Hidden Genetic Diversity in an Asexually Reproducing Lichen Forming Fungal Group

Asexual species with vegetative propagation of both symbiont partners (soredia) in lichens may harbor lower species diversity because they may indeed represent evolutionary dead ends or clones. In this study we aim to critically examine species boundaries in the sorediate lichen forming fungi Parmotrema reticulatum–Parmotrema pseudoreticulatum complex applying coalescent-based approaches and other recently developed DNA-based methods. To this end, we gathered 180 samples from Africa, Asia, Australasia, Europe, North and South America and generated sequences of internal transcribed spacer of nuclear ribosomal DNA (ITS) and DNA replication licensing factor MCM7 (MCM7). The dataset was analysed using different approaches such as traditional phylogeny–maximum likelihood and Bayesian–genetic distances, automatic barcode gap discovery and coalescent-based methods–PTP, GMYC, spedeSTEM and *Beast–in order to test congruence among results. Additionally, the divergence times were also estimated to elucidate diversification events. Delimitations inferred from the different analyses are comparable with only minor differences, and following a conservative approach we propose that the sampled specimens of the P. reticulatum–P. pseudoreticulatum complex belong to at least eight distinct species-level lineages. Seven are currently classified under P. reticulatum and one as P. pseudoreticulatum. In this work we discuss one of only few examples of cryptic species that have so far been found in sorediate reproducing lichen forming fungi. Additionally our estimates suggest a recent origin of the species complex–during the Miocene. Consequently, the wide distribution of several of the cryptic species has to be explained by intercontinental long-distance dispersal events.

地衣中，共生双方均以营养繁殖（粉芽（soredia））繁衍的无性物种，其物种多样性往往更低，因为此类类群或许确实代表演化死胡同或克隆类群。本研究旨在通过基于溯祖的分析方法（coalescent-based approaches）及其他新近开发的DNA分析手段，对产粉芽的地衣共生真菌Parmotrema reticulatum–Parmotrema pseudoreticulatum复合群的物种边界进行严谨厘定。为此，我们从非洲、亚洲、大洋洲、欧洲、北美及南美采集了180份样本，并扩增获得了核核糖体DNA内部转录间隔区（internal transcribed spacer of nuclear ribosomal DNA，ITS）与DNA复制许可因子MCM7（DNA replication licensing factor MCM7）的序列。本数据集采用多种分析方法进行处理，包括传统系统发育分析——最大似然法与贝叶斯法——遗传距离分析、自动条形码间隙发现法，以及基于溯祖的分析方法：PTP、GMYC、spedeSTEM与*Beast，以检验不同分析结果的一致性。此外，我们还估算了分化时间以阐明类群的多样化事件。不同分析方法得到的物种界定结果仅存在细微差异且整体一致性较好，秉持保守分类原则，我们认为本次采样的P. reticulatum–P. pseudoreticulatum复合群标本至少隶属于8个独立的物种级支系，其中7个支系目前被归入P. reticulatum，1个支系被归入P. pseudoreticulatum。本研究探讨了目前仅在少数产粉芽地衣共生真菌中发现的隐存物种案例之一。此外，我们的估算结果显示该物种复合群的起源时间较近，处于中新世（Miocene）时期。因此，多个隐存物种的广泛分布需通过洲际长距离扩散事件来解释。