The discovery, made in the laboratory of biological control extension specialist Mark Hoddle, has been included in the latest issue of the journal Proceedings of the National Academy of Sciences. It is a critical piece of the puzzle in the search for ways to combat mosquito-carried illnesses, such as yellow fever and dengue, because transgenic mosquitoes must be able to compete in the wild in order to combat the illnesses.
Up to now, scientists have debated whether transgenic mosquitoes would have similar or reduced levels of fitness relative to their untransformed counterparts. This work shows that their fitness is dramatically decreased.
Postgraduate researcher Nicola Irvin, under Hoddle's supervision and in collaboration with Professor Peter Atkinson, was able to quantify the fitness of three different transgenic strains of Aedes aeypti, the mosquito vector of yellow fever and dengue. Irvin found that nearly all aspects of development and reproduction of transgenic mosquitoes was severely impaired when compared to non-engineered mosquitoes of the same type.
For example, in four consecutively laid batches of eggs, non-transformed mosquitoes survived from egg to adulthood between 17 and 64 percent of the time. That percentage was between 0 and 23 for transgenic mosquitoes. The average number of eggs laid by non-engineered mosquitoes ranged between 46 and 90, while for transgenic mosquitoes the range was between 14 and 58.
"These data have major implications for the competitiveness of transgenic mosquitoes with non-transformed wild-types," said Hoddle. "Analyses indicate that since engineered mosquitoes lay fewer eggs and egg-adult survivorship is lower they will not be able to increase their population mass after release and therefore will be unable to displace disease-carrying mosquitoes."
Atkinson, the professor who leads a major research program to genetically modify mosquitoes to combat mosquito-borne disease, was not surprised that there was a fitness cost associated with transgenesis, but was surprised with the magnitude of it. "Once we determine the genetic basis of these fitness costs it should be possible to generate competitive mosquitoes that will prevent the transmission of human diseases," he said.
Atkinson uses a jelly fish "marker gene" that glows under ultraviolet light so he can quickly identify which mosquitoes have successfully incorporated the new genes into their DNA. The next step is to tightly link "effector genes" to them that will block the mosquito's ability to carry the disease. "Theoretically, once released into the wild they should compete with disease carrying mosquitoes and reduce the incidence of malaria, dengue fever, and other mosquito-borne maladies," Atkinson said.