Resolving Amphitropical Phylogeographic Histories in the Common Dung Moss Tetraplodon (Bryopsida: Splachnaceae).

Many plants have geographic disjunctions, with one of the more rare, yet extreme being the amphitropical, or bipolar disjunction. Bryophytes (namely mosses and liverworts) exhibit this pattern more frequently relative to other groups of plants and typically at or below the level of species. The processes that have shaped the amphitropical disjunction have been infrequently investigated, with notably a near absence of studies focusing on mosses. This dissertation explores the amphitropical disjunction in the dung moss Tetraplodon, with a special emphasis on the origin of the southernmost South American endemic T. fuegianus. Chapter 1 delimits three major lineages within Tetraplodon with distinct yet overlapping geographic ranges, including an amphitropical lineage containing the southernmost South American endemic T. fuegianus. Based on molecular divergence date estimation and phylogenetic topology, the American amphitropical disjunction is traced to a single direct long-distance dispersal event across the tropics. Chapter 2 provides the first evidence supporting the role of migratory shore birds in dispersing bryophytes, as well as other plant, fungal, and algal diaspores across the tropics. Chapter 3 describes the complete chloroplast and mitochondrial genomes and nuclear ribosomal repeat across seven patches of the endemic T. fuegianus. Screening of variation within distinct patches of moss revealed inter-individual polymorphism within single patches of moss, and intra-individual variation in the nuclear ribosomal repeat. Chapter 4 employs a RAD-seq approach to sequence thousands of loci across the range of the amphitropical lineage inferred in Chapter 1 allowing for resolution of a monophyletic T. fuegianus, which shares an ancestor with populations from northwestern North America. Within the lineage, geographic structure is identified, suggesting a complex phylogeographic history for this group, likely shaped by Pleistocene glaciations in northwestern North America