Gerardo Nicole M, Mueller Ulrich G, Price Shauna L, Currie Cameron R
Section of Integrative Biology, Patterson Laboratories, University of Texas, Austin, TX 78712, USA.
Proc Biol Sci. 2004 Sep 7;271(1550):1791-8. doi: 10.1098/rspb.2004.2792.
Fungus-growing ants, their cultivated fungi and the cultivar-attacking parasite Escovopsis coevolve as a complex community. Higher-level phylogenetic congruence of the symbionts suggests specialized long-term associations of host-parasite clades but reveals little about parasite specificity at finer scales of species-species and genotype-genotype interactions. By coupling sequence and amplified fragment length polymorphism genotyping analyses with experimental evidence, we examine (i) the host specificity of Escovopsis strains infecting colonies of three closely related ant species in the genus Cyphomyrmex, and (ii) potential mechanisms constraining the Escovopsis host range. Incongruence of cultivar and ant relationships across the three focal Cyphomyrmex spp. allows us to test whether Escovopsis strains track their cultivar or the ant hosts. Phylogenetic analyses demonstrate that the Escovopsis phylogeny matches the cultivar phylogeny but not the ant phylogeny, indicating that the parasites are cultivar specific. Cross-infection experiments establish that ant gardens can be infected by parasite strains with which they are not typically associated in the field, but that infection is more likely when gardens are inoculated with their typical parasite strains. Thus, Escovopsis specialization is shaped by the parasite's ability to overcome only a narrow range of garden-specific defences, but specialization is probably additionally constrained by ecological factors, including the other symbionts (i.e. ants and their antibiotic-producing bacteria) within the coevolved fungus-growing ant symbiosis.
培育真菌的蚂蚁、它们培育的真菌以及攻击培育品种的寄生虫埃斯科沃普斯菌作为一个复杂的群落共同进化。共生体较高层次的系统发育一致性表明宿主 - 寄生虫分支之间存在特殊的长期关联，但对于物种 - 物种和基因型 - 基因型相互作用的更精细尺度上的寄生虫特异性揭示较少。通过将序列和扩增片段长度多态性基因分型分析与实验证据相结合，我们研究了：（i）感染三种近缘的弯颚蚁属蚂蚁蚁群的埃斯科沃普斯菌菌株的宿主特异性；（ii）限制埃斯科沃普斯菌宿主范围的潜在机制。在三种重点研究的弯颚蚁属物种中，培育品种与蚂蚁关系的不一致使我们能够测试埃斯科沃普斯菌菌株是追踪它们的培育品种还是蚂蚁宿主。系统发育分析表明，埃斯科沃普斯菌的系统发育与培育品种的系统发育相匹配，但与蚂蚁的系统发育不匹配，这表明寄生虫具有培育品种特异性。交叉感染实验表明，蚁巢可以被在野外通常与之无关联的寄生虫菌株感染，但当蚁巢接种其典型的寄生虫菌株时，感染的可能性更大。因此，埃斯科沃普斯菌的特异性是由寄生虫仅克服狭窄范围的蚁巢特异性防御的能力所塑造的，但特异性可能还受到生态因素的额外限制，包括共同进化的培育真菌的蚂蚁共生关系中的其他共生体（即蚂蚁及其产生抗生素的细菌）。
