Faculty of Biology, Department I, Systematic Botany and Mycology, University of Munich (LMU), Menzinger Straße 67, 80638 München, Germany
Institute of Biology, Division of Plant Sciences, NAWI Graz, University of Graz, Holteigasse 6, 8010 Graz, Austria.
Proc Biol Sci. 2018 Oct 17;285(1889):20180640. doi: 10.1098/rspb.2018.0640.
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.
地衣在其定殖的表面上表现出不同程度的特化，从基质广义种到严格基质专化种不等。尽管早已认识到，但基质特化的原因和后果还知之甚少。利用一个 1.5 亿至 2 亿年前的地衣真菌进化枝的系统发育，我们询问了基质生态位是否在系统发育上得到保守，哪些基质是祖先的，专家是从广义种进化而来还是反之亦然，以及特化如何影响物种形成/灭绝过程。我们发现生态位保守性具有很强的系统发育信号。专家从广义种进化而来，又回到广义种，但从广义种进化为专化种的情况比反过来的情况更为常见。我们的模型表明，对于这群真菌来说，“逃避”对土壤、岩石和树皮的特化发生了，但对木材的特化阻止了其脱离该基质类型的进化。同时，物种形成模型显示，土壤和岩石栖息地的多样化率为正，但其他专家则不然。研究组的模式表明，真菌的基质特异性是整个地衣共生体进化轨迹的关键决定因素。
