Data from: Genetic and genomic evidence of niche partitioning and adaptive radiation in mountain pine beetle fungal symbionts

Bark beetles form multipartite symbiotic associations with blue stain fungi (Ophiostomatales, Ascomycota). These fungal symbionts play an important role during the beetle's life cycle by providing nutritional supplementation, overcoming tree defences and modifying host tissues to favour brood development. The maintenance of stable multipartite symbioses with seemingly less competitive symbionts in similar habitats is of fundamental interest to ecology and evolution. We tested the hypothesis that the coexistence of three fungal species associated with the mountain pine beetle is the result of niche partitioning and adaptive radiation using SNP genotyping coupled with genotype–environment association analysis and phenotypic characterization of growth rate under different temperatures. We found that genetic variation and population structure within each species is best explained by distinct spatial and environmental variables. We observed both common (temperature seasonality and the host species) and distinct (drought, cold stress, precipitation) environmental and spatial factors that shaped the genomes of these fungi resulting in contrasting outcomes. Phenotypic intraspecific variations in Grosmannia clavigera and Leptographium longiclavatum, together with high heritability, suggest potential for adaptive selection in these species. By contrast, Ophiostoma montium displayed narrower intraspecific variation but greater tolerance to extreme high temperatures. Our study highlights unique phenotypic and genotypic characteristics in these symbionts that are consistent with our hypothesis. By maintaining this multipartite relationship, the bark beetles have a greater likelihood of obtaining the benefits afforded by the fungi and reduce the risk of being left aposymbiotic. Complementarity among species could facilitate colonization of new habitats and survival under adverse conditions.树皮甲虫与蓝变真菌（blue stain fungi，分类学上隶属于子囊菌门Ascomycota长喙霉目Ophiostomatales）形成多伙伴共生关系。这些真菌共生体在甲虫的生活史中发挥关键作用：通过提供营养补充、抵御宿主树木的防御机制，并修饰宿主组织以利于子代幼虫的发育。在相似生境中与看似竞争力较弱的共生体维持稳定的多伙伴共生关系，是生态学与进化生物学领域的核心研究议题之一。本研究以与山松甲虫相关联的三种真菌为对象，针对“其共存是生态位分化与适应性辐射的结果”这一假说展开验证，研究手段包括单核苷酸多态性基因分型（SNP genotyping）、基因型-环境关联分析，以及不同温度条件下的生长速率表型特征鉴定。研究发现，各真菌物种内部的遗传变异与种群结构，均可通过特异性的空间与环境变量得到最优解释。研究团队同时观测到两类塑造这些真菌基因组的环境与空间因子：一类为共有因子（温度季节性与宿主物种），另一类为特有因子（干旱、冷胁迫与降水），二者对真菌基因组的塑造效果存在显著差异。长喙壳菌（Grosmannia clavigera）与长枝长喙霉（Leptographium longiclavatum）的种内表型变异，结合较高的遗传力水平，表明这两个物种存在适应性选择的潜力。与之相对，山生长喙霉（Ophiostoma montium）的种内变异范围较窄，但对极端高温的耐受性更强。本研究揭示了这些共生体独特的表型与基因型特征，与本研究提出的假说高度契合。通过维持这种多伙伴共生关系，树皮甲虫更有可能获取真菌所提供的各项益处，同时降低自身陷入无共生状态的风险。物种间的功能互补性，可助力甲虫拓展新的定植生境，并提升其在逆境条件下的存活能力。