Studies On Population Genetics Of A Mixed-ploidy Species Chamerion Angustifolium Based On Microsatellite Markers

Mixed-ploidy species provide a unique opportunity to study mechanisms of polyploid evolution.Chamerion angustifolium is a perennial plant belonging to Chamerion genus of family Onagraceae,with highly medical and ornamental values.It is widely distributed in Asia,Europe and North America.C.angustifolium has three cytotypes with diploid,autotetraploid and autohexaploid(2n=36,72,108).Therefore,as an example of C.angustifolium,the study aims to determine the dominant factor for the genetic diversity and structure of a mixed-ploidy species.In the study,959 C.angustifolium individuals from forty natural populations were collected.Among populations,there are 30 domestic populations and one from UK,one from Finland and eight from Canada.The ploidy level was detected by flow cytometry.In China,there are ten diploidy,twelve nineteen tetraploidy and eight hexaploidy populations;the populations from UK and Finland are diploidy;whereas one diploidy and seven tetraploidy populations are in Canada.At the species level,genetic diversity of C.angustifolium was high(HO=0.561,HE=0.697,AR=12.500 and I=1.523),suggesting that species C.angustifolium is of high environmental adaptability.The genetic diversity among cytotypes was ranged:tetraploids>diploids>hexaploids;and the effective population size increased with the ploidy level.However,it is the major factor influencing the pattern of inter-cytotype genetic diversity of C.angustifolium.Furthermore,the numerical solution suggested that inter-cytotype gene flow exhibited a unimodal distribution,i.e.,tetraploids can receive more gene flow than diploids and hexaploids.Besides,tetraploids C.angustifolium received a significantly higher average migration rate than the others.Thus,this can explain the difference of genetic diversity among C.angustifolium cytotypes.What’s more,the inbreeding coefficients of polyploids are higher than that of diploid,likely due to selfing and clonal reproduction.The result of AMOVA,Bayesian clustering,UPGMA clustering and PCoA revealed that the overall population genetic divergence being high among continents but low among cytotypes.Furthermore,both partial Mantel test and MMRR showed only a significantly positive correlation between genetic and geographical distances.Thus,population genetic structure of C.angustifolium only satisfies the isolation-by-distance pattern.These results suggest the existing gene flow among cytotype.Therefore,the current study suggested that the inter-cytotype gene flow may play an important role in shaping patterns of genetic diversity and population genetic structure of a mixed-ploidy species.