Résumé
Pathogens, which have recently colonized a new host species or new
populations of the same host, are interesting models for understanding how
populations may evolve in response to novel environments. During its
colonization of South America from Africa Plasmodium falciparum, the main
agent of malaria, has been exposed to new conditions in distinctive new
human populations (Amerindian and populations of mixed origins), that
likely exerted new selective pressures on the parasite's genome.
Among the genes that might have experienced strong selective pressures in
response to these environmental changes, the eba genes (erythrocyte
binding antigens genes), which are involved in the invasion of the human
red blood cells, constitute good candidates. In this study, we analyzed,
in South America, the polymorphism of three eba genes (eba-140, eba-175,
eba-181) and compared it to the polymorphism observed in African
populations. The aim was to determine whether these genes faced selective
pressures in South America distinct from what they experienced in Africa.
Patterns of genetic variability of these genes were compared to the
patterns observed at two housekeeping genes (adsl and serca) and 272 SNPs
to separate adaptive effects from demographic effects. We show that,
conversely to Africa, eba-140 seemed to be under stronger diversifying
selection in South America than eba-175. In contrast, eba-181 did not show
any sign of departure from neutrality. These changes in the patterns of
selection on the eba genes could be the consequence of changes in the host
immune response, the host receptor polymorphisms, and / or the ability of
the parasite to silence or express differentially its invasion proteins.