Population Genetic Structure And Outbreak Mechanism Of Holcocerus Hippophaecolus Disaster Analyzed By Molecular Ecology Method

The seabuckthorn carpenter moth (Holcocerus hippophaecolus Hua. Chou, Fang et Chen) is a native species throughout the north of China and is considered the main threat to seabuckthorn, Hippophae rhamnoides L. in last 15 years. The influence of outbreaks, environmental factors and host species in shaping the genetic variation and structure of H. hippophaecolus were assessed by using Amplified Fragment Length Polymorphism (AFLP). The phylogenetic relationships among H. hippophaecolus and its closely related species were analyzed, the results uncovered important role of host selection in the evolutionary history of H. hippophaecolus.1. The fluorescence labeling technique of AFLP was established. Three primers combinations were used for amplification of genomic DNA by both fluorescence labeling technique and silver staining technique. The results showed that, compared with silver staining technique, using fluorescence labeling work efficiency and could get much more bands. Nine selective primer combinations which revealed sufficient amplified bands with high resolution and polymorphism were selected from 100 pairs of primer and clear fingerprints were obtained. The fluorescence labeling technique AFLP analyze system can be used to study population genetic diversity and structure.2. The population genetic variation and structure of H. hippophaecolus from 10 different areas across its range with contrasting historical patterns of outbreak events were described by using AFLP markers. The evidence of limited gene flow among samples collected from 10 locations was detected. Independent population structure of H. hippophaecolus can be explained by geographical isolation, environmental heterogeneity and low dispersal capacity. H. hippophaecolus did not follow an isolation-by-distance pattern. The results also rejected the hypothesis that outbreak and drought events were driving the genetic structure of H. hippophaecolus. Rather, the genetic structure appears to be influenced by various confounding bio-geographical factors. 3. The hypothesis that outbreak-associated genetic divergence exist among populations was rejected, as evidenced by genetic clusters containing a combination of populations from historical outbreak areas, as well as non-outbreak areas. AMOVA results confirmed the presence of mild and nonsignificant genetic differentiation total variability was due to the variation between outbreak and non-outbreak groups. A small number of markers (4 of 933 loci) were identified as candidates under selection in response to population densities.4. Our results support the notion that outbreak events were likely to be endemic population changes from latent to epidemic rather than being due to insects with an outbreak-associated genotype spreading to outbreak areas. H. hippophaecolus samples were collected from both plantation and natural forestry in two different locations. The genetic relationship among samples based on mtDNA CO I sequences indicated that H. hippophaecolus in plantation are indigenous to those two locations respectively.5. Genetic diversity and differentiation of H. hippophaecolus sympatric populations from four different host trees were detected in Jianping. Higher Nei's heterozygosity was found in the population feeding on seabuckthorn than other hosts populations. There were detectable genetic differences between H. hippophaecolus populations occupying different host trees. Host races might exist in H. hippophaecolus used seabuckthorn and other host plant. In Jianping, genetic divergence pre-dating the introduction of seabuckthorn, the possibilities of an ancestral host shift in seabuckthorn carpenter moth are suggested.6. Based on MP and Bayes tree reconstructed from the mtDNA CO I sequences. The H. hippophaecolus and H. vicarious were interspersed throughout the tree indicated they are the most closely related. Variation within and between species from population genetic perspectives were detected. Divergence between H. hippophaecolus and H. Vicariou has been relatively recent. There is little phylogenetic resolution and no significant genetic variance between species. Genome scan approach was further used to detect positive loci under divergent selection among populations of H. hippophaecolus / H. vicariou complex feeding on different host plant. Based on 242 Amplified Fragment Length Polymorphism (AFLP) markers, four loci (1.6%) were identified as candidates for adaptation to host plants. The evidence for positive selection suggests an important role of host selection in the evolutionary history of H. hippophaecolus.The results provide scientific evidence in revealing the molecular mechanism of outbreak of H. hippophaecolus disaster. Furthermore, they are also useful in establishing control measures to H. hippophaecolus.