Evolution of genome size in Carex (Cyperaceae) in relation to chromosome number and genomic base composition

Centromere drive may propel the evolution of chromosome and genome size in plants

BACKGROUND

Genome size is influenced by natural selection and genetic drift acting on variations from polyploidy and repetitive DNA sequences. We hypothesized that centromere drive, where centromeres compete for inclusion in the functional gamete during meiosis, may also affect genome and chromosome size. This competition occurs in asymmetric meiosis, where only one of the four meiotic products becomes a gamete. If centromere drive influences chromosome size evolution, it may also impact post-polyploid diploidization, where a polyploid genome is restructured to function more like a diploid through chromosomal rearrangements, including fusions. We tested if plant lineages with asymmetric meiosis exhibit faster chromosome size evolution compared to those with only symmetric meiosis, which lack centromere drive as all four meiotic products become gametes. We also examined if positive selection on centromeric histone H3 (CENH3), a protein that can suppress centromere drive, is more frequent in these asymmetric lineages.

METHODS

We analysed plant groups with different meiotic modes: asymmetric in gymnosperms and angiosperms, and symmetric in bryophytes, lycophytes and ferns. We selected species based on available CENH3 gene sequences and chromosome size data. Using Ornstein-Uhlenbeck evolutionary models and phylogenetic regressions, we assessed the rates of chromosome size evolution and the frequency of positive selection on CENH3 in these clades.

RESULTS

Our analyses showed that clades with asymmetric meiosis have a higher frequency of positive selection on CENH3 and increased rates of chromosome size evolution compared to symmetric clades.

CONCLUSIONS

Our findings support the hypothesis that centromere drive accelerates chromosome and genome size evolution, potentially also influencing the process of post-polyploid diploidization. We propose a model which in a single framework helps explain the stability of chromosome size in symmetric lineages (bryophytes, lycophytes and ferns) and its variability in asymmetric lineages (gymnosperms and angiosperms), providing a foundation for future research in plant genome evolution.

Survey sequencing and flow cytometry reveal the genomic characteristics and genetic markers of six wild sweetpotato species

BACKGROUND

The lack of genomic and genetic research on wild sweetpotato species has hindered the advancement of sweetpotato variety development through modern crop improvement techniques.

METHODS AND RESULTS

To facilitate the use of genomic and genetic approaches in sweetpotato variety development, we conducted a comprehensive assessment of the genome size and ploidy of six closely related wild sweetpotato species using flow cytometry and chromosome counting. Additionally, we acquired insights into their genomic characteristics through high-throughput sequencing. Based on the 17-mer frequency distribution, the genome sizes of these species ranged from 518.47 Mb to 1,505.04 Mb. Notably, most diploid species exhibited genome sizes of approximately 500 Mb, with the diploid wild species I. purpurea standing out as having a significantly larger genome size compared to other diploid species. A substantial proportion of repeats (ranging from 57.47 to 81.07%) was identified across the genomes of the six species. Heterozygosity levels varied from 0.24 to 2.21%. SSR analysis revealed that the distribution of microsatellite patterns was largely consistent among the genomes of I I. lacunosa, I. tenuissima, and I. tiliacea, with mono-, di-, and trinucleotide motifs dominated by A/T, AT/AT, and AAT/ATT, respectively, indicating a strong A/T base preference. SNPs in this study were unevenly distributed across chromosomes, and non-synonymous SNVs in exonic accounted for 3.199% of the total number of SNPs, which may lead to genetic functional variation between species. In addition, the cross-regional annotation of SNPs highlights the diversity of gene regulatory regions and may provide insights into gene regulation, the underlying genetics of complex traits, and genetic differences between species.

CONCLUSION

The current data reinforce the established positive correlation between genome size and ploidy in the genus Ipomoea. In particular, the diploid I. purpurea had a larger genome compared to other diploid species. The genome survey indicated that I. lacunosa(2x), I. tiliacea(2x), and I. tenuissima(2x) possess simple genomes with low heterozygosity (0.36%, 0.37%, and 0.24%, respectively). In contrast, I. purpurea(2x) has a simple genome but exhibits high heterozygosity (1.95%), while I. tabascana(4x) and I. trifida(6x) have complex genomes with high heterozygosity (2.21% and 1.54%, respectively). These results provide a reasonable basis for the selection of whole genome sequencing strategies for these species and would provide references for research into the genetic diversity of wild relatives of sweetpotato.

Evolutionary patterns of variations in chromosome counts and genome sizes show positive correlations with taxonomic diversity in tropical gingers

PREMISE

Cytogenetic traits such as an organism's chromosome number and genome size are taxonomically critical as they are instrumental in defining angiosperm diversity. Variations in these traits can be traced to evolutionary processes such as polyploidization, although geographic variations across cytogenetic traits remain underexplored. In the pantropical monocot family Zingiberaceae (~1500 species), cytogenetic traits have been well documented; however, the role of these traits in shaping taxonomic diversity and biogeographic patterns of gingers is not known.

METHODS

A time-calibrated Bayesian phylogenetic tree was constructed for 290 taxa covering three of the four subfamilies in Zingiberaceae. We tested models of chromosome number and genome size evolution within the family and whether lineage age, taxonomic diversity, and distributional range explain the variations in the cytogenetic traits. Tests were carried out at two taxonomic ranks: within Zingiberaceae and within genus Hedychium using correlations, generalized linear models and phylogenetic least square models.

RESULTS

The most frequent changes in chromosome number within Zingiberaceae were noted to be demi-polyploidization and polyploidization (~57% of the time), followed by ascending dysploidy (~27%). The subfamily Zingiberoideae showed descending dysploidy at its base, while Alpinioideae showed polyploidization at its internal nodes. Although chromosome counts and genome sizes did not corroborate with each other, suggesting that they are not equivalent; higher chromosome number variations and higher genome size variations were associated with higher taxonomic diversity and wider biogeographic distribution.

CONCLUSIONS

Within Zingiberaceae, multiple incidences of polyploidization were discovered, and cytogenetic events appear to have reduced the genome sizes and increased taxonomic diversity, distributional ranges and invasiveness.

Chromosomal evolution in Cryptangieae Benth. (Cyperaceae): Evidence of holocentrism and pseudomonads

Cryptangieae has recently been revised based on morphology and molecular phylogeny, but cytogenetic data is still scarce. We conducted this study with the aim of investigating the occurrence of holocentric chromosomes and pseudomonads, as well as understanding the mode of chromosomal evolution in the tribe. We performed analyses of meiotic behavior, chromosome counts, and reconstruction of the ancestral state for the haploid number. We present novel cytogenetic data for eight potentially holocentric species: Cryptangium verticillatum, Krenakia junciforme, K. minarum, Lagenocarpus bracteosus, L. griseus, L. inversus, L. rigidus, and L. tenuifolius. Meiotic abnormalities were observed, with parallel spindles being particularly noteworthy. Intra-specific variations in chromosome number were not found, which may indicate an efficient genetic control for the elimination of abnormal nuclei. The inferred ancestral haploid number was n = 16, with dysploidy being the main evolutionary mechanism. At least five chromosomal fissions occurred in Krenakia (n = 21), followed by a further ascending dysploidy event in Lagenocarpus (n = 17). As proposed for Cyperaceae, it is possible that cladogenesis events in Cryptangieae were marked by numerical and structural chromosomal changes.

PloiDB: the plant ploidy database

See also the Commentary on this article by Spoelhof et al., 240: 909–911.

Genome size, chromosome number variation and its correlation with stomatal characters for assessment of ploidy levels in a core subset of mulberry (Morus spp.) germplasm

The large size of the germplasm collection along with scanty information on their cytological and genome constitution have hindered well-planned breeding schemes in mulberry. To address the issue, a study was undertaken to investigate the variability in DNA content and genome size, chromosome number, ploidy and its relation with important stomatal characteristics among 162 mulberry germplasm. These germplasm comprise a core subset of 150 collections along with a representative collection of different mulberry species including the wild. Among the germplasm belonging to 16 species, we identified 122 diploids (2n = 28), 4 aneuploids (2n = 30), 13 triploids (2n = 42), 15 tetraploids (2n = 56), 7 hexaploids (2n = 84) and 1 dodecosaploid (2n = 308) based on the chromosome count. Most of the cultivated mulberries are found to be diploids. The mean nuclear 2C DNA content estimated by Flow cytometry, varied from 0.723±0.006 pg (M. australis, 2n = 2x) to 7.732 pg (M. nigra, 2n = 22x). The 2C DNA content positively correlated with the ploidy status and stomatal length (r = 0.814, p<0.001). Based on the 1Cx value, the study also suggests that the majority of the polyploid species have experienced genome downsizing in relation to their diploid progenitors. This study provides the most essential information on chromosome number, ploidy and DNA content to facilitate the utilization of a core subset of germplasm in the mulberry breeding program.

Complex patterns of ploidy in a holocentric plant clade (Schoenus, Cyperaceae) in the Cape biodiversity hotspot

BACKGROUND AND AIMS

It is unclear how widespread polyploidy is throughout the largest holocentric plant family - the Cyperaceae. Because of the prevalence of chromosomal fusions and fissions, which affect chromosome number but not genome size, it can be impossible to distinguish if individual plants are polyploids in holocentric lineages based on chromosome count data alone. Furthermore, it is unclear how differences in genome size and ploidy levels relate to environmental correlates within holocentric lineages, such as the Cyperaceae.

METHODS

We focus our analyses on tribe Schoeneae, and more specifically the southern African clade of Schoenus. We examine broad-scale patterns of genome size evolution in tribe Schoeneae and focus more intensely on determining the prevalence of polyploidy across the southern African Schoenus by inferring ploidy level with the program ChromEvol, as well as interpreting chromosome number and genome size data. We further investigate whether there are relationships between genome size/ploidy level and environmental variables across the nutrient-poor and summer-arid Cape biodiversity hotspot.

KEY RESULTS

Our results show a large increase in genome size, but not chromosome number, within Schoenus compared to other species in tribe Schoeneae. Across Schoenus, there is a positive relationship between chromosome number and genome size, and our results suggest that polyploidy is a relatively common process throughout the southern African Schoenus. At the regional scale of the Cape, we show that polyploids are more often associated with drier locations that have more variation in precipitation between dry and wet months, but these results are sensitive to the classification of ploidy level.

CONCLUSIONS

Polyploidy is relatively common in the southern African Schoenus, where a positive relationship is observed between chromosome number and genome size. Thus, there may be a high incidence of polyploidy in holocentric plants, whose cell division properties differ from monocentrics.

Chromosome size matters: genome evolution in the cyperid clade

BACKGROUND AND AIMS

While variation in genome size and chromosome numbers and their consequences are often investigated in plants, the biological relevance of variation in chromosome size remains poorly known. Here, we examine genome and mean chromosome size in the cyperid clade (families Cyperaceae, Juncaceae and Thurniaceae), which is the largest vascular plant lineage with predominantly holocentric chromosomes.

METHODS

We measured genome size in 436 species of cyperids using flow cytometry, and augment these data with previously published datasets. We then separately compared genome and mean chromosome sizes (2C/2n) amongst the major lineages of cyperids and analysed how these two genomic traits are associated with various environmental factors using phylogenetically informed methods.

KEY RESULTS

We show that cyperids have the smallest mean chromosome sizes recorded in seed plants, with a large divergence between the smallest and largest values. We found that cyperid species with smaller chromosomes have larger geographical distributions and that there is a strong inverse association between mean chromosome size and number across this lineage.

CONCLUSIONS

The distinct patterns in genome size and mean chromosome size across the cyperids might be explained by holokinetic drive. The numerous small chromosomes might function to increase genetic diversity in this lineage where crossovers are limited during meiosis.

Pulse grazing by reindeer (Rangifer tarandus) can increase the phylogenetic diversity of vascular plant communities in the Fennoscandian tundra

Herbivore grazing is an important determinant of plant community assemblages. Thus, it is essential to understand its impact to direct conservation efforts in regions where herbivores are managed. While the impacts of reindeer (Rangifer tarandus) grazing on plant biodiversity and community composition in the Fennoscandian tundra are well studied, the impact of reindeer grazing on phylogenetic community structure is not. We used data from a multiyear quasi-experimental study in northern Fennoscandia to analyze the effect of reindeer grazing on plant community diversity including its phylogenetic structure. Our study design used a permanent fence constructed in the 1960s and temporary fences constructed along the permanent fence to expose plant communities to three different grazing regimes: light (almost never grazed), pulse (grazed every other year), and press (chronic grazing for over 40 years). Similar to previous studies on low productivity ecosystems in this region, the species richness and evenness of plant communities with pulse and press grazing did not differ from communities with light grazing. Also consistent with previous studies in this region, we observed a transition from shrub-dominated communities with light grazing to graminoid-dominated communities with pulse and press grazing. Interestingly, communities with pulse, but not press, grazing were more phylogenetically dispersed than communities with light grazing. If grazing pulses can increase the phylogenetic diversity of plant communities, our result suggests changes in reindeer management allowing for pulses of grazing to increase phylogenetic diversity of plant communities.

Disentangling the components of triploid block and its fitness consequences in natural diploid-tetraploid contact zones of Arabidopsis arenosa

Hybrid seed inviability (HSI) is an important mechanism of reproductive isolation and speciation. HSI varies in strength among populations of diploid species but it remains to be tested whether similar processes affect natural variation in HSI within ploidy-variable species (triploid block). Here we used extensive endosperm, seed and F₁ -hybrid phenotyping to explore HSI variation within a diploid-autotetraploid species. By leveraging 12 population pairs from three ploidy contact zones, we tested for the effect of interploidy crossing direction (parent of origin), ploidy divergence and spatial arrangement in shaping reproductive barriers in a naturally relevant context. We detected strong parent-of-origin effects on endosperm development, F₁ germination and survival, which was also reflected in the rates of triploid formation in the field. Endosperm cellularization failure was least severe and F₁ -hybrid performance was slightly better in the primary contact zone, with genetically closest diploid and tetraploid lineages. We demonstrated overall strong parent-of-origin effects on HSI in a ploidy variable species, which translate to fitness effects and contribute to interploidy reproductive isolation in a natural context. Subtle intraspecific variation in these traits suggests the fitness consequences of HSI are predominantly a constitutive property of the species regardless of the evolutionary background of its populations.

Application-based guidelines for best practices in plant flow cytometry

Flow cytometry (FCM) is currently the most widely-used method to establish nuclear DNA content in plants. Since simple, 1-3-parameter, flow cytometers, which are sufficient for most plant applications, are commercially available at a reasonable price, the number of laboratories equipped with these instruments, and consequently new FCM users, has greatly increased over the last decade. This paper meets an urgent need for comprehensive recommendations for best practices in FCM for different plant science applications. We discuss advantages and limitations of establishing plant ploidy, genome size, DNA base composition, cell cycle activity, and level of endoreduplication. Applications of such measurements in plant systematics, ecology, molecular biology research, reproduction biology, tissue cultures, plant breeding, and seed sciences are described. Advice is included on how to obtain accurate and reliable results, as well as how to manage troubleshooting that may occur during sample preparation, cytometric measurements, and data handling. Each section is followed by best practice recommendations; tips as to what specific information should be provided in FCM papers are also provided.

Speciation by triparental hybridization in genus Sorbus (Rosaceae)

Hybridization associated with polyploidization and apomixis is a frequent mechanism of speciation. Sorbus is a genus with ongoing hybridization resulting in a polyploid complex with different parental lineage. Triparens is the smallest hybridogenous subgenus of Sorbus so far known to comprise only two taxa, S. intermedia and S. × liljeforsii that combine the genomes of three taxa (S. aria agg., S. aucuparia and S. torminalis). To elucidate the origins of S. dacica, S. paxiana and S. tauricola, three new trigenomic candidates formerly believed to be of biparental origin with either S. aria agg. × S. aucuparia or S. aria agg. × S. torminalis lineage we combined data from HPLC and chloroplast DNA analysing additional 33 related taxa as well. We concluded that the 'torminalis-type' flavonoid profile and the 'aucuparia-type' plastid indicate the participation of both S. torminalis and S. aucuparia resulting in the formation of S. dacica, S. paxiana and S. tauricola. Sorbus aria agg. as the third ancestor and as a necessary link to meet genes of S. torminalis and S. aucuparia in one genome is obvious from morphological features (densely tomentose undersides of leaves). The tetraploid cytotypes and obligate pseudogamy of S. dacica and S. paxiana were determined by flow cytometry and are published here for the first time. The most probable evolutionary scenario for Triparens species is: 1. a diploid sexual S. aucuparia as pollen acceptor hybridized with a tetraploid apomictic taxon from the S. aria agg. producing a triploid apomictic taxon with 'aucuparia-type' plastid inherited maternally; 2. during a second crossing event this subgenus Soraria hybrid as maternal progenitor hybridized with the sexual diploid S. torminalis (providing gene(s) of apigenin O-glucuronide synthesis) forming a tetraploid Triparens hybrid with 'aucuparia-type' plastid and 'torminalis-type' flavonoids.

Relative performance of customized and universal probe sets in target enrichment: A case study in subtribe Malinae

PREMISE

Custom probe design for target enrichment in phylogenetics is tedious and often hinders broader phylogenetic synthesis. The universal angiosperm probe set Angiosperms353 may be the solution. Here, we test the relative performance of Angiosperms353 on the Rosaceae subtribe Malinae in comparison with custom probes that we specifically designed for this clade. We then address the impact of bioinformatically altering the performance of Angiosperms353 by replacing the original probe sequences with orthologs extracted from the Malus domestica genome.

METHODS

To evaluate the relative performance of these probe sets, we compared the enrichment efficiency, locus recovery, alignment length, proportion of parsimony-informative sites, proportion of potential paralogs, the topology and support of the resulting species trees, and the gene tree discordance.

RESULTS

Locus recovery was highest for our custom Malinae probe set, and replacing the original Angiosperms353 sequences with a Malus representative improved the locus recovery relative to Angiosperms353. The proportion of parsimony-informative sites was similar between all probe sets, while the gene tree discordance was lower in the case of the custom probes.

DISCUSSION

A custom probe set benefits from data completeness and can be tailored toward the specificities of the project of choice; however, Angiosperms353 was equally as phylogenetically informative as the custom probes. We therefore recommend using both a custom probe set and Angiosperms353 to facilitate large-scale systematic studies, where financially possible.

Morphological variability and genetic diversity in Carex buxbaumii and Carex hartmaniorum (Cyperaceae) populations

Background

Carex buxbaumii and C. hartmaniorum are sister species of the clade Papilliferae within the monophyletic section Racemosae. An unambiguous identification of these species is relatively difficult due to the interspecific continuum of some morphological characters as well as the intraspecific variability. The study was aimed at determining the range of variability, both morphological and genetic, within and between these two closely related and similar species.

Methods

The sedges were collected during botanical expeditions to Armenia, Estonia, the Netherlands, and Poland. The morphological separation of the two species and their populations was tested using the Discriminant Function Analysis (DFA). The genetic variability of the 19 Carex populations was assessed in the presence of eight Inter Simple Sequence Repeat (ISSR) primers.

Results

Results of the study indicate a considerable genetic affinity between the two sedge species (mean Si = 0.619). However, the populations of C. hartmaniorum are, morphologically and genetically, more homogenous than the populations of C. buxbaumii. Compared to C. hartmaniorum, C. buxbaumii usually has wider leaf blades, a shorter inflorescence, a lower number of spikes which are shorter, but wider, and longer bracts and utricles. The AMOVA showed a larger variation between the populations of C. buxbaumii, representing 25.65% of the total variation in the taxon. Two populations of C. buxbaumii (from Poland and Estonia) are separated from the remaining populations, both genetically and morphologically; their individuals show shorter utricles and glumes, compared to the typical specimens of C. buxbaumii, and correspond with the morphology of putative infraspecific taxa described by Cajander (var. brevisquamosa and var. confusa).

Conclusions

The taxonomic status of the putative infraspecific taxa within C. buxbaumii requires further studies throughout the distribution range of C. buxbaumii, addressing habitats, morphology and genetics (including a chromosome count or a combination of different genetic methods), particularly as the variability in C. buxbaumii may be associated with the species’ polyploid origin.

Correlation Analysis Reveals an Important Role of GC Content in Accumulation of Deletion Mutations in the Coding Region of Angiosperm Plastomes

Variation in GC content is assumed to correlate with various processes, including mutation biases, recombination, and environmental parameters. To date, most genomic studies exploring the evolution of GC content have focused on nuclear genomes, but relatively few have concentrated on organelle genomes. We explored the mechanisms maintaining the GC content in angiosperm plastomes, with a particular focus on the hypothesis of phylogenetic dependence and the correlation with deletion mutations. We measured three genetic traits, namely, GC content, A/T tracts, and G/C tracts, in the coding region of plastid genomes for 1382 angiosperm species representing 350 families and 64 orders, and tested the phylogenetic signal. Then, we performed correlation analyses and revealed the variation in evolutionary rate of selected traits using RRphylo. The plastid GC content in the coding region varied from 28.10% to 43.20% across angiosperms, with a few non-photosynthetic species showing highly reduced values, highlighting the significance of functional constraints. We found strong phylogenetic signal in A/T tracts, but weak ones in GC content and G/C tracts, indicating adaptive potential. GC content was positively and negatively correlated with G/C and A/T tracts, respectively, suggesting a trade-off between these two deletion events. GC content evolved at various rates across the phylogeny, with significant increases in monocots and Lamiids, and a decrease in Fabids, implying the effects of some other factors. We hypothesize that variation in plastid GC content might be a mixed strategy of species to optimize fitness in fluctuating climates, partly through influencing the trade-off between AT → GC and GC → AT mutations.

Genome sequence of Kobresia littledalei, the first chromosome-level genome in the family Cyperaceae

Kobresia plants are important forage resources in the Qinghai-Tibet Plateau and are essential in maintaining the ecological balance of grasslands. Therefore, it is beneficial to obtain Kobresia genome resources and study the adaptive characteristics of Kobresia plants in the Qinghai-Tibetan Plateau. We assembled the genome of Kobresia littledalei C. B. Clarke, which was about 373.85 Mb in size. 96.82% of the bases were attached to 29 pseudo-chromosomes, combining PacBio, Illumina and Hi-C sequencing data. Additional investigation of the annotation identified 23,136 protein-coding genes. 98.95% of these were functionally annotated. According to phylogenetic analysis, K. littledalei in Cyperaceae separated from Poaceae about 97.6 million years ago after separating from Ananas comosus in Bromeliaceae about 114.3mya. For K. littledalei, we identified a high-quality genome at the chromosome level. This is the first time a reference genome has been established for a species of Cyperaceae. This genome will help additional studies focusing on the processes of plant adaptation to environments with high altitude and cold weather.

Chromosome numbers of Carex (Cyperaceae) and their taxonomic implications

Counting chromosomes is the first step towards a better understanding of the karyotype evolution and the role of chromosome evolution in species diversification within Carex; however, the chromosome count is not known yet for numerous sedges. In this paper chromosome counts were performed for 23 Carex taxa from Armenia, Austria, the Czech Republic, and Poland. Chromosome numbers were determined for the first time in three species (Carex cilicica, 2n = 54; C. phyllostachys, 2n = 56; C. randalpina, 2n = 78), two subspecies (C. muricata subsp. ashokae, 2n = 58; C. nigra subsp. transcaucasica, 2n = 84) and two hybrids (C. ×decolorans, 2n = 74; C. ×walasii, 2n = 108). Among the taxa whose number of chromosomes had been known before, the largest difference was found in C. hartmaniorum (here 2n = 52) and C. aterrima subsp. medwedewii (here 2n = 52). A difference in the chromosome count was demonstrated for C. cilicica (2n = 54) versus the species of the section Aulocystis (2n = 30 to 40) and for C. tomentosa (2n = 48) versus the species of the section Acrocystis (2n = 18 to 38). The results of this study indicate that the position of C. cilicica in Aulocystis section may raise doubts. Attention was paid to the relationship between C. phyllostachys and taxa of the subgenus Carex section Gynobasidae.

Review of resistance to chronic ionizing radiation exposure under environmental conditions in multicellular organisms

Ionizing radiation resistance occurs among many phylogenetic groups and its mechanisms remain incompletely understood. Tolerances to acute and chronic irradiation do not always correlate because different mechanisms may be involved. The radioresistance phenomenon becomes even more complex in the field than in the laboratory because the effects of radioactive contamination on natural populations are intertwined with those of other factors, such as bioaccumulation of radionuclides, interspecific competition, seasonal variations in environmental conditions, and land use changes due to evacuation of humans from contaminated areas. Previous reviews of studies performed in radioactive sites like the Kyshtym, Chernobyl, and Fukushima accident regions, and of protracted irradiation experiments, often focused on detecting radiation effects at low doses in radiosensitive organisms. Here we review the literature with a different purpose: to identify organisms with high tolerance to chronic irradiation under environmental conditions, which maintained abundant populations and/or outcompeted more radiosensitive species at high dose rates. Taxa for which consistent evidence for radioresistance came from multiple studies conducted in different locations and at different times were found among plants (e.g. willow and birch trees, sedges), invertebrate and vertebrate animals (e.g. rotifers, some insects, crustaceans and freshwater fish). These organisms are not specialized "extremophiles", but tend to tolerate broad ranges of environmental conditions and stresses, have small genomes, reproduce quickly and/or disperse effectively over long distances. Based on these findings, resistance to radioactive contamination can be examined in a more broad context of chronic stress responses.

Holocentric Karyotype Evolution in Rhynchospora Is Marked by Intense Numerical, Structural, and Genome Size Changes

Cyperaceae is a family of Monocotyledons comprised of species with holocentric chromosomes that are associated with intense dysploidy and polyploidy events. Within this family the genus Rhynchospora has recently become the focus of several studies that characterize the organization of the holocentric karyotype and genome structures. To broaden our understanding of genome evolution in this genus, representatives of Rhynchospora were studied to contrast chromosome features, C-CMA/DAPI band distribution and genome sizes. Here, we carried out a comparative analysis for 35 taxa of Rhynchospora, and generated new genome size estimates for 20 taxa. The DNA 2C-values varied up to 22-fold, from 2C = 0.51 pg to 11.32 pg, and chromosome numbers ranged from 2n = 4 to 61. At least 37% of our sampling exhibited 2n different from the basic number x = 5, and chromosome rearrangements were also observed. A large variation in C-CMA/DAPI band accumulation and distribution was observed as well. We show that genome variation in Rhynchospora is much larger than previously reported. Phylogenetic analysis showed that most taxa were grouped in clades corresponding to previously described taxonomic sections. Basic chromosome numbers are the same within every section, however, changes appeared in all the clades. Ancestral chromosome number reconstruction revealed n = 5 as the most likely ancestral complements, but n = 10 appears as a new possibility. Chromosome evolution models point to polyploidy as the major driver of chromosome evolution in Rhynchospora, followed by dysploidy. A negative correlation between chromosome size and diploid number open the discussion for holokinetic drive-based genome evolution. This study explores relationships between karyotype differentiation and genome size variation in Rhynchospora, and contrasts it against the phylogeny of this holocentric group.

Partitioning genetic and species diversity refines our understanding of species-genetic diversity relationships

Disentangling the origin of species-genetic diversity correlations (SGDCs) is a challenging task that provides insight into the way that neutral and adaptive processes influence diversity at multiple levels. Genetic and species diversity are comprised by components that respond differently to the same ecological processes. Thus, it can be useful to partition species and genetic diversity into their different components to infer the mechanisms behind SGDCs. In this study, we applied such an approach using a high-elevation Andean wetland system, where previous evidence identified neutral processes as major determinants of the strong and positive covariation between plant species richness and AFLP genetic diversity of the common sedge Carex gayana. To tease apart putative neutral and non-neutral genetic variation of C. gayana, we identified loci putatively under selection from a dataset of 1,709 SNPs produced using restriction site-associated DNA sequencing (RAD-seq). Significant and positive relationships between local estimates of genetic and species diversities (α-SGDCs) were only found with the putatively neutral loci datasets and with species richness, confirming that neutral processes were primarily driving the correlations and that the involved processes differentially influenced local species diversity components (i.e., richness and evenness). In contrast, SGDCs based on genetic and community dissimilarities (β-SGDCs) were only significant with the putative non-neutral datasets. This suggests that selective processes influencing C. gayana genetic diversity were involved in the detected correlations. Together, our results demonstrate that analyzing distinct components of genetic and species diversity simultaneously is useful to determine the mechanisms behind species-genetic diversity relationships.

Peripatric speciation associated with genome expansion and female-biased sex ratios in the moss genus Ceratodon

PREMISE OF THE STUDY

A period of allopatry is widely believed to be essential for the evolution of reproductive isolation. However, strict allopatry may be difficult to achieve in some cosmopolitan, spore-dispersed groups, like mosses. We examined the genetic and genome size diversity in Mediterranean populations of the moss Ceratodon purpureus s.l. to evaluate the role of allopatry and ploidy change in population divergence.

METHODS

We sampled populations of the genus Ceratodon from mountainous areas and lowlands of the Mediterranean region, and from Western and Central Europe. We performed phylogenetic and coalescent analyses on sequences from five nuclear introns and a chloroplast locus to reconstruct their evolutionary history. We also estimated genome size using flow cytometry (employing propidium iodide) and determined the sex of samples using a sex-linked PCR marker.

KEY RESULTS

Two well-differentiated clades were resolved, discriminating two homogeneous groups: the widespread C. purpureus and a local group mostly restricted to the mountains in Southern Spain. The latter also possessed a genome size 25% larger than the widespread C. purpureus, and the samples of this group consist entirely of females. We also found hybrids, and some of them had a genome size equivalent to the sum of the C. purpureus and Spanish genome, suggesting that they arose by allopolyploidy.

CONCLUSIONS

These data suggest that a new species of Ceratodon arose via peripatric speciation, potentially involving a genome size change and a strong female-biased sex ratio. The new species has hybridized in the past with C. purpureus.

Are holocentrics doomed to change? Limited chromosome number variation in Rhynchospora Vahl (Cyperaceae)

Karyotype evolution in species with non-localised centromeres (holocentric chromosomes) is usually very dynamic and associated with recurrent fission and fusion (also termed agmatoploidy/symploidy) events. In Rhynchospora (Cyperaceae), one of the most species-rich sedge genera, all analysed species have holocentric chromosomes and their numbers range from 2n = 4 to 2n = 84. Agmatoploidy/symploidy and polyploidy were suggested as the main processes in the reshuffling of Rhynchospora karyotypes, although testing different scenarios of chromosome number evolution in a phylogenetic framework has not been attempted until now. Here, we used maximum likelihood and model-based analyses, in combination with genome size estimation and ribosomal DNA distribution, to understand chromosome evolution in Rhynchospora. Overall, chromosome number variation showed a significant phylogenetic signal and the majority of the lineages maintained a karyotype of 2n = 10 (~48% of the species), the most likely candidate for the ancestral number of the genus. Higher and lower chromosome numbers were restricted to specific clades, whilst polyploidy and/or fusion/fission events were present in specific branches. Variation in genome size and ribosomal DNA site number showed no correlation with ploidy level or chromosome number. Although different mechanisms of karyotype evolution (polyploidy, fusion and fission) seem to be acting in distinct lineages, the degree of chromosome variation and the main mechanisms involved are comparable to those found in some monocentric genera and lower than expected for a holocentric genus.

Fourteen polymorphic microsatellite markers for a widespread limestone endemic, Carex eburnea (Cyperaceae: Carex sect. Albae)

PREMISE OF THE STUDY

Microsatellite primers were developed for a widespread limestone endemic sedge, Carex eburnea, to facilitate investigation of the genetic diversity and phylogeography of this taxon and its closest relative, C. mckittrickensis.

METHODS AND RESULTS

Forty-eight primer pairs were designed from Illumina sequence data and screened for suitability. Fourteen of these primer pairs were polymorphic and generated one to seven alleles per locus. Cross-species amplifications were conducted for all four members of Carex sect. Albae.

CONCLUSIONS

These primer pairs can be used to assess the genetic diversity and population structure in future studies of C. eburnea and C. mckittrickensis, and likely in other members of Carex sect. Albae.

Karyological patterns in the European endemic genus Soldanella L.: Absolute genome size variation uncorrelated with cytotype chromosome numbers

PREMISE OF THE STUDY

Detailed knowledge about the karyological diversity of organisms undoubtedly represents one of the crucial steps toward a better understanding of their evolutionary trends and history. We investigated the cytotype and absolute genome size (AGS) patterns in the European mountain-dwelling genus Soldanella (Primulaceae) in light of its geographic distribution and ecological diversification.

METHODS

Our chromosome number survey was based on 34 newly determined and 125 previously published chromosome counts. AGS was estimated on the basis of propidium iodide (PI) flow cytometry (299 individuals, 110 populations).

KEY RESULTS

We confirmed the existence of two cytotypes with the same ploidy level, i.e., euploid 2n = 40 and dysploid 2n = 38. The overall infrageneric AGS variation ranged between 2.97 and 3.99 pg (25.6% variation). The 2n = 40 cytotype harbors a modest amount of continuous AGS variation. With regard to its distribution area and ecology, the cytotype is ubiquitous. By contrast, the 2n = 38 cytotype was detected only in six forest-dwelling taxa with AGS variation segregated into three discrete, geographically separated groups. The AGS variation of the 2n = 38 cytotype was strongly correlated with elevation and longitude.

CONCLUSIONS

Despite the apparent morphological and ecological variation, members of the genus Soldanella have not undergone any pronounced cytotype and AGS diversification during their evolutionary history. The lack of correlation between chromosome numbers and AGS indicates that the evolutionary mechanism behind the origin of the dysploid cytotype 2n = 38 was a chromosomal fusion.

Evolution of genome size and genomic GC content in carnivorous holokinetics (Droseraceae)

BACKGROUND AND AIMS

Studies in the carnivorous family Lentibulariaceae in the last years resulted in the discovery of the smallest plant genomes and an unusual pattern of genomic GC content evolution. However, scarcity of genomic data in other carnivorous clades still prevents a generalization of the observed patterns. Here the aim was to fill this gap by mapping genome evolution in the second largest carnivorous family, Droseraceae, where this evolution may be affected by chromosomal holokinetism in Drosera METHODS: The genome size and genomic GC content of 71 Droseraceae species were measured by flow cytometry. A dated phylogeny was constructed, and the evolution of both genomic parameters and their relationship to species climatic niches were tested using phylogeny-based statistics.

KEY RESULTS

The 2C genome size of Droseraceae varied between 488 and 10 927 Mbp, and the GC content ranged between 37·1 and 44·7 %. The genome sizes and genomic GC content of carnivorous and holocentric species did not differ from those of their non-carnivorous and monocentric relatives. The genomic GC content positively correlated with genome size and annual temperature fluctuations. The genome size and chromosome numbers were inversely correlated in the Australian clade of Drosera CONCLUSIONS: Our results indicate that neither carnivory (nutrient scarcity) nor the holokinetism have a prominent effect on size and DNA base composition of Droseraceae genomes. However, the holokinetic drive seems to affect karyotype evolution in one of the major clades of Drosera Our survey confirmed that the evolution of GC content is tightly connected with the evolution of genome size and also with environmental conditions.

Agmatoploidy and symploidy: a critical review

Agmatoploidy is a type of chromosome rearrangement that involves the fragmentation of an entire chromosome complement, generating a diploid with double its original chromosome number. Agmatoploidy and other related karyotype changes, such as symploidy (the opposite change, promoted by chromosome fusion), partial agmatoploidy, polyagmatoploidy, etc., are restricted to species with holokinetic chromosomes and are assumed to play an important role in their karyotype evolution. However, a critical review of the literature shows that examples of chromosome number doubling by agmatoploidy are rare and not clearly demonstrated, while partial agmatoploidy and partial symploidy seem to be the same as ascending and descending disploidy, respectively. It is therefore proposed here that these terms should be avoided or even abolished.

Hybrid Origins of Carex rostrata var. borealis and C. stenolepis, Two Problematic Taxa in Carex Section Vesicariae (Cyperaceae)

Hybridization is frequent in the large and ecologically significant genus Carex (Cyperaceae). In four important sections of the northern regions (Ceratocystis, Glareosae, Phacocystis and Vesicariae), the frequent occurrence of hybrids often renders the identification of "pure" species and hybrids difficult. In this study we address the origins and taxonomic rank of two taxa of section Vesicariae: Carex rostrata var. borealis and C. stenolepis. The origin and taxonomic status of C. stenolepis has been the subject of substantial debate over the years, whereas C. rostrata var. borealis has received very little attention in the years since its first description in the 19th century. By performing an extensive sampling of relevant taxa from a broad distribution range, and analyzing data from fifteen microsatellite loci developed specifically for our study together with pollen stainability measures, we resolve the hybrid origins of C. rostrata var. borealis and C. stenolepis and provide new insights into this taxonomically challenging group of sedges. Our results are in accordance with previous findings suggesting that C. stenolepis is a hybrid between C. vesicaria and C. saxatilis. They are also in accordance with a previous proposition that C. rostrata var. borealis is a hybrid between C. rostrata and C. rotundata, and furthermore suggest that both hybrids are the result of multiple, recent (i.e., postglacial) hybridization events. We found little evidence for successful sexual reproduction within C. rostrata var. borealis and C. stenolepis, but conclude that the common and recurrent, largely predictable occurrence of these taxa justifies accepting both hybrids as hybrid species with binomial names. There are, however, complications as to types and priority names, and we therefore choose to address these problems in a separate paper.

Evaluating the role of genome downsizing and size thresholds from genome size distributions in angiosperms

PREMISE OF THE STUDY

Whole-genome duplications (WGDs) can rapidly increase genome size in angiosperms. Yet their mean genome size is not correlated with ploidy. We compared three hypotheses to explain the constancy of genome size means across ploidies. The genome downsizing hypothesis suggests that genome size will decrease by a given percentage after a WGD. The genome size threshold hypothesis assumes that taxa with large genomes or large monoploid numbers will fail to undergo or survive WGDs. Finally, the genome downsizing and threshold hypothesis suggests that both genome downsizing and thresholds affect the relationship between genome size means and ploidy.

METHODS

We performed nonparametric bootstrap simulations to compare observed angiosperm genome size means among species or genera against simulated genome sizes under the three different hypotheses. We evaluated the hypotheses using a decision theory approach and estimated the expected percentage of genome downsizing.

KEY RESULTS

The threshold hypothesis improves the approximations between mean genome size and simulated genome size. At the species level, the genome downsizing with thresholds hypothesis best explains the genome size means with a 15% genome downsizing percentage. In the genus level simulations, the monoploid number threshold hypothesis best explains the data.

CONCLUSIONS

Thresholds of genome size and monoploid number added to genome downsizing at species level simulations explain the observed means of angiosperm genome sizes, and monoploid number is important for determining the genome size mean at the genus level.

Flow cytometry may allow microscope-independent detection of holocentric chromosomes in plants

Two chromosomal structures, known as monocentric and holocentric chromosomes, have evolved in eukaryotes. Acentric fragments of monocentric chromosomes are unequally distributed to daughter cells and/or lost, while holocentric fragments are inherited normally. In monocentric species, unequal distribution should generate chimeras of cells with different nuclear DNA content. We investigated whether such differences in monocentric species are detectable by flow cytometry (FCM) as (i) a decreased nuclear DNA content and (ii) an increased coefficient of variance (CV) of the G1 peak after gamma radiation-induced fragmentation. We compared 13 monocentric and 9 holocentric plant species. Unexpectedly, monocentrics and holocentrics did not differ with respect to parameters (i) and (ii) in their response to gamma irradiation. However, we found that the proportion of G2 nuclei was highly elevated in monocentrics after irradiation, while holocentrics were negligibly affected. Therefore, we hypothesize that DNA-damaging agents induce cell cycle arrest leading to endopolyploidy only in monocentric and not (or to much lesser extent) in holocentric plants. While current microscope-dependent methods for holocentrism detection are unreliable for small and numerous chromosomes, which are common in holocentrics, FCM can use somatic nuclei. Thus, FCM may be a rapid and reliable method of high-throughput screening for holocentric candidates across plant phylogeny.

Genome size stability despite high chromosome number variation in Carex gr. laevigata

PREMISE OF THE STUDY

In organisms with holocentric chromosomes like Carex species, chromosome number evolution has been hypothesized to be a result of fission, fusion, and/or translocation events. Negative, positive, or the absence of correlations have been found between chromosome number and genome size in Carex.

METHODS

Using the inferred diploid chromosome number and 80 genome size measurements from 26 individuals and 20 populations of Carex gr. laevigata, we tested the null hypothesis of chromosome number evolution by duplication and deletion of whole chromosomes.

KEY RESULTS

Our results show a significant positive correlation between genome size and chromosome number, but the slope of such correlation supports the hypothesis of proliferation and removal of repetitive DNA fragments to explain genome size variation rather than duplication and deletion of whole chromosomes.

CONCLUSIONS

Our results refine the theory of the holokinetic drive: this mechanism is proposed to facilitate repetitive DNA removal (or any segmental deletion) when smaller homologous chromosomes are preferentially inherited, or repetitive DNA proliferation (or any segmental duplication) when larger homologs are preferred. This study sheds light on how karyotype evolution plays an important role in the diversification of the species of the genus Carex.

Ecological and evolutionary significance of genomic GC content diversity in monocots

Genomic DNA base composition (GC content) is predicted to significantly affect genome functioning and species ecology. Although several hypotheses have been put forward to address the biological impact of GC content variation in microbial and vertebrate organisms, the biological significance of GC content diversity in plants remains unclear because of a lack of sufficiently robust genomic data. Using flow cytometry, we report genomic GC contents for 239 species representing 70 of 78 monocot families and compare them with genomic characters, a suite of life history traits and climatic niche data using phylogeny-based statistics. GC content of monocots varied between 33.6% and 48.9%, with several groups exceeding the GC content known for any other vascular plant group, highlighting their unusual genome architecture and organization. GC content showed a quadratic relationship with genome size, with the decreases in GC content in larger genomes possibly being a consequence of the higher biochemical costs of GC base synthesis. Dramatic decreases in GC content were observed in species with holocentric chromosomes, whereas increased GC content was documented in species able to grow in seasonally cold and/or dry climates, possibly indicating an advantage of GC-rich DNA during cell freezing and desiccation. We also show that genomic adaptations associated with changing GC content might have played a significant role in the evolution of the Earth's contemporary biota, such as the rise of grass-dominated biomes during the mid-Tertiary. One of the major selective advantages of GC-rich DNA is hypothesized to be facilitating more complex gene regulation.

Holokinetic drive: centromere drive in chromosomes without centromeres

Similar to how the model of centromere drive explains the size and complexity of centromeres in monocentrics (organisms with localized centromeres), our model of holokinetic drive is consistent with the divergent evolution of chromosomal size and number in holocentrics (organisms with nonlocalized centromeres) exhibiting holokinetic meiosis (holokinetics). Holokinetic drive is proposed to facilitate chromosomal fission and/or repetitive DNA removal (or any segmental deletion) when smaller homologous chromosomes are preferentially inherited or chromosomal fusion and/or repetitive DNA proliferation (or any segmental duplication) when larger homologs are preferred. The hypothesis of holokinetic drive is supported primarily by the negative correlation between chromosome number and genome size that is documented in holokinetic lineages. The supporting value of two older cross-experiments on holokinetic structural heterozygotes (the rush Luzula elegans and butterflies of the genus Antheraea) that indicate the presence of size-preferential homolog transmission via female meiosis for holokinetic drive is discussed, along with the further potential consequences of holokinetic drive in comparison with centromere drive.

Karyotypic changes through dysploidy persist longer over evolutionary time than polyploid changes

Chromosome evolution has been demonstrated to have profound effects on diversification rates and speciation in angiosperms. While polyploidy has predated some major radiations in plants, it has also been related to decreased diversification rates. There has been comparatively little attention to the evolutionary role of gains and losses of single chromosomes, which may or not entail changes in the DNA content (then called aneuploidy or dysploidy, respectively). In this study we investigate the role of chromosome number transitions and of possible associated genome size changes in angiosperm evolution. We model the tempo and mode of chromosome number evolution and its possible correlation with patterns of cladogenesis in 15 angiosperm clades. Inferred polyploid transitions are distributed more frequently towards recent times than single chromosome gains and losses. This is likely because the latter events do not entail changes in DNA content and are probably due to fission or fusion events (dysploidy), as revealed by an analysis of the relationship between genome size and chromosome number. Our results support the general pattern that recently originated polyploids fail to persist, and suggest that dysploidy may have comparatively longer-term persistence than polyploidy. Changes in chromosome number associated with dysploidy were typically observed across the phylogenies based on a chi-square analysis, consistent with these changes being neutral with respect to diversification.

Shifts in diversification rates and clade ages explain species richness in higher-level sedge taxa (Cyperaceae)

PREMISE OF THE STUDY

Understanding heterogeneity in species richness across the tree of life is a challenge in evolutionary biology. The sedge family, Cyperaceae, is classified into tribes that exhibit a roughly 200-fold range in species richness. The Cyperaceae present an excellent case study in the determinants of species richness within higher-level taxa.

METHODS

We used secondary calibration based on prior studies and fossils from a rush (Juncaceae) and five sedges to calibrate two previously published Cyperaceae phylogenies, then compared our results to previous molecular clock analyses. We used an information-theoretic approach to identify shifts in lineage diversification rates and phylogenetic generalized least squares to fit alternative models of clade species richness.

KEY RESULTS

Our results suggest a late Cretaceous origin for Cyperaceae (76-89 mya). The inferred 0.06 speciation events Ma(-1) is comparable to overall diversification rates in the order Poales but faster than angiosperm background rates. A threefold increase in diversification rate at the base of the species-rich SDC+FAEC clade is correlated with climatic changes during the Paleocene-Eocene boundary (ca. 55 mya). The greater driver of among-clade variance in species richness, however, is clade age (simple R(2) = 0.334, P = 0.0006).

CONCLUSIONS

Although shifts in diversification rates play a role in the generation of heterogeneous patterns of species richness, our study demonstrates that variance in clade age alone explains ca. 33% of among-clade variation in species diversity, which stands in contrast to the general pattern for angiosperms.

Effect of phosphorus availability on the selection of species with different ploidy levels and genome sizes in a long-term grassland fertilization experiment

Polyploidy and increased genome size are hypothesized to increase organismal nutrient demands, namely of phosphorus (P), which is an essential and abundant component of nucleic acids. Therefore, polyploids and plants with larger genomes are expected to be selectively disadvantaged in P-limited environments. However, this hypothesis has yet to be experimentally tested. We measured the somatic DNA content and ploidy level in 74 vascular plant species in a long-term fertilization experiment. The differences between the fertilizer treatments regarding the DNA content and ploidy level of the established species were tested using phylogeny-based statistics. The percentage and biomass of polyploid species clearly increased with soil P in particular fertilizer treatments, and a similar but weaker trend was observed for the DNA content. These increases were associated with the dominance of competitive life strategy (particularly advantageous in the P-treated plots) in polyploids and the enhanced competitive ability of dominant polyploid grasses at high soil P concentrations, indicating their increased P limitation. Our results verify the hypothesized effect of P availability on the selection of polyploids and plants with increased genome sizes, although the relative contribution of increased P demands vs increased competitiveness as causes of the observed pattern requires further evaluation.

Insights into the dynamics of genome size and chromosome evolution in the early diverging angiosperm lineage Nymphaeales (water lilies)

Nymphaeales are the most species-rich lineage of the earliest diverging angiosperms known as the ANA grade (Amborellales, Nymphaeales, Austrobaileyales), and they have received considerable attention from morphological, physiological, and ecological perspectives. Although phylogenetic relationships between these three lineages of angiosperms are mainly well resolved, insights at the whole genome level are still limited because of a dearth of information. To address this, genome sizes and chromosome numbers in 34 taxa, comprising 28 species were estimated and analysed together with previously published data to provide an overview of genome size and chromosome diversity in Nymphaeales. Overall, genome sizes were shown to vary 10-fold and chromosome numbers and ploidy levels ranged from 2n = 2x = 18 to 2n = 16x = ∼224. Distinct patterns of genome diversity were apparent, reflecting the differential incidence of polyploidy, changes in repetitive DNA content, and chromosome rearrangements within and between genera. Using model-based approaches, ancestral genome size and basic chromosome numbers were reconstructed to provide insights into the dynamics of genome size and chromosome number evolution. Finally, by combining additional data from Amborellales and Austrobaileyales, a comprehensive overview of genome sizes and chromosome numbers in these early diverging angiosperms is presented.

Timing and consequences of recurrent polyploidy in meadow-rues (thalictrum, ranunculaceae)

The discovery of ancient whole-genome duplications in eukaryotic lineages has renewed the interest in polyploidy and its effects on the diversification of organisms. Polyploidy has large-scale effects on both genotype and phenotype and has been linked to the evolution of genome size, dioecy, and changes in ecological interactions, such as pollinator visitation. Here, we take a molecular systematics approach to examine the evolution of polyploidy in the plant genus Thalictrum (Ranunculaceae) and test its correlation to changes in genome size, sexual system, and pollination mode. Thalictrum is an ideal study system due to its extensive ploidy range and floral diversity. Phylogenetic analyses were used for character reconstructions, correlation tests, and dating estimates. Our results suggest that polyploidization occurred frequently and recently in the evolution of Thalictrum, mostly within the last 10.6-5.8 My, coinciding with the diversification of particular clades. In spite of an overall trend of genomic downsizing accompanying polyploidy in angiosperms and proportional increases observed at finer scales, our genome size estimates for Thalictrum show no correlation with chromosome number. Instead, we observe genomic expansion in diploids and genomic contraction in polyploids with increased age. Additionally, polyploidy is not correlated with dioecy in Thalictrum; therefore, other factors must have influenced the evolution of separate sexes in this group. A novel finding from our study is the association of polyploidy with shifts to wind pollination, in particular, during a time period of global cooling and mountain uplift in the Americas.