Using RADseq to understand the circum-Antarctic distribution of a lichenized fungus,Pseudocyphellaria glabra

Aim The Southern Ocean landmasses have intrigued biologists for centuries because they share many taxonomic groups. Such disjunct taxa can provide insight into evolutionary processes that connect populations or drive divergence. The lichenized fungusPseudocyphellaria glabra, for example, has a disjunct distribution-separated by the Tasman Sea and the Pacific Ocean-yet whether these locations should be genetically distinct is unclear. The large distances between continents may be expected to prohibit gene flow, but strong and sustained winds in the Southern Hemisphere and the small size ofP. glabrapropagules may facilitate migration. We compared support for these two hypotheses. Location Southeastern Australia, Tasmania, New Zealand and Southern Chile. Taxon Pseudocyphellaria glabra(Hook. f. & Taylor) C.W. Dodge, 1948 (Ascomycota, Peltigeraceae) Methods We collected 371 samples across the disjunct range ofP. glabra. We generated genomic data using restriction site-associated DNA sequencing and reconstructed a Maximum Likelihood phylogeny using 29,098 unlinked SNPs. We then conducted population genomic analyses using 3,756 SNPs including a minimum-spanning network, principal components analysis, discriminate analysis of principal components, and k-means clustering. Results Maximum likelihood analysis recovered multiple well-supported clades that roughly corresponded to geography. Population genomic analyses identified genetic structuring that generally corresponded with geographic distance; however, some individuals from Chile and Australia were assigned to genetic clusters found in New Zealand, suggesting that recent dispersal events from New Zealand have successfully colonized Chile and Australia. Main conclusion Populations ofP. glabrafrom Australia, Chile and New Zealand are genetically distinct, but frequent long-distance dispersal during the Quaternary probably prevented speciation. This study demonstrates the power of restriction-site associated DNA sequencing for discernment between divergent and connective evolutionary forces that simultaneously influence the population structure of species with disjunct ranges in the Southern Ocean landmasses.

Automated summary

The study reveals that populations of P. glabra from Australia, Chile, and New Zealand are genetically distinct, but frequent long-distance dispersal may have prevented speciation.