View an illustration about the life cycle of the malaria parasite.
A pair of studies conducted by NIAID grantees at the University of Notre Dame recently found evidence of emerging speciation between two forms of Anopheles gambiae mosquitoes, designated as M and S. In a new study, also at the University of Notre Dame and led by Nora Besansky, Ph.D., a group of researchers funded by NIAID examined the relationship between M and S and the TEP1 gene. The new paper was published in December 2010 in the Proceedings of the National Academy of Sciences.
Previous research in rodents showed that TEP1 is involved in mosquito immunity, with one variant conferring resistance to malaria. In this study, the scientists performed genome-wide comparisons of M and S to find the genetic differences behind mosquitoes’ adaptation to different larval habitats. One of the genome regions that they found to be especially different between M and S contained the TEP1 gene. Researchers found a distinct resistance allele of TEP1 that exists almost exclusively in M and not in S mosquitoes, even in areas where M and S co-exist, and showed that this allele confers resistance to rodent and human malaria parasites. The patterns of genetic variation found in M populations suggest this resistance allele evolved recently in response to pathogen-mediated selection.
Although the resistance conferred by TEP1 variants is not specific to malaria parasites, and probably did not evolve in response to malaria infection in the adult mosquito, it may still have a role in malaria transmission and control. “In adapting to different larval habitats, changes in mosquito physiology and behavior can occur that are not related directly to malaria transmission, but can still affect how the mosquito will encounter or respond to our control efforts. While the differences between M and S in the TEP1 gene may be driven by differences in their larval biology, adult M mosquitoes carry the same resistance alleles as the immature larvae, and so may not transmit malaria quite as well,” said Dr. Besansky. To date, this research has taken place in the laboratory with lab-bred mosquitoes and parasite lines; an important next step will be to examine the resistance phenotype of TEP1 alleles in natural populations.
For information on earlier research into these emerging species, see the NIAID media availability.
White BJ, Lawniczak MK, Cheng C, Coulibaly M, Wilson MD, Sagnon N, Costantini C, Simard F, Christophides GK, Besansky N. Adaptive divergence between incipient species of Anopheles gambiae increases resistance to Plasmodium. Proc Natl Acad Sci. (online 2010).
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Last Updated January 12, 2011