Insights into evolution in Andean Polystichum (Dryopteridaceae) from expanded understanding of the cytosolic phosphoglucose isomerase gene.

Cytosolic phosphoglucose isomerase (pgiC) is an enzyme essential to glycolysis found universally in eukaryotes, but broad understanding of variation in the gene coding for pgiC is lacking for ferns. We used a substantially expanded representation of the gene for Andean species of the fern genus Polystichum to characterize pgiC in ferns relative to angiosperms, insects, and an amoebozoan; assess the impact of selection versus neutral evolutionary processes on pgiC; and explore evolutionary relationships of selected Andean species. The dataset of complete sequences comprised nine accessions representing seven species and one hybrid from the Andes and Serra do Mar. The aligned sequences of the full data set comprised 3376 base pairs (70% of the entire gene) including 17 exons and 15 introns from two central areas of the gene. The exons are highly conserved relative to angiosperms and retain substantial homology to insect pgiC, but intron length and structure are unique to the ferns. Average intron size is similar to angiosperms; intron number and location in insects are unlike those of the plants we considered. The introns included an array of indels and, in intron 7, an extensive microsatellite array with potential utility in analyzing population-level histories. Bayesian and maximum-parsimony analysis of 129 variable nucleotides in the Andean polystichums revealed that 59 (1.7% of the 3376 total) were phylogenetically informative; most of these united sister accessions. The phylogenetic trees for the Andean polystichums were incongruent with previously published cpDNA trees for the same taxa, likely the result of rapid evolutionary change in the introns and contrasting stability in the exons. The exons code a total of seven amino-acid substitutions. Comparison of non-synonymous to synonymous substitutions did not suggest that the pgiC gene is under selection in the Andes. Variation in pgiC including two additional accessions represented by incomplete sequences provided new insights into reticulate relationships among Andean taxa.

Phylogeny and biogeography of exindusiate Andean Polystichum (Dryopteridaceae).

PREMISE OF THE STUDY: Uplift of the tropical Andes had a significant impact on the diversification of South American flora and fauna. Recent biogeographic inquiries have established patterns of Andean divergence, but investigations on ferns are scant. The fern genus Polystichum Roth (Dryopteridaceae) combines widespread geographic and elevational distribution with a large number of species to form an ideal system for investigation of the origin and diversification patterns of a fern lineage in the tropical Andes. METHODS: The relationships among 42 Polystichum species, including taxa from all major biogeographic regions, were analyzed with 2591 aligned nucleotides from four plastid markers using maximum parsimony and Bayesian inference. The resulting phylogeny was then used to estimate divergence times and reconstruct both ancestral areas and ancestral elevations. KEY RESULTS: Tropical Andean South American polystichums that lack an indusium (sori exindusiate) were confirmed to form a monophyletic group. This exindusiate Andean Polystichum clade diverged from a middle-elevation forest lineage now rich in species endemic to Mexico during the middle Miocene (13.12 million years ago). The majority of diversification that followed took place in the montane regions of the central Andes with radiations to the northern Andes, southeastern Brazil, and alpine regions. CONCLUSIONS: The monophyletic exindusiate Andean Polystichum lineage diverged from a Mexican lineage in the middle Miocene and diversified in the central Andes before dispersing northward. This south-to-north dispersal pattern, documented for many other Andean lineages, corresponds with episodes of uplift in the tropical Andes.

Typifications and synonymy in Polystichum (Dryopteridaceae) from Chile and Argentina.

Polystichum Roth is one of the largest and most taxonomically challenging fern genera. South American species have a rich and complex nomenclatural history; many of the early names are inadequately typified. Based on extensive examination of original type material, we designate eleven lectotypes (including Aspidium mohrioides, Aspidium montevidense f. imbricata, Aspidium montevidense f. squamulosa, Aspidium plicatum, Aspidium pycnolepis, Dicksonia andina, Polystichum elegans, Polystichum mohrioides f. latifolia, Polystichum multifidum var. autranii, Polystichum platyphyllum var. kurtziana, and Polypodium polystichoides), and one neotype (Polystichum brongniartianum) for Polystichum taxa. Furthermore, three new synonyms are proposed.

Resumen Polystichum Roth es uno de los géneros de helechos más grandes y de mayor complejidad taxonómica. Las especies sudamericanas tienen una rica y compleja historia nomenclatural, con muchos de los nombres inadecuadamente tipificados. En base a un minucioso examen del material tipo original, designamos lectotipos para once taxones de Polystichum (que incluyen Aspidium mohrioides, Aspidium montevidense f. imbricata, Aspidium montevidense f. squamulosa, Aspidium plicatum, Aspidium pycnolepis, Dicksonia andina, Polystichum elegans, Polystichum mohrioides f. latifolia, Polystichum multifidum var. autranii, Polystichum platyphyllum var. kurtziana y Polypodium polystichoides) y un neotipo (Polystichum brongniartianum). Además, se proponen 3 nuevos sinónimos.