Nees Institute for Biodiversity of Plants, University of Bonn, Meckenheimer Allee 170, 53115 Bonn, Germany.
Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901-6509, USA.
Mol Phylogenet Evol. 2019 Feb;131:106-115. doi: 10.1016/j.ympev.2018.10.041. Epub 2018 Nov 3.
Besides their alleged therapeutic effects, mistletoes of the genus Viscum L. (Viscaceae) are keystone species in many ecosystems across Europe, Africa, Asia and Australia because of their complex faunal interactions. We here reconstructed the evolutionary history of Viscum based on plastid and nuclear DNA sequence data. We obtained a highly resolved phylogenetic tree with ten well-supported clades, which we used to understand the spatio-temporal evolution of these aerial parasites and evaluate the contribution of reproductive switches and shifts in host ranges to their distribution and diversification. The genus Viscum originated in the early Eocene in Africa and appeared to have diversified mainly through geographic isolation, in several cases apparently coinciding with shifts in host preferences. During its evolution, switches in the reproductive mode from ancestral dioecy to monoecy imply an important role in the long-distance dispersal of the parasites from Africa to continental Asia and Australia. We also observed multiple cases of photosynthetic surface reduction (evolution of scale leaves) within the genus, probably indicative of increasing specialization associated with the parasitic lifestyle. Even compared with other parasitic angiosperms, where more host generalists than specialists exist, Viscum species are characterized by extraordinarily broad host ranges. Specialization on only a few hosts from a single family or order occurs rarely and is restricted mostly to very recently evolved lineages. The latter mostly derive from or are closely related to generalist parasites, implying that niche shifting to a new host represents an at least temporary evolutionary advantage in Viscum.
除了它们据称的治疗效果外，槲寄生属（桑寄生科）的槲寄生在欧洲、非洲、亚洲和澳大利亚的许多生态系统中也是关键物种，因为它们与动物群有着复杂的相互作用。我们在这里基于质体和核 DNA 序列数据重建了槲寄生的进化历史。我们获得了一个高度分辨率的系统发育树，其中有十个支持良好的分支，我们用它来理解这些空中寄生虫的时空进化，并评估生殖转换和宿主范围的变化对它们的分布和多样化的贡献。槲寄生属起源于早始新世的非洲，似乎主要通过地理隔离而多样化，在几种情况下，这种多样化显然与宿主偏好的转变相一致。在其进化过程中，从祖先的雌雄异株到雌雄同株的生殖模式的转变意味着寄生虫从非洲向亚洲大陆和澳大利亚的长距离传播中发挥了重要作用。我们还观察到属内多次发生光合作用表面减少（鳞片叶的进化），这可能表明与寄生生活方式相关的特化程度增加。即使与其他具有更多非专性宿主的寄生被子植物相比，槲寄生物种的宿主范围也非常广泛。只从一个科或一个目中的少数几个宿主中特化的情况很少见，而且主要局限于最近进化的谱系。后者主要来自或与广宿主的寄生虫密切相关，这意味着在槲寄生中，向新宿主的生态位转移至少在短期内是一种进化优势。
