Fricke Jennifer M, Vardo-Zalik Anne M, Schall Jos J
Department of Biology, University of Vermont, Burlington, Vermont 05405, USA.
J Parasitol. 2010 Apr;96(2):308-13. doi: 10.1645/GE-2304.1.
Gene flow, and resulting degree of genetic differentiation among populations, will shape geographic genetic patterns and possibly local adaptation of parasites and their hosts. Some studies of Plasmodium falciparum in humans show substantial differentiation of the parasite in locations separated by only a few kilometers, a paradoxical finding for a parasite in a large, mobile host. We examined genetic differentiation of the malaria parasite Plasmodium mexicanum, and its lizard host, Sceloporus occidentalis, at 8 sites in northern California, with the use of variable microsatellite markers for both species. These lizards are small and highly territorial, so we expected local genetic differentiation of both parasite and lizard. Populations of P. mexicanum were found to be differentiated by analysis of 5 markers (F(st) values >0.05-0.10) over distances as short as 230-400 m, and greatly differentiated (F(st) values >0.25) for sites separated by approximately 10 km. In contrast, the lizard host had no, or very low, levels of differentiation for 3 markers, even for sites >40 km distant. Thus, gene flow for the lizard was great, but despite the mobility of the vertebrate host, the parasite was locally genetically distinct. This discrepancy could result if infected lizards move little, but their noninfected relatives were more mobile. Previous studies on the virulence of P. mexicanum for fence lizards support this hypothesis. However, changing prevalence of the parasite, without changes in density of the lizard, could also result in this pattern.
基因流动以及由此导致的种群间遗传分化程度，将塑造地理遗传模式，并可能影响寄生虫及其宿主的局部适应性。一些针对人类恶性疟原虫的研究表明，仅相隔几公里的不同地点的寄生虫存在显著分化，这对于寄生于大型移动宿主的寄生虫来说是一个矛盾的发现。我们利用两种物种的可变微卫星标记，研究了加利福尼亚北部8个地点的疟原虫墨西哥疟原虫及其蜥蜴宿主西部强棱蜥的遗传分化情况。这些蜥蜴体型小且领地意识强，因此我们预计寄生虫和蜥蜴都会出现局部遗传分化。通过对5个标记的分析发现，墨西哥疟原虫种群在短至230 - 400米的距离内就出现了分化（Fst值>0.05 - 0.10），而相隔约10公里的地点之间则出现了极大的分化（Fst值>0.25）。相比之下，蜥蜴宿主的3个标记的分化水平很低或没有分化，即使是距离超过40公里的地点也是如此。因此，蜥蜴的基因流动很大，但尽管脊椎动物宿主具有移动性，寄生虫在局部仍具有遗传独特性。如果感染的蜥蜴移动很少，而它们未感染的亲属移动性更强，就可能导致这种差异。先前关于墨西哥疟原虫对围栏蜥蜴毒力的研究支持了这一假设。然而，寄生虫患病率的变化，而蜥蜴密度没有变化，也可能导致这种模式。
