The Population Dispersion Of Chinese White-Bellied Rats (Niviventer Confucianus) In Thousnad Island Lake

Population dispersal has always been an hot subject in analysis of small mammals. An in-depth survey on population diffusion characteristics of small mammals plays an positive role in protecting species being beneficail to small mammals and in preventing species being harmful to small mammals.We tested two populations of Chinese white-bellied rats (Niviventer confucianus) that were trapped in Thousand Island Lake region using capture-mark-recapture (CMR) method from July to November in 2009 and March to September in 2010. The method of ecology and molecular biology was used to analyze the effects of sex, age and dispersal distance on the number of dispersers.Explored the dispersal characteristics of N. confucianus populations.The main results and conclusions are as follows:1. Our results showed that the dispersal ratio of N. confucianus was 37.96%, which is much higher than the Meriones unguiculatus and Microtus fords that lived in the mainland. We considered that food and space limitation on islands might lead to the higher dispersal ratio than that of mainland populations.2. Dispersal ratio showed significant difference in different seasons, and the dispersal peak was in spring, especially in March. Previous studies showed that the peak breeding of N. confucianus was in April and May. We thought that the breeding behavior was high in spring, producing to the larger population quantity, and the breeding pressure lead to the disperse of some individuals.3. Sex-biased dispersal was found, and the males were apt to disperse (x2=12.542, df=1, P<0.001). We considered that more males diseprsed in order to avoide inbreeding or get more breeding opportunity, but the point still need the support of genetics verification. Significant difference was found on the breeding period (χ2=4.504, df=1, P=0.034) when the pregnant rats were counted, which meant the pregnant females affected the disperse model during breeding period.4. Compared to the immature males in sub-adult stage, sexually mature males were apt to disperse. The body weight of different sexual rats showed no significant difference. The number of dispersers was related with their age, and more dispersers were found in the sub-adult group compared with other groups. The juvenile group was limited by their capacity of activity, and the adult group had enough food and spouse resources for their dominant positions in the population, but the sub-adult group had larger pressures on food resource or reproductive opportunity.5. There was a significantly positive relationship between the number of dispersers and the size of social groups, and the larger social group had more dispersers. Social group size reflected the level of competitive pressure on spouse resource, which meant the social pressure might be a reason for disperse of N. confucianus.6. The dispersal distance exhibited highly significant difference between males and females, and the dispersal distance of females (282.97±16.14 m) was farther than that of males (146.70±6.80 m). Such phenomenon may be caused by the promiscuity system of N. confucianus or avoiding inbreeding. Female offsprings tend to disperse farther away from maternal nest to establish a new territory to avoid resource competition, meanwhile reduce the inbreeding probability. While no matter males or females, dispersal distance had no significant relationship with age, body mass, and the maximum movement distance.7. In this study, we reported the gene flow, population bottlenecks and dispersal pattern of N. confucianus populations, using seven microsatellite loci based on 138 individuals.The gene flows of all loci were larger, Gene flow is bound to the decreasing trend in different Niviventer confucianus population over time. Population bottleneks showed that all geogaphic populations had experienced bottleneck effects during the recent period. The sex-biased dispersal analyses. The results of five different genetic index from microsatellite: Hs, Fsr, r, mAIC and vAIC were tested of both sexes over all populations. The value of females in the Fst, r and mAIC were greater than male. However, the value of male in the vAIC and Hs were greater than females. But the difference in the mAIC (♀:mAIC=0.67468, ♂:mAIC=-0.54152, P<0.05) and Hs (♀:Hs=0.8788,♂:Hs=0.8914, P<0.05) were significant. All the genetic information suggested that it is male-biased dispersal in Niviventer confucianus.