The importance of spatio-temporal photobiont patterns of association for comprehensive phylogenetic revisions and macroevolutionary studies of lichens: a worldwide case study of the genus Peltigera.

Within the framework of a worldwide revision of Peltigera, several thousand specimens were gath
ered to attempt to sequence all main partners (i.e., Peltigera, nrITS, nrLSU, RPB1, EFT2.1, ß-tubulin, COR1b, COR3, COR16; Nostoc, rbcLX; and Coccomyxa, nrITS and rbcL). We succeeded to sequence
the fungal and cyanobacterial partners for 1900 and 650 specimens, respectively. The difficulty to identify Peltigera species and to understand the observed phenotypic variation was due to a high number of cryptic species within phenotypically defined species. This study identified 900 unique fungal ITS haplotypes and increased the number of Peltigera species from 90 known species to > 170 species when using various species discovery and validation methods. Sixty Nostoc phylogroups were found in association with Peltigera. Patterns of Peltigera species and Nostoc phylogroup diversity, iogeographical distributions, and specificity towards their respective partners, greatly differ among
Peltigera sections. The overarching trend is that nearly 85% of Peltigera species are specialized on one or two Nostoc phylogroups, whereas > 55% of Nostoc phylogroups associates with at least three Peltigera species. The number of species in sections Peltigera (~95 species) and Polydactylon (~55 species) was much higher than expected and Nostoc phylogroups can help delimit and identify Peltigera species