Clonal diversity within infections and the virulence of a malaria parasite,Plasmodium mexicanum

Abstract

SUMMARYBoth verbal and mathematical models of parasite virulence predict that genetic diversity of microparasite infections will influence the level of costs suffered by the host. We tested this idea by manipulating the number of co-existing clones ofPlasmodium mexicanumin its natural vertebrate host, the fence lizardSceloporus occidentalis. We established replicate infections ofP.mexicanummade up of 1, 2, 3, or >3 clones (scored using 3 microsatellite loci) to observe the influence of clone number on several measures of parasite virulence. Clonal diversity did not affect body growth or production of immature erythrocytes. Blood haemoglobin concentration was highest for the most genetically complex infections (equal to that of non-infected lizards), and blood glucose levels and rate of blood clotting was highest for the most diverse infections (with greater glucose and more rapid clotting than non-infected animals). Neither specific clones nor parasitaemia were associated with virulence. In this first experiment that manipulated the clonal diversity of a naturalPlasmodium-host system, the cost of infection with 1 or 2 clones ofP.mexicanumwas similar to that previously reported for infected lizards, but the most complex infections had either no cost or could be beneficial for the host.