The expression of virulence during double infections by different parasites with conflicting host exploitation and transmission strategies
The expression of virulence during double infections by different parasites with conflicting host exploitation and transmission strategies
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DOI：
10.1111/j.1420-9101.2011.02264.x
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发表时间：
2011-06-01
影响因子：
2.1
通讯作者：
Ebert, D.
中科院分区：
文献类型：
--
作者：
Ben-Ami, F.;Rigaud, T.;Ebert, D.
在许多自然种群中，发现宿主被一种以上的寄生虫物种感染。当这些寄生虫具有不同的宿主利用策略和传播模式时，它们之间可能会产生冲突。这种冲突可能会减少两种寄生虫的成功，但可能会对宿主有利。例如，毒性较低的寄生虫可以保护宿主免受毒性更强的竞争者的侵害。我们研究这种冲突使用水蚤大型和两个同域寄生虫：血液感染细菌多枝巴氏杆菌，水平传播和细胞内微孢子虫sporidium bayeri，可以同时传播水平和垂直感染后，卵巢和脂肪组织的主机。我们量化主机和寄生虫健身后，暴露水蚤一种或两种寄生虫，同时和顺序。在严格的水平传播条件下，巴氏杆菌竞争性地排除了同时和连续双重感染中的孢子菌，无论暴露的顺序如何。双重感染的宿主寿命、宿主繁殖和寄生孢子产生与单次感染相似。当宿主首次垂直（transovarilly）感染O. bayeri，P.ramosa在一定程度上能够抵抗与P.ramosa的竞争，但两种寄生虫的传播阶段都比它们在单一感染中产生的传播阶段少。与此同时，宿主的繁殖力和寿命下降。我们的研究表明，即使竞争的寄生虫物种利用不同的宿主组织增殖，双重感染导致更高的毒力表达，并最终可能选择更高的毒力。此外，我们没有发现证据表明，毒性较低和垂直传播的O。bayeri保护其宿主免受高毒性的多枝假单胞菌的侵害。
In many natural populations, hosts are found to be infected by more than one parasite species. When these parasites have different host exploitation strategies and transmission modes, a conflict among them may arise. Such a conflict may reduce the success of both parasites, but could work to the benefit of the host. For example, the less-virulent parasite may protect the host against the more-virulent competitor. We examine this conflict using the waterflea Daphnia magna and two of its sympatric parasites: the blood-infecting bacterium Pasteuria ramosa that transmits horizontally and the intracellular microsporidium Octosporea bayeri that can concurrently transmit horizontally and vertically after infecting ovaries and fat tissues of the host. We quantified host and parasite fitness after exposing Daphnia to one or both parasites, both simultaneously and sequentially. Under conditions of strict horizontal transmission, Pasteuria competitively excluded Octosporea in both simultaneous and sequential double infections, regardless of the order of exposure. Host lifespan, host reproduction and parasite spore production in double infections resembled those of single infection by Pasteuria. When hosts became first vertically (transovarilly) infected with O. bayeri, Octosporea was able to withstand competition with P. ramosa to some degree, but both parasites produced less transmission stages than they did in single infections. At the same time, the host suffered from reduced fecundity and longevity. Our study demonstrates that even when competing parasite species utilize different host tissues to proliferate, double infections lead to the expression of higher virulence and ultimately may select for higher virulence. Furthermore, we found no evidence that the less-virulent and vertically transmitting O. bayeri protects its host against the highly virulent P. ramosa.