Neo‐ and Paleopolyploidy contribute to the species diversity of Asplenium—the most species‐rich genus of ferns

Abstract

Polyploidy is widely considered as a major process in the evolution of plants but the accumulation of polyploid species diversity is still controversial. Some recent studies proposed increased extinction risk in neopolyploids compared with their diploid ancestors. The high proportion of polyploid ferns is expected to be formed mainly by neopolyploids, whereas paleopolyploid species are predicted to be clustered in clades founded by whole genome duplications. Here, we test this prediction by exploring the evolution of polyploidy in the derived fern family Aspleniaceae. The family has a global distribution and shows the highest frequency of polyploid taxa among all ferns. To test the hypothesis, we obtained a comprehensive phylogeny using chloroplast DNA sequences of 883 specimens representing 292 species. All published chromosome counts were mapped onto this phylogenetic framework in order to explore the evolution of polyploids. We recovered evidence for several whole genome duplications in the history of Aspleniaceae. Phylogenetic relationships of polyploids exceeding the tetraploid level suggest that tetraploid Asplenium species may have replaced their diploid ancestors as the main evolutionary players in some clades of this family.

Polyploidy does not control all: Lineage‐specific average chromosome length constrains genome size evolution in ferns

“…with 12 accessions, whereas 49% of the sampled taxa were represented by a single specimen (Data S1). The sampling comprised at least one representative of six out of the eight main clades of the crown group of Asplenium (Schneider et al, ), including the Camptosorus clade (32 spp. ; Schneider et al, ), Phyllitis clade including the Ceterach subclade (7 spp.…”

“…The sampling comprised at least one representative of six out of the eight main clades of the crown group of Asplenium (Schneider et al, ), including the Camptosorus clade (32 spp. ; Schneider et al, ), Phyllitis clade including the Ceterach subclade (7 spp. ; Schneider et al, ), Asplenium clade (3 spp; Schneider et al, ), Neottopteris clade (3 spp; Schneider et al, ), Pleurosorus clade (6 spp; Schneider et al, ), and Tarachia clade (3 spp; Schneider et al, ).…”

“…Phylogenetic signal was tested by randomizing the character states observed in a matrix containing 500 characters. The phylogenetic tree used for the analysis was reconstructed using rbcL sequence data that were made available in previous phylogenetic analyses of Aspleniaceae (Schneider et al, ). The phylogenetic tree was reconstructed using RaxML (Stamatakis, ) and MrBayes (Ronquist & Huelsenbeck, ).…”

“…The phylogenetic tree was reconstructed using RaxML (Stamatakis, ) and MrBayes (Ronquist & Huelsenbeck, ). The obtained topology was critically inspected by considering the topology of a large‐scale phylogenetic analysis of spleenworts that included approximately half of the extant diversity (Schneider et al, ). The statistical test carried out included linear regression, generalized least squares, and phylogenetic independent contrast analyses (Felsenstein, ).…”

JSE IBC Special Issue on Frontiers in Plant Systematics and Evolution

“…They also report that allopolyploids have evolved separately long enough from direct diploid progenitors for signals of genotypes to be obscured. Schneider et al () explore the evolution of polyploidy in the derived fern family Aspleniaceae, which has the highest frequency of polyploid taxa among all ferns. The authors used a comprehensive phylogenetic framework and mapped chromosome counts data onto the phylogeny to trace the evolution of polyploids.…”