Dataset Information

Microsatellite and mitochondrial markers reveal strong gene flow barriers for Anopheles farauti in the Solomon Archipelago: implications for malaria vector control.

ABSTRACT: Anopheles farauti is the primary malaria vector throughout the coastal regions of the Southwest Pacific. A shift in peak biting time from late to early in the night occurred following widespread indoor residue spraying of dichlorodiphenyltrichloro-ethane (DDT) and has persisted in some island populations despite the intervention ending decades ago. We used mitochondrial cytochrome oxidase I (COI) sequence data and 12 newly developed microsatellite markers to assess the population genetic structure of this malaria vector in the Solomon Archipelago. With geographically distinct differences in peak A. farauti night biting time observed in the Solomon Archipelago, we tested the hypothesis that strong barriers to gene flow exist in this region. Significant and often large fixation index (FST) values were found between different island populations for the mitochondrial and nuclear markers, suggesting highly restricted gene flow between islands. Some discordance in the location and strength of genetic breaks was observed between the mitochondrial and microsatellite markers. Since early night biting A. farauti individuals occur naturally in all populations, the strong gene flow barriers that we have identified in the Solomon Archipelago lend weight to the hypothesis that the shifts in peak biting time from late to early night have appeared independently in these disconnected island populations. For this reason, we suggest that insecticide impregnated bed nets and indoor residue spraying are unlikely to be effective as control tools against A. farauti occurring elsewhere, and if used, will probably result in peak biting time behavioural shifts similar to that observed in the Solomon Islands.

SUBMITTER: Ambrose L

PROVIDER: S-EPMC3982969 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature

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Microsatellite and mitochondrial markers reveal strong gene flow barriers for Anopheles farauti in the Solomon Archipelago: implications for malaria vector control.

Ambrose Luke L Cooper Robert D RD Russell Tanya L TL Burkot Thomas R TR Lobo Neil F NF Collins Frank H FH Hii Jeffrey J Beebe Nigel W NW

International journal for parasitology 20140116 3-4

Anopheles farauti is the primary malaria vector throughout the coastal regions of the Southwest Pacific. A shift in peak biting time from late to early in the night occurred following widespread indoor residue spraying of dichlorodiphenyltrichloro-ethane (DDT) and has persisted in some island populations despite the intervention ending decades ago. We used mitochondrial cytochrome oxidase I (COI) sequence data and 12 newly developed microsatellite markers to assess the population genetic structu ...[more]

PMID: 24440418

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Project description:The north coast of Guadalcanal has some of the most intense malaria transmission in the Solomon Islands. And, there is a push for intensified vector control in Guadalcanal, to improve the livelihood of residents and to minimize the number of cases, which are regularly exported to the rest of the country. Therefore, the bionomics of the target vector, Anopheles farauti, was profiled in 2007-08; which was after 20 years of limited surveillance during which time treated bed nets (ITNs) were distributed in the area.In three villages on northern Guadalcanal, blood-seeking female mosquitoes were caught using hourly human landing catches by four collectors, two working indoors and two outdoors, from 18.00-06.00 for at least two nights per month from July 2007 to June 2008. The mosquitoes were counted, identified using morphological and molecular markers and dissected to determine parity.Seasonality in vector densities was similar in the three villages, with a peak at the end of the drier months (October to December) and a trough at the end of the wetter months (March to May). There was some variability in endophagy (indoor biting) and nocturnal biting (activity during sleeping hours) both spatially and temporally across the longitudinal dataset. The general biting pattern was consistent throughout all sample collections, with the majority of biting occurring outdoors (64%) and outside of sleeping hours (65%). Peak biting was 19.00-20.00. The proportion parous across each village ranged between 0.54-0.58. Parity showed little seasonal trend despite fluctuations in vector densities over the year.The early, outdoor biting behaviour of An. farauti documented 20 years previously on north Guadalcanal was still exhibited. It is possible that bed net use may have maintained this biting profile though this could not be determined unequivocally. The longevity of these populations has not changed despite long-term ITN use. This early, outdoor biting behaviour led to the failure of the eradication programme and is likely responsible for the continued transmission in Guadalcanal following the introduction of ITNs. Other vector control strategies which do not rely on the vector entering houses are needed if elimination or intensified control is to be achieved.

Project description:BACKGROUND:In the 1970s, Anopheles farauti in the Solomon Island responded to indoor residual spraying with DDT by increasingly feeding more outdoors and earlier in the evening. Although long-lasting insecticidal nets (LLINs) are now the primary malaria vector control intervention in the Solomon Islands, only a small proportion of An. farauti still seek blood meals indoors and late at night where they are vulnerable to being killed by contract with the insecticides in LLINs. The effectiveness of LLINs and indoor residual spraying (IRS) in controlling malaria transmission where the vectors are exophagic and early biting will depend on whether the predominant outdoor or early biting phenotypes are associated with a subpopulation of the vectors present. METHODS:Mark-release-recapture experiments were conducted in the Solomon Islands to determine if individual An. farauti repeat the same behaviours over successive feeding cycles. The two behavioural phenotypes examined were those on which the WHO recommended malaria vector control strategies, LLINs and IRS, depend: indoor and late night biting. RESULTS:Evidence was found for An. farauti being a single population regarding time (early evening or late night) and location (indoor or outdoor) of blood feeding. Individual An. farauti did not consistently repeat behavioural phenotypes expressed for blood feeding (e.g., while most mosquitoes that fed early and outdoors, and would repeat those behaviours, some fed late at night or indoors in the next feeding cycle). CONCLUSIONS:The finding that An. farauti is a homogeneous population is significant, because during the multiple feeding cycles required to complete the extrinsic incubation period, many individual female anophelines will enter houses late at night and be exposed to the insecticides used in LLINs or IRS. This explains, in part, the control that LLINs and IRS have exerted against a predominantly outdoor feeding vector, such as An. farauti. These findings may be relevant to many of the outdoor feeding vectors that dominate transmission in much of the malaria endemic world and justifies continued use of LLINs. However, the population-level tendency of mosquitoes to feed outdoors and early in the evening does require complementary interventions to accelerate malaria control towards elimination.

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Project description:BACKGROUND:Anopheles nili is a major vector of malaria in the humid savannas and forested areas of sub-Saharan Africa. Understanding the population genetic structure and evolutionary dynamics of this species is important for the development of an adequate and targeted malaria control strategy in Africa. Chromosomal inversions and microsatellite markers are commonly used for studying the population structure of malaria mosquitoes. Physical mapping of these markers onto the chromosomes further improves the toolbox, and allows inference on the demographic and evolutionary history of the target species. RESULTS:Availability of polytene chromosomes allowed us to develop a map of microsatellite markers and to study polymorphism of chromosomal inversions. Nine microsatellite markers were mapped to unique locations on all five chromosomal arms of An. nili using fluorescent in situ hybridization (FISH). Probes were obtained from 300-483 bp-long inserts of plasmid clones and from 506-559 bp-long fragments amplified with primers designed using the An. nili genome assembly generated on an Illumina platform. Two additional loci were assigned to specific chromosome arms of An. nili based on in silico sequence similarity and chromosome synteny with Anopheles gambiae. Three microsatellites were mapped inside or in the vicinity of the polymorphic chromosomal inversions 2Rb and 2Rc. A statistically significant departure from Hardy-Weinberg equilibrium, due to a deficit in heterozygotes at the 2Rb inversion, and highly significant linkage disequilibrium between the two inversions, were detected in natural An. nili populations collected from Burkina Faso. CONCLUSIONS:Our study demonstrated that next-generation sequencing can be used to improve FISH for microsatellite mapping in species with no reference genome sequence. Physical mapping of microsatellite markers in An. nili showed that their cytological locations spanned the entire five-arm complement, allowing genome-wide inferences. The knowledge about polymorphic inversions and chromosomal locations of microsatellite markers has been useful for explaining differences in genetic variability across loci and significant differentiation observed among natural populations of An. nili.

Dataset Information

Microsatellite and mitochondrial markers reveal strong gene flow barriers for Anopheles farauti in the Solomon Archipelago: implications for malaria vector control.

Publications

Microsatellite and mitochondrial markers reveal strong gene flow barriers for Anopheles farauti in the Solomon Archipelago: implications for malaria vector control.

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