Andersen Sandra B, Gerritsma Sylvia, Yusah Kalsum M, Mayntz David, Hywel-Jones Nigel L, Billen Johan, Boomsma Jacobus J, Hughes David P
Centre for Social Evolution, Department of Biology, University of Copenhagen, 2100 Copenhagen, Denmark.
Am Nat. 2009 Sep;174(3):424-33. doi: 10.1086/603640.
Specialized parasites are expected to express complex adaptations to their hosts. Manipulation of host behavior is such an adaptation. We studied the fungus Ophiocordyceps unilateralis, a locally specialized parasite of arboreal Camponotus leonardi ants. Ant-infecting Ophiocordyceps are known to make hosts bite onto vegetation before killing them. We show that this represents a fine-tuned fungal adaptation: an extended phenotype. Dead ants were found under leaves, attached by their mandibles, on the northern side of saplings approximately 25 cm above the soil, where temperature and humidity conditions were optimal for fungal growth. Experimental relocation confirmed that parasite fitness was lower outside this manipulative zone. Host resources were rapidly colonized and further secured by extensive internal structuring. Nutritional composition analysis indicated that such structuring allows the parasite to produce a large fruiting body for spore production. Our findings suggest that the osmotrophic lifestyle of fungi may have facilitated novel exploitation strategies.
特殊的寄生虫预计会表现出对宿主的复杂适应性。操纵宿主行为就是这样一种适应性。我们研究了虫草菌，它是树栖莱氏弓背蚁的一种本地专性寄生虫。已知感染蚂蚁的虫草菌会让宿主在死亡前咬住植被。我们表明，这代表了一种经过精细调整的真菌适应性：一种扩展表型。在树叶下发现了死亡的蚂蚁，它们用下颌附着在距离土壤约25厘米的树苗北侧，那里的温度和湿度条件最适合真菌生长。实验性重新安置证实，在这个操纵区域之外，寄生虫的适应性较低。宿主资源通过广泛的内部结构迅速被定殖并得到进一步保障。营养成分分析表明，这种结构使寄生虫能够产生一个大型子实体用于孢子生产。我们的研究结果表明，真菌的渗透营养生活方式可能促进了新的利用策略。
