One-factor sex determination evolves without linkage between feminizing and masculinizing mutations.

The evolution of separate sexes from cosexuality requires at least two mutations: a feminizing allele to cause female development and a masculinizing allele to cause male development. Classically, the double mutant is assumed to be sterile, which leads to two-factor sex determination where male and female sex chromosomes differ at two loci. However, several species appear to have one-factor sex determination where sexual development depends on variation at a single locus. We show that one-factor sex determination evolves when the double mutant develops as a male or a female. The feminizing allele fixes when the double mutant is male, and the masculinizing allele fixes when the double mutant is female. The other locus then gives XY or ZW sex determination based on dominance: for example, a dominant masculinizer becomes a Y chromosome. Although the resulting sex determination system differs, the conditions required for feminizers and masculinizers to spread are the same as in classical models, with the important difference that the two alleles do not need to be linked. Thus, we reveal alternative pathways for the evolution of sex determination and discuss how they can be distinguished using new data on the genetics of sex determination.

Sexually dimorphic acetyl-CoA biosynthesis and utilization in response to drought and exogenous acetic acid.

Female willows exhibit greater drought tolerance and benefit more from exogenous acetic acid (AA)-improved drought tolerance than males. However, the potential mechanisms driving these sex-specific responses remain unclear. To comprehensively investigate the sexually dimorphic responsive mechanisms of willows to drought and exogenous AA, here, we performed physiological, proteomic, Lys-acetylproteomic, and transgenic analyses in female and male Salix myrtillacea exposed to drought and AA-applicated drought treatments, focusing on protein abundance and lysine acetylation (LysAc) changes. Drought-tolerant females suffered less drought-induced photosynthetic and oxidative damage, did not activate AA and acetyl-CoA biosynthesis, TCA cycle, fatty acid metabolism, and jasmonic acid signaling as strongly as drought-sensitive males. Exogenous AA caused overaccumulation of endogenous AA and inhibition of acetyl-CoA biosynthesis and utilization in males. However, exogenous AA greatly enhanced acetyl-CoA biosynthesis and utilization and further enhanced drought performance of females, possibly determining that AA improved drought tolerance more in females than in males. Interestingly, overexpression of acetyl-CoA synthetase (ACS) could reprogram fatty acids, increase LysAc levels, and improve drought tolerance, highlighting the involvement of ACS-derived acetyl-CoA in drought responses. In addition, drought and exogenous AA induced sexually dimorphic LysAc associated with histones, transcription factors, and metabolic enzymes in willows. Especially, exogenous AA may greatly improve the photosynthetic capacity of S. myrtillacea males by decreasing LysAc levels and increasing the abundances of photosynthetic proteins. While hyperacetylation in glycolysis, TCA cycle, and fatty acid biosynthesis potentially possibly serve as negative feedback to acclimate acetyl-CoA biosynthesis and utilization in drought-stressed males and AA-applicated females. Thus, acetyl-CoA biosynthesis and utilization determine the sexually dimorphic responses of S. myrtillacea to drought and exogenous AA.

Sex-specific phosphorus acquisition strategies and cycling in dioecious Populus euphratica forests along a natural water availability gradient.

Soil phosphorus (P) availability affects plant growth and distribution. However, it is still unknown how sex-specific variation in functional traits affects plants' P acquisition and soil P transformation. On wet sites, female poplars had a greater specific root length (SRL), and a higher diversity of arbuscular mycorrhizal fungi (AMF) and phosphate-solubilizing bacteria (PSB). Male poplars living on wet sites increased the abundance of AMF and PSB communities and enhanced moderately labile and highly resistant organic P mineralisation via increased phosphatase activity. In contrast, on the dry site, the abundance and diversity of AMF and PSB communities increased in females, enhancing moderately labile and highly resistant organic P mineralisation via elevating phosphatase activities. Males maintained greater SRL and promoted Ca-P mobilisation via the release of root carboxylic acids and rhizosphere acidification on the dry site. The AMF community diversity followed a similar pattern as that of the PSB community when altering the P availability of different-sex plants. Our results indicated that organic P and Ca-P are the major sources of plant-available P in natural P. euphratica forests. Seasonal shifts and geographic locations affected the share of organic and inorganic P pools, and AMF and PSB diversities, ultimately altering sex-specific P acquisition strategies of plants.

Two novel PCR-based assays for sexing of Silene latifolia and Silene dioica plants.

Silene latifolia and S. dioica are model systems in studies of plant reproduction, chromosome evolution and sexual dimorphism, but sexing of plants based on morphology is only possible from flowering stage onwards. Both species show homogametic females (XX) and heterogametic males (XY).•Here we developed two assays (primer pairs ss816 and ss441) for molecular sexing of S. latifolia and S. dioica, targeting length polymorphisms between the X and Y-linked copies of the spermidine synthase gene.The two assays were successful in identifying known (flowering-stage) males and females from UK and Spanish populations, with an error rate of 3.1% (ss816; successful for both species) and 0% (ss441, only successful for S. latifolia). Our assays therefore represent novel tools for rapid, robust and simple determination of the genotypic sex of S. latifolia and S. dioica.

Rethinking pathways to the dioecy-polyploidy association: Genera with many dioecious species have fewer polyploids.

PREMISE: Numerous studies have found a positive association between dioecy and polyploidy; however, this association presents a theoretical conflict: While polyploids are predicted to benefit from self-reproduction for successful establishment, dioecious species cannot self-reproduce. We propose a theoretical framework to resolve this apparent conflict. We hypothesize that the inability of dioecious species to self-reproduce hinders their establishment as polyploids. We therefore expect that genera with many dioecious species have fewer polyploids, leading to a negative association between polyploidy and dioecy across genera. METHODS: We used three publicly available databases to determine ploidy and sexual systems for 131 genera and 546 species. We quantified (1) the relationship between the frequency of polyploid species and the frequency of dioecious species across genera, and (2) the proportion of polyploids with hermaphroditism and dioecy across species, adjusting for phylogenetic history. RESULTS: Across genera, we found a negative relationship between the proportion of polyploids and the proportion of dioecious species, a consistent trend across clades. Across all species, we found that sexual system (dioecious or not) was not associated with polyploidy. CONCLUSIONS: Polyploids are rare in genera in which the majority of species are dioecious, consistent with the theory that self-reproduction favors polyploid establishment. The low frequency of polyploidy among dioecious species indicates the association is not as widespread as previously suggested. Our findings are consistent with previous studies identifying a positive relationship between the two traits, but only if polyploidy promotes a transition to dioecy, and not the reverse.

Young evolutionary origins of dioecy in the genus Asparagus.

PREMISE: Dioecy (separate sexes) has independently evolved numerous times across the angiosperm phylogeny and is recently derived in many lineages. However, our understanding is limited regarding the evolutionary mechanisms that drive the origins of dioecy in plants. The recent and repeated evolution of dioecy across angiosperms offers an opportunity to make strong inferences about the ecological, developmental, and molecular factors influencing the evolution of dioecy, and thus sex chromosomes. The genus Asparagus (Asparagaceae) is an emerging model taxon for studying dioecy and sex chromosome evolution, yet estimates for the age and origin of dioecy in the genus are lacking. METHODS: We use plastome sequences and fossil time calibrations in phylogenetic analyses to investigate the age and origin of dioecy in the genus Asparagus. We also review the diversity of sexual systems present across the genus to address contradicting reports in the literature. RESULTS: We estimate that dioecy evolved once or twice approximately 2.78-3.78 million years ago in Asparagus, of which roughly 27% of the species are dioecious and the remaining are hermaphroditic with monoclinous flowers. CONCLUSIONS: Our findings support previous work implicating a young age and the possibility of two origins of dioecy in Asparagus, which appear to be associated with rapid radiations and range expansion out of Africa. Lastly, we speculate that paleoclimatic oscillations throughout northern Africa may have helped set the stage for the origin(s) of dioecy in Asparagus approximately 2.78-3.78 million years ago.

Genomic analyses provide insights into sex differentiation of tetraploid strawberry (Fragaria moupinensis).

The strawberry genus, Fragaria, exhibits a wide range of sexual systems and natural ploidy variation. Nearly, all polyploid strawberry species exhibit separate sexes (dioecy). Research has identified the sex-determining sequences as roughly conserved but with repeatedly changed genomic locations across octoploid strawberries. However, it remains unclear whether tetraploid wild strawberries evolved dioecy independently or shared a common origin with octoploid strawberries. In this study, we investigated the sex determinants of F. moupinensis, a dioecious plant with heterogametic females (ZW). Utilizing a combination of haplotype-resolved genome sequencing of the female F. moupinensis, k-mer-based and coverage-based genome-wide association studies (GWAS), and transcriptomic analysis, we discovered a non-recombining, approximately 33.6 kb W-specific region on chromosome 2a. Within this region, only one candidate sex-determining gene (FmoAFT) was identified. Furthermore, an extensive resequencing of the entire Fragaria genus indicated that the W-specific region displays conservative female specificity across all tetraploid species. This observation suggests that dioecy evolved independently in tetraploid and octoploid strawberries. Moreover, employing virus-induced gene silencing (VIGS), we knocked down the expression of the FmoAFT homologue transcript in cultivated strawberries, revealing its potential role in promoting female functions during early carpel development. We also applied DNA affinity purification sequencing (DAP-seq) and yeast one-hybrid assays to identify potential direct targets of FmoAFT. These insights shed new light on the genetic basis and evolutionary history of sex determination in strawberries, thereby facilitating the formulation of strategies to manipulate sex determination in breeding programs.

Gender specific SNP markers in Coscinium fenestratum (Gaertn.) Colebr. for resource augmentation.

BACKGROUND: Unregulated extraction of highly traded medicinal plant species results in drastic decline of the natural resources and alters viable sex ratio of populations. Conservation and long-term survival of such species, require gender specific restoration programs to ensure reproductive success. However, it is often difficult to differentiate sex of individuals before reaching reproductive maturity. C. fenestratum is one of the medicinally important and overexploited dioecious woody liana, with a reproductive maturity of 15 years. Currently, no information is available to identify sex of C. fenestratum in seedling stage while augmenting the resources. Thus, the current study envisages to utilize transcriptomics approach for gender differentiation which is imperative for undertaking viable resource augmentation programmes. METHODS AND RESULTS: Gender specific SNPs with probable role in sexual reproduction/sex determination was located using comparative transcriptomics approach (sampling male and female individuals), alongside gene ontology and annotation. Nine sets of primers were synthesized from 7 transcripts (involved in sexual reproduction/other biological process) containing multiple SNP variants. Out of the nine primer pairs, only one SNP locus with no available information of its role in reproduction, showed consistent and accurate results (males-heterozygous and females-homozygous), in the analyzed 40 matured individuals of known sexes. Thus validated the efficiency of this SNP marker in differentiating male and female individuals. CONCLUSIONS: The study could identify SNPs linked to the loci with apparent role in gender differentiation. This SNP marker can be used for early sexing of seedlings for in-situ conservation and resource augmentation of C. fenestratum in Kerala, India.

Germinación, crecimiento vegetativo y morfología floral de Dasylirion cedrosanum del matorral rosetófilo de Coahuila / Germination, vegetative growth and floral morphology of Dasylirion cedrosanum from the rosetophyllous scrub of Coahuila

RESUMEN El sotol (Dasylirion cedrosanum Trel.), especie endémica del noreste de México, presenta interés económico y social por su aprovechamiento comercial. El objetivo del presente trabajo fue caracterizar la germinación, crecimiento vegetativo y morfología floral de D. cedrosanum del matorral rosetófilo de Coahuila. Se sometieron 3 lotes de 100 semillas a un proceso de imbibición y se registró el porcentaje de germinación. La caracterización de la germinación se realizó a las plántulas cultivadas en laboratorio, mientras que la morfología vegetativa se determinó en plantas adultas tomadas de un jardín botánico, con fecha de siembra conocida y a las cuales no se les dio un manejo de cultivo. La descripción de la morfología floral se realizó en plantas silvestres del cañón de San Lorenzo, Saltillo, Coahuila, México. La primera fase de la imbibición duró 48 h e incrementó 52 % el peso; la segunda o de latencia duró 48 h alcanzando un 55 %; y la tercera concluyó a las 120 h con un incremento total del 60 % de peso. Las semillas emitieron el hipocótilo a partir del quinto día. En el décimo día se obtuvo 98 % de germinación. Entre las características morfológicas distintivas de la especie, las inflorescencias, conocidas como "escapos florales", registraron una altura promedio de 3.39 m. Las flores fueron actinomorfas y unisexuales. La flor estaminada presentó perianto sin diferenciación de tépalos y sépalos. Las flores pistiladas mostraron pedicelos y receptáculo corto. El polen fue elíptico, de abertura monosulcada, con dimensión de 15 μm x 30 μm. Los frutos fueron secos e indehiscentes, conocidos como samara. Las semillas fueron turbinadas de contorno trigonal. El análisis de las características de germinación y morfología vegetativa y floral del sotol permitieron comprender las adaptaciones que esta planta ha desarrollado para crecer en los ambientes semiáridos del país.

ABSTRACT Sotol (Dasylirion cedrosanum Trel.), endemic species of northeastern Mexico, has attracted economic and social interest due to its commercial potencial. The objective of this work was to characterize the germination, vegetative growth and floral morphology of D. cedrosanum from the rosetophyllous scrub of Coahuila. Three batches of 100 seeds were submitted to an imbibition process and the germination percentage was recorded. The characterization of the germination was carried out on the seedlings grown in the laboratory, while the vegetative morphology was determined in adult plants taken from a botanical garden, with a known planting date and which were not given a crop management. The description of the floral morphology was carried out on wild plants from the San Lorenzo canyon, near the municipality of Saltillo, Coahuila, Mexico. The imbibition showed the first phase of absorption within 48 h, with an increase of 52 % in weight. The third phase began at 96 h with an increase of 55 % in weight. The seeds emitted the hypocotyl from the fifth day. On the tenth day 98 % germination was obtained. Among the distinctive morphological characteristics of the species, the inflorescences, known as "floral scapes", recorded an average height of 3.39 m. The flowers were actinomorphic and unisexual. The staminate flower presented perianth without differentiation of tepals and sepals, while the pistillate flowers showed pedicels and a short receptacle. The pollen was elliptical, with a monosulcate opening, with a dimension of 15 μm x 30 μm. The fruits were dry and indehiscent, known as samara. The seeds were turbinated with a trigonal contour. The germination and characteristics of the sotol corresponded to adaptations that allow it to grow in the semi-arid environment of this region of the country.

A taxonomic revision of Garcinia section Xanthochymus (Clusiaceae) in Thailand.

Garcinia section Xanthochymus (Clusiaceae) is revised for Thailand with four native species, i.e., G. dulcis, G. nervosa, G. prainiana, and G. xanthochymus. All species are described with updated morphological descriptions, illustrations, and an identification key, together with notes on distributions, distribution maps, habitats and ecology, phenology, conservation assessments, etymology, vernacular names, uses, and specimens examined. Four taxa, G. andamanica, G. andamanica var. pubescens, G. cambodgiensis and G. vilersiana, are synonymized under G. dulcis, and two taxa, G. nervosa var. pubescens and G. spectabilis, are newly synonymized under G. nervosa. Nine names are lectotypified: G. dulcis and its associated synonyms (G. cambodgiensis and G. vilersiana), G. nervosa and its associated synonyms (G. andersonii, G. nervosa var. pubescens, and G. spectabilis), G. prainiana, and G. xanthochymus. All species have a conservation assessment of Least Concern (LC). The fruits of all species are edible and have a sour or sweet-sour taste.

Cosexuality Reduces Pollen Production and Fitness in Cannabis sativa L.

Cannabis sativa L. is cultivated globally for its cannabinoid-dense inflorescences. Commercial preference for sinsemilla has led to the development of methods for producing feminized seeds through cross-pollination of cosexual (masculinized) female plants. Although the induction of cosexuality in Cannabis plants is common, to date, no work has empirically tested how masculinization of female Cannabis plants impacts male flowering, pollen production, pollen fitness, and related life-history trade-offs. Here, we cultivated a population of Cannabis plants (CFX-2) and explored how the route to cosexuality (drought vs. chemical induction) impacted flowering phenology, pollen production, and pollen fitness, relative to unsexual male plants. Unisexual males flowered earlier and longer than cosexual plants and produced 223% more total pollen (F2,28 = 74.41, p < 0.001), but per-flower pollen production did not differ across reproductive phenotypes (F2,21 = 0.887, p = 0.427). Pollen viability was 200% higher in unisexual males and drought-induced cosexuals (F2,36 = 189.70, p < 0.001). Pollen non-abortion rates only differed in a marginally significant way across reproductive phenotypes (F2,36 = 3.00, p = 0.06). Here, we demonstrate that masculinization of female plants impacts whole-plant pollen production and pollen fitness in Cannabis sativa.

Influence of sexual dimorphism and dichromatism on reproductive success in a rare native cactus.

Identifying plant sexual dimorphic traits is critical in advancing our knowledge on plant-pollinator interactions. For example, dimorphism in floral colors, or sexual dichromatism, is a crucial mediator of pollinator choice on foraging decisions. We studied Cylindropuntia wolfii, a model system, with diverse flower colors and a functionally dioecious sexual system. However, evidence suggests that sexual reproduction is limited in this species as it has a low seed set especially in naturally pollinated fruits. Thus, it is critical to this native species' conservation to investigate its relationship with pollinators. Our goals were to: (a) investigate the sexual dimorphism including the sexual dichromatism in the flowers of the cactus, and (b) determine whether sexually dimorphic traits affect the pollinator attraction of both the sexes. We measured several quantitative and qualitative traits and compared them between male and female flowers. Then we recorded the pollinator visitation rate in nature for both sexes and tracked pollinator color preference using fluorescent dyes as pollen analogues. Our study showed that male flowers of C. wolfii are bigger and brighter, and they attract more potential pollinators than females, supporting the hypothesis that sexual dimorphism influences pollinator visitation preference. Fluorescence dichromatism, in which female flowers' anthers fluoresce more than male flower anthers suggest this could be female flowers' strategy to compensate for their dark colors and small size. The results from this study showed that C. wolfii exhibits sexual dichromatism and fluorescence dichromatism, which is a novel finding in plant research.

Functional analysis of Salix purpurea genes support roles for ARR17 and GATA15 as master regulators of sex determination.

The Salicaceae family is of growing interest in the study of dioecy in plants because the sex determination region (SDR) has been shown to be highly dynamic, with differing locations and heterogametic systems between species. Without the ability to transform and regenerate Salix in tissue culture, previous studies investigating the mechanisms regulating sex in the genus Salix have been limited to genome resequencing and differential gene expression, which are mostly descriptive in nature, and functional validation of candidate sex determination genes has not yet been conducted. Here, we used Arabidopsis to functionally characterize a suite of previously identified candidate genes involved in sex determination and sex dimorphism in the bioenergy shrub willow Salix purpurea. Six candidate master regulator genes for sex determination were heterologously expressed in Arabidopsis, followed by floral proteome analysis. In addition, 11 transcription factors with predicted roles in mediating sex dimorphism downstream of the SDR were tested using DAP-Seq in both male and female S. purpurea DNA. The results of this study provide further evidence to support models for the roles of ARR17 and GATA15 as master regulator genes of sex determination in S. purpurea, contributing to a regulatory system that is notably different from that of its sister genus Populus. Evidence was also obtained for the roles of two transcription factors, an AP2/ERF family gene and a homeodomain-like transcription factor, in downstream regulation of sex dimorphism.

Allelochemicals and soil microorganisms jointly mediate sex-specific belowground interactions in dioecious Populus cathayana.

Little is known about how sex differences in root zone characteristics, such as contents of allelochemicals and soil microbial composition, mediate intra- and intersexual interactions in dioecious plants. We examined the processes and mechanisms of sex-specific belowground interactions mediated by allelochemicals and soil microorganisms in Populus cathayana females and males in replicated 30-yr-old experimental stands in situ and in a series of controlled experiments. Female roots released a greater amount and more diverse phenolic allelochemicals into the soil environment, resulting in growth inhibition of the same sex neighbors and deterioration of the community of soil microorganisms. When grown with males, the growth of females was consistently enhanced, especially the root growth. Compared with female monocultures, the presence of males reduced the total phenolic accumulation in the soil, resulting in a shift from allelopathic inhibition to chemical facilitation. This association was enhanced by a favorable soil bacterial community and increased bacterial diversity, and it induced changes in the orientation of female roots. Our study highlighted a novel mechanism that enhances female performance by males through alterations in the allelochemical content and soil microbial composition. The possibility to improve productivity by chemical mediation provides novel opportunities for managing plantations of dioecious plants.

Comparative floral development in male and female plants of Palmer amaranth (Amaranthus palmeri).

PREMISE: Characterizing the developmental processes in the transition from hermaphroditism to unisexuality is crucial for understanding floral evolution. Amaranthus palmeri, one of the most devastating weeds in the United States, is an emerging model system for studying a dioecious breeding system and understanding the biological traits of this invasive weed. The objectives of this study were to characterize phases of flower development in A. palmeri and compare organogenesis of flower development in female and male plants. METHODS: Flower buds from male and female plants were dissected for light microscopy. Segments of male and female inflorescences at different stages of development were cut longitudinally and visualized using scanning electron microscopy. RESULTS: Pistillate flowers have two to three styles, one ovary with one ovule, and five obtuse tepals. Staminate flowers have five stamens with five acute tepals. Floral development was classified into 10 stages. The distinction between the two flower types became apparent at stage four by the formation of stamen primordia in staminate flowers, which developed female and male reproductive organs initially, as contrasted to pistillate flowers, which produced carpel primordia only. In staminate flowers, the putative carpel primordia changed little in size and remained undeveloped. CONCLUSIONS: Timing of inappropriate organ termination varies across the two sexes in A. palmeri. Our study suggests that the evolution of A. palmeri from a cosexual ancestral state to complete dioecy is still in progress since males exhibited transient hermaphroditism and females produced strictly pistillate flowers.

Evolution of sex in crops: recurrent scrap and rebuild.

Sexuality is the main strategy for maintaining genetic diversity within a species. In flowering plants (angiosperms), sexuality is derived from ancestral hermaphroditism and multiple sexualities can be expressed in an individual. The mechanisms conferring chromosomal sex determination in plants (or dioecy) have been studied for over a century by both biologists and agricultural scientists, given the importance of this field for crop cultivation and breeding. Despite extensive research, the sex determining gene(s) in plants had not been identified until recently. In this review, we dissect plant sex evolution and determining systems, with a focus on crop species. We introduced classic studies with theoretical, genetic, and cytogenic approaches, as well as more recent research using advanced molecular and genomic techniques. Plants have undergone very frequent transitions into, and out of, dioecy. Although only a few sex determinants have been identified in plants, an integrative viewpoint on their evolutionary trends suggests that recurrent neofunctionalization events are potentially common, in a "scrap and (re)build" cycle. We also discuss the potential association between crop domestication and transitions in sexual systems. We focus on the contribution of duplication events, which are particularly frequent in plant taxa, as a trigger for the creation of new sexual systems.

Comparative transcriptomic analysis of male and females in the dioecious weeds Amaranthus palmeri and Amaranthus tuberculatus.

BACKGROUND: Waterhemp (Amaranthus tuberculatus (Moq.) Sauer) and Palmer amaranth (Amaranthus palmeri S. Wats.) are two dioecious and important weed species in the world that can rapidly evolve herbicide-resistance traits. Understanding these two species' dioecious and sex-determination mechanisms could open opportunities for new tools to control them. This study aims to identify the differential expression patterns between males and females in A. tuberculatus and A. palmeri. Multiple analyses, including differential expression, co-expression, and promoter analyses, used RNA-seq data from multiple tissue types to identify putative essential genes for sex determination in both dioecious species. RESULTS: Genes were identified as potential key players for sex determination in A. palmeri. Genes PPR247, WEX, and ACD6 were differentially expressed between the sexes and located at scaffold 20 within or near the male-specific Y (MSY) region. Multiple genes involved with flower development were co-expressed with these three genes. For A. tuberculatus, no differentially expressed gene was identified within the MSY region; however, multiple autosomal class B and C genes were identified as differentially expressed and possible candidate genes. CONCLUSIONS: This is the first study comparing the global expression profile between males and females in dioecious weedy Amaranthus species. Results narrow down putative essential genes for sex-determination in A. palmeri and A. tuberculatus and also strengthen the hypothesis of two different evolutionary events for dioecy within the genus.

A Foundational Population Genetics Investigation of the Sexual Systems of Solanum (Solanaceae) in the Australian Monsoon Tropics Suggests Dioecious Taxa May Benefit from Increased Genetic Admixture via Obligate Outcrossing.

Solanum section Leptostemonum is an ideal lineage to test the theoretical framework regarding proposed evolutionary benefits of outcrossing sexual systems in comparison to cosexuality. Theoretically, non-cosexual taxa should support more genetic diversity within populations, experience less inbreeding, and have less genetic structure due to a restricted ability to self-fertilize. However, many confounding factors present challenges for a confident inference that inherent differences in sexual systems influence observed genetic patterns among populations. This study provides a foundational baseline of the population genetics of several species of different sexual systems with the aim of generating hypotheses of any factor-including sexual system-that influences genetic patterns. Importantly, results indicate that dioecious S. asymmetriphyllum maintains less genetic structure and greater admixture among populations than cosexual S. raphiotes at the same three locations where they co-occur. This suggests that when certain conditions are met, the evolution of dioecy may have proceeded as a means to avoid genetic consequences of self-compatibility and may support hypotheses of benefits gained through differential resource allocation partitioned across sexes. Arguably, the most significant finding of this study is that all taxa are strongly inbred, possibly reflective of a shared response to recent climate shifts, such as the increased frequency and intensity of the region's fire regime.

Genomic data provide a robust phylogeny backbone for Rhodiola L. (Crassulaceae) and reveal extensive reticulate evolution during its rapid radiation.

The Tibetan Plateau and adjacent mountain regions (TP; including the Tibetan Plateau, Himalaya, Hengduan Mountains and Mountains of Central Asia) harbor great biodiversity, some lineages on which may have undergone rapid radiations. However, only a few studies have investigated the evolutionary pattern of such diversification in depth using genomic data. In this study, we reconstructed a robust phylogeny backbone of Rhodiola, a lineage that may have undergone rapid radiation in the TP, using Genotyping-by-sequencing data, and conducted a series of gene flow and diversification analyses. The concatenation and coalescent-based methods yield similar tree topologies, and five well-supported clades were revealed. Potential gene flow and introgression events were detected, both between species from different major clades and closely related species, suggesting pervasive hybridization and introgression. An initial rapid and later slowdown of the diversification rate was revealed, indicating niche filling. Molecular dating and correlation analyses showed that the uplift of TP and global cooling in the mid-Miocene might have played an important role in promoting the rapid radiation of Rhodiola. Our work demonstrates that gene flow and introgression might be an important contributor to rapid radiation possibly by quickly reassembling old genetic variation into new combinations.