Characterization of eight single nucleotide polymorphism markers inAedes aegypti

Genetic variability and spatial distribution in small geographic scale of Aedes aegypti (Diptera: Culicidae) under different climatic conditions in Northeastern Brazil

BACKGROUND

The study of the genetic structure of Aedes aegypti is essential to understanding their population dynamics as well as for the analysis of factors responsible for their resistance and ecological adaptation. The use of molecular markers in identifying differences amongst populations of Ae. aegypti in different geographical areas as well as the temporal variation of the vector populations has contributed to the improvement of vector control strategies. The present study aims to determine the genetic variability of Ae. aegypti populations in a small geographical area (state of Sergipe, Northeastern Brazil) by means of inter-simple sequence repeat (ISSR) and single nucleotide polymorphism (SNP) molecular markers.

RESULTS

ISSR markers revealed a more heterogeneous pattern of genetic diversity among the populations with an expected heterozygosity (H _E) ranging from 0.261 ± 0.03 to 0.120 ± 0.032, while a similar trend was detected through SNPs across populations with an H _E between 0.375 ± 0.054 and 0.269 ± 0.042. The population's genetic differentiation assessed with ISSR and SNP markers indicated a very low structuring among the populations with the highest diversity observed within the populations 72 % (ISSR) and 92 % (SNP). Clustering analysis also suggested little variation among populations: the seven populations were grouped into only three ISSR clusters and a single panmictic group based on SNP markers. The present study identified a close relationship between the populations, which probably results mainly from passive gene flow between mosquitoes from distinct geographic regions, influenced by humans commuting along roads.

CONCLUSIONS

There was an intense migration of mosquitos across municipalities, leading to a potential increase in risk of arbovirus and insecticide resistance associated-alleles spreading between mosquito populations.

Detection and Distribution of V1016Ikdr Mutation in the Voltage-Gated Sodium Channel Gene in Aedes aegypti (Diptera: Culicidae) Populations From Sergipe State, Northeast Brazil

Aedes aegypti (L.) resistance to pyrethroids was recorded in Brazil few years after its introduction as the adulticide in the National Dengue Control Program campaigns. Altered susceptibility to pyrethroids had been reported in the state of Sergipe, northeast Brazil, through biological assays, even before its use against Ae. aegypti in the state. Metabolic and target-site resistance mechanisms were also revealed in samples from Aracaju, the capital of Sergipe. Herein, we investigated the presence and distribution of the kdr mutation V1016I^kdr in Ae. aegypti populations from different municipalities of the state. Aedes aegypti eggs were collected from seven municipalities located in areas showing different climatic types and infestation levels. Approximately 20 Ae. aegypti females from each municipality (total of 135 subjects) were individually submitted to allele-specific polymerase chain reaction (AS-PCR) for the 1016 site of the voltage-gated sodium channel (Na_V). The V1016I^kdr mutation was found in subjects from all the municipalities under study with a high frequency of heterozygotes in several locations. Homozygous recessive subjects (resistant kdr genotype) were found only in one municipality. The results suggest a wide distribution of the V1016I^kdr mutation in the northeast Brazil, which indicates urgent need for monitoring the effectiveness of the pyrethroids currently used for vector control.

Contrasting genetic structure between mitochondrial and nuclear markers in the dengue fever mosquito from Rio de Janeiro: implications for vector control

Dengue is the most prevalent global arboviral disease that affects over 300 million people every year. Brazil has the highest number of dengue cases in the world, with the most severe epidemics in the city of Rio de Janeiro (Rio). The effective control of dengue is critically dependent on the knowledge of population genetic structuring in the primary dengue vector, the mosquito Aedes aegypti. We analyzed mitochondrial and nuclear genomewide single nucleotide polymorphism markers generated via Restriction-site Associated DNA sequencing, as well as traditional microsatellite markers in Ae. aegypti from Rio. We found four divergent mitochondrial lineages and a strong spatial structuring of mitochondrial variation, in contrast to the overall nuclear homogeneity across Rio. Despite a low overall differentiation in the nuclear genome, we detected strong spatial structure for variation in over 20 genes that have a significantly altered expression in response to insecticides, xenobiotics, and pathogens, including the novel biocontrol agent Wolbachia. Our results indicate that high genetic diversity, spatially unconstrained admixing likely mediated by male dispersal, along with locally heterogeneous genetic variation that could affect insecticide resistance and mosquito vectorial capacity, set limits to the effectiveness of measures to control dengue fever in Rio.

Microhabitat partitioning of Aedes simpsoni (Diptera: Culicidae)

Yellow fever virus is a reemerging infection responsible for widespread, sporadic outbreaks across Africa. Although Aedes aegypti (L.) is the most important vector globally, in East Africa, epidemics may be vectored by Aedes bromeliae (Theobald), a member of the Aedes simpsoni (Theobald) species complex. The Ae. simpsoni complex contains 10 subspecies, of which Ae. bromeliae alone has been incriminated as a vector of yellow fever virus. However, morphological markers cannot distinguish Ae. bromeliae from conspecifics, including the sympatric and non-anthropophilic Aedes lilii (Theobald). Here, we used three sequenced nuclear markers to examine the population structure of Ae. simpsoni complex mosquitoes collected from diverse habitats in Rabai, Kenya. Gene trees consistently show strong support for the existence of two clades in Rabai, with segregation by habitat. Domestic mosquitoes segregate separately from forest-collected mosquitoes, providing evidence of habitat partitioning on a small spatial scale (< 5 km). Although speculative, these likely represent what have been described as Ae. bromeliae and Ae. lilii, respectively. The observation of high levels of diversity within Rabai indicates that this species complex may exhibit significant genetic differentiation across East Africa. The genetic structure, ecology, and range of this important disease vector are surprisingly understudied and need to be further characterized.

Application of single nucleotide polymorphisms to non-model species: a technical review

Single nucleotide polymorphisms (SNPs) have gained wide use in humans and model species and are becoming the marker of choice for applications in other species. Technology that was developed for work in model species may provide useful tools for SNP discovery and genotyping in non-model organisms. However, SNP discovery can be expensive, labour intensive, and introduce ascertainment bias. In addition, the most efficient approaches to SNP discovery will depend on the research questions that the markers are to resolve as well as the focal species. We discuss advantages and disadvantages of several past and recent technologies for SNP discovery and genotyping and summarize a variety of SNP discovery and genotyping studies in ecology and evolution.

Seasonal population dynamics and the genetic structure of the mosquito vector Aedes aegypti in São Paulo, Brazil

Population genetic studies of insect vectors can generate knowledge to improve epidemiological studies focused on the decrease of pathogen transmission. In this study, we used nine SNPs across the Aedes aegypti genome to characterize seasonal population variations of this important dengue vector. Mosquito samples were obtained by ovitraps placed over Botucatu SP from 2005 to 2010. Our data show that, regardless of the large variation in mosquito abundance (deduced from the number of eggs obtained from ovitraps), the effective population size remained stable over the years. These results suggest that Ae. aegypti is able to maintain a sufficiently large active breeding population during the dry season to keep genetic frequencies stable. These results open new perspectives on mosquito survey and control methods.