Dal Forno Manuela, Lawrey James D, Sikaroodi Masoumeh, Gillevet Patrick M, Schuettpelz Eric, Lücking Robert
Botanical Research Institute of Texas, Fort Worth, TX, USA.
Department of Botany, Smithsonian Institution, National Museum of Natural History, Washington, DC, USA.
Mol Ecol. 2021 Apr;30(8):1755-1776. doi: 10.1111/mec.15700. Epub 2020 Nov 10.
Recent studies have uncovered remarkable diversity in Dictyonema s.lat. basidiolichens, here recognized as subtribe Dictyonemateae. This group includes five genera and 148 species, but hundreds more await description. The photobionts of these lichens belong to Rhizonema, a recently resurrected cyanobacterial genus known by a single species. To further investigate photobiont diversity within Dictyonemateae, we generated 765 new cyanobacterial sequences from 635 specimens collected from 18 countries. The ITS barcoding locus supported the recognition of 200 mycobiont (fungal) species among these samples, but the photobiont diversity was comparatively low. Our analyses revealed three main divisions of Rhizonema, with two repeatedly recovered as monophyletic (proposed as new species), and the third mostly paraphyletic. The paraphyletic lineage corresponds to R. interruptum and partnered with mycobionts from all five genera in Dictyonemateae. There was no evidence of photobiont-mycobiont co-speciation, but one of the monophyletic lineages of Rhizonema appears to partner predominantly with one of the two major clades of Cora (mycobiont) with samples collected largely from the northern Andes. Molecular clock estimations indicate the Rhizonema species are much older than the fungal species in the Dictyonemateae, suggesting that these basidiolichens obtained their photobionts from older ascolichen lineages and the photobiont variation in extant lineages of Dictyonemateae is the result of multiple photobiont switches. These results support the hypothesis of lichens representing "fungal farmers," in which diverse mycobiont lineages associate with a substantially lower diversity of photobionts by sharing those photobionts best suited for the lichen symbiosis among multiple and often unrelated mycobiont lineages.
最近的研究发现，广义的网衣属（Dictyonema）担子地衣具有显著的多样性，在此被认定为网衣亚族（Dictyonemateae）。该类群包括五个属和148个物种，但还有数百个物种有待描述。这些地衣的光合生物属于根藻属（Rhizonema），这是一个最近复活的蓝藻属，仅以一个物种为人所知。为了进一步研究网衣亚族内光合生物的多样性，我们从18个国家收集的635个标本中生成了765条新的蓝藻序列。内转录间隔区（ITS）条形码位点支持在这些样本中识别出200种共生菌（真菌）物种，但光合生物的多样性相对较低。我们的分析揭示了根藻属的三个主要分支，其中两个分支多次被发现为单系（提议作为新物种），第三个分支大多为并系。并系谱系对应于间断根藻（R. interruptum），并与网衣亚族中所有五个属的共生菌配对。没有证据表明光合生物与共生菌存在共同物种形成，但根藻属的一个单系谱系似乎主要与科拉属（Cora，共生菌）的两个主要分支之一配对，样本主要采集自安第斯山脉北部。分子钟估计表明，根藻属物种比网衣亚族中的真菌物种古老得多，这表明这些担子地衣从较古老的子囊地衣谱系中获得了它们的光合生物，并且网衣亚族现存谱系中的光合生物变异是多次光合生物转换的结果。这些结果支持了地衣代表“真菌农夫”的假说，即不同的共生菌谱系通过在多个且通常不相关的共生菌谱系中共享最适合地衣共生的光合生物，与多样性低得多的光合生物谱系相关联。
