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Polyploidy is a prominent force in the evolution of plant genomes, and the ferns are no exception. The genus Polystichum is particularly rich in polyploids, with 44% of the genus estimated to be polyploid. A waypoint between the Andean and Mayan centers of diversity, the Cordillera Talamanca of Costa Rica and Panama harbors three allotetraploid species of Polystichum, two of which are endemic. We leverage coding and non-coding DNA sequences from the chloroplast and nucleus to elucidate the allopolyploid origins of the three species. Consistent with, and building upon earlier works, we find evidence that the páramo tetraploid most recently named as Polystichum orbiculatum is derived from two distinct Andean progenitors, P. lilianiae is derived from two Mayan progenitors, and P. talamancanum is derived from one Andean and one Mayan progenitor. The Costa Rican polyploids incorporate the legacy of the Andean and Mayan regions into their genomes, forming new lineages with novel genotypes.
Botrychium furculatum S. J. Popovich & Farrar is a new species widespread in the central and southern Rocky Mountains from Alberta and Montana south to New Mexico, with additional populations in the Cypress Hills of Saskatchewan and the Black Hills of Wyoming and South Dakota. Based on allozyme banding patterns, it is inferred to be an allotetraploid with B. pallidum W. H. Wagner as one parent and another, as yet undescribed, diploid species (B. “farrarii”) as the other parent. Genetically, B. furculatum is distinguished from B. pallidum by exhibiting fixed heterozygous loci in which expressed alleles of one of the genomic contributions matches those of B. pallidum, whereas many alleles of the other genomic contribution have not been detected in B. pallidum, but are displayed by B. “farrarii.” Morphologically, a suite of leaf characters differentiates B. furculatum from B. pallidum, particularly a more pronounced bowed or wishbone-like junction of sporophore and trophophore. Gradations in morphology and color between the two species have led to erroneous reports of B. pallidum in the Rocky Mountains. A key to differentiate B. furculatum from similar species is presented.
Goniopteris baorucensis, a species known only from the Sierra Baoruco in the southern Dominican Republic, is illustrated and described as new to science. Recent phylogenetic studies have inferred it as a member of a clade of predominantly calciphilic Goniopteris that are largely endemic to the Antilles. New records of two additional uncommon species in this clade, G. hildae and G. nigricans, are noted. A short discussion of the history of pteridology in Hispaniola is provided, with special reference to the contributions of Erik Ekman and Carl Christensen.
Examples of reticulate evolution are known from throughout the tree of life, but are particularly common in ferns due to their unique reproductive biology and few prezygotic reproductive barriers. However, untangling the complex evolution history of these groups can be challenging. Often, several different types of data are needed to understand the full story of reticulate evolution; for example, chloroplast markers trace maternal inheritance, while nuclear markers complete the picture by suggesting paternal inheritance. Next generation sequencing can provide thousands of nuclear loci, which are informative for estimating reticulate evolutionary histories. The model fern genus Ceratopteris is known to have cryptic allotetraploid taxa, and hybridization is common between many species in the genus. To better understand the patterns of hybridization and reticulate evolution in the genus, we constructed a split network analysis using thousands of single nucleotide polymorphisms from samples collected throughout the pan-tropical range of Ceratopteris. Our split network organizes taxa based on genomic similarity, revealing potential introgression between lineages. Combining this analysis with Patterson's D to measure gene flow, as well as contributions by previous authors, we show extensive hybridization and reticulate evolution in Old World Ceratopteris, and also provide evidence for natural hybridization events involving the model species C. richardii.
Almost fifty years ago Dr. Rolla M. Tryon investigated the patterns of neotropical fern diversity and discovered that sites of exceptional richness and endemism are found in five predominantly montane regions. Here, we revisit these sites with the aid of contemporary methodologies. We integrate phylogenetic, ecological, climatic, and occurrence data to better understand what factors contribute to the patterns of fern diversity throughout the neotropics. With this dataset we are able to reassess Tryon's neotropical hotspots fifty years later and take one step closer to understanding the processes governing the distribution of fern species. We recover six hotspots of neotropical species richness and endemism that closely mirror those delineated by Tryon. Like Tryon, we find that hotspots are found predominantly in montane regions with more climatic space compared to surrounding areas. Patterns of species richness and lineage diversification can largely be explained by the extent of available habitats, especially in association with montane ecosystems. We also show that patterns of species assemblages across the neotropics are largely dictated by distance and elevation. In synthesis, we propose that, in addition to migration and persistence of relictual lineages, patterns of species richness and endemism in the neotropics are driven by in situ speciation in montane regions.
A review of work on the origin and phylogenetic relationships of six systems of allopolyploid homosporous ferns and their progenitors serves as the basis for assessing the history and status of ideas relating to the biogeography of polyploid ferns. The likely dates of origin for the polyploids from recent analyses provide a historical context not previously available, making possible rigorous tests of hypotheses about the history of polyploids, especially the origin, distribution, and duration of polyploid ferns as lineages. Insularity figures prominently in developing an understanding of polyploid fern biogeography. The origin and persistence of polyploid ferns is enhanced by the empty niche space and high disturbance on Darwinian islands. In addition, the greater precinctiveness of polyploid ferns related to larger spore size is likely a selective advantage on islands, consistent with the number of high polyploids encountered among ferns on oceanic islands. Though recently originated polyploid ferns usually have identifiable progenitors with which they are partially sympatric, the rate of expansion of these ferns beyond the range of their progenitors varies. In two cases from Austral regions, long-term persistence and divergent speciation have been demonstrated in widespread polyploids and polyploid lineages with unknown diploid progenitors, though the general consensus is that polyploids do not persist in the long term.