Studies On Genetic Variation Among Natural Populations Of Euseius Nicholsi (Acari:Phytoseiidea) From China By Mitochondrial Coi And Nuclear Rdna Its Sequences

As a widely distributed species across southern China, the phytoseiid mite Euseius nicholsi (Ehara et Lee)(Arthropoda:Chelicerata:Acari) is an important natural enemy of many species of pest mites. The COI and ITS sequences from10geographical populations of Euseius nicholsi were used to investigate the genetic diversity. We first examined the levels and patterns of nucleotide variation in natural populations of E. nicholsi from China, and then determined whether these populations are genetically differentiated. Lastly, we also evaluated the usefulness of DNA sequence data for population genetic studies on E. nicholsi.(1) A658bp portion of the COI gene was amplified and sequenced revealing46polymorphic nucleotide sites representing33COI haplotypes. The AT content of COI ranged from65.4%to66.5%. For the COI gene region, nucleotide (π) and haplotype (hd) diversity varied from0.0034to0.0111and0.385to0.809, respectively. High levels of nucleotide diversity were observed in CQ (π=0.1111and hd=0.809) and GZ (71=0.01022and hd=0.788). The lowest levels of haplotype and nucleotide diversity were observed in SG (π=0.0034and hd=0.385). In the COI region, no statistically significant deviation from neutrality was found using Tajima’s test. The southwestern population CQ had the most haplotypes (n=7). The haplotype CH29was found in five populations (CQ, CS, NP, WH, and CD) at high frequencies. Haplotypes that were specific to individual populations were also observed (haplotypes CH02and CH03in CD, CH06and CH07in GZ). Haplotype networks in this region were more complicated than those of the ITS region.(2) The complete ITS region was successfully sequenced for145individuals. The length of ITS varied from648to649bp. The ITS region had16parsimony informative segregating sites of which9were transitions,6were transversions, and1was an indel. A total of16haplotypes were identified, of which11were found only once (singleton haplotypes). The overall nucleotide diversity computed for all E. nicholsi populations was0.00136. The lowest genetic diversity was observed in the GZ (π=0.0000, hd=0.0000), which had only one haplotype. The highest levels of haplotype and nucleotide diversity were observed in Chengdu (π=0.00185, hd=0.803). In the ITS region, the Tajima’s test for total sequences was significantly negative (Tajima’s D:-1.77962, P<0.05). All populations shared the haplotype IH02. Several haplotypes were found in only one population. For instance, the haplotype IH05was only observed in SG. The haplotypes IH09, IH10, and IH15were unique to population CD. CD was the most heterogeneous population, with six haplotypes. It was followed by NN and CS, which each had five haplotypes. Haplotype networks in ITS region were simpler. Some haplotypes were up to two mutational steps apart from each other.(3) Most of population pairs had statistically significant FST values. In the COI region, the FST values estimated between the populations ranged from-0.03858(WH-NP) to0.71485(CD-SG). In the ITS region, the values ranged between-0.04776(NP-CS) and0.42424(NP-GZ). The pairwise FST values for COI region were higher than ITS. No differentiation was observed among CS, WH, or NP populations (except CS-WH for COI). In COI region, the values of FST/(1-FST) for all pairs of populations were significantly and positively correlated with geographical distance (COI:r=0.303, P=0.047). That of ITS was not correlated with geographical distance (ITS:r=0.0110, P=0.441). This indicated that genetic differentiation of COI significantly increases as distance between populations increases. However, we also found significant FST values for pairs of certain other geographically adjacent populations (SG-GZ). We compared the neighbor-joining trees and results of PCA (COI:PC1=33.74%, PC2=21.74%; ITS:PC1=74.53%, PC2=15.84%) based on the COI and ITS sequences. As revealed by the Mantel test, there was a significant positive correlation between FST values for the ITS and COI regions (r=0.4069, P=0.0270). The results of population differentiation suggest that E. nicholsi comprises at least three geographically distinct populations or even more than one species.