Temporal And Spatial Patterns Of Population Genetic Differentiation Of Tyrophagus Putrescentiae

Tyrophagus putrescentiae(Schrank,1781)is one of the most common storage mites living in stored food,suach as grains,feed and Chinese herbal medicine.This leads to a serious decline in the quality of storages.People who eat T.putrescentiae-contaminated food,or are prolonged exposed to T.putrescentiae may cause mite dermatitis and human mite diseases.In addition,similar to Dermatophagoides farinae and Dermatophagoides pteronyssinus,secretions,excretions and dead bodies of mites have the common antigen,which is currently considered as one of the most important allergens,inducing mite allergic diseases.Due to the importance to grain storage and medicines in T.putrescentiae has been researched early.However,most reports mainly focused on morphology,biology,experimental population ecology and prevention of T.putrescentiae.Up to date,temporal and spatial dynamics of population genetic structure of T.putrescentiae natural populations have not been reported.Thus,the present study investigated the population dynamics and population genetic structure of T.putrescentiae among different seasons in Wuhu City as well as gernetic differentiation among different geographical populations,which might provide theoretical basis to prevention of T.putrescentiae.The main research contents and results are listed below.1.From January 2013 to December 2013,T.putrescentiae were monthly collected five flourmill and noodle processing factories at Wuhu City to investigate dynamics of population density among seasons.Taylor's equation(lgS~2–lg?x)and Iwao's equation(m*/-?x)of linear regression were used to characterize the distribution of T.putrescentiae in stored flours.The results indicated that seasonal variation of T.putrescentiae natural populations display unimodal pattern in storage flour,and the peaks of population density were observed in July and September.In the stored flours,T.putrescentiae natural populations showed an aggregation distribution.Thus,we can take appropriate prevention and control strategies before appearance of population density peak to improve T.putrescentiae prevention.2.Based on the mitochondrial COI and ribosomal ITS sequence,the genetic diversity and differentiation of nine geographic T.putrescentiae populations collected from four faunal regions of China were analyzed.In total 127 mitochondrial COI sequences were obtained from 127 T.putrescentiae individuals,defining a total of 88haplotypes.In total 211 ribosomal ITS sequences were obtained from 211 individuals,resulting in 204 haplotypes.The phylogenetic trees using the maximum likelihood,Bayesian and Neighbor-Joining methods were basically similar.The haplotypes from the same geographic population were not clustered together,but scattered throughout the trees.Haplotype networks showed that all haplotypes did not display significant distribution pattern.The haplotypes from the same geographic population did not converge in the same lingage of network,but all haplotypes generally distributed in a star shape and did not aggregate as the 9 geographic populations.AMOVA analysis of mitochondrial COI gene showed that there was significant genetic differentiation among geographic populations(P<0.05).However,variation within populations accounted for63.85%of the total variation.AMOVA analysis based on the ribosomal ITS sequence showed that there was no significant genetic differentiation among geographic populations(P>0.05).Variation within populations accounted for 99.62%of the total variation.Mantel test of mitochondrial COI gene showed that the genetic distance was not significantly related to geological distance(correlation coefficient r=0.555,P=0.067).Similarly,no significant correlation was observed based on ITS sequences(r=-0.157,P=0.790).These results suggested that the geographical isolation was not the reason for the genetic differentiation of T.putrescentiae populations.The neutral test of mitochondrial COI gene and ribosomal ITS sequence found that the nine geographical populations of T.putrescentiae followed the neutral evolution and had a selective effect.Tajima's D test showed that Tyrophagus putrescentiae was negatively selected during evolution and followed the neutral model.Mismatch distribution analysis based on mitochondrial COI gene showed that nine geographical populations of T.putrescentiae displayed the stable population growth model.The mismatch distribution based on the ITS gene sequence indicated that T.putrescentiae had experienced rapid expansion.3.T.putrescentiae were collected from Wuhu City during spring,summer and autumn.Analyses of COI and ITS sequences showed significant different parterns of haplotype diversity and nucleotide diversity,probably due to the different rate or patterns of evolution between these two molecular markers.The phylogenetic trees reconstructed by the maximum likelihood,bayesian and Neighbor-joining methods were basically the same.The haplotypes from the same season did not cluster together,but scattered throughout the tree.The AMOVA based on mitochondrial COI gene showed that there was a significant genetic differentiation among different seasons(P<0.01),but ribosomes ITS sequences showed no significant genetic differentiation(P>0.05).These results suggested that prevention and control of T.putrescentiae populations can adopt a unified control strategy in Wuhu City.