| Betula is a taxonomically complex group due to its considerable morphological variation,polyploidy and frequent hybridization.The taxonomy and phylogenetic position of dwarf birch species in the Daxing’an Range remain unsolved despite some previous researches on it.We integrated morphology,microsatellite markers and high-throughput sequencing to solve the taxonomic issues of dwarf birch species in the Daxing’an Range.In this thesis,we performed morphometric analyses on 1,000 leaves from 200 individual dwarf birch species;We genotyped 310 individuals using microsatellite markers;We performed RAD-seq for 44 individuals.We integrated morphological analysis,population genetic structure,ploidy,and phylogenomics.Our study clarified the phylogenetic positions of Betula fruticosa and B.middendorfii and resolved the taxonomic disputes of dwarf birch species in the Daxing’an Range.Our results are as follows:First,we prelimitary grouped our samples from the Daxing’an Range into two species,namely,B.fruticosa and B.middendorfii according to morphological descriptions from Flora of China.Morphometric analyses showed that the two species can be partially distinguished based on leaf morphology.Second,ploidy inferred from RAD-seq data showed that B.fruticosa was diploid and B.middendorfii was tetraploid.Third,population genetic structure based on microsatellite markers and RAD-seq showed that B.fruticosa and B.middendorfii formed distinct genetic clusters.Microsatellite markers revealed bidirectional genetic admixture between B.fruticosa and B.middendorfii.RAD-seq result showed unidirectional genetic admixture occurred from B.fruticosa to B.middendorfii.Fourth,phylogenomics analyses showed that B.fruticosa and B.humilis formed a cluster and B.middendorfii and B.nana formed a cluster.This suggests that B.fruticosa and B.humilis were closely related species and B.nana may be one diploid parent of B.middendorfii.In summary,this thesis systematically investigated the classification of dwarf birch species in the Daxing’an Range.We resolved the phylogenetic position of the two species and pointed out the taxonomic mistakes of B.fruticosa and B.middendorfii.These results provided scientific guidance for protection and utilization of Betula germplasm resources. |
