Abstract
BackgroundThere is growing evidence that the widespread use of Long-Lasting Insecticidal Nets (LLINs) is prompting malaria vectors to shift their biting towards times and places where people are not protected, such as earlier in the evening and/or outdoors. It is uncertain whether these behavioural shifts are due to phenotypic plasticity and/or ecological changes within vector communities that favour more exophilic species, or involve genetic factors within vector species to limit their contact with LLINs. Possibly variation in the time and location of mosquito biting has a genetic basis, but as yet this phenomenon has received little investigation. Here we used a candidate gene approach to investigate whether polymorphisms in selected circadian clock genes could explain variation in the time and location of feeding (indoors versus outside) within a natural population of the major African malaria vector Anopheles arabiensis.MethodsHost-seeking An. arabiensis were collected from two villages (Lupiro and Sagamaganga) in Tanzania by Human Landing Catch (HLC) technique. Mosquitoes were classified into phenotypes of “early” (7 pm–10 pm) or “late” biting (4 am –7 am), and host-seeking indoors or outdoors. In these samples we genotyped 34 coding SNPs in 8 clock genes (PER, TIM, CLK, CYC, PDP1, VRI, CRY1, and CRY2), and tested for associations between these SNPs and biting phenotypes. SNPs in 8 mitochondrial genes (ATP6, ATP8, COX1, COX2, COX3, ND3, ND5 and CYTB) were also genotyped to test population subdivision within An. arabiensis.ResultsThe candidate clock genes exhibited polymorphism within An. arabiensis, but it was unrelated to variation in the timing and location of their biting activity. However, there was evidence of strong genetic structure within An. arabiensis populations in association with the TIM, which was unrelated to geographic distance. Substructure within An. arabiensis was also detected using mitochondrial markers.ConclusionsThe variable timing and location of biting in An. arabiensis could not be linked to candidate clock genes that are known to influence behaviour in other Diptera. This finding does not rule out the possibility of a genetic basis to biting behaviour in this malaria vector, but suggests these are complex phenotypes that require more intensive ecological, neuronal and genomic analyses to understand.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1394-8) contains supplementary material, which is available to authorized users.
Highlights
There is growing evidence that the widespread use of Long-Lasting Insecticidal Nets (LLINs) is prompting malaria vectors to shift their biting towards times and places where people are not protected, such as earlier in the evening and/or outdoors
We discovered an average of one single nucleotide polymorphisms (SNPs) in every 46.8 ± 34.5 base-pairs in 8 clock genes, with CYC and VRI having the highest and the lowest densities of 1 SNP per every 10 and 125 bp respectively
This was comparable to the overall SNP density previously reported for An. arabiensis (1 every 47 bp [62])
Summary
There is growing evidence that the widespread use of Long-Lasting Insecticidal Nets (LLINs) is prompting malaria vectors to shift their biting towards times and places where people are not protected, such as earlier in the evening and/or outdoors. The stereotypical pattern of host-seeking in these vector species was described in early work by Gillies [2], and is characterised by the onset of a daily period of host-seeking which begins after dusk and increases to a peak around midnight, with 60– 80 % of bites estimated to occur between 9 pm and 3 am [3] This host-seeking activity coincides with the period when most people are indoors and asleep [1, 4]. Its sibling species An. arabiensis can be relatively exophagic and zoophagic (feeding on cattle as well as humans) [6, 8,9,10], and can spread its biting over a wider period of the night with less distinct peaks in activity [11] This provides opportunities for vectors like An. arabiensis to evade control using LLINs [12]
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