Temporal And Spatial Heterogeneity Of Genetic Diversity Of Daphnia Galeata In Four Large Reservoirs In Tropical And Subtropical China

To understand the spatial and temporal heterogeneity of the genetic diversity of Daphnia galeata populations in tropical and subtropical regions,we used microsatellite DNA and mitochondrial CO? to investigate the population genetic structure in Daphnia galeata from four large reservoirs in two spatial scales in China.By using a long-term monitoring data,we analyzed the temporal changes in genetic structure in a deep subtropical reservoir(Liuxihe reservoir in Guangdong Province).We aimed to investigate the inter-annual differences in the genetic structure of D.galeata populations and explored spatial heterogeneity in the genetic structure within an individual reservoir.For Liuxihe reservoir,D.galeata was sampled and collected for six years from 2012 to 2017,and its expected heterozygosity ranged from 0.284 to 0.546.The population collected in May of 2013 was the highest,and the lowest in January of 2017.There are two modes for the variation of genetic diversity of D.galeata: 1)the highest genetic diversity occurred exactly at the peak of population abundance;2)the genetic diversity is highest in the beginning of the growing season.And the shared Multilocus genotype(MLG)appeared between years.Using Discriminant Analysis of Principal Components(DAPC),the genetic structures of all populations was grouped into three temporal groups: 2012,2013,and 2014-2017.The genetic structure of the nine temporal populations of D.galeata in 2016-2017 was also divided into three groups.The populations at the end growing season in 2016 and those at the initial growing season in 2017 were clustered into one group.The genetic structure was regulated by both the over-summering populations and eggs bank.We comparatively analyzed the genetic diversity of D.galeata in the four large reservoirs,including Liuxihe reservoir(Guangdong Province),the Xinanjiang Reservoir(Zhejiang Province),Xujiahe Reservoir(Hubei Province),and Chaishitan reservoir(Yunnan Province).The genetic diversity(He)based on microsatellite DNA and the haplotype diversity(Hd)of mitochondrial CO? were consistent for the D.galeata populations in Xinanjiang,Xujiahe and Liuxihe reservoirs.The highest genetic diversity occurred in Xinanjiang reservoir,followed by Xujiahe and Liuxihe reservoirs.However,the expected heterozygosity of the Chiashitan reservoir was higher(He=0.410)and the haplotype diversity was lower(Hd=0.071).This inconsistency between He and Hd may be due to interspecific hybridization within the complex species or the loss of mitochondrial diversity faster under strong selective pressures.The mitochondrial CO? based haplotype diversity was positively correlated with the reservoir size.One of the thirty-two observed COI haplotypes were shared by the populations in four reservoirs.There was no significant differentiation in the genetic structure of the populations between the four reservoirs.In the analysis for a single reservoir,the highest genetic diversity occurs mainly in the transitional zone or the central lacustrine zone.At the initial growing season,there were obvious spatial difference in the genetic structure between the four sampling sites of Chaishitan reservoir,and the difference disappeared in the end growing season.The population genetic diversity in the center lacustrine zone of the Liuxihe reservoir shown rather different from those for the other three sampling sites at the initial growing season,and this difference reduced in the end growing season.The populations near the dam and at Xiaojinshan in Xinanjiang reservoirs differed greatly at the initial growing season,and the four populations at the end growing season were divided into three distinct groups.There was no significant difference in the genetic structure among the four populations in the Xujiahe reservoir between the initial and end growing season.Except for Xujiahe reservoir,there was spatial difference in genetic structure between the other three reservoirs.There are two reasons for the spatial difference of genetic structure: 1)dormant eggs randomly germinated lead to differences in the genetic structure of the initial population;2)the environmental conditions between sampling locations created different selection pressures,resulting in genetic differences between populations in different regions.