INTERSPECIFIC INTERACTIONS TESTED - 2 SPECIES OF MALARIAL PARASITE INA WEST-AFRICAN LIZARD

Plasmodium giganteum and P. agamae, parasites of the rainbow lizard, A gama agama, in West Africa were studied to determine the nature of any interspecific interactions between the two malaria species. The plasm odia are distributed in A. agama throughout the mesic zone of Africa; P. agamae is sometimes found as a solitary malaria species in populati ons of the lizard, but P. giganteum has not been found alone. In 3170 lizards from Sierra Leone the prevalence of lizard malaria at 22 sites varied considerably (8-90% of lizards were infected), but the ratio o f the two species was similar among sites (52-91% P. agamae). Larger l izards were more often infected. Mixed infections occurred 2-5 times m ore often than expected by chance. Parasite density within individual hosts, or parasitemia, was similar for each species when alone or in m ixed infection. Natural infections followed in laboratory lizards stay ed at constant levels for as long as 211 days. The two species use dif ferent classes of host cells (P. giganteum in immature cells and P. ag amae in mature erythrocytes) and may have different periods of peak tr ansmission. Analysis of the data does not support a neutral relationsh ip between P. giganteum and P. agamae, nor ongoing competition for res ources or heterologous immunity. The data best support facilitation in which P. agamae alters the host in a way that allows more successful establishment of P. giganteum.