Study On Population Quantity Dynamics Prediction And Mitochondrial DNA Polymorphism In Lagurus Lagurus

Lagurus lagurus is one of major rodent pests in desert grassland. In China, it only distributes in Xinjiang. The harmfulness of L. lagurus is a serious problem for long time, because of undulation of population number and perniciousness. We captured all L. lagurus in delimited areas of Mu-lei county where has been constantly infested by L.lagurus annually. We have captured total of 396 L. lagurus as samples (male:204, female:192) for the biological measurements including average number of litters, reproductive features, testis sizes and sexual distinctions. We divided L. lagurus into four age groups (I, II, III and IV) and observed that the age ratio of the population was changed from September 2000 to September 2001. In September, 2000,majority age groups wereⅡ-age (subadult) and Ⅲ-age (adult) with their age ratio of 0:4.62:5.24:1. Whereas, the majority age groups were changed toⅠ-age (juvenile) and Ⅲ-age which were accounted for 48.5 percent and 40.6 percent in April, 2001 due to the growth results of September, 2000 and the ratio was 4.46:0:3.73:1. In July 2001, the percentage of Ⅰ-age was only 7.2 and the ratio was changed to 1:5.58:3.61:3.41. However, in September 2001,the populations of L. lagurus were disappeared completely. According to measured data, testis sizes from animals captured in September 2000 were different remarkably from that in April and July 2001, and not differences among their age groups, which was indicated that L. lagurus in September 2000 did not have reproductive abilities. By use the same method, we have observed that L. lagurus in April 2001 and groups from Ⅲ-age and Ⅳ-age (old) in July 2001 have reproductive abilities. In addition, the reproductive ability from theⅡ-age group in July 2001 was intermediated between the groups in September 2000, Ⅲ-age group in April and Ⅳ-age group in July 2001.To female L. lagurus, Ⅳ-age group in September 2000 participated in reproduction with their rate of pregnancy around 15.38 percent and yet with average litters reached to 10.50±0.71 per animal; the groups from Ⅲ-age and Ⅳ-age L.lagurus in April 2001 participated in reproduction with their pregnant rate at comparatively high and accounted for 86.96 percent and 100 percent, whileas their average litters were only 7.00±1.59 and 6.80±1.10, respectively, which were lower than that of September 2000. The pregnant rates from Ⅲ-age and Ⅳ-age groups in July 2001 were 67 percent and 86 percent with their average litters around 4.38±1.69 and 7.00±1.55,respectively, which were lower than before.We have predicted the numbers of L. lagurus in different periods by using several prediction factors such as sexual ratio, pregnant rate and average litters, and Leslie matrix model. With the exception ofⅠ-age group, the predicted results have been identical to actual field data. Based on the results from the calculated and field, we have obtained a live coefficient C in Ⅰ-age group. According to the live coefficient C, we modified the predictions for this age group and come to a conclusion that is corresponding to actual field data. In other words, the numbers of Ⅰ-age and Ⅱ-age were nearly zero with their densities below 4/hm2. These results suggest that L. Lagurus population began to decline. In this study, we have also investigated the genetic polymorphisms from these animals by means of mithochondrial DNA RFLP analysis. After isolation of mitochondrial DNA of L. lagurus by using an improved method, samples were digested with 6 restriction endonucleases, HindIII, EcoRI, EcoRV, PstI, ApaI and BstxI. The patterns from the restrition digestions were examined by electrophoresis in an agarose gel and six of polymorphisms have been observed. Extensive mitochondrial DNA polymorphisms were found among lagurus lagurus, Mus musculu,Rattus norvegicus and mice. The findings will help us to understand the dispersion and evolution of these animals.