| It is fundamentally crucial to study on population dynamics, genetic diversity and population structure for species management and conservation strategies. The purpose of this study is to explore the factors that influence the current structure pattern of two closely related species. This study consists of three parts. The first is the population structure and population dynamics of Nesidiocoris tenuis, the second is the population genetics of Nesidiocoris poppiusi and the third is a powerful method to discriminate between two closely related species.1. The zoophytophagous plant bug, N. tenuis (Hemiptera:Miridae), is one of the most thermophilous dicyphines in agroecosystems and is widely distributed in China. Little is known regarding the genetic structure of N. tenuis and the effect of historical climatic fluctuations on N. tenuis populations. We analyzed partial sequences of three mitochondrial protein-coding genes (COI, ND2 and CytB) and nuclear markers (5.8S, ITS2 and 28S) for 516 specimens collected from 37 localities across China. The main results are as follows.(1) A total of 130 haplotypes were detected in a combined mitochondrial dataset, which included 2,226 bp of protein-coding regions (COI: 726 bp, ND2:837 bp and CytB:663 bp). Among these identified haplotypes,102 were unique haplotypes and six haplotypes (H1, H4, H6, H12, H13 and H17) were most widely shared. Fewer haplotypes (HN=30) were observed in the nuclear data.(2) The spatially explicit BAPS model for clustering of individuals identified three clusters in the 37 populations. The first cluster mainly distributed in three populations from Southwestern China. The second cluster was distributed in the rest of the 34 populations as a majority and the third cluster was distributed as a minority.(3) Analyses of the combined mitochondrial dataset indicated that the Southwestern China group (SWC) was significantly differentiated from the remaining populations, other Chinese group (OC). Asymmetric migration and high level of gene flow across a long distance within the OC group was detected.(4) Both the neutrality tests and mismatch distributions revealed the occurrence of historical population expansion. Bayesian skyline plot analyses with two different substitution rates indicated that N. tenuis might follow the post-LGM (the Last Glacial Maximum) expansion pattern for temperate species. Pleistocene climatic fluctuation, complicated topography and anthropogenic factors, along with other ecological factors (e.g. temperature and air current) might have accounted for the current population structure of N. tenuis.2. Little is known regarding the genetic structure of N. poppiusi, which is a species closely related to N. tenuis. We analyzed partial sequences of mitochondrial COI gene for 7 localities across China. The main results are as follows.(1) All specimens are divided into Western group (We) and Eastern group (Ea), and significant genetic variation are detected between groups. Phylogenetic analyses among the mitochondrial haplotypes identified two groups.(2) One group was the clustering of four Western populations, which contained the Nph9 and Nph10 haplotypes only. The other group included remaining 9 haplotypes from three Eastern populations.(3) Both the neutrality tests and mismatch distributions revealed historical population expansion of Nesidiocoris poppiusi.3. N. tenuis and N. poppiusi are morphologically similar and sometimes difficult to separate using tranditional methods. We have sequenced partial COI gene from many individuals for two closely related species. The calculation of genetic distances indicated little genetic variation within species but much genetic variation between species. Median-joining network was consistent with tranditional identification. Above analyses suggest that DNA barcoding is a powerful method to discriminate between two closely related species in genus Nesidiocoris, instead of using male genitalias. |
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