Department of Biology, University of Vermont, Burlington, Vermont 05405, USA.
Parasitology. 2010 Nov;137(13):1851-9. doi: 10.1017/S0031182010000909. Epub 2010 Jul 12.
Sex ratio theory predicts that malaria parasites should bias gametocyte production toward female cells in single-clone infections because they will experience complete inbreeding of parasite gametes within the vector. A higher proportion of male gametocytes is favoured under conditions that reduce success of male gametes at reaching females such as low gametocyte density or attack of the immune system later in the infection. Recent experimental studies reveal genetic variation for gametocyte sex ratio in single-clone infections. We examined these issues with a study of experimental single-clone infections for the lizard malaria parasite Plasmodium mexicanum in its natural host. Gametocyte sex ratios of replicate single-clone infections were determined over a period of 3-4 months. Sex ratios were generally female biased, but not as strongly as expected under simple sex ratio theory. Gametocyte density was not related to sex ratio, and male gametocytes did not become more common later in infections. The apparent surplus of male gametocytes could be explained if male fecundity is low in this parasite, or if rapid clotting of the lizard blood reduces male gamete mobility. There was also a significant clone effect on sex ratio, suggesting genetic variation for some life-history trait, possibly male fecundity.
性比理论预测，疟疾寄生虫应该偏向于雌性配子体的产生，因为它们将在媒介中经历寄生虫配子的完全近亲繁殖。在降低雄性配子成功到达雌性的条件下，例如配子体密度低或感染后期免疫系统攻击，会有利于产生更多的雄性配子体。最近的实验研究揭示了单克隆感染中配子体性比的遗传变异。我们通过对蜥蜴疟原虫 Plasmodium mexicanum 在其自然宿主中的实验性单克隆感染进行了研究，来检验这些问题。在 3-4 个月的时间内，我们确定了重复的单克隆感染的配子体性比。性比通常偏向雌性，但不如简单性比理论所预期的那样强烈。配子体密度与性比无关，感染后期雄性配子体也没有变得更常见。如果这种寄生虫的雄性繁殖力较低，或者蜥蜴血液的快速凝固降低了雄性配子的活动性，那么雄性配子体的明显过剩就可以得到解释。性比也存在显著的克隆效应，这表明某些生活史特征（可能是雄性繁殖力）存在遗传变异。
