The trophic vacuum and the evolution of complex life cycles in trophically transmitted helminths
The trophic vacuum and the evolution of complex life cycles in trophically transmitted helminths
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DOI：
10.1098/rspb.2014.1462
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发表时间：
2014-10-22
影响因子：
4.7
通讯作者：
Parker, Geoff A.
中科院分区：
文献类型：
--
作者：
Benesh, Daniel P.;Chubb, James C.;Parker, Geoff A.
寄生蠕虫(蠕虫)通常有复杂的生命周期，它们在两个或更多连续的宿主之间滋养地传播。有性生殖通常发生在高营养级(TL)脊椎动物中，那里的寄生虫可以长到大尺寸和高繁殖力。直接感染高TL宿主虽然是有利的，但对于被限制为滋养传播的寄生虫来说，可能是不可能实现的，因为蠕虫繁殖不太可能被大型捕食者摄取。繁殖体和最终寄主之间缺乏生态位重叠(营养传递真空)可以解释中间寄主的起源和/或维持，从而克服了这种传递障碍。我们发现，感染高TL最终宿主的线虫在其生命周期中往往有更多的连续宿主。然而，这种关系是温和的，主要是由宿主的最小TL驱动的，这表明通向宿主的最短营养链定义了传播真空的边界。我们还表明，替代的传播方式，如宿主渗透，允许线虫在没有中间宿主的情况下达到高TLS。我们认为，广泛的杂食性动物和寄生虫的适应增加了传播，可能会减少但不会消除蠕虫通过食物网传播的障碍。
Parasitic worms (helminths) frequently have complex life cycles in which they are transmitted trophically between two or more successive hosts. Sexual reproduction often takes place in high trophic-level (TL) vertebrates, where parasites can grow to large sizes with high fecundity. Direct infection of high TL hosts, while advantageous, may be unachievable for parasites constrained to transmit trophically, because helminth propagules are unlikely to be ingested by large predators. Lack of niche overlap between propagule and definitive host (the trophic transmission vacuum) may explain the origin and/or maintenance of intermediate hosts, which overcome this transmission barrier. We show that nematodes infecting high TL definitive hosts tend to have more successive hosts in their life cycles. This relationship was modest, though, driven mainly by the minimum TL of hosts, suggesting that the shortest trophic chains leading to a host define the boundaries of the transmission vacuum. We also show that alternative modes of transmission, like host penetration, allow nematodes to reach high TLs without intermediate hosts. We suggest that widespread omnivory as well as parasite adaptations to increase transmission probably reduce, but do not eliminate, the barriers to the transmission of helminths through the food web.