No support for the emergence of lichens prior to the evolution of vascular plants

Abstract

The early‐successional status of lichens in modern terrestrial ecosystems, together with the role lichen‐mediated weathering plays in the carbon cycle, have contributed to the long and widely held assumption that lichens occupied early terrestrial ecosystems prior to the evolution of vascular plants and drove global change during this time. Their poor preservation potential and the classification of ambiguous fossils as lichens or other fungal–algal associations have further reinforced this view. As unambiguous fossil data are lacking to demonstrate the presence of lichens prior to vascular plants, we utilize an alternate approach to assess their historic presence in early terrestrial ecosystems. Here, we analyze new time‐calibrated phylogenies of ascomycete fungi and chlorophytan algae, that intensively sample lineages with lichen symbionts. Age estimates for several interacting clades show broad congruence and demonstrate that fungal origins of lichenization postdate the earliest tracheophytes. Coupled with the absence of unambiguous fossil data, our work finds no support for lichens having mediated global change during the Neoproterozoic‐early Paleozoic prior to vascular plants. We conclude by discussing our findings in the context of Neoproterozoic‐Paleozoic terrestrial ecosystem evolution and the paleoecological context in which vascular plants evolved.

Amphitropical variation of the algal partners of Pseudephebe (Parmeliaceae, lichenized fungi)

“…Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13199-020-00709-5) contains supplementary material, which is available to authorized users. Independent dating analyses on the origin of the main myco-and photobiont lineages suggest that lichens postdated vascular plants (Nelsen et al 2020), and this means that these symbiotic interactions have been evolving from less than 250 million years to the present. Actual species-level associations among lichen partners seem to have a more recent origin, from the Miocene onwards, provided several estimates of mycobiont's divergence and diversification times (e.g.…”

Cryptogamic ground covers as analogues for early terrestrial biospheres: Initiation and evolution of biologically mediated proto‐soils

“…Molecular dating places the first divergences in Mucoromycota (the symbiotic fungi) at 578 Ma (Berbee et al., 2017), and the initial diversification of the Pezizomycotina (Ascomycota) is reported from the Ordovician, around 485 Ma (Beimforde et al., 2014) using the early Devonian Ascomycota for dating the phylogeny. Fossil macrolichens with internal stratification have been described from the Lower Devonian (ca 415 Ma) (Edwards et al., 2013; Honegger et al., 2013); however, evidence of lichens in the early fossil record is scant and controversial, with recent research suggesting that lichens did not emerge prior to the evolution of the vascular plants (Nelsen et al., 2019). Thus, the evolutionary context of fungi and lichens is also unclear.…”

Sharing and double‐dating in the lichen world

“…They then ask how this age relates to that of Rhizonema cyanobacteria. A comparative approach has increasingly been employed to relate the ages of a diverse range of interacting lineages to one another, including insects and plants (Allio et al, 2021; Nelsen et al, 2018; Vea & Grimaldi, 2016; Ward & Branstetter, 2017), plants and their parasitic or mutualistic fungi (Hibbett & Matheny, 2009; Peterson et al, 2010), and lichen symbionts (Nelsen et al, 2020a; Ortiz‐Álvarez et al, 2015; Spribille et al, 2016). Individual molecular clock analyses of 16S and rbcLX cyanobacterial sequences suggest the crown node of Rhizonema likely predated both the crown node and stem of Dictyonemateae.…”