Species Delimitation And Phylogenetic Studies Of The Adiantum Pedatum Complex

Adiantum pedatum complex(Adiantum,Pteridaceae)is distributed in North America and eastern Asia(extending to the Himalaya).Previous studies divided this complex into three independent geographically isolated subspecies by cytology,molecular biology,and morphology.Other research suggested that this complex could be divided into four clades by five chloroplast DNA regions,which implied that the A.pedatum complex probably should be divided into several species.There may be cryptic species,as morphological variation of species in the A.pedatum complex is indistinctive while the molecular differences are notable.Based on an expanded sampling of the A.pedatum complex across the distributional range,a total of 499 samples were collected from 43 populations(including outgroups).We reconstructed the phylogenetic framework of this complex using four cpDNA regions.The haplotype network map was constructed by DnaSP.The haplotype diversity,nucleotide diversity,and genetic differentiation coefficients were calculated by Arlequin.Ancestral areas were reconstructed by RASP.The origin and divergence time of this complex was estimated using BEAST.We discussed the possible refuges during the glacial period in the Qarternary and migration routes of the complex.Meanwhile,we observed and measured morphological characteristics of A.pedatum complex.The main results are presented as follows:1.Phylogenetic research of Adiantum pedatum complexFour chloroplast DNA regions(psbC-trnS?rpS4-trnS?trnL-F?and trnP-petG),the whole chloroplast genomes,and one nuclear DNA region(SQD1)were used to reconstruct the phylogenetic relationships among the A.pedatum complex using Bayesian Inference and Maximum Likelihood methods.The results showed that:(1)the A.pedatum complex is a monophyletic group.(2)Our results strongly supported A.pedatum complex divided into five lineages,i.e.,the Japanese lineage,the eastern North American lineage,the western North American lineage,the western Chinese lineage,and the northeastern Chinese lineage.2.Phylogeographic structure of the Adiantum pedatum complexThe results showed that:(1)There are 30 haplotypes of the Adiantum pedatum complex.(2)Haplotype diversity and nucleotide diversity of the A.pedatum complex were high,and genetic diversity suggested significant differentiation among populations.(3)A.pedatum complex has a distinct phylogeographic structure,because of NST>GST.(4)This complex originated from eastern Asia,the Japanese lineage was formed first;the Japanese lineage dispersed to North America through the Bering Land Bridge,formed the eastern North American lineage;eastern North American lineage dispersed to western North America and after isolation and differentiation the western North American lineage formed;the western North American lineage across the Bering Land Bridge dispersed back to eastean Asia,formed the northeastern Chinese and the western Chinese lineages through isolation and differentiation.There may be a glacial refuge in the Quarternary in eastern North America.3.Biogeography of Adiantum pedatum complexUsing chloroplast genomes of 57 samples in the family Pteridaceae combined two fossil calibrations,we estimated the divergence time by BEAST.The divergence time of the A.pedatum complex is about 4.57 Ma(95%HPD:2.66,7.06).The first divergent clade was the Japanese lineage,and then eastern North American lineage divergented.In North America,the western lineage was formed later,and dispersed back to eastern Asia where that northeastern Chinses lineage was formed earlier and the western Chinese lineage was formed the latest.4.Morphological study of Adiantum pedatum complex.Nineteen key characteristics of fronds and rhizomes were observed and spores were scanned.Major results are:(1)the fronds part of the Adiantum pedatum in North America,Japan and China had no significant difference.(2)Rhizome of this complex can be distinctly divided into two types:creeping rhizomes include A.viridimontanum,A.pedatum(North America),and A.pedatum(northeastern China);erect rhizomes include A.aleuticum,A.pedatum(Japan),and A.pedatum(western China).(3)Spore surface ornamentation of each lineage is different.Spores of A.aleuticum and A.pedatum(Japan)is scabrate;and while those of A.pedatum(eastern North America and China)is rugate.5.A new species should be recognizedThe Japanese lineage of this complex was isolated by erect rhizome,dispersal arrangement of fronds,and scabrate spore and should be recognized as a new species,namely Adiantum japonicum T.Zhao,Z.Y.Zuo,J.Wen?Jin Mei Lu,sp.nov.We reconstructed the phylogeny and carried out phylogeography study of the Adiantum pedatum complex.The results implied that the eastern Asian origin of this complex,set forth migration routes and inferred possible glacial refuges of the complex.The results provided additional evidence for the origin and mechanism of disjunct distribution pattern between East Asia and North America of ferns.Based on multiple lines of evidence,the Japenese lineage of the complex was recognized as a new species,A.japonicum.