Species in section Peltidea (aphthosa group) of the genus Peltigera remain cryptic after molecular phylogenetic revision

Abstract

AbstractClosely related lichen-forming fungal species circumscribed using phenotypic traits (morphospecies) do not always align well with phylogenetic inferences based on molecular data. Using multilocus data obtained from a worldwide sampling, we inferred phylogenetic relationships among five currently accepted morphospecies ofPeltigerasectionPeltidea(P. aphthosagroup). Monophyletic circumscription of all currently recognized morphospecies (P. britannica, P. chionophila, P. frippiiandP. malacea) exceptP. aphthosa, which containedP. britannica, was confirmed with high bootstrap support. Following their re-delimitation using bGMYC and Structurama, BPP validated 14 putative species including nine previously unrecognized potential species (five withinP. malacea, five withinP. aphthosa, and two withinP. britannica). Because none of the undescribed potential species are corroborated morphologically, chemically, geographically or ecologically, we concluded that these monophyletic entities represent intraspecific phylogenetic structure, and, therefore, should not be recognized as new species. Cyanobionts associated withPeltideamycobionts (51 individuals) represented 22 uniquerbcLXhaplotypes from five phylogroups in Clade II subclades 2 and 3. With rare exceptions,Nostoctaxa involved in trimembered and bimembered associations are phylogenetically closely related (subclade 2) or identical, suggesting a mostly shared cyanobiont pool with infrequent switches. Based on a broad geographical sampling, we confirm a high specificity ofNostocsubclade 2 with their mycobionts, including a mutualistically exclusive association between phylogroup III and specific lineages ofP. malacea.