Data from: 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 ratio. These results are explained by the P. mexicanum life history of naturally low clonal diversity and high gametocyte production. This is the first study of a natural malaria system that examines all traits relevant to LMC in individual vertebrate hosts and suggests a striking example of sex ratio theory having significance for human public health.

疟原虫（Plasmodium）的生活史与性比理论中的局部配偶竞争（Local Mate Competition, LMC）假说高度契合。在吸血媒介的单次吸血过程中，雌雄二态的配子细胞（gametocyte cells）会产生配子（gametes）：雌性仅产生1个配子，雄性则产生多个，配子结合后会发生有性重组。该理论提出，多个因素驱动疟原虫的性比：雄性生育力（male fecundity，即每个雄性配子细胞产生的配子数）、寄生虫克隆的数量与相对丰度，以及配子细胞密度（gametocyte density）。我们针对蜥蜴疟原虫墨西哥疟原虫（P. mexicanum）的上述性状开展了测定，样本涵盖大量自然感染样本与经克隆多样性操控的实验感染样本。单克隆感染（single-clone infections）的性比略呈雌性偏倚（female-biased），但与该低生育力物种（low-fecundity species）的理论预测相符。在克隆多样的感染（clonally diverse infections）中，性比的雌性偏倚程度更低，这一结果符合LMC的预测，但仅见于实验感染样本，而非自然感染样本。配子细胞密度与性比并无显著正相关关系。上述结果可通过墨西哥疟原虫的生活史特征解释：其自然条件下克隆多样性较低，且配子细胞产生量较高。本研究是首个在单个脊椎动物宿主（vertebrate hosts）中检验与LMC相关的全部性状的自然疟原虫系统研究，同时揭示了性比理论对人类公共卫生具有重要意义的典型案例。