Osgood S M, Schall J J
Department of Biology, University of Vermont, Burlington, Vermont 05405, USA.
Parasitology. 2004 Jan;128(Pt 1):23-9. doi: 10.1017/s0031182003004207.
Sex ratio theory posits that the adaptive proportion of male to female gametocytes of a malaria parasite within the vertebrate host depends on the degree of inbreeding within the vector. Gametocyte sex ratio could be phenotypically flexible, being altered based on the infection's clonal diversity, and thus likely inbreeding. This idea was tested by manipulating the clonal diversity of infections of Plasmodium mexicanum in its lizard host, Sceloporus occidentalis. Naive lizards were inoculated with infected blood from a single donor or 3 pooled donors. Donors varied in their gametocyte sex ratios (17-46%, male), and sex ratio theory allowed estimation of the clonal diversity within donor and recipient infections. Phenotypic plasticity would produce a correlation between donor and recipient infections for infections initiated from a single donor, and a less female-biased gametocyte sex ratio in recipients that received a mixed blood inoculum (with predicted higher clonal diversity) than recipients receiving blood from a single donor. Neither pattern was observed. Gametocyte sex ratio of most infections ranged from 35 to 42% male, expected if clonal diversity was high for all infections. Alternative explanations are suggested for the observed variation of gametocyte sex ratio among P. mexicanum infections.
性别比例理论认为，疟原虫在脊椎动物宿主体内雄配子体与雌配子体的适应性比例取决于媒介体内的近亲繁殖程度。配子体性别比例在表型上可能具有灵活性，会根据感染的克隆多样性而改变，因此可能与近亲繁殖有关。通过操纵墨西哥疟原虫在其蜥蜴宿主西部强棱蜥体内感染的克隆多样性，对这一观点进行了验证。将未感染的蜥蜴接种来自单个供体或3个混合供体的感染血液。供体的配子体性别比例各不相同（雄性为17% - 46%），性别比例理论使得能够估计供体和受体感染中的克隆多样性。对于由单个供体引发的感染，表型可塑性会导致供体和受体感染之间产生相关性，并且与接受单一供体血液的受体相比，接受混合血液接种（预计克隆多样性更高）的受体中配子体性别比例的雌性偏向性更低。但未观察到这两种模式。如果所有感染的克隆多样性都很高，大多数感染的配子体性别比例预计在雄性35%至42%之间。针对在墨西哥疟原虫感染中观察到的配子体性别比例变化，提出了其他解释。
