Genetic Diversity and Population Differentiation of Main Species of Dendrolimus (Lepidoptera) in China and Influence of Environmental Factors on Them

As the major forestry pest insects in China, Dendrolimus included Dendrolimus punctatus Walker, D. punctatus tabulaeformis Tsai et liu, D. punctatus spectabilis Butler, D. superans Butler, D. houi Lajonquiere and D. kikuchii Matsumura. During sequential outbreaks, economical damage can be so extensive for forest appears to be burned and unable to withstand such a long period of defoliation. Gene diversity and genetic structure among the main species of Dendrolimus were assessed using morphological diversities, allozyme, Random Amplified Polymorphism DNA(RAPD), Amplified Fragment Length Polymorphism (AFLP), Inter-Simple Sequence Repeat (ISSR), mitochondrial DNA and Simple Sequence Repeat (SSR), which provide the powerful tool for investigation of genetic variation. The influence of ecological factors on the genetic diversity is also discussed by the correlation analysis.


Introduction
As the major forestry pest insects in China, Dendrolimus included Dendrolimus punctatus Walker, D. punctatus tabulaeformis Tsai et liu, D. punctatus spectabilis Butler, D. superans Butler, D. houi Lajonquiere and D. kikuchii Matsumura. During sequential outbreaks, economical damage can be so extensive for forest appears to be burned and unable to withstand such a long period of defoliation. Gene diversity and genetic structure among the main species of Dendrolimus were assessed using morphological diversities, allozyme, Random Amplified Polymorphism DNA(RAPD), Amplified Fragment Length Polymorphism (AFLP), Inter-Simple Sequence Repeat (ISSR), mitochondrial DNA and Simple Sequence Repeat (SSR), which provide the powerful tool for investigation of genetic variation. The influence of ecological factors on the genetic diversity is also discussed by the correlation analysis.

Morphological diversities among 4 species of Dendrolimus
For investigating the morphological diversity, many pupae of D. punctatus Walker, D.

Genetic diversities among 3 species of Dendrolimus by ISSR
A set of optimized response system of ISSR has been developed, which provides a powerful tool for investigation of genetic variation of 9 natural populations(D. punctatus spectabilis; D. punctatus tabulaeformis; D. superans) (figure4-8,table7). Shannon index shows highest genetic diversity in Weichang population(D. superans) and lowest genetic diversity in Shenyang population(D. spectabilis), which is identical with Nei′s index(table8-10). Different geographical groups in the same populations has a genetic divergence in some extent. Genetic similarities and cluster analysis shows that inter-species heredity difference is obviously bigger than the homogeneous between populations in the heredity difference, which reflects the heredity difference degree is consistent from the DNA level with the phenotype level. D. punctatus spectabilis has nearer genetic distance with D. punctatus tabulaeformis than D. superans, which is identical with that researched in sexual information of pine caterpillars(figure9).

The genetic polymorphism and genetic differentiation in mitochondrial DNA of 3 species of Dendrolimus
In order to provide the scientific basis for prevention and treatment of Dendrolimus, the genetic structure of 3 species of Dendrolimus were probed by mitochondrial DNA. Cyt b exhibits an A/T (73.6%) bias across all sites which was the most prominent at the third position of codon with the highest content of 86.5%. A/T bias was no significant difference among the populations. Nucleotide substitution occurred mostly at the third position (table14,15). Transitions were greater than transversions, while substitutions of intraspecific populations were higher than interspecific populations.        In total, 88 bands whose size ranged between 350 to 1500 bp were produced using 8 primers in RAPD analysis method (figure12-13,table23-24). Out of 88 loci, 73 bands were polymorphic at the species level. The percentages of polymorphic loci (P) was 25.19 ℅, the mean number of alleles per locus (A) was 1.252, the mean Nei's gene diversity (h) was 0.052, the mean Shannon's information index (I) was 0.090. For the species level, P= 82.95 ℅, A= 1.830, h= 0.234(table25). The coefficient of genetic differentiation between populations based on Shannon information index was 0.7490, which revealed a very high level of genetic differentiation among populations, the number of migrants per generation among populations (Nm) was 0.168, which revealed a very low gene flow among populations. The coefficient of genetic differentiation between populations based on Nei's genetic diversity was 0.7780 which revealed a very high level of genetic differentiation among populations, the number of migrants per generation among populations (Nm) was 0.143(table26,27).

The effect of environmental conditions on the genetic diversity of D. punctatus tabulaeformis populations
The genetic diversity among 3 natural populations of the Chinese pine caterpillar (Dendrolimus punctatus tabulaeformis) were tested by AFLP method in one Pinus tabulaeformis-Dahurian larch mixed forest and two Pinus tabulaeformis pure forests in Pingquan county. Besides, investigations on plant species diversity, forest crown density, incidence extent, gradient and exposure of three forest communities were taken, while dilution heat method and semi-micro Macro Kjeldahl method were used to determine the content of organic matter and nitrogen in soil(table32-36). The result of principle component analysis shows that the growth status is main factor which influent genetic diversity of D. punctatus tabulaeformis populations. Besides, site conditions had some effects on it. An integrated effect was produced by all site conditions, so main factor could not be judged(table37). Mixed forest has a great influence on gene flow among different populations of D. punctatus tabulaeformis, because gene flow between populations in mixed forest and in pure forests was lower than that of two pure forests. Gene flow between populations in pure forest with larger species abundance and in mixed forest was higher than between population in pure forest with lower species abundance and in mixed forest, which showed that the correlation between gene flow among different populations and species abundance of pine forests is negative.

Community
Tree height

The influence of ecological factors on the genetic diversity of D. punctatus spectabilis
Correlation analysis by SPSS software of 4 populations of D. punctatus spectabilis in different geographical areas shows a significant negative relation between genetic diversity and elevation, and the genetic diversity within populations was positively related with the annual temperature and moisture. In opposite, the genetic diversity was weakly related with latitude. Besides, there was a positive relation between the genetic distance and the distance of elevation, which shows that geographic isolation has obstruct effect on gene flow (table38,39). Generally, the genetic distance between groups in the same population is certainly related with the geographical distance and host(p<0.01,high notable correlativity

The influence of ecological factors on the genetic diversity of 5 sub-populations of D. punctatus tabulaeformis
The population genetic variability and genetic structure of 5 sub-populations of D. punctatus tabulaeformis in Pingquan city, Hebei province were analyzed using SSR. The influence of ecological factors on the genetic diversity is also discussed by the correlation analysis. The genetic index has positive relation with ecological factors weakly. The genetic index has positive relationship with ecological factors but not significant(table42). Stand type, slope, aspect and altitude were the main traits account for the genetic diversity according to the Principal Component Analysis (PCA).

Conclusions
For Dendrolimus, beside of population control, there were a few evidences for genetic structure and population differentiation of them. For such aspect, this paper may be a more effective approach, and morphological diversities, allozyme, RAPD, AFLP, ISSR, mitochondrial DNA and SSR should be the best probe tools.
The results shows that a very high level of genetic differentiation and a very low gene flow among the species of populations of D. punctatus When Nm < 1, the mutational pressure is not strong enough to prevent that allele from reaching high frequency, gene flow can't counterbalance genetic drift, and genetic drift will result in substantial local differentiation. There are great differences on genetic diversity of Dendrolimus populations in different www.intechopen.com Driven by the increasing necessity to define the biological diversity frame of widespread, endemic and threatened species, as well as by the stimulating chance to describe new species, the study of the evolutive and spatial dynamics is in constant execution. Systematic overviews, biogeographic and phylogenic backgrounds, species composition and distribution in restricted areas are focal topics of the 15 interesting independent chapters collected in this book, chosen to offer to the reader an overall view of the present condition in which our planet is.

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