Testing sex ratio theory with the malaria parasite Plasmodium mexicanum in natural and experimental infections

The malaria parasite (Plasmodium) life history accords well with the assumptions of Local Mate Competition (LMC) of sex ratio theory. Within a single meal of the blood-feeding vector, sexually dimorphic gametocyte cells produce gametes (females produce 1, males several) that mate and undergo sexual recombination. The theory posits several factors drive the Plasmodium sex ratio: male fecundity (gametes/ male gametocyte), number and relative abundance of parasite clones, and gametocyte density. We measured these traits for the lizard malaria parasite, P. mexicanum, with a large sample of natural infections and infections from experiments which manipulated clonal diversity. Sex ratio in single-clone infections was slightly female-biased, but matched predictions of theory for this low-fecundity species. Sex ratio was less female-biased in clonally diverse infections as predicted by LMC for the experimental, but not natural infections. Gametocyte density was not positively related to sex rat...