Dose effects and density-dependent regulation of two microparasites of Daphnia magna
Dose effects and density-dependent regulation of two microparasites of Daphnia magna
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DOI：
10.1007/pl00008847
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发表时间：
2000-02-01
期刊：
影响因子：
2.7
通讯作者：
Carius, HJ
中科院分区：
文献类型：
--
作者：
Ebert, D;Zschokke-Rohringer, CD;Carius, HJ
个体宿主构成了寄生虫的有限资源，这表明密度依赖性效应可能在宿主内生长和寄生虫调节中发挥作用。这一假设已被测试的几个蠕虫寄生虫，但不是微寄生虫。因此，我们研究了微寄生细菌多枝巴斯德菌和真菌Metschnikowiella biscuspidata感染的浮游甲壳动物大型水蚤的剂量反应模式。我们发现，随着越来越多的传播阶段管理的主机，主机的繁殖力和生存和寄生虫传播阶段的生产下降。使用k值分析，一种方法，量化密度依赖的强度，我们发现这两种寄生虫的密度依赖作用在所有剂量，表明没有一个最小密度低于寄生虫健身密度无关。在低剂量下，密度完全补偿，但在高剂量下过度补偿。在高剂量下，多枝假单胞菌的过度补偿较弱，而M. biscuspidata在两个最高剂量M. biscuspidata在任何传播阶段产生之前就杀死了它的宿主。我们的数据表明，密度依赖性是通过延迟孢子发育在多枝假单胞菌，但通过主机死亡率和降低寄生虫繁殖力在M。biscuspidata进一步的实验（仅多枝单孢菌）显示，在营养良好的宿主中比在营养不良的宿主中产生更多的寄生虫传播阶段，这表明对宿主资源的竞争阻碍了多枝单孢菌的发育。多枝假单胞菌（P.ramosa）的数据与多枝假单胞菌（M. biscuspidata，在很大程度上与微寄生虫流行病学模型中的假设一致。我们提请注意剂量效应和宿主内竞争对毒力演变的相关性。
Individual hosts constitute a limited resource for parasites, suggesting that density-dependent effects may play a role in within-host growth and parasite regulation. This hypothesis has been tested for several helminth parasites, but not for microparasites. We therefore examined dose-response patterns for the microparasitic bacterium Pasteuria ramosa and the fungus Metschnikowiella biscuspidata infecting the planktonic crustacean Daphnia magna. With increasing numbers of transmission stages administered to the host we found that host fecundity and survival and parasite transmission-stage production declined. Using a k-value analysis, a method that quantifies the strength of density dependence, we found for both parasites that density dependence acted at all doses, indicating the absence of a minimum density below which parasite fitness is density-independent. At low doses density was exactly compensated, but it was overcompensated at high doses. Overcompensation at high doses was weak for P. ramosa, but high for M. biscuspidata. At the two highest doses M. biscuspidata killed its hosts before any transmission stages were produced. Our data indicate that density dependence is expressed through retarded spore development in P. ramosa, but through both host mortality and reduced parasite fecundity in M. biscuspidata. A further experiment (P. ramosa only) revealed that in well-fed hosts more parasite transmission stages are produced than in poorly fed hosts, suggesting that competition for host resources retards P. ramosa development. Our data for P. ramosa, but not for M. biscuspidata, are largely consistent with assumptions made in models on microparasite epidemiology. We draw attention to the relevance of dose effects and within-host competition for the evolution of virulence.