An investigation into the fitness and mating competitiveness of laboratory and transgenic strains of Anopheles gambiae sensu stricto

Abstract

Malaria is a deadly parasitic disease of humans spread through the bite of Anopheles spp. mosquitoes. Current control methods for the disease are broadly effective, but the spread of insecticide resistance in the principle Anopheline vectors of the disease raises the possibility of an increase in disease burden in the future. Transgenesis offers a novel alternative approach to vector control but requires the mass-release of virile, competitive, genetically altered male mosquitoes, thus the success of future transgenic release programmes depends greatly on how capable the transgenic strain is of surviving in field conditions and successfully introgressing with wild mosquito populations.
Using a combination of laboratory and field-based ecological experiments, along with molecular biological and genomic approaches, we assessed both the fitness of two transgenic strains of Anopheles gambiae s.s. and the genetic and environmental factors determining survival, mating success and assortative mating behaviour in lab and field derived samples of non-transgenic Anopheles gambiae s.s.
We found that imposed a fitness cost in both a transgenic strain carrying a phenotypic marker, and a second strain carrying a putative anti-malarial peptide sequence. Overt fitness costs were confined to larval development in both strains, although there was some evidence of a difference in egg production and morphology between strains. The anti-malarial peptide-carrying strain was significantly less fit, and suffered a fitness burden in hemizygote individuals as well as homozygotes. The possible sources of fitness differences are discussed. In semi-field-based crosses, we observed a significant interaction between the genetic and environmental background in the survival and mating success of non-transgenic strains; furthermore, the combination of laboratory rearing and a laboratory genetic background was sufficient to abolish the assortative mating behaviour normally observed between M- and S-molecular form An. gambiae populations.