Phylogeography Of Tamarix Austromongolica And T.chinensis,endemic Tree Species Distributed Along The Yellow River

The uplift of the Qinghai-Tibet Plateau(QTP)dramatically changed the topography of Asia,and the direction of flow of the Yellow River system from west to east is closely tied to this uplift.The Yellow River is not only known as the cradle of China's ancient civilization but also act as one of the factors that affect the geographical distribution of species.She can provide moist habitat for seed germination and plant growth of hydrochorous riparian species.The present work analyzed the systematic relationship,phylogeography and population genetics of two tree species that are widely distributed along the Yellow River,Tamarix austromongolica and T.chinensis,to understand the role of the Yellow River and Pleistocene climate in shaping their distribution patterns.The main results are listed as following:(1)Both morphology and chloroplast DNA sequences of Tamaricaceae containing nine species revealed that T.austromongolica and T.chinensis clustered together within a clade;(2)Two cp DNA fragments from a total of 382 individuals and n DNA ITS fragments of 45 populations and two out-group individuals were sequenced.The mismatch distributions,neutrality tests and extended Bayesian skyline plots analysis indicated the two species experienced a continuous demographic expansion,and the occurrence of the expansion was closely matched to the formation of the modern Yellow River and the occurrence of dramatic climatic and temperature shifts.Our results provide support for the roles of the Yellow River and the Pleistocene climate in driving demographic expansion of the populations of two Tamarix species.Additionally,the models of paleodistribution also revealed that these two species experienced a demographic expansion in population size during the Quaternary period;(3)The estimate of divergence time for chlorotypes indicated that divergence of chlorotype C1,the most widely distributed in the Yellow River basin,was 0.19 Ma(95% HPD = 0–0.54).The divergence time of C10(found in GYJ)was 1.85Ma(95%HPD = 0.70–3.23),and the divergence time of C5(found in NMDK,NMWH,and NXYC)was 1.23 Ma(95% HPD = 0.45–2.13).Approximate Bayesian computation indicated that Tamarix in the lower reaches of the Yellow River came from the upstream was the best-supported scenario;(4)The haplotype and nucleotide diversities inferred from cp DNA sequences show that a low level of variation existed among the populations.The haplotype diversity Hd of NMDK was 0.60 and the nucleotide diversity ? was 0.41×10-3;the haplotype diversity of GLZ was 0.56;the Hd and ? of SHQ was 0.17 and 0.10×10-3,respectively;Hd = 0.13 and ? = 0.08×10-3 was detected in HKF and SJN;the Hd and? of RHK was 0.11 and 0.07×10-3.As a whole,it was found that populations in the upper reaches of the Yellow River displayed a higher genetic diversity,whereas populations in the lower reaches displayed a lower genetic diversity;(5)We used microsatellite to evaluate the genetic structure of T.austromongolica and T.chinensis and the role of the Yellow River drainages in shaping the structure.We found only 4.21% of the variation was distributed among T.austromongolica populations.For T.chinensis,the genetic variation among populations only explained2.0% of the total variation;and the low levels of genetic differentiation was detected between populations within species on the north and south banks.Additionally,discriminant analysis of principal components(DAPC)and Bayesian analysis revealed a weak population structure in T.austromongolica and T.chinensis.Thus,the Yellow River would not act as a barrier to long-distance dispersal of Tamarix;(6)The biparentally inherited nuclear markers indicated that both species exhibited moderate levels of genetic diversity.The Nei's gene diversity H of NMWH populations located in the upper reaches of the Yellow River was 0.74 and the allelic richness AR was 3.39;the allelic richness of NMBY and NXYCX was 2.82;whereas the Nei's gene diversity of SDH located in the lower reaches of the river was 0.36,and the allelic richness was the lowest(1.80)in comparison to other populations.Therefore,wild Tamarix resources with high genetic diversity located in the upper reaches need to be given priority for conservation.The sequencing and SSR technique were used to analysis the demographic history and the evolution of two Tamarix species,as well as the genetic diversity and population genetic structure.The results are useful for understanding the geologicalhistory of the Yellow River from the biological perspective and the response of temperate tree species to past climate change.Simultaneously,the results can provide references for the evaluation and protection of wild Tamarix resources.