Population Genetic Differentiation Of Melaphis Rhois Inferring From DNA Sequences

Rhus gall aphids（Insecta:Hemiptera:Aphididae:Eriosomatinae:Fordini）include six genera and 12 species with only one species,Melaphis rhois,in North America,which show a classic disjunct distribution in eastern Asia and North America.Rhus gall aphids live on Rhus plants to form Chinese gallnuts,which are rich in tannin acid.The extracted products have widely been used in various field,such as medicines,foods and chemistry-industry.In this study,the genetic variation and structure of M.rhois population were analyzed by amplifying and sequencing the mtDNA Cytb and COI gene and nuclear DNA EF-1αgene of M.rhois.The main results are as followings:1)We obtained mtDNA sequences 1,680bp in length with Cytb 432bp and COI 1,248bp,EF-1αsequences 918bp,and the combined mtDNA and EF-1αsequences conserved 2,598bp.In Melaphis rhois,variable sites in Cytb,COI and EF-1αsequences are 66（about 15.28%）,126（about 10.10%）and 35（about 4.81%）,respectively.There are 228 variable sites（about 9.47%）in all the three combined sequences.2)The content of T,C,A,G of Cytb,COI and EF-1αare 45.1%,14.8%,32.1%,8.10%;40.7%,14.9%,33.3%,11.1%and 25.6%,21.8%,26.0%,26.6%,respectively;The content of T,C,A,G of mtDNA and EF-1αare36.9%,16.9%,30.9%,15.3%.The content of A+T in mtDNA is higher than that of G+C,however,the nuclear gene has similar content of A+T and G+C.3)The haplotypes of Cytb,COI and EF-1αgenes have 41,54 and 63,respectively.All the three combined sequences have 120 haplotypes.The total haplotype diversity of Cytb,COI and EF-1αgenes are 0.921±0.010,0.960±0.005 and 0.970±0.005,respectively.All the three combined sequences are 0.994±0.002;the average nucleotide diversity Cytb,COI and EF-1αare 0.02953±0.00150,0.02618±0.00070 and 0.00708±0.00042,respectively;all the three combined sequences are 0.01999±0.00070.The data analysis showed that M.rhois nucleotide diversity is lower than other insects.4)Analysis of molecular variance（AMOVA）of Melaphis rhois showed that the genetic variation among populations was higher than within populations.The results also showed that the genetic diversity of M.rhois is higher in Cleveland population from Ohio than that in other populations.5)TCS network showed that different haplotypes of Melaphis rhois in Cleveland and Dayton population from Ohio grouped into a single cluster without shared nodes with other haplotypes,which indicated that the Cleveland population in Ohio of M.rhois had higher differentiation from other populations.6)MP phylogeny showed that the haplotypes from Cleveland population in Ohio grouped into one cluster,which is sister group with all the remaining haplotypes.In addition,F_STT value and genetic distance between the Cleveland population in Ohio and the other populations were relatively high,which suggested that Cleveland population in Ohio population might be a new species of Melaphis rhois.7)Based on Tajima’s D value and distribution of bifurcation point,we could draw a conclusion that population expansion event was not supposed to happen in Melaphis rhois.8)There are two species of the primary host plants of Melaphis rhois:Rhus typhina and R.glabra.By comparing with the host plants,the M.rhois populations using the same host plant firstly grouped exception for only two populations（New Jersey and New Hampshare）,which indicated that the host plants effected the genetic differentiation of aphids.