High-throughput sequencing confirms the boundary between traditionally considered species pairs in a group of lichenized fungi (Peltigeraceae, Pseudocyphellaria)

Accurate species delimitations are fundamental to our understanding of the genetic diversity on Earth and a vital part in evolutionary and conservation biology research. In lichenized fungi, species pairs have the same morphology and chemistry. They only differ in how they reproduce with one species using sexual reproductive structures and the other using asexual propagules. To classify these as one species or two has been a point of contention, and conclusions based on Sanger sequencing, where sequence data are limited and species boundaries are usually not observed, have been refuted after analysis with genome-scale data such as restriction site-associated DNA sequencing that tends to find fixed genetic differences between the two morphs. Pseudocyphellaria glabra and P. homoeophylla have long been considered a species pair that differ in geographical ranges but co-occur in New Zealand. We used restriction site-associated DNA sequencing data and generated thousands of genetic loci across 53 individuals. The RADseq data provided high-resolution phylogenetic and population genomic information. A maximum-likelihood phylogenetic reconstruction recovered both species as separate lineages, whereas population genetics indicated some evidence for admixture among P. glabra and P. homoeophylla from New Zealand. It is not clear whether the latter is due to ancient polymorphism or recent gene flow. Our study represents another example of the usefulness of RADseq to test species boundaries that segregate closely related species in lichenized fungi.

Automated summary

Accurate species delimitations are crucial for understanding genetic diversity and conducting research in evolutionary and conservation biology. In lichenized fungi, there has been a debate on whether species pairs with similar morphology and chemistry should be classified as one species or two. Recent analysis using RADseq data has found fixed genetic differences between the two morphs, contradicting earlier conclusions based on limited Sanger sequencing data.