusion, high levels of genetic diversity and divergence were observed within C. suppressalis populations at two different spatial scales in Fujian province. At the fine spatial scale of Wuyishan, patterns of genetic variations within and among C. suppressal populations were structured mainly by agricultural landscape features such as mountain ridges, elevation difference and land cover. In contrast, at the large spatial scale of Fujian, the climatic (e.g., annual average temperature, annual average date of frost, and relative humidity) and geomorphic (e.g., elevation difference, and land cover) differences were the landscape factors that were associated with genetic divergence within and among C. suppressalis populations in the research area. Therefore, landscape features are effective in structuring genetic diversity and divergence within and among C. suppressalis populations. The landscape genetic studies of pests can provide valuable information for identifying the sources of insect pest spread and the potential barriers to further dispersal, which can then be used to optimize the spatial patterns of the landscape and make proper management decisions for area-wide pest management programs. |
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