Studies On Genetic Diversity And Population Genetic Structure Of The Whorl-leaf Watermilfoil Myriophyllum Verticillatum

Myriophyllum verticillatum L.,is a perennial aquatic plant widespread in Eurasia,North America and Northwest Africa.This species is tetraploid and can propagate by both sexual seeds and asexual stolons,plant fragments and turions.Previous studies on Myriophyllum species mainly focused on Eurasian watermilfoil M.spicatum.None of them were related to the genetic diversity and population structure of M.verticillatum.In this study,we successfully developed 17 microsatellite loci for M.verticillatum and used these microsatellite loci and two chloroplast DNA regions to examine the genetic diversity and population genetic structure of 33 populations in China by using the developed microsatellite loci and two chloroplast regions.The main results are listed as follows:1.Five microsatellite loci were successfully developed for M.verticillulatum using the microsatellite-enriched library method.Twelve microsatellite loci were selected from 20 published loci of M.spicatum.These 17 loci were tested to be easily amplified and have good polymorphism for M.verticillatum.2.The results of microsatellite loci showed that the genetic diversity of populations from high to low was Northeast China,Northwest China,and the QTP plus Southwest China.One third of populations were monomorphic.The AMOVA revealed that genetic variation mainly occurred among populations.According to STRUCTURE and PCOA analyses,33 populations were divided into two genetic clusters A and B.Populations form Northwest China were assigned to Cluster A,and populations from Northeast China and the QTP plus Southwest China were assigned to Cluster B.Genetic differentiation among three regions was significant and the overall genetic differentiation among populations was high(FST=0.3441).The level of genetic differentiation for each region from high to low was the QTP plus Southwest China,Northwest China and Northeast China.The IBD pattern was presented in Northwest China,the QTP plus Southwest China,and in the whole range,rather than Northeast China.3.The results of cpDNA markers showed that the overall genetic differentiation is high(FST=0.5344).The IBD pattern was presented in the whole range.Five haplotypes were detected in 33 populations and 27 populations consisted of only one haplotype.No obviously phylogeographic pattern(NST=0.588<GST=0.664)was detected in China.Mismatch distribution analysis and netural tests suggested recent population expansion and bottleneck effect did not occur in M.verticillatum.In conclusion,the level of genetic diversity of M.verticillatum is relatively low and the percentage of monomorphic populations is high.The level of genetic differentiation among populations is high.There is a significant correlation between genetic distance and geographical distance,indicating that geographical isolation is the main factor of genetic differentiation.Most of genetic variation existed among populations.The QTP plus Southwest China populations shows highest level of population genetic differentiation among three regions,which is mainly caused by its topography,geographic isolation and high percentage of clonal reproduction.This study reveals the genetic diversity and population genetic structure of M.verticillatum in China and the effects of topography and geographic isolation,which can help people further understand the evolutionary process of aquatic plants.