Analysis Of Social Forms & Genetic Diversity In Different Geographic Populations Of Solenopsis Invicta Buren In China

The Ministry of Agriculture of China(MAC) solemnly declared that the red imported fire ant(RIFA),Solenopsis invicta Buren(Hymenoptera:Formicidae) have been discovered in Guangdong Province of China on January 17 of 2005.Then,MAC also confirmed the distribution of RIFA in Guangxi,Fujian and Hunan Province,and the area of distribution was over 32,000 hectares.In order to minimize the loss caused by RIFA, studies on RIFA were carried out immediately.For the purpose of providing a scientific and effective theoretical basis for quarantine inspection,monitoring and controlling,we carried out a discriminating Gp-9^Bb alleles test to analyze the social forms and distribution of RIFA,and analyzed the phylogenetic relationship and population structure of different RIFA geographical populations with microsatellite technology to show the origin of invasion.The results are as follows:There are monogynous and polygynous colonies in RIFA,which are highly associated with the variations in their behavior and ecology.Investigating and understanding the social forms of RIFA colony were therefore an important step to develop a sound monitoring and controlling program for the pest in a given area.In this study,fire ant workers collected in 16 counties of 4 provinces in mainland China were tested by discriminating Gp-9Bb alleles with multiplex PCR technique.Results obtained showed that both monogyne and polygyne were presented in mainland China,but with polygynes dominant.The ratio of polygynous to monogyfious colonies was 97:23(4:1) in the 120 fire ant colonies collected and tested,but differed as location varied.The ratio of polygynes to monogynes in Guangdong province,i.e.was 66:20(3:1) whereas that in Guangxi province was 21:3(7:1).Six microsatellite loci(sol-6,sol-11,sol-20,sol-42,sol-49 and sol-55) were selected and the results of the PCR from 238 samples of the 6 grographical populations(Guangxi, Yuexi,Zhusanjiao,Hunan,Fujian and Taiwan) of RIFA were obtained.45 alleles were tested in all the loci and the mean allelic number was 7.5 per locus,the least one was 4. The efficient allelic number was 18.75,tested efficient allelic number was less than the number observed,this was result from the unequal alleles distribution. Six chosen microsatellite loci showed a good polymorphism in the 6 different geographical populations.The Hardy-Weinberg equilibrium analysis revealed a remarkable genetic equilibrium and an obvious diversity at most of the loci in 6 geographical populations.Nonequilibrium population might be caused by exotic population invasion,natural selection,and random mating change.The average polymorphism information content(PIC) varied between 0.0000～0.8011 within different geographical populations.The observed heterozygosity(Ho) ranged from 0 to 1.000,and the expected heterozygosity(He) ranged from 0 to 0.8371,and the average Ho was between 0.5740～0.7778.The Ho of Fujian population was the highest(0.7778),while the Ho of the Guangxi population was the lowest(0.5740).It showed an obvious genetic variation in Fujian population.The average He was between 0.6104～0.7068,and it was the lowest in Guangxi population,while the highest in Zhusanjiao population.Moreover, we found that average Ho were entirely lower than average He except Fujian population and Hunan population according to the comparison of He and Ho.Although the genetic diversity was high,there were certain self-crossing rate existed in most area.The average Ho was higher than He in Fujian population and Hunan population,it demonstrated that individual self-crossing rate was low in this two populations.The F-statistic analysis indicated that the Fsr value of different locus varied from 0.0595(sol-20) to 0.1304(sol-11),and the average value was 0.0961.Although there existed high levels of intraspecific genetic variation,the interspecific genetic differentiation were moderate,genetic variation changed a little.The result was the same as judgment of gene flow(Nm).A cluster analysis of genetic distances obtained form SSR analysis was conducted by UPMGA.The results showed that Guangxi population and Yuexi population were firstly clustered,and then Zhusanjiao and Hunan were clustered,Fujian and Taiwan population was finally clustered respectively.Further UPGMA cluster analysis of the genetic distances data separated 16 populations into 4 categories,we found that Guangxi,Yuexi and Fujian populations were in the 1st group,which proved Guangxi and Yuexi populations might be from the same region;Zhusanjiao population were separated into 2 categories,Zhuhai and Zhongshan population were in the 2nd group,while Guangzhou, Shenzhen,Dongguan,Huizhou and Hunan population were in the 3rd group.The point is that,our results support the initial judgement of experts that the population of RIFA in the city of Zhangjiajie,Hunan province might be introduced from Shenzhen,which the Shenzhen and Hunan population were firstly Clustered.Taiwan population was in the 4th group independently.According to the cluster analyse,we found a certain genetic diversity among grographical populations,and a number of RIFA invasion from different origin had happened in China.