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Flowers of Meliaceae are traditionally described as bisexual, but functionally unisexual flowers have been reported for many genera. For Trichilia, several reproductive systems have been previously reported: subdioecy, gynodioecy, polygamy and hermaphroditism. The aim of this study was to analyze the occurrence of floral dimorphism and sexual-functional aspects of the flower of Trichilia claussenii. Structural and developmental analyses of flowers of Trichilia claussenii were performed using light and electron microscopy. In addition, male and female function of flowers was investigated through pollen viability and stigma receptivity tests, hand pollination and seed germination. Two floral morphotypes were identified in Trichilia claussenii: one morphologically male with a reduced gynoecium and the other morphologically female with anthers which do not release pollen. In the supposedly male flower, anthers are well developed and produce viable pollen grains. A conspicuous nectary disk differentiates at the base of the gynoecium, and the ovary has small ovules; however, our study proved that this ovary develops into a fruit, which contains viable seeds. In contrast, the supposedly female flower has larger gynoecium and ovules, and the nectary is smaller and inconspicuous. The stamens of female flowers have inviable pollen grains due to a tapetal necrotic product that keeps them united into an amorphous mass within the anthers. Male flowers are geitonogamous. Our results demonstrate that Trichilia claussenii exhibits subtle sexual floral dimorphism with female flowers and bisexual flowers distributed in different individuals. Our results indicate that male sterility occurs in only one morphotype; therefore, the species is gynodioecious.

Premise of research. Whole-genome duplication is often associated with the evolution of dimorphic sexual systems; however, the association is not universal, and the evolutionary pathway(s) underlyi...

Background and Aims Most angiosperms rely on pollinators to transport pollen and effect fertilization. While some floral visitors are effective pollinators, others act as thieves, consuming pollen but effecting little pollination in return. The importance of pollen theft in male and female reproductive success has received little attention. Here, we examined if pollen consumption by flies altered pollen receipt and exacerbated pollen limitation for a bumblebee-pollinated plant, Polemonium foliosissimum (Polemoniaceae). Methods To examine the effect of pollen-thieving flies, we took a three-pronged approach. First, we used single-visit observations to quantify pollen removal and pollen deposition by flies and bumblebees. Second, we manipulated pollen in the neighbourhood around focal plants in two years to test whether pollen reduction reduced pollen receipt. Third, we combined pollen reduction with hand-pollination to test whether pollen thieving exacerbated pollen limitation. Polemonium foliosissimum is gynodioecious in most populations in the Elk Mountains of central Colorado, USA. Thus, we also tested whether pollen theft affected hermaphrodites and females differently. Results Flies removed significantly more pollen and deposited less pollen per visit than did bumblebees. Reduction of pollen in the neighbourhood around focal plants reduced pollen receipt in both years but only nearly significantly so in 2015. In 2016, plants were significantly pollen-limited; hand-pollination significantly increased seeds per fruit for both hermaphrodites and females. However, the reduction of pollen around focal plants did not exacerbate pollen limitation for either hermaphrodites or females. Conclusions Our results suggest that plants tolerate significant consumption of pollen by thieves and pollinators by producing ample pollen to feed both and fertilize available ovules. Our results demonstrate that pollen limitation in P. foliosissimum is driven by lack of effective pollinators rather than lack of pollen. Teasing out these effects elucidates the relative importance of drivers of reproductive success and thus the expected response to selection by different floral visitors.

Generalized pollination systems may be favored in early spring flowering plants, as during this period pollinator activity is unpredictable. Many previous studies have concentrated on the importance of diurnal visitors in pollination, and consequently, information on the contribution of nocturnal visitors to pollination in early spring is limited. This study was conducted to evaluate the relative importance of diurnal and nocturnal pollinators in the early spring flowering dioecious shrub Stachyurus praecox (Stachyuraceae), in two temperate forests in central Japan. Visitors to the female and male flowers were observed during day and night, and their relative contributions to seed set were compared. The pollinator observations revealed that the diurnal and nocturnal insects visited both male and female flowers, and that the main flower visitors were diurnal small bees and flies as well as nocturnal settling moths. The diurnal and nocturnal flower visitors also acted as pollinators, as the pollen grains of S. praecox were attached to the insects collected from the female flowers. Pollination experiments demonstrated that the contributions of diurnal pollinators to the seed set were higher than those of the nocturnal pollinators. The results of this study indicate that S. praecox has a generalized pollination system, comprising both diurnal insects and nocturnal settling moths. Although the roles of diurnal insects are more important in the pollination of S. praecox, nocturnal settling moths may have a complementary role in early spring.

Thyme (Thymus spp.) is a valuable genus of Lamiaceae family presents a wide range of functional possibilities in the cosmetic, pharmacy, and food industries. T. daenensis and T. pubescens are thymol and carvacrol rich species growing in Iran. The aim of this study was to compare the macro- and micro-morphological, cytogenetical, and biochemical traits present in hermaphrodites and females of T. daenensis and T. pubescens. The analyses were performed by light microscopy (LM) to be compatible with scanning electron microscope (SEM) and gas chromatograph–mass spectrometry (GC–MS). The principal component analysis (PCA) loading plot was carried out using the original numerical data of quantitative characters (e.g., morphological, functional, and life-history traits). Results of gynodioecy analysis showed that the distribution of females in T. daenensis (58.33%) was significantly more than T. pubescens (9.1%). Peltate and capitate glandular trichomes (PGTs and CGTs, respectively) existed in both hermaphrodites and females of T. daenensis and T. pubescens. The size of PGTs in hermaphrodites was significantly larger than these GTs in females. The highest level of thymol and carvacrol was observed in both sexes of T. daenensis and T. pubescens, respectively. The results of the non-metric multidimensional scaling (NMDS) ordination showed separation of hermaphrodite and female types according to essential oil (EO) components. Based on the flow cytometric analysis, the obtained histograms confirmed that T. pubescens and T. daenensis were diploid and tetraploid, respectively. Variation among species and environmental/geographical factors result is differences in the content of thymol and carvacrol in various Thymus species which should be taken into consideration when applying these plants as therapeutic products.

Toji, Tsubasa, Itino, Takao (2021): Differences in the flower visitor behaviour on female and hermaphroditic flowers of Cimicifuga simplex. Journal of Natural History 55 (19-20): 1289-1298, DOI: 10.1080/00222933.2021.1946611, URL: http://dx.doi.org/10.1080/00222933.2021.1946611

In gynodioecious systems, female plants must counteract the selective disadvantage of not passing genes via pollen production, as hermaphrodites can. Theory predicts that females must produce more or better-quality seeds than hermaphrodites in order to be maintained within the same population. This female advantage has been widely measured and reported for seed number, but whether female advantage is gained through the production of better seeds remains relatively under-studied. Here, a meta-analysis approach was used to investigate whether females in gynodioecious species produce seeds of better quality than hermaphrodites (measured as seed mass, seed nutrient content, seed germinability and seedling survival and performance) in addition to achieving a larger seed production. In total, 50 studies were included, reporting traits for 34 gynodioecious species in 17 different families. Female advantage was significant for seed number and seed germination, but was not detected for seed mass, seed nutrient content or seedling performance. A female advantage in seed number was corroborated in this meta-analysis, which together with better seed germination, may explain maintenance of female plants within gynodioecious populations.

Background Gynodioecy, a sexual system with hermaphrodite and female individuals in a population, raises the question how the two sexual morphs are maintained. Salvia pratensis is a gynodioecious species featured by its modified stamens that act as a lever mechanism in pollination. Given sexual dimorphism in floral traits of the species, it is predictable that two sexual morphs differ in their interplay with pollinators and thus in their fitness. In this study, we investigated sex-specific reproduction success and floral adaptation in a population of S. pratensis. Results We found that two sexual morphs in S. pratensis distinctly differed in their floral proportions. Female flowers fitted better to the pollinators than hermaphrodites in terms of touching the stigmas when being probed, and hence were more efficient in pollen deposition. Floral traits overall underwent stronger selection in the population, with stigma position and corolla length subject to disruptive selection mediated by different body-sized bumble bees; some selections on floral traits were significantly different in the strength, even opposite in the direction between two morphs. Flower production tended to be under correlational selection with floral structural traits, implying that a large plant with many flowers did not show an advantage in fitness unless its flower construction mechanically matched the pollinators well. Conclusions In conclusion, the pollinator-mediated selection likely played an important role in the evolution and maintenance of sexual dimorphism in the gynodioecious S. pratensis; and sex-divergent mechanical interaction with pollinators served as a critical mechanism by which female individuals were maintained in the population with a female advantage in pollen deposition efficiency (i.e. receiving pollen).

Minthostachys (Benth.) Spach (Lamiaceae) is one of the most important genus in Andean folk medicine. Minthostachys species are harvested in the wild rather than cultivated. Beyond the key socio-cultural role of these species, there have been no studies to evaluate their reproductive requirements as part of their conservation. M. verticillata is a gynodioecious species endemic from Argentina, whose populations are threatened because of overexploitation and habitat loss. The level of reproductive dependence on animal pollination, the diversity and composition of floral visitors’ assemblages, flower morphology, fruit and seed set and the progeny vigour of female and hermaphrodite plants were evaluated. Both sex morphs rely absolutely on animal pollination for seed production and were visited by a similar and diverse assemblage of insects (Diptera, Lepidoptera and Hymenoptera); however, the tachinind fly Ptilodexia cf. cingulipes was the main pollinator. Female plants have smaller flowers, higher fruit set, fruits with more seeds, and a higher percentage of seed germination than hermaphrodites. There were no differences in growth rate and biomass of seedlings produced by female and hermaphrodite plants. Lower reproductive success of hermaphrodites could be due to self-incompatibility or inbreeding depression. These results suggest that it is a fragile system where hermaphrodite plants perform mainly as pollen donors, females as seed producers, and seed production relies almost exclusively on a native tachinid species, which is furthermore parasitoid. This knowledge can be applied in conservation programs in order to promote the sexual reproduction and so the conservation in situ of this key medicinal resource. Fil: Glinos, Evangelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina Fil: Condat, María Eugenia. Universidad Nacional de Córdoba; Argentina Fil: Mulieri, Pablo Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Ashworth, Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina. Universidad Nacional Autónoma de México; México

Many Arctic plants overcome limited time budgets and energy budgets by selfing, increasing the risk of inbreeding. Gynodioecious breeding systems allows for selfing by hermaphrodites, whereas enforced outcrossing through females lowers risk of inbreeding. Females persist due to female advantage in the system. Using the gynodioecious species Silene acaulis (L.) Jacq., we compared establishment performance and female frequency in 17 populations in open, sparsely vegetated habitats versus closed, denser vegetated habitats, across a regional climate gradient in high-Arctic Svalbard. For two populations, genetics were performed using microsatellites to compare inbreeding levels between habitats. As S. acaulis is a pioneer species, we expected denser vegetation to represent more competitive environments, reducing establishment performance and increasing female frequency due to female advantage. We expected similar responses to harsher regional climate. Establishment performance was reduced in closed habitats and harsher climate, but female frequency was slightly lower in closed habitats and did not differ between regional climates. High inbreeding levels may indicate that female advantage is counteracted by pollen limitation. However, female frequency increased with latitude. Lower sun angle at higher latitudes reduce the heat-trap effect of the cushion growth form, and female advantage might be expressed as response to reduced microclimate amelioration.

Background: Sex determination in cyto-nuclear gynodioecious plants (those with females and hermaphrodites) is complex, with maternally inherited mitochondrial genes (CMS factors) causing ma...

Cortaderia selloana is an invasive, gynodioecious species prevalent in Mediterranean area which contains both female and hermaphrodite specimens in the wild population. Using voltammetric data we show that the female and hermaphrodite specimens exhibit differential electrochemical response. Cortaderia selloana leaves from two different provenances in the Valencia Mediterranean area, Sueca and Cullera (Comunitat Valenciana, Spain), in the surroundings of the Albufera Natural Park, a peculiar ecosystem containing unspoilt dune beaches and forests, were studied to determine correlation of flower morphology with the plant's ability to adapt to stress conditions. Our data suggests that gynodioecy may contribute to increasing versatility in the plant under stress by efficiently neutralizing reactive oxygen species (ROS). Keywords: Electrochemistry, Invasive species, Cortaderia, Gynodioecy, Reactive oxygen species

Plant speciation results from intricate processes such as polyploidization, reproductive strategy shifts and adaptation. These evolutionary processes often co-occur, blurring their respective contributions and interactions in the speciation continuum. Here, relying on a large-scale study, we tested whether gynodioecy triggers the divergent evolution of flower morphology and genome between sexes, and contributes to the establishment of polyploids and colonization of ecological niches in Stellaria graminea. We found that gynodioecy in S. graminea leads to flower morphology divergence between females and hermaphrodites, likely due to sexual selection. Contrary to our expectations, gynodioecy occurs evenly in diploids and tetraploids, suggesting that this reproductive strategy was not involved in the establishment of polyploids. Both diploid and tetraploid females have a larger genome size than hermaphrodites, suggesting the presence of sex chromosomes. Finally, ecology differs between cytotypes and to a lesser extent between sexes, suggesting that the link between environment and presence of females is indirect and likely explained by other aspects of the species’ life history. Our study shows that gynodioecy leads to the consistent evolution of sexual traits across a wide range of populations, cytotypes and environments within a given species, and this likely contributes to the phenotypic and genetic distinctiveness of the species from its sister clades.

Female flowers of gynodioecious plants usually have smaller corollas than bisexual flowers. This difference is explained as a developmental consequence of stamen abortion and as a result of stronger selection for larger corolla size in hermaphroditic flowers that solely ensure male function within populations. This study evaluated whether the size difference of zygomorphic corollas in a widely distributed gynodioecious herb Glechoma hederacea is accompanied by variation in shape and bilateral fluctuating asymmetry of sexually differentiated flowers. Geometric morphometric analyses of bilateral symmetry in the shapes of corolla lower lips showed that male-sterile flowers were significantly more plastic and asymmetric, implying that they may be subjected to weaker stabilizing selection for corolla shape in comparison to hermaphrodites. These results illustrated that sexual differentiation may be an important factor contributing to bilateral fluctuating asymmetry in the shape of zygomorphic flowers., Gynodioecy is dimorphic sexual system where female and hermaphrodite flowers are borne on different individuals. We used geometric morphometrics of bilateral symmetry in corolla shapes of gynodioecious Glechoma hederacea (Lamiaceae) to test for the differences in shape plasticity and fluctuating asymmetry between the sexually differentiated flowers. The analyses showed that male-sterile flowers were significantly more plastic and asymmetric, implying that they may be subjected to weaker stabilizing selection for corolla shape in comparison to hermaphrodites. These results illustrated that sexual differentiation may be an important factor contributing to bilateral fluctuating asymmetry in the shape of zygomorphic flowers.

The diversity of inflorescences among flowering plants is captivating. Such charm is not only due to the variety of sizes, shapes, colors, and flowers displayed, but also to the range of reproductive systems. For instance, hermaphrodites occur abundantly throughout the plant kingdom with both stamens and carpels within the same flower. Nevertheless, 10% of flowering plants have separate unisexual flowers, either in different locations of the same individual (monoecy) or on different individuals (dioecy). Despite their rarity, dioecious plants provide an excellent opportunity to investigate the mechanisms involved in sex expression and the evolution of sex-determining regions (SDRs) and sex chromosomes. The SDRs and the evolution of dioecy have been studied in many species ranging from Ginkgo to important fruit crops. Some of these studies, for example in asparagus or kiwifruit, identified two sex-determining genes within the non-recombining SDR and may thus be consistent with the classical model for the evolution of dioecy from hermaphroditism via gynodioecy, that predicts two successive mutations, the first one affecting male and the second one female function, becoming linked in a region of suppressed recombination. On the other hand, aided by genome sequencing and gene editing, single factor sex determination has emerged in other species, such as persimmon or poplar. Despite the diversity of sex-determining mechanisms, a tentative comparative analysis of the known sex-determining genes and candidates in different species suggests that similar genes and pathways may be employed repeatedly for the evolution of dioecy. The cytokinin signaling pathway appears important for sex determination in several species regardless of the underlying genetic system. Additionally, tapetum-related genes often seem to act as male-promoting factors when sex is determined via two genes. We present a unified model that synthesizes the genetic networks of sex determination in monoecious and dioecious plants and will support the generation of hypothesis regarding candidate sex determinants in future studies.

Prunella vulgaris is a gynodioecious species that forms two types of flowers, perfect and female, on different plants. These two sexual types of flowers have significant differences in some characters of calyx, corolla, androecium, and gynoecium. The distinctiveness of gynodioecy in P. vulgaris consists in insignificant size differences in anthers, the formation of sterile pollen in female flowers, and the shape of a corolla in two sexual types of flowers. Hermaphrodite plants are dominated in P. vulgaris (59.8 to 87 percent). In flood plain meadows, the proportion of females is significantly higher (from 25.9 to 40.2 percent) than in dry and forest meadows (from 13 to 19.1 percent).

Cytoplasmic male sterility (CMS), encoded by the interacting mitochondrial and nuclear genes, causes pollen abortion or non-viability. CMS is widely used in agriculture and extensively studied in crops. Much less is known about CMS in wild species. We performed a comparative transcriptomic analysis of male sterile and fertile individuals of Silene vulgaris, a model plant for the study of gynodioecy, to reveal the genes responsible for pollen abortion in this species. We used RNA-seq datasets previously employed for the analysis of mitochondrial and plastid transcriptomes of female and hermaphrodite flower buds, making it possible to compare the transcriptomes derived from three genomes in the same RNA specimen. We assembled de novo transcriptomes for two haplotypes of S. vulgaris and identified differentially expressed genes between the females and hermaphrodites, associated with stress response or pollen development. The gene for alternative oxidase was downregulated in females. The genetic pathways controlling CMS in S. vulgaris are similar to those in crops. The high number of the differentially expressed nuclear genes contrasts with the uniformity of organellar transcriptomes across genders, which suggests these pathways are evolutionarily conserved and that selective mechanisms may shield organellar transcription against changes in the cytoplasmic transcriptome.

Background. In gynodioecious species, populations of two types of individuals are found – bisexual and female. The morphological and biological characteristics of these two morphs are different. A. reptans is an example of a gynodioecious species. However, information about the flowering biology of both its sexual forms is extremely fragmented. The aim of our research is to study the flowering of A. reptans’ bisexual and female morphs in the Moscow region. Materials and methods. Anthecological observations were made in natural conditions in the Moscow region from 2015 to 2019 according to generally accepted methods. Results. The floral unit of A. reptans is the apical open bracteose thyrsus, which has constituent elements of 3 or 5 flower cymoids. In lateral dichasium, the flower opens acropetally; in the thyrsus, flowers on the axis bloom almost simultaneously. Bisexual flowers of A. reptans are characterized by a weak protandry. Bisexual and pistillate flowers have a long lifespan, surviving for 12–13 days without pollination. A. reptans is characterized by a daily flowering rhythm, with two maximums at 9 a.m and 12 a.m. Bisexual and pistillate flowers open simultaneously. Conclusions. A number of anthecological characters of A. reptans demonstrate that it flowers in spring: the lack of a clear acropetal sequence in the order of flowers blooming in a thyrsus, the long lifespan of both bisexual and pistillate flowers, the opening of flowers during almost all daylight hours, and a fairly short flowering period, due to the need for development in a strictly defined period of vegetation.

The high occurrence of dioecy on oceanic islands has attracted much attention from plant evolutionary biologists. Tournefortia argentea (Boraginaceae), an Indo-Pacific strand plant, has an unusual sexual system which remains poorly understood. Here, we investigated the sexual system of T. argentea based on morphological and micromorphological studies, as well as manipulated pollination treatments. Two morphs of plants were found in the natural populations on Xisha Islands: hermaphrodite and female plants. Each sexual morph exhibited different floral traits, showing a modest form of sexual dimorphism. Flowers of hermaphrodites display significantly larger size in corolla and anther than those of females. Fruit sets under natural condition and hand pollination in hermaphroditic individuals were both far lower than that of female ones, which shows characteristics of both leaky dioecy and gynodioecy. We investigated how these differences in floral traits between females and hermaphrodites affect the choice of pollinators. Although females and hermaphroditic flowers in T. argentea attracted the same assemblage of pollinator species, including Apidae, Syrphidae and Utetheisa lotrix (Arctiidae), the reduction in allocation to pollinator-attracting structures (corolla) and rewarding products caused a significant reduction in Apidae visitation to female flowers. Accordingly, T. argentea is another example of a gynodioecious species of flowering plants in Boraginaceae with clear sexual dimorphism occurring in oceanic islands. The sexual system in T. argentea may imply a transitional stage in the evolution to dioecy and may have been favored during colonization to newly reclaimed habitats, where mating partners may be limited.

Hepatica maxima is native to Ulleungdo, which is one of the oceanic islands in Korea, and it likely originated via anagenetic speciation from the Korean mainland species H. asiatica. However, the relationships among the Asian lineages remain unresolved. Phylogenomics based on plant genomes can provide new insights into the evolutionary history of plants. We first generated plastid, mitochondrial and transcriptome sequences of the insular endemic species H. maxima. Using the genomic data for H. maxima, we obtained a phylogenomic dataset consisting of 76 plastid, 37 mitochondrial and 413 nuclear genes from Asian Hepatica and two outgroups. Coalescent- and concatenation-based methods revealed cytonuclear and organellar discordance in the lineage. The presence of gynodioecy with cytoplasmic male sterility in Asian Hepatica suggests that the discordance is correlated with potential disruption of linkage disequilibrium between the organellar genomes. Species network analyses revealed a deep history of hybridization and introgression in Asian Hepatica. We discovered that ancient and recent introgression events occurred throughout the evolutionary history of the insular endemic species H. maxima. The introgression may serve as an important source of genetic variation to facilitate adaptation to the Ulleungdo environment.

Trioecy, the co-occurrence of males, females and hermaphrodites in natural populations, is a relatively common sexual system in plants, but is rare and poorly understood in animals. Previously, the marine mussel, Semimytilus algosus, has been described as a simultaneous hermaphrodite and there are reports of unisex animals in the wild. Here, we confirm trioecy in this bivalve, the first report of trioecy in the phylum Mollusca. We examined the frequencies of females, males and hermaphrodites in seven natural populations along a latitudinal gradient of ∼2500 km and carried out a phylogenetic analysis with mussel species of the family Mytilidae with known sexual systems. Hermaphrodites (∼95.3%), females (∼3.6%), and males (∼1.1%) were found in all seven populations across the species’ range in Chile. The consistent sex ratios across all populations suggest that the sexual system is stable in space. Phylogenetic analysis (mtDNA) of members of the family Mytilidae indicates that this species alone has developed trioecy from dioecious ancestors. As unisex animals were the least common in the wild, it is likely that these animals, especially males, might be in the process of being lost in this species, and that trioecy might be an intermediate step towards gynodioecy or hermaphroditism. The reproductive characteristics of S. algosus make it an excellent model species for the study of the evolution of sexual systems in animals and also possibly the processes underlying sex determination in molluscs.

Spontaneous fertility reversion has been documented in cytoplasmic male sterile (CMS) plants of several species, influenced in frequency by nuclear genetic background. In this study, we found that MutS HOMOLOG1 (MSH1) mediates fertility reversion via substoichiometric shifting (SSS) of the CMS-associated mitochondrial Open Reading Frame 220 (ORF220), a process that may be regulated by pollination signalling in Brassica juncea. We show that plants adjust their growth and development in response to unsuccessful pollination. Measurable decrease in MSH1 transcript levels and evidence of ORF220 SSS under non-pollination conditions suggest that this nuclear-mitochondrial interplay influences fertility reversion in CMS plants in response to physiological signals. Suppression of MSH1 expression induced higher frequency SSS in CMS plants than occurs normally. Transcriptional analysis of floral buds under pollination and non-pollination conditions, and the response of MSH1 expression to different sugars, supports the hypothesis that carbon flux is involved in the pollination signalling of fertility reversion in CMS plants. Our findings suggest that facultative gynodioecy as a reproductive strategy may incorporate environmentally responsive genes like MSH1 as an "on-off" switch for sterility-fertility transition under ecological conditions of reproductive isolation.

Gynodioecy is typically associated with a smaller perianth size in purely pistillate flowers than in hermaphrodite flowers. However, it is unclear whether this size differentiation is associated with any differences in flower shape between the two sexual groups. A geometric morphometric analysis of the symmetry of tetrameric corolla shapes was used in the study ofEuonymus europaeusL., Darwin’s classical system of floral sexual differentiation. I investigated whether there are any shape differences between the female and bisexual flowers, with respect to both purely symmetric variation involving coordinated shape changes of the four petals and asymmetry among petals within flowers. The corolla shapes of the female and bisexual flowers and the variability among flowers within each sexual group were very similar in the purely symmetric components of shape variation. However, the female flowers were significantly more asymmetric with respect to both the lateral and transversal asymmetry of their corolla shapes. This is the first study to apply geometric morphometrics in the analysis of morphological patterns in a sexually differentiated gynodioecious plant system. The results showed that subtle shape differences in corolla asymmetry differ between the sexual groups and indicate diverging developmental or selection signals between the sexes.

Marjoram (Origanum majorana L.) is an aromatic plant of the same genus as oregano, but with a completely different flavour, characterized by the ‘marjoramy’ monoterpenes cis- and trans-sabinene hydrate as well as terpinen-4-ol, an artefact arising from the two compounds mentioned before. Marjoram has also an undesired compound (arbutin). However, minimizing this compound has not a breeding aim so far. Origanum is a gynodioecious genus, often with female (male-sterile) and hermaphrodite flowers in a population. In marjoram, a stable cytoplasmic male sterility was identified and developed into a hybrid system.

Rosemary, a well-known Mediterranean aromatic evergreen, up to 3-m-high perennial shrub, is widely cultivated since ancient times for medicinal, culinary and ornamental purposes. The Mediterranean genus Rosmarinus L. (Lamiaceae) includes three species; among them the most common and most widely distributed is Rosmarinus officinalis L. “The dew of the sea” (the meaning of rosemary) with small white, pink to bluish hermaphrodite flowers can grow and reproduce under diverse climate and soil conditions. It can be found in an abundant morphological and biochemical variation (e.g. growth habit, leaf size, flower size and colour, volatile compounds). This variation can be explained by high phenotypic plasticity and genetic diversity within and among populations. Self-compatibility is predominant in rosemary breeding system, but automatic self-pollination is prevented by strong protandry in combination with nonsimultaneous maturation of anthers and stigma. The proportion of male-sterile flowers in R. officinalis shows large temporal variation during the breeding season. This temporal gynodioecy, the length of the flowering season and flowering synchrony of individuals within populations all favour high rates of cross-pollination, therefore increasing allogamy rates.

The article is dedicated to the results of study of introduction of the Dianthus caucaseus Sm. on the basis of the South-Ural Botanical Garden-Institute. The gynodioecy of specie was studied. The stage of fl owering, their duration, morphology and size of the fl owers in hermaphrodite and pistillate forms were studied. It is shown that individuals of D. caucaseus have good seed yield, which is due to high productivity and a large number of fl owers per plant. The rhythm of the development of specie refers its to long-term vegetative evergreen plant summer fl owering.

The exotic mangrove species Laguncularia racemosa (Combretaceae) is fast-growing and was used for forestation in recent years along the southeast coast of China. The breeding system of L. racemosa is variable among populations, such as hermaphroditism, gynodioecy, and androdioecy. To determine whether androdioecy is widespread in L. racemosa, 19 planted populations were surveyed along the southeast coast of China. To determine whether local environmental factors could affect the sex ratio in androdioecious populations, the observed male frequency of different populations was compared to local average annual temperature, rainfall, and salinity. The results showed that the 19 L. racemosa populations along the southeast coast of China were androdioecious. The male frequencies of these populations varied from 31.0 to 88.9%. Partial correlation analysis showed that average annual salinity explained 74.7% of the male frequency (p = 0.001). It is reasonable to note that the male frequency followed a general trend, presenting peak that coincided with the low salinity. The average annual rainfall explained only 30.4% of the male frequency (p = 0.403). And the average annual temperature explained only 20.2% of the male frequency (p = 0.206). The variable male frequency in different androdioecious L. racemosa populations may presumably be caused by ecological or genetical processes; these hypotheses will be tested in future studies.

In gynodioecious species, hermaphrodite plants invest both in seed and pollen production, whereas female plants only produce fruits. For both sexes to coexist, such unbalanced investment is expected to translate in some kind of reproductive compensation, particularly under severe nutrient shortage or environmental stress. This study investigates 1) whether females of the gynodioecious boreo-alpine plant Silene acaulis show any overall compensation in fitness components; 2) the existence of sexual dimorphism in flowers that favor different modes in each sex; 3) whether environmental severity, characterized by means of a Species Distribution Model, strength these patterns. Flower size, fruit and seed production, and germination success were recorded in six populations across the Pyrenees and the Alps. Fruit set was significantly higher in female (59%) than in hermaphrodite plants (17%), and female organs (ovary and style) were larger in female than in hermaphrodite plants, but female flowers were smaller. Contrary to expectations, environment severity was not related with most of the biological traits studied and only germination was associated to environmental gradients. These results confirm that fruit production plays an important role as a compensatory strategy between sexes and, consequently, may favor the presence of both sexes in a gynodioecious species.

We address the evolution of effective number of individuals under androdioecy and gynodioecy. We analyze dynamic models of autosomal modifiers of weak effect on sex expression. In our zygote control models, the sex expressed by a zygote depends on its own genotype, while in our maternal control models, it depends on the genotype of its maternal parent. Our analysis unifies full multi-dimensional local stability analysis with the Li-Price equation, which for all its heuristic appeal, describes evolutionary change over a single generation. We define a point in the neighborhood of a fixation state from which a single-generation step indicates the asymptotic behavior of the frequency of a modifier allele initiated at an arbitrary point near the fixation state. A concept of heritability appropriate for the evolutionary modification of sex emerges from the Li-Price framework. We incorporate our theoretical analysis into our previously-developed Bayesian inference framework to develop a new method for inferring the viability of gonochores (males or females) relative to hermaphrodites. Applying this approach to microsatellite data derived from natural populations of the gynodioecious plantSchiedea salicariaand the androdioecious killifishKryptolebias marmoratus, we find that while female and hermaphroditeS. salicariaappear to have similar viabilities, maleK. marmoratusappear to survive to reproductive age at less than half the rate of hermaphrodites.

Studies on breeding systems and flower morphology are valuable to infer how environmental factors impose evolutionary change in plants. This study focused on the characterization of floral morphs and reproductive systems in Pachycereus pringlei and how this iconic columnar cactus might be a useful genus to understand the evolution of these highly variable structures. We determined breeding systems, characterized floral morphs in five genetic populations, and used pollen:ovule ratios and stamen-stigma distance to verify the sexual system in bisexual flowers. Our inquiries provide insights into the factors driving intra-specific disparity in flower attributes and the reproductive versatility in P. pringlei . Foremost, the lability of breeding systems is expressed primarily as gynodioecy in the North, trioecy in the South, mainly dioecy in CBS, and hermaphroditic in Catalana and Cerralvo Islands. A latitudinal trend in ovule production, dimensions in gynoecium, androecium, and floral display characters is consistent with a northward increase in vegetative traits suggesting physiological responses to the environmental variation characterizing the Baja California Peninsula (BCP). Also, nectary size decreases northwards in staminate flower, but these flowers are larger in the CBS and South populations suggesting sex-specific selection, e.g., pollinator-driven, acting in different magnitudes on sexual attributes of floral morphs and populations. The presence of rudimentary structures of the dysfunctional sex support the hypothesis of the evolution of unisexuality from an early bisexual ancestor. In conclusion, this investigation provides insights into the factors driving intra-specific disparity in flower attributes and the reproductive versatility in P. pringlei to replace ancestral conditions, specifically the substitution of the hermaphrodite phase with dioecious, gynodioecious, and trioecious breeding systems throughout mainland BCP and Sonora. We posit that the biogeographic patterns of breeding systems and floral traits of this emblematic cactus resulted from the interaction of past factors (northwards range expansion) and contemporary biotic and abiotic factors.

Gynodioecy, the co-occurrence of hermaphrodite and female individuals within a species, is maintained by differential reproductive success between sexes. Recently, researchers recognized that not only pollinators but also herbivores are important agents in the evolution and maintenance of gynodioecy, when herbivory is hermaphrodite biased. In this study, we investigated whether there is hermaphrodite-biased herbivory in a gynodioecious plant, Dianthus superbus var. longicalycinus, and if so, what floral traits influenced hermaphrodite-biased herbivory. We measured flower morphology (flower diameter, calyx tube length, corolla height and petal width) and phenology of flowers of female individuals, hermaphrodites and gynomonoecious individuals in a natural population. We also investigated seed predation and predator species. At the study site, Sibinia weevils (Curculionidae; Coleoptera) and Coleophora moths (Coleophoridae; Lepidoptera) were common pre-dispersal seed predators in this species. The weevil appeared early in the flowering season, and weevil predation correlated with flower phenology. Because female individuals did not flower early in the season, weevil predation was less frequent in female individuals. Moth predation correlated with calyx length. The calyx length of flowers of female individuals was smaller than those of hermaphrodites, but a direct comparison of moth predation rates failed to find a significant difference among sex morphs. We found that the two seed predators had different effects on floral traits in D. superbus var. longicalycinus. We suggest that weevil predation contributes to the maintenance of gynodioecy because female individuals successfully escaped weevil predation by flowering late. It remains unclear why flower phenology is different among sex morphs.

• In gynodioecious plants, females are expected to produce more or better seeds than hermaphrodites in order to be maintained within the same population. Even though rarely measured, higher seed production can be achieved through differences in physiology. • In this work, we measured sexual dimorphism in several physiological traits in the gynodioecious plant Geranium sylvaticum. Photosynthetic rate, stomatal conductivity, transpiration rate, water use efficiency and isotopic signatures were measured in plants growing in two habitats differing in light availability. • Females have been reported to produce more seeds than hermaphrodites. However, we did not observe any significant difference in seed output between the sexes in these experimental populations. Similarly, the sexes did not differ in any physiological trait measured. Seed production was strongly limited by light availability. Likewise, differences between plants growing in full light vs. low light were detected in most physiological parameters measured. • Our results show that the sexes in G. sylvaticum do not show any evidence of sexual dimorphism in physiology which concurred with the lack of sexual differences in seed output.

Examining variations in pollinator effectiveness can enhance our understanding of how pollinators and plants interact. Pollen deposition and seed production after a single visit by a pollinator are often used to estimate pollinator effectiveness. However, seed production is not always directly related to pollen deposition because not all pollen grains that are deposited on a stigma are compatible or conspecific. In the field, we tested pollinator effectiveness based on pollen deposition and the resulting seed production after single visits by different pollinator groups in a gynodieocious alpine plant Cyananthus delavayi (Campanulaceae). Our results showed that mean pollen deposition was generally inconsistent with mean seed production when comparisons were performed among different pollinator groups and sexes. In general, the correlations were not significant between pollen deposition and seed production in both perfect and female flowers after single visits by halictid bees, bumble bees, and hoverflies. We suggest seed set of virgin flowers after single visits is a more reliable indicator of pollinator effectiveness than pollen deposition and would be a better indicator of pollinator effectiveness for future studies.

Resource allocation trade-offs between sexual functions are predicted, but these are usually measured only at the whole plant level. In some gynodioecious species, individuals with partially restored male fertility exist providing an opportunity to investigate whether the costs associated with male fertility restoration are linked to seed production. In this study, we examined whether there is a relationship between the numbers of stamens and seeds produced both at the flower level and at the plant level in the gynodioecious herb Geranium sylvaticum. We individually marked flowers in plants varying in the degree of male sterility in the field and counted the number of seeds produced. There was no significant correlation between the numbers of stamens and seeds produced at the flower level suggesting an absence of resource trade-off between female and male functions. Furthermore, the numbers of stamens and seeds were positively correlated at the plant level. The lack of trade-offs between the two sexual functions in this species indicates that relative sex allocation was not affected by resources within a single season and/or that the male costs were relatively small.

Reproductive isolation can rise either as a consequence of genomic divergence in allopatry or as a byproduct of divergent selection in parapatry. To determine whether reproductive isolation in gynodioecious Silene nutans results from allopatric divergence or from ecological adaptation following secondary contact, we investigated the pattern of postzygotic reproductive isolation and hybridization in natural populations using two phylogeographic lineages, western (W1) and eastern (E1). Experimental crosses between the lineages identified strong, asymmetric postzygotic isolation between the W1 and the E1 lineages, independent of geographic overlap. The proportion of ovules fertilized, seeds aborted, and seeds germinated revealed relatively little effect on the fitness of hybrids. In contrast, hybrid mortality was high and asymmetric: while half of the hybrid seedlings with western lineage mothers died, nearly all hybrid seedlings with E1 mothers died. This asymmetric mortality mirrored the proportion of chlorotic seedlings, and is congruent with cytonuclear incompatibility. We found no evidence of hybridization between the lineages in regions of co-occurrence using nuclear and plastid markers. Together, our results are consistent with the hypothesis that strong postzygotic reproductive isolation involving cytonuclear incompatibilities arose in allopatry. We argue that the dynamics of cytonuclear gynodioecy could facilitate the evolution of reproductive isolation.

This study has been carried out to assess and explore the sexual diversity in an important medicinal plant, Valeriana jatamansi. The species is gynodioecious and produces hermaphrodite and female f...

Premise of the study Gynodioecy is a sexual polymorphism whereby female and hermaphroditic plants co-occur within populations. In many gynodioecious species, stressful abiotic environments are associated with higher frequencies of females. This association suggests that abiotic stress affects the relative fitness of females and hermaphrodites and, thus, the maintenance of gynodioecy. Methods To test whether abiotic stress affects the fitness of females and hermaphrodites, we grew open-pollinated Lobelia siphilitica families in temperature regimes characteristic of the southern portion of the species' range (where females are common) and the northern portion of the range (where females are rare). We measured physiological and phenological traits that are indicative of heat stress, and fitness components of females and hermaphrodites that could affect the maintenance of gynodioecy. Key results Contrary to expectations if growth at high temperatures is stressful, we found that the hot treatment increased leaf chlorophyll content, decreased the percentage of plants that delayed flowering initiation, and did not affect the quantum efficiency of photosystem II. Growth at high temperatures did not affect the magnitude of the difference in rosette size (a correlate of flower number) between females and hermaphrodites, or the variance in pollen viability among hermaphrodites. Conclusions We found that growing-season temperatures typical of high female L. siphilitica populations were not stressful and did not affect either the fitness of females compared to hermaphrodites or variation in fitness among hermaphrodites. Consequently, further research is necessary to explain correlations between abiotic environmental factors and the frequency of females in this and other gynodioecious species.

Premise of the study Floral morphology is expected to evolve following the transition from cosexuality to gender dimorphism in plants, as selection through male and female function becomes dissociated. Specifically, male-biased dimorphism in flower size can arise through selection for larger flowers through male function, selection for smaller flowers through female function, or both. The evolutionary pathway to floral dimorphism can be most effectively reconstructed in species with intraspecific variation in sexual system. We examined the evolution of flower size and shape in Lycium californicum, whose populations are either gender dimorphic with male and female plants, or cosexual with hermaphroditic plants. Methods Floral morphology was characterized in populations spanning the species' complete range. For a subset of the range where cosexual and dimorphic populations are in close proximity, we compared the size and shape of flowers from female and male plants in dimorphic populations to hermaphrodites in cosexual populations, accounting for variation associated with abiotic environmental conditions. Key results The magnitude of flower size dimorphism varied across dimorphic populations. After controlling for environmental variation across cosexual and dimorphic populations, flowers on males were larger than flowers on females and hermaphrodites, whereas flower size did not differ between females and hermaphrodites. Flower shape differences were associated with mating type, sexual system, and environmental variation. Conclusions While abiotic environmental gradients shape both overall flower size and shape, male-biased flower size dimorphism in L. californicum appears to arise through selection for larger flowers in males but not smaller flowers in females.

Urtica L. (Urticaceae) is generally reported as a genus of monoecious and dioecious taxa. However, the gender information found in the literature does not at all reflect the actual diversity of gender patterns in Urtica. Dioecy appears to be truly absent from Urtica, but otherwise there has been a major diversification in the geometry of gender and no comparable patterns exist in other plant groups. Thus, we here define technical terms for all unique architectural types of monoecy found in Urtica and closely related genera and reconstruct the ancestral gender states in a Bayesian framework. Our studies are based on a near-comprehensive sampling, including 61 of the 63 Urtica species recognized. We report polygamy, two types of gynodioecy and five different architectural types of monoecy. A total of 15 switches appear to have taken place within the genus. Although gender characteristics have diversified strongly, they are relatively conserved within clades. Monoecy is the predominant sexual system within Urtica and specifically basiandrous monoecy (i.e. basal inflorescence branches of each individual male only, apical branches female) is the most widespread type, reported for 11 different clades. In particular, it characterizes the basally branching pilulifera-clade and the sister genus Zhengyia, and may thus represent the plesiomorphic condition for Urtica. Gender distribution and gross morphology appear to evolve largely independently from each other and gender distribution is largely independent of growth habit. However, polygamous taxa are most common amongst rhizomatous perennials (one-third of the taxa).

We report on how a long-term study of the reproductive biology of the Critically Endangered Schiedea adamantis (Caryophyllaceae), one of Hawai‘i's rarest plant species, was leveraged for conservation purposes. Our major goals were to provide seeds with the greatest genetic variation possible for reintroduction and to ensure that both female and hermaphroditic plants of this wind-pollinated species were reintroduced in a manner that maximized both outcrossing and seed production. Schiedea adamantis was one of the first Hawaiian plant species listed under the Endangered Species Act (USA). The species has been studied intensively to test hypotheses addressing the evolution of breeding systems. Information on outcrossing levels and the extent of inbreeding depression was integrated into ongoing reintroduction efforts. Population size peaked in 1994, when 267 flowering individuals were found on Lē‘ahi (Diamond Head Crater). By 2016 only 17 flowering individuals were present, with drought and invasive species being possible causes of this decline. Reintroduction attempts in 1998 using genetically diverse seeds were unsuccessful because of drought and a lack of sufficient supplemental irrigation. Additional reintroduction attempts in 2012 and 2014 were more successful because of increased supplemental irrigation. Plants used in reintroductions represent genotypes long since absent in the natural population, and may contain the genetic variability essential for evolutionary responses to climate change and the spread of invasive species. The destruction of many plants reintroduced in 2015 and 2016 by a fire in March 2016 highlights the need for additional restoration areas at Lē‘ahi and elsewhere, and storage of seeds for future use.

tIn gynodioecious plants females need a reproductive advantage over hermaphrodites to be maintainedin the same population. Generally, three main proximate causes for a female advantage are considered:inbreeding avoidance, different resource allocation patterns, and differences in ecological interactions.A mechanism potentially causing a female advantage that is rarely discussed is a difference in flo-ral longevity between the genders. Females may have a longer stigma lifespan than hermaphrodites,which can affect pollination. Stigma and flower lifespan are rarely documented in gynodioecious species,although it is a common observation in dioecious species that female plants flower longer than males.Here we focus on the stigma and flower lifespan of gynodioecious Geranium sylvaticum, which couldpotentially contribute to the female advantage observed in this and other closely related species. Wemeasured the stigma and flower lifespan in unpollinated flowers of female, hermaphrodite and plantswith an intermediate gender expression. Our results show that stigma lifespan is almost twice as long infemales as in hermaphrodites and intermediate plants. Also flower lifespan is longest in females. We dis-cuss the potential mechanisms through which an increased floral lifespan can lead to a female advantagedespite the generally lower pollinator visitation rates observed in females by reviewing available studies.Our study shows that increased floral persistence in females can be an important aspect in the mainte-nance of females in gynodioecious plants and should be taken into account as a potential proximate causefor a female advantage.

Gynodioecy is a sexual system in which females and hermaphrodites co-occur. In most gynodioecious angiosperms, sex is determined by an interaction between mitochondrial male-sterility genes (CMS) that arise via recombination and nuclear restorer alleles that evolve to suppress them. In theory, gynodioecy occurs when multiple CMS types are maintained at equilibrium frequencies by balancing selection. However, some gynodioecious populations contain very high frequencies of females. High female frequencies are not expected under balancing selection, but could be explained by the repeated introduction of novel CMS types. To test for balancing selection and/or the repeated introduction of novel CMS, we characterised cytoplasmic haplotypes from 61 populations of Lobelia siphilitica that vary widely in female frequency. We confirmed that mitotype diversity and female frequency were positively correlated across populations, consistent with balancing selection. However, while low-female populations hosted mostly common mitotypes, high-female populations and female plants hosted mostly rare, recombinant mitotypes likely to carry novel CMS types. Our results suggest that balancing selection maintains established CMS types across this species, but extreme female frequencies result from frequent invasion by novel CMS types. We conclude that balancing selection alone cannot account for extreme population sex-ratio variation within a gynodioecious species.

The Asteraceae have a high diversity of reproductive mechanisms, as shown by studies conducted mainly with species from temperate regions. Aiming to contribute knowledge on the reproduction of tropical species, we compared the floral biology and breeding systems of the co-occurring species Adenostemma brasilianum, Bidens segetum and Grazielia intermedia, and additionally identified their pollinators. The study was conducted in a seasonal semideciduous forest fragment in southeastern Brazil. Florets opened in early morning and were protandrous. In the first day of anthesis, secondary pollen presentation occurred during the staminate phase, mainly in the morning. In the same day, the pistillate phase began, being long in A. brasilianum and B. segetum (up to 4 days) and short in G. intermedia (1 day). Pollen viability was high in all three species, except for two G. intermedia individuals which showed male sterility, thus characterising a gynodioecious population. Self-compatibility was observed in A...

Premise of research. The development of male sterility in gynodioecious species has long been of considerable interest to plant biologists. Knautia arvensis is a gynodioecious species, but no detailed description of gender morphs is available for the species. In order to reveal the developmental variation of gender morphs, we conduct a detailed examination of sex expression in K. arvensis and compare the development of bisexual and male-sterile (functionally female) flowers in three different localities.Methodology. The development of bisexual and male-sterile flowers was investigated using SEM. The lengths of the style, anther, and filament of bisexual and male-sterile flowers from three different localities were measured. The data were compared in four developmental stages (S1–S4) and statistically analyzed.Pivotal results. In addition to bisexual and male-sterile individuals, intermediate bisexual plants carrying male-sterile flowers (gynomonoecious) as well as intermediate male-sterile plants were fou...

In Styrax (Ericales: Styracaceae), gynodioecy is known or likely in ten species. A previous morphological analysis of the genus placed these species into a single highly derived clade within S. series Valvatae. In contrast, DNA sequence data from the nuclear ribosomal internal transcribed spacer (ITS) region yielded two distinct gynodioecious clades within the series, one (South American species) as sister to the rest of S. series Valvatae, the other (S. obtusifolius only; Cuba) as phylogenetically nested within a clade of otherwise hermaphroditic species. Here we test these contrasting phylogenetic placements with analyses that include the plastid ndhF-rpl32-trnL, trnL-trnF, trnS-trnG, and trnV-ndhC genic regions in addition to ITS. Results strongly corroborate the phylogenetic positions of the two gynodioecious clades based on ITS data alone. Clade-specific ITS-plastid phylogenetic discordance provides evidence for hybridization and suggests a pattern of reticulate evolution among some of the s...

This study sought to document potential insect pollinators of Neil Rock checkerbloom, Sidalcea hickmanii ssp. petraea (Malvaceae) and measure the effects of pollinator exclusion and plant type on flower, fruit, and seed production. Prior to this study, the pollination requirements of this gynodioecious plant were unknown and potentially complicated by its hermaphroditic and female-only plant types. Analyses showed that pollinator exclusion had no effect on mean number of flowers produced per raceme but significantly reduced the mean number of fruits produced per raceme and mean number of fruits produced per flower, as well as the mean number of seeds produced per raceme in both female-only and hermaphroditic plants. These results suggested that S. hickmanii ssp. petraea is pollinator dependent. Six orders (Hymenoptera, Coleoptera, Homoptera, Lepidoptera, Diptera, and Hemiptera) representing 29 taxa of insects (primarily Hymenoptera – notably Osmia and Hoplitis, and Coleoptera – notably Anthonomus and Trichodes) were collected from flowering S. hickmanii ssp. petraea plants. Adult Anthonomus weevils were observed selectively feeding on the developing fruits of hermaphroditic over female-only plants. This selective predation may have a significant impact on the maintenance of gynodioecy in this endemic, narrowly-isolated subspecies of Sidalcea hickmanii.

In flowering plants, the evolution of females is widely hypothesized to be the first step in the evolutionary pathway to separate male and female sexes, or dioecy. Natural enemies have the potential to drive this evolution if they preferentially attack hermaphrodites over females. We studied sex-based differences in exposure to anther-smut (Microbotryum), a sterilizing pollinator-transmitted disease, in Dianthus pavonius, a gynodioecious perennial herb. We found that within a heavily diseased population, females consistently had lower levels of Microbotryum spore deposition relative to hermaphrodites and that this difference was driven by rapid floral closing in females following successful pollination. We further show that this protective closing behavior is frequency-dependent; females close faster when they are rare. These results indicate that anther-smut disease is an important source of selection for females, especially since we found in a common garden experiment no evidence that females have any inherent fecundity advantages over hermaphrodites. Finally, we show that among populations, those where anther-smut is present have a significantly higher frequency of females than those where the disease is absent. Taken together our results indicate that anther-smut disease is likely an important biotic factor driving the evolution and maintenance of females in this gynodioecious species.

A sexual system is the pattern of gender allocation that characterizes a species. In both plants and animals, simultaneous hermaphroditism and dioecy are the most common and stable sexual systems. Other sexual systems, sequential hermaphroditism, environmental sex determination, gynodioecy, androdioecy, and trioecy, are less stable and less widely distributed. The boundaries between these sexual systems are not always clear, largely because phenotypic plasticity is an important and prevalent component of sexual reproduction. One can view sexual systems in the Metazoa as lying on a gradient of phenotypic plasticity from simultaneous hermaphroditism at the high end through sequential hermaphroditism and environmental sex determination to genetically determined dioecy, which has a minimum of phenotypic plasticity in sex allocation. The distribution of sexual systems across the Metazoa gave rise to Williams’ Paradox, which states that the pattern is best explained by phylogeny rather than sex allocation theory. Today, sex allocation theory seems to explain transitions in sexual system in those taxa with labile sexual systems adequately. However, the stability of either dioecy or simultaneous hermaphroditism in many major taxa, such as phyla and classes, remains inexplicable. While in angiosperms the evolutionary pathways between dioecy and simultaneous hermaphroditism are fairly well understood, a plausible evolutionary sequence for transitions between dioecy and simultaneous hermaphroditism in animals has been lacking. Here, the proposal is made that it is useful to view transitions from simultaneous hermaphroditism to dioecy as the result of selection for decreasing phenotypic plasticity and vice versa. A scenario for evolutionary transitions between simultaneous hermaphroditism and dioecy, in animals, through intermediate stages of sequential hermaphroditism and environmental sex determination is proposed.

The chloroplast (cp) genome sequence of a gynodioecious Satyrium ciliatum female type has been characterized using Illumina pair-end sequencing. The complete cp genome was 154,418 bp in length, con...