Gerardo Nicole M, Mueller Ulrich G, Currie Cameron R
Section of Integrative Biology, University of Texas at Austin, Austin, TX, USA.
BMC Evol Biol. 2006 Nov 3;6:88. doi: 10.1186/1471-2148-6-88.
The fungus-growing ant-microbe symbiosis consists of coevolving microbial mutualists and pathogens. The diverse fungal lineages that these ants cultivate are attacked by parasitic microfungi of the genus Escovopsis. Previous molecular analyses have demonstrated strong phylogenetic congruence between the ants, the ants-cultivated fungi and the garden pathogen Escovopsis at ancient phylogenetic levels, suggesting coevolution of these symbionts. However, few studies have explored cophylogenetic patterns between these symbionts at the recent phylogenetic levels necessary to address whether these parasites are occasionally switching to novel hosts or whether they are diversifying with their hosts as a consequence of long-term host fidelity.
Here, a more extensive phylogenetic analysis of Escovopsis lineages infecting the gardens of Apterostigma ants demonstrates that these pathogens display patterns of phylogenetic congruence with their fungal hosts. Particular clades of Escovopsis track particular clades of cultivated fungi, and closely-related Escovopsis generally infect closely-related hosts. Discordance between host and parasite phylogenies, however, provides the first evidence for occasional host-switches or acquisitions of novel infections from the environment.
The fungus-growing ant-microbe association has a complex coevolutionary history. Though there is clear evidence of host-specificity on the part of diverse Escovopsis lineages, these pathogens have switched occasionally to novel host fungi. Such switching is likely to have profound effects on how these host and parasites adapt to one another over evolutionary time scales and may impact how disease spreads over ecological time scales.
切叶蚁与微生物的共生关系由共同进化的微生物共生体和病原体组成。这些蚂蚁培育的多种真菌谱系受到埃斯科沃普氏菌属寄生微真菌的攻击。先前的分子分析表明，在古老的系统发育水平上，蚂蚁、蚂蚁培育的真菌和蚁巢病原体埃斯科沃普氏菌之间存在强烈的系统发育一致性，这表明这些共生体是共同进化的。然而，很少有研究在解决这些寄生虫是否偶尔会转换到新宿主，或者它们是否由于长期宿主专一性而与其宿主一起多样化所必需的近期系统发育水平上，探索这些共生体之间的共系统发育模式。
在这里，对感染无刺切叶蚁蚁巢的埃斯科沃普氏菌谱系进行的更广泛的系统发育分析表明，这些病原体与其真菌宿主呈现出系统发育一致性模式。埃斯科沃普氏菌的特定分支追踪培育真菌的特定分支，并且密切相关的埃斯科沃普氏菌通常感染密切相关的宿主。然而，宿主和寄生虫系统发育之间的不一致为偶尔的宿主转换或从环境中获得新感染提供了首个证据。
切叶蚁与微生物的共生关系有着复杂的共同进化历史。尽管有明确证据表明不同的埃斯科沃普氏菌谱系具有宿主特异性，但这些病原体偶尔会转换到新的宿主真菌。这种转换可能会对这些宿主和寄生虫在进化时间尺度上如何相互适应产生深远影响，并可能影响疾病在生态时间尺度上的传播方式。
