Weinersmith Kelly L, Warinner Chloe B, Tan Virginia, Harris David J, Mora Adrienne B, Kuris Armand M, Lafferty Kevin D, Hechinger Ryan F
*Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA
*Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA*Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA.
Integr Comp Biol. 2014 Jul;54(2):184-92. doi: 10.1093/icb/icu081. Epub 2014 Jun 15.
For trophically transmitted parasites that manipulate the phenotype of their hosts, whether the parasites do or do not experience resource competition depends on such factors as the size of the parasites relative to their hosts, the intensity of infection, the extent to which parasites share the cost of defending against the host's immune system or manipulating their host, and the extent to which parasites share transmission goals. Despite theoretical expectations for situations in which either no, or positive, or negative density-dependence should be observed, most studies document only negative density-dependence for trophically transmitted parasites. However, this trend may be an artifact of most studies having focused on systems in which parasites are large relative to their hosts. Yet, systems are common where parasites are small relative to their hosts, and these trophically transmitted parasites may be less likely to experience resource limitation. We looked for signs of density-dependence in Euhaplorchis californiensis (EUHA) and Renicola buchanani (RENB), two manipulative trematode parasites infecting wild-caught California killifish (Fundulus parvipinnis). These parasites are small relative to killifish (suggesting resources are not limiting), and are associated with changes in killifish behavior that are dependent on parasite-intensity and that increase predation rates by the parasites' shared final host (indicating the possibility for cost sharing). We did not observe negative density-dependence in either species, indicating that resources are not limiting. In fact, observed patterns indicate possible mild positive density-dependence for EUHA. Although experimental confirmation is required, our findings suggest that some behavior-manipulating parasites suffer no reduction in size, and may even benefit when "crowded" by conspecifics.
对于那些操纵宿主表型的营养传播性寄生虫而言，寄生虫是否经历资源竞争取决于诸多因素，比如寄生虫相对于宿主的大小、感染强度、寄生虫分担抵御宿主免疫系统或操纵宿主成本的程度，以及寄生虫在传播目标上的共享程度。尽管从理论上预期了可能观察到无密度依赖性、正密度依赖性或负密度依赖性的情况，但大多数研究仅记录了营养传播性寄生虫的负密度依赖性。然而，这种趋势可能是大多数研究集中于寄生虫相对于宿主较大的系统所导致的人为现象。不过，寄生虫相对于宿主较小的系统也很常见，而且这些营养传播性寄生虫可能不太容易经历资源限制。我们在加州真雀鲷（Fundulus parvipinnis）体内的两种操纵性吸虫寄生虫——加利福尼亚真雀鲷嗜子宫线虫（Euhaplorchis californiensis，简称EUHA）和布氏肾形吸虫（Renicola buchanani，简称RENB）中寻找密度依赖性的迹象。这些寄生虫相对于雀鲷较小（表明资源不存在限制），并且与雀鲷行为的变化有关，这种变化取决于寄生虫的感染强度，且会增加寄生虫共同终末宿主的捕食率（表明存在成本分担的可能性）。我们在这两个物种中均未观察到负密度依赖性，这表明资源不存在限制。事实上，观察到的模式表明EUHA可能存在轻微的正密度依赖性。尽管需要实验证实，但我们的研究结果表明，一些操纵行为的寄生虫不会出现体型减小的情况，甚至在被同种个体“拥挤”时可能会受益。
