A Study On The Effects Of Environmental Pollutions On The Genetic Structure Of Gammarrus Pulex

The characteristic of population genetic structure is a potentially promising in biomarker development for resistance and environmental indicator. The dynamics of the population genetic composition can be used for monitoring and assessing environmental stress factors. In this thesis, we employed the horizontal starch gel electrophoresis and staining techniques to identify allozyme frequencies at four allozyme loci in a natural Gammarrus pulex population collected from Yunzhong River, Yuanping City, Shanxi, and detected the population's genetic background. A preliminary survey examined the genetic structure of this natural population. A later study determined the relationship of polymorphic genotype frequency and several contamination factors (heavy metal CdCl₂ and pesticides malathion and deltamethrin). It also compared the survivorships among the individuals of different genotypes acutely exposed each of the environmental stressor. In those survivorship tests the individuals were exposed to a selected toxin and the surviving individuals were considered resistant, and the dead individuals as sensitive. The genotypes of both the dead and survivors were determined to identify the resistant and sensitive genotypes.At the concentration that is equivalent to the LC₅₀ values of CdCl₂, malathion and deltamethrin, the Gammarrus pulex samples were acutely exposed to the corresponding concentration solutions respectively. A total of 268 Gammarrus pulex individuals were exposed to CdCl₂, 382 to malathion, and 202 to deltamethrin, the dead individuals were taken out immediately and frozen for allozyme analysis. The allozyme electrophoresis identified 7 lociUDH-1, IDH-2, PGI, PGM-1, PGM-2, AO-1, AO-2) of 4 enzymes (IDH, PGL PGM, AO). The allele frequency were determined at each locus. The population was found at high levels in genetic diversity, but the PGM-2 was found nonmorphic with fixed allele. The percentage of polymorphic loci is 71.4%, the mean number of alleles per locus is 2.9, and the mean heterozygosity per locus is 0.226. The genotype frequencies at all the four polymorphic loci fit to the Hardy-Weinberg's expectations, and therefore the population can be used for effective quantitative genetic analysis.The CdCl2 exposure demonstrated different lethal effects at six genotypes of PGI. Significant genotypic effects on the survivorship was observed between the genotype pair of PGI-AB vs. PGI-CC (P<0.05). The data suggested that PGI-CC genotype related to the sensitivity to CdCl2. The mortality analysis among the allozyme genotypes of G. pulex showed no significant correlation between the genotypes and lethality among the genotype at other four loci: IDH-1, IDH-2\PGM-1and AO-2 (P>0.05). In this case, CdCl2 displayed random lethal effects on each genotype. However, at PGI and AO-1 the mortality of individuals exposed to malathion varied significantly depending on genotypes. Significant genotypic effects on the survivorship between the genotype pair of PGI-AC vs. PGI-AD (P<0.05);AO-l-AC vs. AO-l-BB, AO-l-AC vs. AO-l-CC were observed. The data demonstrated that malathion toxicity displayed nonrandom lethal effects on individuals with different genotype at the loci of PGI and AO-1. The delamethrin displayed random lethal effects on PGM-1 and AO-1, with no significant correlation between the survivals and deaths (P>0.05). In contrast, at the loci of IDH-1, IDH-2, PGM-1 and AO-2, the mortality of individuals deviated with different genotypes. It is likely that the differential survivorship may result in the differentiation in the genetic composition in the population of Gammarus pulex.