Population Genetics Of Tomicus Minor L.in Yunnan Inferred From MtDNA CO? And CO? Sequence

Tomicus minor(Coleoptera:Scolytinae)is a devastating beetle on pine forests(genus Pinus),which exhibits shoot boring and trunk boring stages in its life history.From the 1980s to date,this beetle has been causing serious and yet escalating damage to the dominant pine stands comprised of P.yunnanensis in the southwestern province of Yunnan in China,such damage has brought tremendous economic loss as well as ecological consequences in Yunnan.Analysing population genetics and diversity,understanding population genetic structure and divergence,clarifying population migration and demographic history,and elucidating the potential causes of such history will benefit our knowledge for T.minor,and facilitate forest protection strategy formulation for quarantine departments.The present research collected 79 T.minor individuals from seven populations in Yunnan,analysed population genetic diversity,population genetic structure,population migration,and demographic history using a combined dataset containing mitochondrial CO? and CO? gene fragments.This research clarified the genetic structure,demographic history,and migration of the seven populations with the following findings and conclusions.1.Seventy-nine sequences for both of the CO? and CO? gene fragments were obtained from double-directional sequencing of the 79 individuals of T.minor collected from seven populations across Yunnan,namely Shilin,Yanshan,Chuxiong,Ninglang,Xiangyun,Qujing,and Lijiang.Sequence alignment and trimming produced 720 bp length CO? sequences and 565 bp length CO? sequences for all samples.Forty haplotypes were defined by the combined CO? and CO? sequences,including only four shared haplotypes found in at least two populations and 36 locally private haplotypes.Diversity analysis showed high genetic diversity indices in all of the seven populations of T.minor,indicating a stronger adaptability and a wider potential geographic distribution range of this beetle.2.Genetic structure analysis identified two population groups in Yunnan with significant divergence.Among the seven populations,Shilin,Yanshan,Chuxiong,and Xiangyun clustered in Group 1,while Ninglang,Qujing,and Lijiang clustered in Group However,isolation-by-distance(IBD)analysis failed to establish regression correlation between genetic distances(Fst)and geographic distances(earth surface distance between two populations).The author believes that the climate oscillation in the montane area of northwestern Yunnan should be the main driving force of the genetic divergence.Providing the economic development history of Yunnan,our analyses of gene flow and population migration implied that human-mediated relocation of this beetle also influenced its genetic structure.3.Neutrality tests using both of the Fu's Fs and Tajima's D did not flagged significant negative values for each of the seven T.minor populations,but flagged significant negative values for both of the two population groups and when treating all populations in Yunnan as an entity.Furthermore,the mismatch distribution analysis only produced a simulated unimodal curve for Ninglang,while the curves for all other six populations,both of the two population groups,and the entire seven populations were all multimodal.Combining the above-mentioned two types of analyses,the author believes that the seven T.minor populations in Yunnan have been exist as stable status in the history without experiencing recent expansion and typical bottlenecks.But as an entity in general,the population is undergoing expansion.Based on the above research results,the present research proposes that,the controlling strategy of this beetle must be emphasised on wood quarantine and inspection in each infested areas,to minimise the possibility of human-mediated relocation of this beetle in to non-infested areas.Meanwhile,regular monitoring mechanism must be established in non-infested areas to ensure timely detection of early infestation.