Mosquito Gene Flow in Shandong Flows One Way, Resistance Map Shows

A genetic survey of the primary malaria vector in Shandong Province, China, has mapped how Anopheles sinensis populations across nine locations are connected, and the picture is strikingly lopsided. Combining mitochondrial COI sequencing with analysis of the voltage-gated sodium channel gene, researchers found high mitochondrial diversity, weak population structure, and a directional pattern of gene flow: mosquitoes appear to move predominantly out of the northwestern plains into the southern plains and the eastern hilly areas, with little movement in the reverse direction. The work, published as open access research in BMC Genomics, also charted the distribution of insecticide-resistance mutations at a key codon of the sodium channel gene.

The mitochondrial analysis covered 183 samples and identified 121 haplotypes, a high level of haplotype diversity for the region. Analysis of molecular variance attributed almost all observed genetic variation to differences among individuals within populations rather than between populations, with 97.6 percent of variation explained by within-population differences and a fixation index of just 0.024. That low Fst value indicates weak to moderate population differentiation, meaning the nine sampled populations are not sharply isolated from one another despite spanning plains, coasts and hills.

Neutrality tests and mismatch distributions pointed to a recent population expansion in the Linyi population, one of the nine sampling sites. Coalescent-based maximum-likelihood estimates of asymmetric migration rates then revealed the directional bias in gene flow. Rather than a symmetric exchange of migrants among neighbouring populations, the data support essentially one-way movement from the northwestern plains into the southern plains and into the eastern hilly areas. This kind of asymmetric connectivity matters for control planning, because mosquitoes dispersing from a source region can carry their genetic background, including resistance alleles, into areas that contribute few migrants in return.

The voltage-gated sodium channel gene is a standard target in resistance monitoring because mutations at codon 1014, often called knockdown resistance or kdr mutations, are associated with resistance to pyrethroid and related insecticides. At this codon the survey detected two predominant mutant types across Shandong: L1014F, in which phenylalanine replaces leucine, and a combined F1014/C1014 pattern. The frequency of these mutations showed significant spatial heterogeneity. L1014F was relatively common across most of the province, but it was not detected at all in the Jining population in this study, a notable absence in an otherwise widespread mutation.

Bayesian clustering of the genetic data resolved three clades among the sampled mosquitoes. The resistance-associated mutations were restricted to Clades 1 and 2, so mosquitoes in the third clade lacked the kdr variants even though they belong to the same species and region. A discriminant analysis of principal components based on kdr genotypes retrieved three principal components and two discriminant axes that together explained 98.9 percent of the among-population variance, a result consistent with the three clades identified by the Bayesian analysis. In other words, the resistance genotype patterns and the broader genetic clustering tell the same story.

The study’s authors frame the findings as baseline data for future population genomics work and for insecticide resistance monitoring in Shandong. That framing matters practically: Shandong is an eastern coastal province with frequent international exchanges and occasionally reports imported malaria cases, and Anopheles sinensis serves as its primary malaria vector. Understanding how vector populations are structured, how they exchange genes, and where resistance mutations are common or absent provides a foundation for deciding where surveillance should be intensified and how resistance management might be coordinated across neighbouring areas.

Technically, the study paired two marker systems with complementary strengths. Mitochondrial COI sequencing captures maternal lineages and historical demographic signals, which is why it could reveal both the high haplotype diversity and the recent expansion signature in Linyi. The nuclear VGSC fragment, by contrast, links directly to a phenotype of operational concern, insecticide resistance, and its codon 1014 mutations can be tracked spatially. The combination allowed the researchers to describe both the demographic connectivity of populations and the distribution of a resistance-relevant mutation within the same sampling framework.

The asymmetric migration result deserves emphasis because it departs from the simpler assumption that weak differentiation implies uniform exchange. Populations can show low Fst while still exchanging genes unevenly, and the coalescent estimates here suggest exactly that: high gene flow with a strong directional bias, exported from the northwestern plains toward the southern plains and the eastern hilly areas. For resistance monitoring, this raises the possibility that resistance alleles arising or becoming common in a source population could spread along these routes, although the study reports the migration pattern itself and does not demonstrate the spread of any particular mutation along it.

Several caveats keep the interpretation grounded. The mitochondrial sample comprised 183 mosquitoes from nine locations within a single province, so the findings describe Shandong’s populations rather than the species across its wider Asian range. The L1014F absence in Jining is reported for this study’s samples and may reflect sampling or local conditions. The article was shared early as a peer-reviewed accepted manuscript carrying a permanent DOI, a citable version that will be replaced by the final Version of Record after further edits. Within those limits, the study delivers a concrete, quantified picture: high haplotype diversity, weak to moderate differentiation, recent expansion in one population, strongly directional gene flow, and a resistance-mutation landscape that varies sharply from one part of the province to another.

Subject of Research: Population genetic structure and insecticide resistance mutations of Anopheles sinensis mosquitoes in Shandong Province, China

Article Title: Genetic structure of Anopheles sinensis populations in Shandong Province based on genetic analysis

Article References: Peng, K., Xu, Y., Zhao, H., Kong, X., Yin, H., Lv, W., Pan, X., Xu, N., Yang, Y., Han, C., Gong, M., Wang, Y., & Liu, H. (2026). Genetic structure of Anopheles sinensis populations in Shandong Province based on genetic analysis. BMC Genomics. https://doi.org/10.1186/s12864-026-13537-6

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13537-6

Keywords: Anopheles sinensis, malaria vector, Shandong Province, population genetics, COI haplotypes, VGSC gene, knockdown resistance, gene flow, population differentiation, insecticide resistance monitoring, mitochondrial DNA, BMC Genomics