In collaboration with the Jeffrey Powell lab at Yale University, we are involved in a study of the evolution of anti-malarial immune genes in the Anopheles gambiae complex. Co-evolution between Plasmodium and its Anopheline vectors is expected to affect genes that play a role in the vector’s defense against the parasite. That is, genes that are crucial to the mosquito’s defense against Plasmodium should exhibit signs of adaptive evolution. If this is the case, we will be able to determine which anti-malarial genes are most important by identifying genes that show clear signs of positive selection in malaria vectors, but not in closely related non-vectors. One major advantage of such an approach is that it identifies genes that are important to the interaction of Anopheles with its natural parasite Plasmodium falciparum, rather than the model species often used in laboratory studies.
We are applying this approach to proven and suspected anti-malarial genes in natural populations of six species in the Anopheles gambiae complex, including vector and non-vector species. Using various statistical tests; such as the MacDonald-Kreitman test and phylogeny-based maximum likelihood tests, patterns of selection acting on these genes can be inferred.
The majority of the immune genes in the Anopheles gambiae complex examined so far evolve primarily under purifying selection. However, we did find evidence for adaptive evolution in the anti-malarial gene LRIM1 in An. arabiensis, one of the main African malaria vectors (see Slotman et al. 2007). Our data also clearly indicate that this adaptive LRIM1 allele has introgressed from An. arabiensis into An. gambiae. This indicates that LRIM1 may play an important role in the defense of An. arabiensis against Plasmodium, and if so, should be variable for Plasmodium resistance in An. gambiae s.s.
Publications from this work:
Anopheles immune genes and amino acid sites evolving under the effect of positive selection (2010) Parmakelis A, M Moustaka, N Poulakakis, C Louis, MA Slotman, JC Marshall, PH Awono-Ambene, C Antonio-Nkondjio, F Simard, A Caccone, JR Powell. PLoS ONE 5 (1): e8885
The molecular evolution of four anti-malarial immune genes in the Anopheles gambiae complex (2008) Parmakelis A, MA Slotman, JC Marshall, P Awono-Ambene, C Antonio-Nkondjio, F Simard, A Caccone, JR Powell. BMC Evolutionary Biology 8:79
Patterns of selection in anti-malarial immune genes in malaria vectors: evidence for adaptive evolution in LRIM1 in Anopheles arabiensis (2007) Slotman MA, A Parmakelis, JC Marshall, PH Awono-Ambene, C Antonio-Nkondjo, F Simard, A Caccone and JR Powell. PLoS One 2(8): e793