The Lecanoromycetes is the largest class of lichenized Fungi, and one of the
most species-rich classes in the kingdom. Here we provide a multigene phylogenetic
synthesis (using three ribosomal RNA-coding and two protein-coding genes) of the
Lecanoromycetes based on 642 newly generated and 3329 publicly available sequences
representing 1139 taxa, 317 genera, 66 families, 17 orders and five subclasses (four
currently recognized: Acarosporomycetidae, Lecanoromycetidae, Ostropomycetidae,
Umbilicariomycetidae; and one provisionarily recognized,
‘Candelariomycetidae’). Maximum likelihood phylogenetic analyses on four
multigene datasets assembled using a cumulative supermatrix approach with a progressively
higher number of species and missing data (5-gene, 5+4-gene, 5+4+3-gene and 5+4+3+2-gene
datasets) show that the current classification includes non-monophyletic taxa at various
ranks, which need to be recircumscribed and require revisionary treatments based on denser
taxon sampling and more loci. Two newly circumscribed orders (Arctomiales and Hymeneliales
in the Ostropomycetidae) and three families (Ramboldiaceae and Psilolechiaceae in the
Lecanorales, and Strangosporaceae in the Lecanoromycetes inc. sed.) are introduced. The
potential resurrection of the families Eigleraceae and Lopadiaceae is considered here to
alleviate phylogenetic and classification disparities. An overview of the photobionts
associated with the main fungal lineages in the Lecanoromycetes based on available
published records is provided. A revised schematic classification at the family level in
the phylogenetic context of widely accepted and newly revealed relationships across
Lecanoromycetes is included. The cumulative addition of taxa with an increasing amount of
missing data (i.e., a cumulative supermatrix approach, starting with taxa for which
sequences were available for all five targeted genes and ending with the addition of taxa
for which only two genes have been sequenced) revealed relatively stable relationships for
many families and orders. However, the increasing number of taxa without the addition of
more loci also resulted in an expected substantial loss of phylogenetic resolving power
and support (especially for deep phylogenetic relationships), potentially including the
misplacements of several taxa. Future phylogenetic analyses should include additional
single copy protein-coding markers in order to improve the tree of the Lecanoromycetes. As
part of this study, a new module (“Hypha”) of the freely available
Mesquite software was developed to compare and display the internodal support values
derived from this cumulative supermatrix approach.
Patterns of specificity among symbiotic partners are key to a comprehensive understanding of the evolution of symbiotic systems. Specificity of mutualistic partners, within a widespread monophyletic group for which all species are sampled has rarely been explored. Here, we assess the level of specificity between the cosmopolitan lichen-forming fungus (mycobiont) from the genus Peltigera, section Polydactylon, and its cyanobacterial partner Nostoc (cyanobiont). The mycobiont and cyanobiont phylogenies are inferred from five nuclear loci and the rbcLX region, respectively. These sequences were obtained from 206 lichen thalli, representing ca. 40 closely related Peltigera species sampled worldwide, doubling the number of known species in this group. We found a broad spectrum of specificity for both partners ranging from strict specialists to generalists. Overall, mycobionts are more specialized than cyanobionts by associating mostly with one or a few Nostoc phylogroups, whereas most cyanobionts associate frequently with several Peltigera species. Specialist mycobionts are older than generalists, supporting the hypothesis that specialization of mycobionts to one or few cyanobionts, is favored through time in geographic areas where species have been established for long periods of time. The relatively recent colonization of a new geographic area (Central and South America) by members of section Polydactylon is associated with a switch to a generalist pattern of association and an increased diversification rate by the fungal partner, suggesting that switches to generalism are rare events that are advantageous in new environments. We detected higher genetic diversity in generalist mycobionts. We also found that Peltigera species specialized on a single Nostoc phylogroup have narrower geographical distributions compared with generalist species.
This comprehensive phylogenetic revision of sections Peltigera and Retifoveatae of the cyanolichen genus Peltigera is based on DNA sequences from more than 500 specimens from five continents. We amplified five loci (nrITS, β-tubulin and three intergenic spacers part of colinear orthologous regions [COR]) for the mycobiont, and the rbcLX locus for the cyanobacterial partner Nostoc. Phylogenetic inferences (RAxML, BEAST) and species delimitation methods (bGMYC, bPTP, bPP) suggest the presence of 88 species in section Peltigera, including 50 species new to science, hence uncovering a surprisingly high proportion of previously unnoticed biodiversity. The hypervariable region in ITS1 (ITS1-HR) is a powerful marker to identify species within sections Peltigera and Retifoveatae. Most newly delimited species are restricted to a single biogeographic region, however, up to ten species have a nearly cosmopolitan distribution. The specificity of mycobionts in their association with Nostoc cyanobionts ranges from strict specialists (associate with only one Nostoc phylogroup) to broad generalists (up to eight Nostoc phylogroups uncovered), with widespread species recruiting a broader selection of Nostoc phylogroups than species with limited distributions. In contrast, species from the P. didactyla clade characterized by small thalli and asexual vegetative propagules (soredia) associate with fewer Nostoc phylogroups (i.e., are more specialized) despite their broad distributions, and show significantly higher rates of nucleotide substitutions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.