Résumé
Studies of both vertebrates and invertebrates have suggested that
specialists, as compared to generalists, are likely to suffer more serious
declines in response to environmental change. Less is known about the
effects of environmental conditions on specialist vs. generalist
parasites. Here, we study the evolutionary strategies of malaria parasites
(Plasmodium spp.) among different bird host communities. We determined the
parasite diversity and prevalence of avian malaria in three bird
communities in the lowland forests in Cameroon, highland forests in East
Africa, and fynbos in South Africa. We calculated the host specificity
index of parasites to examine the range of hosts parasitized as a function
of the habitat, and investigated the phylogenetic relationships of
parasites. First, using phylogenetic and ancestral reconstruction analyses
we found an evolutionary tendency for generalist malaria parasites to
become specialists. The transition rate at which generalists become
specialists was nearly four times as great as the rate at which
specialists become generalists. We also found more specialist parasites
and greater parasite diversity in African lowland rainforests as compared
to the more climatically variable habitats of the fynbos and the highland
forests. Thus, with environmental changes, we anticipate a change in the
distribution of both specialist and generalist parasites with potential
impacts on bird communities.