| Summary: | Premise of the study—American bipolar plant distributions characterize taxa at various taxonomic ranks but are most common in the bryophytes at infraspecific and infrageneric levels. A previous study on the bipolar disjunction in the dung moss genus Tetraplodon found that direct long-distance dispersal from North to South in the Miocene - Pleistocene accounted for the origin of the Southern American endemic Tetraplodon fuegianus, congruent with other molecular studies on bipolar bryophytes. The previous study, however, remained inconclusive regarding a specific Northern Hemisphere source region for the trans-equatorial dispersal event that gave rise to T. fuegianus. Methods—To estimate spatial genetic structure and phylogeographic relationships within the bipolar lineage of Tetraplodon, which includes T. fuegianus, we analyzed thousands of Restriction-site Associated DNA (RADseq) loci and single nucleotide polymorphisms using Bayesian individual assignment and maximum likelihood and coalescent model based phylogenetic approaches. Key results—Northwestern North America is the most likely source of the recent ancestor to T. fuegianus. Conclusions—Tetraplodon fuegianus, which marks the southernmost populations in the bipolar lineage of Tetraplodon, arose following a single long-distance dispersal event involving a T. mnioides lineage that is now rare in the Northern Hemisphere and potentially restricted to the Pacific Northwest region of North America. Furthermore, gene flow between sympatric lineages of Tetraplodon mnioides in the Northern Hemisphere is limited, possibly due to high rates of selfing or reproductive isolation. Aligned supermatrices & SNP matricesAdd data sets referred to in Table 1 and Table 2 are included. Supermatrices are in nexus format and unlinked SNP files are in .str format, and include sample assignment information based on RAxML analyses (see Figure 1). Sample assignment information should not be used to inform STRUCTURE analyses however, but to help with graphical display and order ...
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