Tavalire Hannah F, Blouin Michael S, Steinauer Michelle L
Department of Integrative Biology, 3029 Cordley Hall, Oregon State University, Corvallis, OR 97330, USA.
Department of Integrative Biology, 3029 Cordley Hall, Oregon State University, Corvallis, OR 97330, USA.
Int J Parasitol. 2016 Feb;46(2):123-31. doi: 10.1016/j.ijpara.2015.10.001. Epub 2015 Nov 10.
Parasite fitness is largely influenced by a variation in host response due to the host's genetic background. Here we investigated the impact of host genotype on pathogen success in the snail vector of its castrating parasite, Schistosoma mansoni. We infected five inbred lines of Biomphalaria glabrata with two infection doses and followed their growth, reproductive output and parasite production throughout the course of infection. There was no difference in resistance to infection among inbred lines, but lines varied in their responses to infection and the numbers of parasites produced. Snails did not compensate for castration by increasing their fecundity during the early phase of infection (fecundity compensation). However, some lines were able to delay parasite shedding for up to 30 weeks, thus prolonging reproduction before the onset of castration. Here we propose this strategy as a novel defense against castrating pathogens in snails. Gigantism, a predicted outcome of castration due to energy reallocation, occurred early in infection (<15 weeks) and was not universal among the snail lines. Lines that did not show gigantism were also characterised by a high parasite production rate and low survivorship, perhaps indicating energy reallocation into parasite production and costly immune defense. We observed no differences in total parasite production among lines throughout the entire course of infection, although lines differed in their parasite reproductive rate. The average rate of parasite production varied among lines from 1300 to 2450 cercariae within a single 2h shedding period, resulting in a total production of 6981-29,509 cercariae over the lifetime of a single snail. Regardless of genetic background, snail size was a strong predictor of parasite reproduction: each millimetre increase in snail size at the time of the first shed resulted in up to 3500 more cercariae over the lifetime of the snail. The results of this study provide a detailed picture of variation in hosts' responses to infection and the resulting impacts on parasite fitness, further defining the intricacies of snail-schistosome compatibility.
寄生虫的适应性在很大程度上受到宿主遗传背景导致的宿主反应差异的影响。在此，我们研究了宿主基因型对其阉割性寄生虫曼氏血吸虫的蜗牛载体中病原体成功感染的影响。我们用两种感染剂量感染了五个光滑双脐螺近交系，并在整个感染过程中跟踪它们的生长、繁殖产出和寄生虫产生情况。近交系之间在感染抗性上没有差异，但各系在对感染的反应以及产生的寄生虫数量上有所不同。蜗牛在感染早期并未通过提高繁殖力来补偿阉割（繁殖力补偿）。然而，一些品系能够将寄生虫排出推迟长达30周，从而在阉割开始前延长繁殖时间。在此，我们将这种策略作为蜗牛抵御阉割性病原体的一种新防御机制提出。由于能量重新分配，阉割的一个预期结果——巨人症，在感染早期（<15周）就出现了，并且在蜗牛品系中并不普遍。未表现出巨人症的品系也具有寄生虫产生率高和存活率低的特征，这可能表明能量重新分配到了寄生虫产生和代价高昂的免疫防御中。在整个感染过程中，我们观察到各品系之间在总寄生虫产生量上没有差异，尽管各系在寄生虫繁殖率上有所不同。在单个2小时的排出期内，各品系的寄生虫平均产生率从1300尾到2450尾尾蚴不等，单个蜗牛一生的总产生量为6981 - 29509尾尾蚴。无论遗传背景如何，蜗牛大小都是寄生虫繁殖的一个有力预测指标：首次排出时蜗牛大小每增加一毫米，蜗牛一生所产生的尾蚴就会增加多达3500尾。这项研究的结果详细描绘了宿主对感染的反应差异及其对寄生虫适应性的影响，进一步明确了蜗牛 - 血吸虫相容性的复杂性。
