Fitness consequences of Anopheles gambiae population hybridization

Abstract

Background: The use of transgenic mosquitoes with parasite inhibiting genes has been proposed as an integral strategy to control malaria transmission. However, release of exotic transgenic mosquitoes will bring in novel alleles along with parasite-inhibiting genes that may have unknown effects on native populations. Thus it is necessary to study the effects and dynamics of fitness traits in native mosquito populations in response to the introduction of novel genes. This study was designed to evaluate the dynamics of fitness traits in a simulation of introduction of novel alleles under laboratory conditions using two strains of Anopheles gambiae: Mbita strain from western Kenya and Ifakara strain from Tanzania.

Methods: The dynamics of fitness traits were evaluated under laboratory conditions using the two An. gambiae strains. These two geographically different strains were cross-bred and monitored for 20 generations to score fecundity, body size, blood-meal size, larval survival, and adult longevity, all of which are important determinants of the vector's potential in malaria transmission. Traits were analysed using pair-wise analysis of variance (ANOVA) for fecundity, body size, and blood-meal size while survival analysis was performed for larval survival and adult longevity.

Results: Fecundity and body size were significantly higher in the progeny up to the 20th generation compared to founder strains. Adult longevity had a significantly higher mean up to the 10th generation and average blood-meal size was significantly larger up to the 5th generation, indicating that hybrids fitness is enhanced over that of the founder strains.

Conclusion: Hybridization of the two mosquito populations used in this study led to increased performance in the fitness traits studied. Given that the studied traits are important determinants of the vector's potential to transmit malaria, these results suggest the need to release genetically modified mosquitoes that have the same or very similar backgrounds to the native populations.

Figure 1

Plot of expected proportion of hybrids against time (Generation). The simulation assumed equal sex ratio and equal number of Anopheles gambiae Mbita and Ifakara strains in random mating, as in the experimental set up.