Phycobiont selection along temperature gradient

Lichens are an iconic example of symbiotic systems whose ecology is shaped by the requirements of the symbionts. Previous studies suggest that fungal (mycobionts), as well as photosynthesizing (phycobionts or cyanobionts) partners have a specific range of acceptable symbionts that can be chosen according to specific environmental conditions. This study aimed to investigate the effects of climatic conditions and mycobiont identity on phycobiont distribution within the lichen genera Stereocaulon, Cladonia, and Lepraria. The study area comprised the Canary Islands, Madeira, Sicily, and the Aeolian Islands, spanning a wide range of climatic conditions. These islands are known for their unique and diverse fauna and flora; however, lichen phycobionts have remained unstudied in most of these areas. In total, we genetically analyzed 339 lichen samples. The phycobiont pool differed significantly from that outside the studied area. Asterochloris mediterranea was identified as the most abundant phycobiont. However, its distribution was limited by climatic constraints. Other species of Asterochloris and representatives of the genera Chloroidium, Vulcanochloris, and Myrmecia were also recovered as phycobionts. The selection of symbiotic partners from the local phycobiont pool was driven by mycobiont specificity (i.e., the taxonomic range of acceptable partners) and the environmental conditions, mainly temperature. Interestingly, the dominant fungal species responded differently in their selection of algal symbionts along the environmental gradients. Cladonia rangiformis associated with its phycobiont A. mediterranea in a broader range of temperatures than Stereocaulon azoreum, which favors other Asterochloris species along most of the temperature gradient. S. vesuvianum associated with Chloroidium spp., which also differed in their temperature optima.
Data: 7 DNA alignments (ITS rDNA: Asterochloris, Chloroidium, Vulcanochloris, Cladonia, Lepraria, Stereocaulon; actin type I gene: Asterochloris)

地衣是共生系统的标志性范例，其生态特征由共生伙伴的需求共同塑造。既往研究表明，真菌共生体（mycobionts）与光合共生伙伴（phycobionts或cyanobionts）均拥有特定的可接受共生伴侣范围，可依据具体环境条件进行选择。本研究旨在探究气候条件与真菌共生体身份对珊瑚枝属（Stereocaulon）、石蕊属（Cladonia）及鳞叶衣属（Lepraria）内地衣的光合共生体分布的影响。本研究的采样区域涵盖加那利群岛、马德拉群岛、西西里岛与埃奥利群岛，覆盖了广泛的气候类型区间。这些岛屿以其独特多样的动植物群落闻名，但绝大多数区域的地衣光合共生体仍未得到研究。本研究总计对339份地衣样本开展了遗传学分析。研究区域内的光合共生体群落与区域外存在显著差异。地中海星孔藻（Asterochloris mediterranea）被确定为优势光合共生体，但其分布受到气候条件的显著限制。本研究同时还鉴定出其他星孔藻属（Asterochloris）物种，以及绿球藻属（Chloroidium）、火山藻属（Vulcanochloris）和切叶蚁藻属（Myrmecia）的类群作为光合共生体。从本地光合共生体群落中选择共生伴侣的过程，受到真菌共生体特异性（即可接受伴侣的分类学范围）与环境条件（主要为温度）的共同驱动。有趣的是，优势真菌类群沿环境梯度选择藻类共生体的模式存在显著差异：与共生光合伙伴A. mediterranea形成关联的瓶刷石蕊（Cladonia rangiformis），其适宜温度范围较珊瑚枝属的Stereocaulon azoreum更广，后者在多数温度梯度下均偏好其他星孔藻属物种；而火山珊瑚枝（Stereocaulon vesuvianum）则与绿球藻属（Chloroidium）物种形成共生关系，该类群同样具有独特的温度适宜区间。
数据集：7组DNA序列比对结果（ITS rDNA：Asterochloris、Chloroidium、Vulcanochloris、Cladonia、Lepraria、Stereocaulon；I型肌动蛋白基因：Asterochloris）