Garrido-Benavent Isaac, Pérez-Ortega Sergio, de Los Ríos Asunción
Department of Biogeochemistry and Microbial Ecology, National Museum of Natural Sciences (MNCN-CSIC), Serrano 115 dpdo, E-28045 Madrid, Spain.
Department of Biogeochemistry and Microbial Ecology, National Museum of Natural Sciences (MNCN-CSIC), Serrano 115 dpdo, E-28045 Madrid, Spain; Real Jardín Botánico (CSIC), Plaza Murillo 2, E-28014 Madrid, Spain.
Mol Phylogenet Evol. 2017 Feb;107:117-131. doi: 10.1016/j.ympev.2016.10.013. Epub 2016 Oct 18.
Symbiotic associations between green algae (Chlorophyta) and fungi give rise to morphologically and eco-physiologically distinct entities, or so-called, lichens. In one of the most peculiar of these associations, the partners are species of the macroscopic genus Prasiola (Trebouxiophyceae) and the ascomycete Mastodia tessellata (Verrucariaceae). This is the only known case of a lichen symbiosis involving a foliose green alga. Despite intense research targeted at understanding the biology of this particular association, little is known about the genetic variability of its symbionts. This study focuses on the photobiont partner of this lichen and was designed to explore and compare its genetic diversity along a latitudinal axis from Alaska to Antarctica. Molecular sequence data were generated for three loci: two nuclear markers (nrITS, RPL10A) and one plastid-encoded marker (tufA). The usefulness of the Prasiola nrITS and RPL10A data was examined at the species and intraspecific levels. We used the population assignment tests implemented in BAPS and STRUCTURE and two algorithmic species delimitation procedures (ABGD, GMYC) to generate species boundary discovery hypotheses, which were subsequently tested using Bayes factors. Population genetic differentiation and structure were also assessed through fixation indices, polymorphism statistics and haplotype networks. Based on the results of the species validation method, we propose that at least two species of Prasiola associate with the lichen-forming fungus Mastodia tessellata. Of these, P. borealis is broadly distributed in Alaska, Tierra del Fuego and the Antarctic Peninsula, whereas the second, undescribed, species is restricted to the Antarctic Peninsula. We detected significant phylogeographic substructure in P. borealis, including greater haplotype diversity in the Tierra del Fuego populations. Our findings provide new data that will be useful to unravel the cryptic diversity and phylogeographic patterns of the green alga partners of lichens.
绿藻（绿藻门）与真菌之间的共生关系产生了形态和生态生理上截然不同的实体，即所谓的地衣。在这些共生关系中最奇特的一种里，共生伙伴是大型的刚毛藻属（绿球藻纲）物种和子囊菌镶嵌疣衣（疣衣科）。这是已知唯一一例涉及叶状绿藻的地衣共生现象。尽管针对理解这种特殊共生关系的生物学特性进行了大量研究，但对其共生体的遗传变异性却知之甚少。本研究聚焦于这种地衣的光合生物伙伴，旨在探索并比较其从阿拉斯加至南极洲的纬度轴上的遗传多样性。针对三个基因座生成了分子序列数据：两个核标记（nrITS、RPL10A）和一个质体编码标记（tufA）。在物种和种内水平上检验了刚毛藻nrITS和RPL10A数据的实用性。我们使用了BAPS和STRUCTURE中实施的种群分配测试以及两种算法物种界定程序（ABGD、GMYC）来生成物种边界发现假设，随后使用贝叶斯因子对其进行检验。还通过固定指数、多态性统计和单倍型网络评估了种群遗传分化和结构。基于物种验证方法的结果，我们提出至少有两种刚毛藻与形成地衣的真菌镶嵌疣衣共生。其中，北方刚毛藻广泛分布于阿拉斯加、火地岛和南极半岛，而另一种未描述的物种则局限于南极半岛。我们在北方刚毛藻中检测到显著的系统地理学亚结构，包括火地岛种群中更高的单倍型多样性。我们的研究结果提供了新的数据，将有助于揭示地衣绿藻伙伴的隐秘多样性和系统地理学模式。
