Evolution of mating systems has become one of the most important research areas in evolutionary biology. Cyrtomium falcatum is a homosporous fern species native to eastern Asia. Two subspecies ...belonging to a sexual diploid race of C. falcatum are recognized: subsp. littorale and subsp. australe. Subspecies littorale shows intermediate selfing rates, while subsp. australe is an obligate outcrosser. We aimed to evaluate the process of mating system evolution and divergence for the two subspecies using restriction site associated DNA sequencing (RAD-seq). The results showed that subsp. littorale had lower genetic diversity and stronger genetic drift than subsp. australe. Fluctuations in the effective population size over time were evaluated by extended Bayesian skyline plot and Stairway plot analyses, both of which revealed a severe population bottleneck about 20,000 years ago in subsp. littorale. This bottleneck and the subsequent range expansion after the LGM appear to have played an important role in the divergence of the two subspecies and the evolution of selfing in subsp. littorale. These results shed new light on the relationship between mating system evolution and past demographic change in fern species.
A new hybrid, Dryopteris ×makabensis (Dryopteridaceae) is described from Ibaraki Prefecture, Japan. Morphological observations, ploidy analysis, as well as nuclear and plastid DNA analyses, indicate ...that this diploid sterile hybrid likely originated from a cross between D. caudipinna and D. tokyoensis. Its occurrence is likely infrequent because the habitats of the parents are usually non-overlapping in Japan.
Polyploidy, hybridization, and agamospory have been considered important mechanisms in fern speciation. By integrating the methods of cytology, molecular phylogeny, and morphology, we examined the ...origins of polyploid species in the Pteris cretica group, which comprises five agamosporous taxa and six sexual species. Phylogenetic analysis was conducted using both cpDNA (rbcL and trnV-trnM) and a low-copy nuclear gene (gapCp). The combined results of cytology and the phylogenetic trees suggested that the sexual diploid P. kidoi had played a central role in the diversification of polyploid species in the P. cretica group. Some triploid clones of agamosporous P. cretica var. cretica originated through hybridization between the diploid cytotype of P. cretica var. cretica and the sexual diploid P. kidoi. The sexual polyploid species, P. henryi, P. multifida, P. ryukyuensis, and P. yamatensis, and the hexaploid race of P. deltodon have arisen through allopolyploidization between their respective ancestral parent species and P. kidoi. Additionally, the agamosporous triploid P. nipponica and P.cretica var. albolineata might have originated through hybridization between P. cretica var. cretica and an unknown ancestral diploid parent of P. ryukyuensis. Agamosporous P. cretica var. cretica harbored considerable genetic variation within both the diploid and triploid cytotypes. Because we could not find clear genetic differences between the diploid and triploid P. cretica, both cytotypes might be autopolyploids, or alternatively have originated through hybridization among the same members of ancestral sexual species.
The impact of variation in mating system on genetic diversity is a well-debated topic in evolutionary biology. The diploid sexual race of Cyrtomium falcatum (Japanese holly fern) shows mating system ...variation, i.e., it displays two different types of sexual expression (gametangia formation) in gametophytes: mixed (M) type and separate (S) type. We examined whether there is variation in the selfing rate among populations of this species, and evaluated the relationship between mating system, genetic diversity and effective population size using microsatellites. In this study, we developed eight new microsatellite markers and evaluated genetic diversity and structure of seven populations (four M-type and three S-type). Past effective population sizes (Ne) were inferred using Approximate Bayesian computation (ABC). The values of fixation index (FIS), allelic richness (AR) and gene diversity (h) differed significantly between the M-type (FIS: 0.626, AR: 1.999, h: 0.152) and the S-type (FIS: 0.208, AR: 2.718, h: 0.367) populations (when admixed individuals were removed from two populations). Although evidence of past bottleneck events was detected in all populations by ABC, the current Ne of the M-type populations was about a third of that of the S-type populations. These results suggest that the M-type populations have experienced more frequent bottlenecks, which could be related to their higher colonization ability via gametophytic selfing. Although high population differentiation among populations was detected (FST = 0.581, F'ST = 0.739), there was no clear genetic differentiation between the M- and S-types. Instead, significant isolation by distance was detected among all populations. These results suggest that mating system variation in this species is generated by the selection for single spore colonization during local extinction and recolonization events and there is no genetic structure due to mating system.
PREMISE OF THE STUDY:
Delimitation of cryptic species provides an understanding of biodiversity and opportunities to elucidate speciation processes. Extensive flavonoid variation has been reported in ...the tetraploid cytotype of the fern, Asplenium normale, although related species have no intraspecific variations in flavonoid composition. We hypothesized that Japanese A. normale still harbors multiple cryptic species with different flavonoid compositions, and tested this hypothesis using chemotaxonomic and multilocus genotyping approaches.
METHODS:
We determined the multilocus genotypes (MLGs) of 230 samples from 37 populations for one chloroplast DNA region and three nuclear genes. MLGs were used to delimit reproductively isolated lineages by population‐genetic approaches. We also tested the correspondence between genetically recognized groups and flavonoid compositions. To identify the origins of putative cryptic species, we conducted phylogenetic analysis of the DNA markers used in genotyping.
KEY RESULTS:
The genetic clusters and flavonoid compositions showed clear correspondence. We recognized three putative cryptic species in tetraploid Asplenium normale in Japan. Phylogenetic analyses revealed that cryptic species I and III originated from allopolyploidization between a diploid A. normale and an unknown diploid of A. boreale, and cryptic species II originated from allopolyploidization between a diploid A. normale and A. oligophlebium.
CONCLUSIONS:
Our study demonstrated that intraspecific variation of secondary metabolites can be a good indicator of cryptic species in ferns. The presence of the two cryptic species having the same progenitor diploid pair suggests that speciation between allopolyploid lineages of independent origin may be more common than previously considered.
Asplenium serratipinnae (Aspleniaceae: Polypodiales), an allotetraploid species between the diploid race of A. normale and A. oligophlebium is described as new. It is endemic to Japan and ...morphologically most similar to A. normale, but differs in having narrower pinnae with an auriculate to hastate acroscopic base and deeply serrated margins.
Borate ester cross-linking of the cell wall pectic polysaccharide rhamnogalacturonan II (RG-II) is required for the growth and development of angiosperms and gymnosperms. Here, we report that the ...amounts of borate cross-linked RG-II present in the sporophyte primary walls of members of the most primitive extant vascular plant groups (Lycopsida, Filicopsida, Equisetopsida, and Psilopsida) are comparable with the amounts of RG-II in the primary walls of angiosperms. By contrast, the gametophyte generation of members of the avascular bryophytes (Bryopsida, Hepaticopsida, and Anthocerotopsida) have primary walls that contain small amounts (approximately 1% of the amounts of RG-II present in angiosperm walls) of an RG-II-like polysaccharide. The glycosyl sequence of RG-II is conserved in vascular plants, but these RG-IIs are not identical because the non-reducing L-rhamnosyl residue present on the aceric acid-containing side chain of RG-II of all previously studied plants is replaced by a 3-O-methyl rhamnosyl residue in the RG-IIs isolated from Lycopodium tristachyum, Ceratopteris thalictroides, Platycerium bifurcatum, and Psilotum nudum. Our data indicate that the amount of RG-II incorporated into the walls of plants increased during the evolution of vascular plants from their bryophyte-like ancestors. Thus, the acquisition of a boron-dependent growth habit may be correlated with the ability of vascular plants to maintain upright growth and to form lignified secondary walls. The conserved structures of pteridophyte, lycophyte, and angiosperm RG-IIs suggests that the genes and proteins responsible for the biosynthesis of this polysaccharide appeared early in land plant evolution and that RG-II has a fundamental role in wall structure.
To test our hypothesis of hybrid formation involving the ‘independent gametophyte’ phenomenon in ferns, we identified the genomic formulae and ploidy level of gametophytes of the Vandenboschia ...radicans complex at the periphery of a sporophyte population. We identified haploid gametophytes of V. kalamocarpa (one of the two putative parents of V.×stenosiphon) in a hybrid sporophyte population in Japan that lacks fertile non‐hybrid individuals. Furthermore, diploid sporophytes of the species were not found within a 50‐km radius. This finding supports a hypothesis of hybridization involving the ‘independent gametophyte’ phenomenon and provides a new perspective on the geographical distribution of fern hybrids.
Dryopteris shibipedis
was once treated as an extinct species in the Red List (2007) by the Japanese Ministry of the Environment, but ‘rediscovered’ in the Tsukuba Botanical Garden. To clarify its ...origin, using ‘overlooked’ cultivated stocks we analyzed nuclear
PgiC
intron sequences. As the
PgiC
genotype of
D. shibipedis
can be explained by a combination of alleles of
D. kinkiensis
and those of
D. pacifica
, the hypothesis of hybrid origin of the species is supported.
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