Kaldonski Nicolas, Perrot-Minnot Marie-Jeanne, Dodet Raphaël, Martinaud Guillaume, Cézilly Frank
Université de Bourgogne, 6 Boulevard Gabriel, Dijon 21000, France.
Proc Biol Sci. 2009 Jan 7;276(1654):169-76. doi: 10.1098/rspb.2008.0798.
Manipulation by parasites is a catchy concept that has been applied to a large range of phenotypic alterations brought about by parasites in their hosts. It has, for instance, been suggested that the carotenoid-based colour of acanthocephalan cystacanths is adaptive through increasing the conspicuousness of infected intermediate hosts and, hence, their vulnerability to appropriate final hosts such as fish predators. We revisited the evidence in favour of adaptive coloration of acanthocephalan parasites in relation to increased trophic transmission using the crustacean amphipod Gammarus pulex and two species of acanthocephalans, Pomphorhynchus laevis and Polymorphus minutus. Both species show carotenoid-based colorations, but rely, respectively, on freshwater fish and aquatic bird species as final hosts. In addition, the two parasites differ in the type of behavioural alteration brought to their common intermediate host. Pomphorhynchus laevis reverses negative phototaxis in G. pulex, whereas P. minutus reverses positive geotaxis. In aquaria, trout showed selective predation for P. laevis-infected gammarids, whereas P. minutus-infected ones did not differ from uninfected controls in their vulnerability to predation. We tested for an effect of parasite coloration on increased trophic transmission by painting a yellow-orange spot on the cuticle of uninfected gammarids and by masking the yellow-orange spot of infected individuals with inconspicuous brown paint. To enhance realism, match of colour between painted mimics and true parasite was carefully checked using a spectrometer. We found no evidence for a role of parasite coloration in the increased vulnerability of gammarids to predation by trout. Painted mimics did not differ from control uninfected gammarids in their vulnerability to predation by trout. In addition, covering the place through which the parasite was visible did not reduce the vulnerability of infected gammarids to predation by trout. We discuss alternative evolutionary explanations for the origin and maintenance of carotenoid-based colorations in acanthocephalan parasites.
寄生虫的操控是一个引人注目的概念，已被应用于寄生虫在其宿主中引发的一系列表型改变。例如，有人提出，棘头虫囊尾蚴基于类胡萝卜素的颜色具有适应性，因为它增加了受感染中间宿主的显眼程度，从而增加了它们被合适的终末宿主（如鱼类捕食者）捕食的可能性。我们利用甲壳纲双足虾虎鱼（Gammarus pulex）以及两种棘头虫——平滑棘头虫（Pomphorhynchus laevis）和微小多形棘头虫（Polymorphus minutus），重新审视了与营养级传播增加相关的棘头虫寄生虫适应性着色的证据。这两种棘头虫都呈现基于类胡萝卜素的颜色，但分别以淡水鱼和水鸟为终末宿主。此外，这两种寄生虫给它们共同的中间宿主带来的行为改变类型也有所不同。平滑棘头虫会使双足虾虎鱼的负趋光性发生逆转，而微小多形棘头虫会使正趋地性发生逆转。在水族箱中，鳟鱼对感染平滑棘头虫的双足虾虎鱼表现出选择性捕食，而感染微小多形棘头虫的双足虾虎鱼在被捕食的易感性方面与未感染的对照组没有差异。我们通过在未感染的双足虾虎鱼的表皮上绘制橙黄色斑点，以及用不显眼的棕色颜料掩盖受感染个体的橙黄色斑点，来测试寄生虫颜色对营养级传播增加的影响。为了增强真实感，使用光谱仪仔细检查了绘制的模拟物与真正寄生虫之间的颜色匹配度。我们没有发现证据表明寄生虫颜色在双足虾虎鱼被捕食的易感性增加中起作用。绘制的模拟物在被捕食的易感性方面与未感染的对照双足虾虎鱼没有差异。此外，覆盖寄生虫可见的部位并没有降低受感染双足虾虎鱼被捕食的易感性。我们讨论了棘头虫寄生虫基于类胡萝卜素的颜色的起源和维持的其他进化解释。
