Data from: The evolution of fungal substrate specificity in a widespread group of crustose lichens

Lichens exhibit varying degrees of specialization with regard to the surfaces they colonize, ranging from substrate generalists to strict substrate specialists. Though long recognized, the causes and consequences of substrate specialization are poorly known. Using a phylogeny of a 150-200 MYA clade of lichen fungi, we asked whether substrate niche is phylogenetically conserved, which substrates are ancestral, whether specialists arise from generalists or vice versa, and how specialization affects speciation/extinction processes. We found strong phylogenetic signal for niche conservatism. Specialists evolved into generalists and back again, but transitions from generalism to specialism were more common than the reverse. Our models suggest that for this group of fungi, “escape” from specialization for soil, rock and bark occurred, but specialization for wood foreclosed evolution away from that substrate type. In parallel, speciation models showed positive diversification rates for soil and rock dwellers but not other specialists. Patterns in the studied group suggest that fungal substrate specificity is a key determinant of evolutionary trajectory for the entire lichen symbiosis.地衣（lichen）对其所定植的表面表现出不同程度的特化性，覆盖从基质泛化者（substrate generalist）到严格基质特化者（strict substrate specialist）的连续谱系。尽管这一现象早已被学界认知，但基质特化的成因与演化后果仍鲜有研究。本研究依托一个拥有1.5至2亿年演化历史的地衣真菌演化支（clade）的系统发育树，探究了四个核心科学问题：基质生态位是否具有系统发育保守性、哪些基质类型属于祖先状态、特化类群是否起源于泛化类群（反之亦然），以及特化如何影响物种形成与灭绝过程。研究结果显示，生态位保守性（niche conservatism）存在显著的系统发育信号。特化类群与泛化类群可双向演化，但从泛化向特化的转换频率显著高于反向转换。我们的模型表明，对于该类群真菌而言，从土壤、岩石与树皮基质的特化中“逃逸”的演化路径确实存在，但针对木质基质的特化则阻断了脱离该基质类型的演化可能。与此同时，物种分化速率（diversification rates）模型显示，栖息于土壤与岩石的类群呈现出正向的分化速率，而其他特化类群则无此特征。本研究类群的相关模式表明，真菌的基质特异性是整个地衣共生体（lichen symbiosis）演化轨迹的关键决定因素。