Neal Allison T, Schall Jos J
Department of Biology, University of Vermont, Burlington, Vermont 05405.
Evolution. 2014 Apr;68(4):1071-81. doi: 10.1111/evo.12334. Epub 2014 Feb 1.
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 one, 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, Plasmodium mexicanum, with a large sample of natural infections and infections from experiments that 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（疟原虫属）的生活史与性比理论中本地配偶竞争（LMC）的假设非常契合。在吸血媒介的单次进食中，具有性别二态性的配子体细胞产生配子（雌性产生一个，雄性产生多个），这些配子交配并进行有性重组。该理论假定有几个因素驱动疟原虫的性比：雄性繁殖力（配子/雄配子体）、寄生虫克隆的数量和相对丰度，以及配子体密度。我们用大量自然感染样本以及来自操纵克隆多样性实验的感染样本，测量了蜥蜴疟原虫墨西哥疟原虫的这些特征。单克隆感染中的性比略微偏向雌性，但与该低繁殖力物种的理论预测相符。如LMC对实验感染（而非自然感染）的预测，在克隆多样的感染中，性比的雌性偏向性较小。配子体密度与性比没有正相关关系。这些结果可以用墨西哥疟原虫自然情况下克隆多样性低且配子体产量高的生活史来解释。这是第一项对自然疟疾系统进行的研究，该研究考察了个体脊椎动物宿主中与LMC相关的所有特征，并表明性比理论对人类公共卫生具有重要意义，是一个引人注目的例子。
