Interspecific Hybridization Of Diaphanosoma And Population Genetics Of D.Dubium In Tropic And Subtropics

In this thesis,several genetic markers were used to study the biogeographic patterns of Diaphanosoma,the most abundant cladocera in tropics and sub-tropics.We first explored its species diversity and interspecific hybridization.We developed the microsatellite markers(SSR)of D.dubium,the most widely distributed species in China,with the next sequencing technology.Its population genetics and spatial structure were analyzed for exploring the pattern of genetic differentiation and the potential mechanism.We also computated the beta genetic diversity of the populations of D.dubium and the main factors contributed to significant beta diversity in ChinaIn total,79 populations of Diaphanosoma were used for biogeographic patterns study,in which 2 populations were collected from Hungary,5 populations from Indonesia,3 populations from Philippines,3 populations from Thailand,2 populations from Viet Nam,2 populations from Cambodia and the other 62 populations from China.In addition,54 D.dubium's populations for analysis of population genetics were all collected from China.We surveyed species diversity in the genus Diaphanosoma in Asia using a morphological approach and found there were seven species.Using two kinds of markers,one from mitochondria(cytochrome c oxidase subunit I,COI)and the other from nuclear(ribosomal internal transcribed spacer 2,ITS2),we performed tests on DNA taxonomy and molecular phylogenies,and assessed the role of hybridization in explaining the cases of mitonuclear discordance.For DNA taxonomy,we used Automatic Barcode Gap Discovery(ABGD)method for both COI and ITS2 datasets and Generalized Mixed Yule Coalescent(GMYC)method for COI dataset to delimit species boundary as Poisson Tree Processes(PTP)model didn't work for our sequences,and gave us seven demonstrated species.We found that(1)cryptic species occurs in Diaphanosoma,(2)mitonuclear discordance was about 6% of the sequenced animals,(3)hybridization is supported as the most likely explanation for the discordance,and(4)there is a potential hybridogenetic species.The pattern analysis of genetic diversity in Diaphanosoma demonstrated the role of the genus as “tropical Daphnia” not only for its ecological aspects but also for its evolutionary aspects.Microsatellite markers were developed for D.dubium using the next sequencing technology.31 pairs of polymorphic and steadily variant markers were screened from the genomic library.Four natural populations were used to test the Hardy-Weinberg equilibrium.These markers can be applied to the con-generic species.To assess the utilities of the developed markers,11 microsatellite markers were applied to the population genetics of 11 tropic populations.Our data indicated that genetic diversity was differentiated between studied populations.Two populations(CQSK from a eutrophicatic reservoir and ZJDHD from an island)had low genetic diversity and other populations had high genetic diversity.The microsatellite markers developed are promising and can be applied to the population genetics of D.dubium.11 selected microsatellite markers as well as mitochondrial DNA(COI)were used to explore the population genetics of D.dubium in tropical and sub-tropical China.54 populations were used in the analysis.For COI,we obtained 552 sequences in which 98 haplotypes were identified.For SSR,1674 individuals from the 54 populations were analyzed.D.dubium didn't have a clear cut population structure,indicating the random dispersal of individuals.D.dubium was mainly composed of younger populations where older populations were rare.Environmental and spatial variables did not significantly explain the genetic differentiation.The genetic structure of the D.dubium's populations was not well explained by the monopolization hypothesis which is based on persistent founder effect and priority effect.Spatial distribution of haplotypes showed that some individuals of D.dubium can disperse as far as 3600 km,which should mainly rely on water flow.Based on haplotype richness of mitochondrial DNA,we did not find the populations with significant local contributions to beta genetic diversity.For microsatellite markers,however,there were the populations locally contributed significantly to beta genetic diversity,and they were located in tropic reservoirs and coastal islands,where hybridization was frequently found.Dispersal was the main factor influencing beta diversity of D.dubium.The beta genetic diversity correlating with latitude indicated that D.dubium may disperse through rivers which flow from west to east in China.The core populations of D.dubium were located in the middle and lower reaches of the Yangtze River,where they had the highest genetic diversity.Stratified dispersal may contribute to the expansion of D.dubium from core populations to peripheral populations.