Science and Education, The Field Museum, 1400 South Lake Shore Drive, Chicago, IL 60605, United States.
Licenciatura en Biología, Universidad Distrital Francisco José de Caldas, Cra. 4 No. 26D-54, Torre de Laboratorios, Herbario, Bogotá, Colombia.
Mol Phylogenet Evol. 2020 Sep;150:106860. doi: 10.1016/j.ympev.2020.106860. Epub 2020 May 28.
Species in the fungal genus Sticta form symbiotic associations primarily with either green algae or cyanobacteria, but tripartite associations or photosymbiodemes involving both types of photobionts occur in some species. Sticta is known to associate with green algae in the genus Symbiochloris. However, previous studies have shown that algae from other genera, such as Heveochlorella, may also be suitable partners for Sticta. We examined the diversity of green algal partners in the genus Sticta and assessed the patterns of association between the host fungus and its algal symbiont. We used multi-locus sequence data from multiple individuals collected in Australia, Cuba, Madagascar, Mauritius, New Zealand, Reunion and South America to infer phylogenies for fungal and algal partners and performed tests of congruence to assess coevolution between the partners. In addition, event-based methods were implemented to examine which cophylogenetic processes have led to the observed association patterns in Sticta and its green algal symbionts. Our results show that in addition to Symbiochloris, Sticta associates with green algae from the genera Chloroidium, Coccomyxa, Elliptochloris and Heveochlorella, the latter being the most common algal symbiont associated with Sticta in this study. Geography plays a strong role in shaping fungal-algal association patterns in Sticta as mycobionts associate with different algal lineages in different geographic locations. While fungal and algal phylogenies were mostly congruent, event-based methods did not find any evidence for cospeciation between the partners. Instead, the association patterns observed in Sticta and associated algae, were largely explained by other cophylogenetic events such as host-switches, losses of symbiont and failure of the symbiont to diverge with its host. Our results also show that tripartite associations with green algae evolved multiple times in Sticta.
地衣属真菌物种主要与绿藻或蓝细菌形成共生关系，但有些物种存在同时涉及两种光共生体的三分体共生或光共生体。地衣属与共生绿藻属 Symbiochloris 有关。然而，先前的研究表明，来自其他属的藻类，如 Heveochlorella，也可能是地衣属的合适伙伴。我们研究了地衣属中绿藻伙伴的多样性，并评估了宿主真菌与其藻类共生体之间的关联模式。我们使用来自澳大利亚、古巴、马达加斯加、毛里求斯、新西兰、留尼汪和南美洲的多个个体的多基因序列数据，推断真菌和藻类伙伴的系统发育，并进行一致性检验，以评估伙伴之间的协同进化。此外，还实施了基于事件的方法，以检验哪些共进化过程导致了地衣及其绿藻共生体中观察到的关联模式。我们的结果表明，除了 Symbiochloris 之外，地衣还与绿藻属 Chloroidium、Coccomyxa、Elliptochloris 和 Heveochlorella 有关，后一种是本研究中与地衣属最常见的藻类共生体。地理在塑造地衣属真菌 - 藻类的关联模式方面起着重要作用，因为真菌与不同地理位置的不同藻类谱系有关。虽然真菌和藻类的系统发育大多是一致的，但基于事件的方法并没有发现伙伴之间有任何协同进化的证据。相反，地衣和相关藻类中观察到的关联模式主要由其他共进化事件解释，例如宿主转换、共生体的丧失以及共生体未能与其宿主分化。我们的结果还表明，地衣属中三分体共生与绿藻多次进化。
