Abstract
Anopheles gambiae sensu stricto, the main vector of malaria in Africa, is characterized by its vast geographical range and complex population structure. Assortative mating amongst the reproductively isolated cryptic forms that co-occur in many areas poses unique challenges for programs aiming to decrease malaria incidence via the release of sterile or genetically-modified mosquitoes. Importantly, whether laboratory-rearing affects the ability of An. gambiae individuals of a given cryptic taxa to successfully mate with individuals of their own form in field conditions is still unknown and yet crucial for mosquito-releases. Here, the independent effects of genetic and environmental factors associated with laboratory rearing on male and female survival, mating success and assortative mating were evaluated in the Mopti form of An. gambiae over 2010 and 2011. In semi-field enclosures experiments and despite strong variation between years, the overall survival and mating success of male and female progeny from a laboratory strain was not found to be significantly lower than those of the progeny of field females from the same population. Adult progeny from field-caught females reared at the larval stage in the laboratory and from laboratory females reared outdoors exhibited a significant decrease in survival but not in mating success. Importantly, laboratory individuals reared as larvae indoors were unable to mate assortatively as adults, whilst field progeny reared either outdoors or in the laboratory, as well as laboratory progeny reared outdoors all mated significantly assortatively. These results highlight the importance of genetic and environment interactions for the development of An. gambiae's full mating behavioral repertoire and the challenges this creates for mosquito rearing and release-based control strategies.
Highlights
In the last 20 years, the mass-distribution of insecticide treated nets (ITNs) and large-scale indoor residual spraying (IRS) of insecticides have been effective in reducing the incidence of malaria in a number of endemic countries [1,2]
There is a real danger that these achievements could be undone by the fast spread of resistance to insecticides observed in the main malaria vectors, An. gambiae sensu stricto, An. arabiensis and An. funestus
In the case of An. gambiae s.s., the most relevant sibling species of the An. gambiae complex in terms of abundance and level of anthropophily, the known presence of sympatric cryptic taxa in many regions combined with the current poor knowledge of processes leading to assortative mating over the majority of its geographical range casts doubt on the feasibility of implementing release projects [12]
Summary
In the last 20 years, the mass-distribution of insecticide treated nets (ITNs) and large-scale indoor residual spraying (IRS) of insecticides have been effective in reducing the incidence of malaria in a number of endemic countries [1,2]. A direct corollary from those observations is that hard-tocolonize chromosomal forms undergo stronger selection and bottle-necks in the colonization process and will require complex out-crossing schemes to regain a wild-type like mating phenotype prior to being released [8] Another complication stems from the fact that colonized cryptic taxa readily cross-mate under laboratory conditions whilst in the wild they are separated by strong pre-mating reproductive barriers [12,39]. The larval progeny of females either fieldcaught or from a recently colonized strain of the local Mopti form were reared either in the insectary or outdoors using otherwise identical rearing techniques This experimental design enabled us to assess the relative importance of genetic and environmental effects associated with laboratory-rearing affecting male and female survival and mating success as well as their ability to choose between mates of their own and a different sympatric subtaxa. The impacts of genetic and environment factors associated with laboratory breeding on the mating behavioural repertoire of this important vector species and their implications for future mosquito-release projects are discussed
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