Genetic Diversity And Microevolution Of Daphnia Galeata In Waters Located In The Middle And Lower Reaches Of The Yangtze River, China

The middle and lower reaches of the Yangtze River are the main areas for the distribution of eutrophic lakes in China.The differences in water environment of different lakes may lead to the variations of cladoceran genetic diversity.D.galeata is widely distributed in the middle and lower reaches of the Yangtze River and often regarded as a model organism.In this paper,the genetic diversity and differentiation of D.galeata populations in seven lakes located in the middle and lower reaches of the Yangtze River were studied using 16 S rDNA and CO I genes as molecular markers,as well as their combination of the two gene sequences.Moreover,the genetic variations of four D.galeata subpopulations from different sedimentary layers(A:1-3 cm,B:4-6 cm,C:7-9 cm,D:? 10 cm)in Lake Chaohu were also analysed.The main results are as follows:1.In the combined 16 S rDNA and COI gene sequences,54 variable sites and 33 haplotypes were observed among 152 individuals from seven D.galeata populations in the middle and lower reaches of the Yangtze River.Haplotype diversity of seven D.galeata populations was 0.69,which ranged from 0.34 to 0.84,and their nucleotide diversity was 0.37%,which ranged from 0.05% to 0.55%.The F-statistics(Fst)value of seven D.galeata populations was 0.05.According to the neutral test,D.galeata located in the middle and lower reaches of the Yangtze River had experienced a bottleneck effect in the history.Molecular variance analysis(AMOVA)indicated that the genetic differentiation of seven D.galeata populations mainly occurred within populations(94.99%).Seven D.galeata populations were clustered into three groups,namely,LG,WC,PH and JS populations from the middle reaches of the Yangtze River,DS and TH populations from the lower reaches of the Yangtze River,and CH population located in the middle and lower reaches of the Yangtze River,which were consistent with their geographical distribution.However,no significant relationship was observed between the genetic differentiation of the seven D.galeata populations and their geographical distance(P=0.08).Our results suggested that the genetic differentiation of D.galeata from the water bodies located in the middle and lower reaches of the Yangtze River resulted mainly from the geographical isolation.2.Mitochondrial 16 S rDNA,COI gene and their combination were used as molecular markers to analysize the genetic diversity of D.galeata subpopulations in different sedimentary layers of Lake Chaohu.In the 16 S rDNA gene sequences,the A+T content(65%)was significantly higher than that of C+G(35%).Using the Kimura 2-parameter model,the genetic distances among four D.galeata subpopulations in different sedimentary layers of Lake Chaohu were from 0 to 0.012.In the CO I gene sequences,the A+T content(54.9%)was significantly higher than that of C+G(45.1%).Using the Kimura 2-parameter model,the genetic distances among four D.galeata subpopulations were from 0 to 0.045.In the combined sequences of 16 S rDNA and CO I gene sequences,the A+T content(60%)was significantly higher than that of C+G(40%).Using the Kimura 2-parameter model,the genetic distances among four D.galeata subpopulations were from 0 to 0.028.N-J tree constructed by the genetic distances of the combined gene sequences of 16 S rDNA and CO I showed that four D.galeata subpopulations from different sedimentary layers of Lake Chaohu were clustered into two branches,of which A,B and C subpopulations were clustered into one branch,whereas subpopulation D was clustered into the other branch.The results suggested that the genetic differentiation had occurred among the D.galeata subpopulations in different sedimentary layers of Lake Chaohu,and the degree of genetic differentiation may be related to the nutritional status of the sediments.In conclusion,the genetic diversity of D.galeata from the waters located in the middle and lower reaches of the Yangtze River was different in both spatial(among the D.galeata populations in different water bodies)and temporal(in different sedimentary layers)levels.Spatially,genetic differences are mainly caused by geographical isolation among lakes,whereas temporal genetic differences may be mainly caused by long-term historical changes of other environmental factors(such as nutrient status).