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Tolerance to prolonged water deficit occurs along a continuum in plants, with dehydration tolerance (DhT) and desiccation tolerance (DT) representing some of the most extreme adaptations to water scarcity. Although DhT and DT presumably vary among individuals of a single species, this variability remains largely unstudied. Here, we characterized expression dynamics throughout a dehydration-rehydration time-course in six diverse genotypes of the dioecious liverwort Marchantia inflexa. We identified classical signatures of stress response in M. inflexa, including major changes in transcripts related to metabolism, expression of LEA and ELIP genes, and evidence of cell wall remodeling. However, we detected very little temporal synchronization of these responses across different genotypes of M. inflexa, which may be related to genotypic variation among samples, constitutive expression of dehydration-associated transcripts, the sequestration of mRNAs in ribonucleoprotein partials prior to drying, or the lower tolerance of M. inflexa relative to most bryophytes studied to date. Our characterization of intraspecific variation in expression dynamics suggests that differences in the timing of transcriptional adjustments contribute to variation among genotypes, and that developmental differences impact the relative tolerance of meristematic and differentiated tissues. This work highlights the complexity and variability of water stress tolerance, and underscores the need for comparative studies that seek to characterize variation in DT and DhT.

Water scarcity, a common stress factor, negatively impacts plant performance. Strategies to cope with it, such as desiccation tolerance, are becoming increasingly important to investigate. However, phenomena, such as intraspecific variation in stress responses have not received much attention. Knowledge of this variability and the environmental drivers can be leveraged to further investigate the mechanisms of desiccation tolerance. Here we tested for variation in desiccation tolerance in

Resilience to abiotic stress is associated with a suite of functional traits related to defense and longevity. Stress tolerant plants are generally slow growing with extended leave lifespans and reduced allocation to reproduction. Resurrection plants are ideal systems to test for trade-offs associated with stress tolerance due to their extreme resiliency. While, growth defense trade-offs are well-characterized, few studies have tested for natural variation associated with tolerating the harshest environments. Here, we surveyed a suite of functional traits related to stress tolerance, leaf economics, and reproductive allocation in natural populations of the South African resurrection plant Myrothamnus flabellifolia. We selected three distinct field sites in South Africa ranging from mesic to xeric. Despite considerable environmental variation across the study area, M. flabellifolia plants were extremely and similarly stress tolerant at all sites. However, we detected notable variation in other life history and morphological traits. Plants in more mesic sites were larger, faster growing, and had more inflorescences. In contrast, plants from the most xeric sites appeared to invest more in persistence and defense, with lower growth rates and less reproductive allocation. Together, this suggests that desiccation tolerance is a binary trait in M. flabellifolia with little natural variation, but that other phenotypes are more labile. The trait syndromes exhibited by plants at the different study sites align with general expectations about growth defense tradeoffs associated with the colonization of extreme environments. We show that plants from the least stressful sites are more reproductive and faster growing, whereas plants from the most stressful sites were slower growing and less reproductive. These findings suggest that M. flabellifolia plants are finely tuned to their environment.

Introduction. A well-supported pattern among dioicous bryophytes is male rarity. However, few assessments of bryophyte sex ratios have been made across environmental gradients to assess the role of...

In dioicous mosses, sex is determined by a single U (female, ♀) or V (male, ♂) chromosome. Although a 1 : 1 sex ratio is expected following meiosis, phenotypic sex ratios based on the production of gametangia are often female-biased. The dryland mossWe reanalyzed 271 non-expressing gametophyte shoots from a previous study onWe recovered a genotypic sex ratio in non-expressing shoots of 18.4♀ : 1♂, which exceeds the female bias of the phenotypic ratio (5.3♀ : 1♂;These findings contribute to our understanding of how the environment may modulate sex ratios in

Desiccation tolerance has evolved recurrently across diverse land plant lineages as an adaptation for survival in regions where seasonal rainfall drives periodic drying of vegetative tissues. Growing interest in this phenomenon has fueled recent physiological, biochemical, and genomic insights into the mechanistic basis of desiccation tolerance. Although, desiccation tolerance is often viewed as binary and monolithic, substantial variation exists in the phenotype and underlying mechanisms across diverse lineages, heterogeneous populations, and throughout the development of individual plants. Most studies have focused on conserved responses in a subset desiccation-tolerant plants under laboratory conditions. Consequently, the variability and natural diversity of desiccation-tolerant phenotypes remains largely uncharacterized. Here, we discuss the natural variation in desiccation tolerance and argue that leveraging this diversity can improve our mechanistic understanding of desiccation tolerance. We summarize information collected from ~600 desiccation-tolerant land plants and discuss the taxonomic distribution and physiology of desiccation responses. We point out the need to quantify natural diversity of desiccation tolerance on three scales: variation across divergent lineages, intraspecific variation across populations, and variation across tissues and life stages of an individual plant. We conclude that this variability should be accounted for in experimental designs and can be leveraged for deeper insights into the intricacies of desiccation tolerance.

Silvery-Thread Moss (Bryum argenteumHedw.) is an undesirable invader of golf course putting greens across North America, establishing colonies and proliferating despite practices to suppress it. The goal was to grow genotypes ofgreen(growing in putting greens) andnative(growing in habitats outside of putting greens)B. argenteumin a common garden experiment, allowing an experimental test of life-history traits between genotypes from these two habitats. Seventeen collections ofgreenand 17 collections ofnative B. argenteumwere cloned to single genotypes and raised through a minimum of two asexual generations in the lab. A culture of each genotype was initiated using a single detached shoot apex and was allowed to grow for 6 mo under conditions of inorganic nutrients present and absent. Compared with genotypes from native habitats, genotypes ofB. argenteumfrom putting greens exhibited earlier shoot regeneration and shoot induction, faster protonemal extension, longer (higher) shoots, lower production of gemmae and bulbils, and greater aerial rhizoid cover, and showed similar tendencies of chlorophyll fluorescence properties and chlorophyll content. Cultures receiving no inorganic nutrients produced less chlorophyll content, greatly reduced growth, and bleaching of shoots. Mosses from putting greens establish more quickly, grow faster, produce more abundant rhizoids, and yet do not produce as many specialized asexual propagules compared with mosses of the same species from native habitats. The highly managed putting green environment has either selected for a suite of traits that allow the moss to effectively compete with grasses, or genotypic diversity is very high in this species, allowing a set of specialized genotypes to colonize the putting green from native habitats. Successful golf course weeds have been able to adapt to this highly competitive environment by selection acting on traits or genotypes to produce plants more successful in competing with golf course grasses.

Plant-microbe interactions impact ecosystem function through nutrient cycling, community interactions, and individual costs/benefits to the organisms involved. However, information on the establishment, diversity, and function of plant-microbe interactions remains limited, especially for non-vascular plants. We hypothesized that variation in the environment and sex of a host plant, impact the composition and diversity of associated microbial communities. To test this hypothesis, we characterized the bacteriome of the non-vascular plant, Marchantia inflexa, in both males and females across multiple habitats by targeted sequencing of the bacterial 16S rRNA gene. We describe the bacteriome for M. inflexa, and find that it is abundant and diverse, showing some similarities with other non-vascular plant lineages. Using these data, we detected a habitat specific component of the bacteriome, and sex differences in the bacteriome under common garden conditions. On the basis of known microbial functions, our analyses suggest that the specific taxonomic assemblages of bacteria detected in particular habitat types may serve functional roles; allowing plants to better acclimate to their local environment, and that sex differences in the bacteriome may correspond to subtle differences in the physiology and morphology of the sexes. Our initial characterization of variation in bacteriome composition of this tropical liverwort lineage provides valuable information for better understanding the patterns of plant-microbe interactions across land plants.

Sexual reproduction depends on mate availability that is reflected by local sex ratios. In species where both sexes can clonally expand, the population sex ratio describes the proportion of males, including clonally derived individuals (ramets) in addition to sexually produced individuals (genets). In contrast to population sex ratio that accounts for the overall abundance of the sexes, the genetic sex ratio reflects the relative abundance of genetically unique mates, which is critical in predicting effective population size but is difficult to estimate in the field. While an intuitive positive relationship between population (ramet) sex ratio and genetic (genet) sex ratio is expected, an explicit relationship is unknown. In this study, we determined a mathematical expression in the form of a hyperbola that encompasses a linear to a nonlinear positive relationship between ramet and genet sex ratios. As expected when both sexes clonally have equal number of ramets per genet both sex ratios are identical, and thus ramet sex ratio becomes a linear function of genet sex ratio. Conversely, if sex differences in ramet number occur, this mathematical relationship becomes nonlinear and a discrepancy between the sex ratios amplifies from extreme sex ratios values towards intermediate values. We evaluated our predictions with empirical data that simultaneously quantified ramet and genet sex ratios in populations of several species. We found that the data support the predicted positive nonlinear relationship, indicating sex differences in ramet number across populations. However, some data may also fit the null model, which suggests that sex differences in ramet number were not extensive, or the number of populations was too small to capture the curvature of the nonlinear relationship. Data with lack of fit suggest the presence of factors capable of weakening the positive relationship between the sex ratios. Advantages of this model include predicting genet sex ratio using population sex ratios given known sex differences in ramet number, and detecting sex differences in ramet number among populations.

Transport of salicylic acid is important for systemic immunity and is regulated by osmotic pressure and cuticle permeability., The plant cuticle is often considered a passive barrier from the environment. We show that the cuticle regulates active transport of the defense hormone salicylic acid (SA). SA, an important regulator of systemic acquired resistance (SAR), is preferentially transported from pathogen-infected to uninfected parts via the apoplast. Apoplastic accumulation of SA, which precedes its accumulation in the cytosol, is driven by the pH gradient and deprotonation of SA. In cuticle-defective mutants, increased transpiration and reduced water potential preferentially routes SA to cuticle wax rather than to the apoplast. This results in defective long-distance transport of SA, which in turn impairs distal accumulation of the SAR-inducer pipecolic acid. High humidity reduces transpiration to restore systemic SA transport and, thereby, SAR in cuticle-defective mutants. Together, our results demonstrate that long-distance mobility of SA is essential for SAR and that partitioning of SA between the symplast and cuticle is regulated by transpiration.

We present a draft genome assembly for the tropical liverwort, Marchantia inflexa, which adds to a growing body of genomic resources for bryophytes and provides an important perspective on the evolution and diversification of land plants. We specifically address questions related to sex chromosome evolution, sexual dimorphisms, and the genomic underpinnings of dehydration tolerance. This assembly leveraged the recently published genome of related liverwort, M. polymorpha, to improve scaffolding and annotation, aid in the identification of sex-linked sequences, and quantify patterns of sequence differentiation within Marchantia. We find that genes on sex chromosomes are under greater diversifying selection than autosomal and organellar genes. Interestingly, this is driven primarily by divergence of male-specific genes, while divergence of other sex-linked genes is similar to autosomal genes. Through analysis of sex-specific read coverage, we identify and validate genetic sex markers for M. inflexa, which will enable diagnosis of sex for non-reproductive individuals. To investigate dehydration tolerance, we capitalized on a difference between genetic lines, which allowed us to identify multiple dehydration associated genes two of which were sex-linked, suggesting that dehydration tolerance may be impacted by sex-specific genes.

Background and aims Adaptations allowing plants to cope with drying are particularly relevant in the light of predicted climate change. Dehydration tolerance (DhT, also dehydration-tolerant) is one such adaptation enabling tissue to survive substantial drying. A great deal of work has been conducted on highly DhT species. However, bryophytes showing less intense and variable DhT are understudied, despite the potential for these species to provide an informative link between highly tolerant and sensitive species. In this study, we tested the degree to which DhT varies across populations and the sexes of a species expected to exhibit a moderate DhT phenotype. Methods To test predicted patterns of tolerance we assessed DhT in males and females of Marchantia inflexa from two distinct habitat types that differ in water availability. Both common garden and field-collected tissue was subjected to drying assays at multiple intensities and recovery was monitored by chlorophyll florescence. Verification studies were conducted to confirm the level of dehydration, the rate of drying and the associated changes in photosynthetic physiology. Key results We confirmed our expectation that M. inflexa is able to tolerate moderate dehydration. We also found that females exhibited higher DhT than males, but populations did not differ in DhT when cultured in a common garden. However, field-collected samples exhibited differences in DhT corresponding to environmental dryness, suggesting plasticity in DhT. Conclusions By studying a less extreme DhT phenotype we gained insight into how more sensitive (yet still tolerant) organisms cope with dehydration. Additionally, the identified sex-specific variation in DhT may explain ecological patterns such as female-biased sex ratios. Furthermore, plasticity in DhT has the potential to inform management practices aimed at increasing tolerance to drought conditions.

Water shortage events negatively impact plant productivity, threaten ecosystem functioning, and are predicted to increase dramatically in the coming years. Consequently, building a detailed understanding of how plants respond to water stress is critical for improving predictions of ecological processes and species range shifts under climate change. Here, we characterized patterns of intraspecific variation in dehydration tolerance (DhT, also dehydration tolerant) across a variable landscape in the tropical plant, Marchantia inflexa. DhT enables tissues to survive substantial drying (below an absolute water content of − 10 MPa) and despite the ecological significance of DhT, many questions remain. We tested if DhT was correlated with an environmental exposure gradient, if male and female plants had contrasting DhT phenotypes, and if variation in DhT had a genetic component. To do so, we collected plants from five populations, spanning an environmental exposure gradient in the forests of northern Trinidad, Republic of Trinidad and Tobago. We measured DhT immediately after collection, and after growing plants for ~ 1 year in a common garden. We found that DhT varied significantly among populations and tracked the characterized exposure gradient. Additionally, we showed that phenotypic differences among populations in DhT were maintained in the common garden, suggesting that underlying genetic differences contribute to DhT variability. Finally, we detected a fluctuating sexual dimorphism where males had lower DhT than females in less exposed sites, but not in more exposed sites. Interestingly, this fluctuating sexual dimorphism in DhT was driven primarily by male variation (females exhibited similar DhT across sites).

BACKGROUND AND AIMS: In dioecious plants, sexual reproduction requires close proximity to potential mates, but clonal growth can increase this distance and, therefore, reduce the probability of mating. Reduction in sexual propagules can lead to decreased dispersal and gene flow between populations. Gene flow and clonal growth may be further influenced by the size of the habitat patch. The effects of habitat size and reproductive mode (sexual or asexual reproduction) on spatial genetic structure and segregation of the sexes were tested by quantifying the distributions of genotypes and the sexes using the dioecious liverwort Marchantia inflexa. METHODS: Plants were sampled from five pairs of small–large habitat patches to identify within- and among-population spatial genetic structure using 12 microsatellite markers. Spatial distributions were calculated as the likelihood that pairs of individuals were the same sex or genotype, and it was determined how that likelihood was affected by habitat patch size (small/large). KEY RESULTS: Asexual reproduction dominates within populations, and asexual dispersal also occurred across populations. Spatial segregation of the sexes was observed within populations; males were more likely to be near individuals of the same sex than were females. Although the likelihood of both sexes being near members of the same sex was similarly greater on small habitat patches, on large habitat patches male genotypes were almost 15 % more likely to be near clonemates than were female genotypes. CONCLUSIONS: The results show a sex difference in clonal clumping that was dependent upon habitat size, suggesting differential colonization and/or survival between males and females. The sexes and genotypes being structured differently within and among populations have implications for the persistence of populations and the interactions between them. This study demonstrates that studying only the sexes and not their genotypes (or vice versa) can limit our understanding of the extent to which reproductive modes (sexual or asexual) influence genetic structure both within and between populations.

Desiccation tolerance (DT) in poikilohydric organisms is dependent upon four principal sequential factors, (1) the rate of drying (RoD), (2) the water content (WC) of the organism deriving from the equilibrating relative humidity (RHeq), (3) the duration of the desiccation event, and (4) the rate of rehydration (RoR). The first two factors are often combined in experiments as the “intensity” of desiccation, and thus the effect of one on the other is relatively unknown but likely to be important ecologically. We hypothesized that more protracted rates of drying should mitigate damage at lower equilibrating RHs in a known inducibly DT species. Cultured uniclonal shoots of the moss Funaria hygrometrica were dried at different RoDs (time from full turgor to leaf curling, from 0.067 to 120 h) at five different RHs (12, 33, 54, 75 and 93%), allowed to equilibrate at each RH, rehydrated and assessed using chlorophyll fluorescence at 0.5 and 24 h postrehydration. At 24 h postrehydration, shoots of F. hygrometrica subjected to a rapid-dry event ( 54%, recovery was complete. At 0.5 h postrehydration, Fv/Fm levels indicated moderate damage at all RHeqs except 93%, with no mitigation of damage when the rate of drying was extended. Intensity of desiccation is normally construed as the ability to tolerate a combination of rate of drying × equilibrating RH. By varying the rate of drying across a range of RHeqs, F. hygrometrica is found to be able to tolerate all water contents tested, providing the rate of drying is extended to at least 15 h from full turgor to leaf curling. By adopting either the “step-down” approach to drying or the “wet substrate” technique used here, future studies on the desiccation tolerance of poikilohydric organisms can more accurately assess responses to desiccation stress.

Allocation to reproductive mode (sexual and asexual) can vary depending on environmental conditions but is often examined at the population level, whereas selection acts upon the individual. We examined individual variation in reproductive mode to identify how the interaction of sex and the environment affect population genetic diversity. Using the plant Marchantia inflexa, we tested whether reproductive allocation pattern varies consistently between males and females and among plants collected from different environments, and determined if morphological responses were the result of individual plasticity or genetic differences. We then quantified genetic variability between the different environments and between the sexes. Male and female plants were collected from two strikingly different habitats within the same region: along natural sites (rivers) and along novel human-modified sites (roadsides). Using a common garden approach, we found a strong sex by habitat interaction: male and female responses differed significantly by their source habitat. For females, relative to river-collected, road-collected plants had higher growth and asexual reproduction, while the pattern was reversed, although not significant, for males. Genetic differentiation was significant between the two habitats with no evidence of individual differences in plasticity for growth, but there was a genotype effect for asexual propagule production. Males and females did not differ genetically; but river-collected plants with lower sexual potential were more diverse than roadside-collected plants, possibly the result of founder events. These results show that individual variation in reproduction is controlled by the interaction of both the environment and genetics. Due to different selection pressures between natural and novel habitats, there are observable differences in life history traits with an associated evolutionary response to the novel habitat.

Three prominent life history patterns attributed to dioecious species of mosses (low sex expression, male rarity, and low frequencies of sexual reproduction) were investigated in the desert moss Syntrichia caninervis along an elevation gradient in the Spring Mountains of the Mojave Desert (U.S.A.). Low elevation patches exhibited significantly lower frequencies of sex expression, individuals with fewer inflorescences, and fewer male individuals. Sexual reproduction was infrequent at all elevations, with only seven of 85 patches showing evidence of recent sporophyte production and only nine of 708 perichaetia being fertilized. After factoring out abortive sporophytes, the percentage of patches maturing sporophytes was 5.9% and the estimated fraction of fertilized perichaetia was 0.7%. In addition, as elevation increased from low to middle/high elevation, individuals of Syntrichia caninervis exhibited significant increases in biomass, total stem length, number of ramets, and ramet length. The decre...

Phenotypic variation occurs in many populations of plants. When this variation occurs along an environmental gradient, the immediate question is whether the variation is attributed to phenotypic plasticity, ecotypes, or some combination of the two. The moss Syntrichia caninervis appears morphologically variable along an environmental gradient changing rapidly from low light, low temperature, and high moisture levels in the understory microhabitat to high light, high temperature, and low moisture levels in the intershrub microhabitat. We tested for the presence of physiological variation using recovery from a heat-shock event in a mimicked microhabitat light environment, and for morphological variation using a common garden with the ultimate goal of attributing observed variation to plasticity, genetic variation, or a combination. The results suggest that plasticity plays a large role in trait variation. Photosynthetic recovery depended on the current light levels of an environment and not the orig...

Bryophyte population sex ratios are predominately female-biased, at least with respect to plants expressing sexual structures. One hypothesis to explain this bias is that males produce sexual structures less often than females, but occur at similar frequencies, a hypothesis termed the "shy male hypothesis." Another nonexclusive possibility is that offspring sex ratios (as sporelings) are biased and populations retain this bias. To test these hypotheses, we examined sex ratios in expressing and nonexpressing shoots for the cosmopolitan moss Bryum argenteum collected in the field, and in shoots grown from spores in the lab. An examination of 154 collections of B. argenteum from native habitats and urban settings in the USA revealed that populations were significantly female-biased (>80% female). Male rarity was most pronounced in aridland regions of the Mojave Desert and California chaparral; males were significantly more common in altered urban habitats and in high elevation native habitats. When all shoots from clumps representing three mixed-sex, sporophytic populations were grown to sex expression, male nonexpressing shoots were not found to be significantly more abundant than expected based on the field expressing shoot sex ratio, lending little support to the "shy male hypothesis." Offspring sex ratios derived from sporelings were not significantly different from 1:1, thus not explaining the sharply female-biased population ratios observed in the field. We propose that factors between spore germination and adult maturation, including clonal dynamics, are causing the female-biased population and within-clump sex ratio imbalance of B. argenteum.

In seed plants, the occurrence of spatial segregation of the sexes (SSS) along environmental gradients is well documented. SSS in bryophytes is usually more extreme than in seed plants, yet few bryophyte studies have explicitly linked SSS to environmental variables. For Marchantia inflexa, in which males are found beneath more tree-canopy openness than are females, we tested whether morphological, physiological and life history patterns are consistent with this sex-specific association to canopy openness. To accomplish this, we quantified morphology, physiology and life history differences between two light conditions for each sex. Responses to light levels were mostly analogous to sun and shade leaves of seed plants. However, we found that males had lower chlorophyll a:b ratios (indicative of low-light plants) than females, contrary to our prediction.

Patches of the dominant biological soil crust moss (Syntrichia caninervis) in the Mojave Desert were subjected to transplant experiments to test the survivability of crustal transplantation due to source or destination microhabitat. After a period of 27 months, all the reciprocally transplanted and replanted sections had survived. However, percent cover of the reciprocally transplanted patches declined 20–50% relative to initial cover compared to a decline in cover of 36–52% for the replanted patches. Similarly, shoot density declined an average of 26% in the transplants and replants. Shoot mortality was essentially negligible through the first 21 months of the study and then declining across all treatments to approximately 5–10 dead shoots/cm2. However, this shoot death was also observed in equivalent densities in the host patches, indicative of a community-wide decline in plant health that was probably related to a regional rainfall deficit over this period. A tendency existed for plants moved from a shaded site to have reduced shoot density in the new site, and plants moved into exposed sites lost significantly more cover than plants moved into shaded sites. These seemingly conflicting trends result from one of the transplant treatments, the shaded to exposed, exhibiting a greater loss in shoot density and decline in cover than its reciprocal transplant, exposed to shaded. For soil restoration of disturbed bryophyte crusts, we recommend using as source material both the exposed and the shaded portions of the crust but avoiding moving Syntrichia from a shaded site into an exposed site.

The cost of sexual reproduction is incurred when the current reproductive episode contributes to a a decline in future plant performance. To test the hypotheses that a trade-off exists between current sexual reproduction and subsequent clonal regeneration and that resources limit reproduction and regeneration, plants of the widespread moss Pterygoneurum ovatum were subjected to induced sporophytic abortion, upper leaf removal, and nutrient amendment treatments. Sexually reproducing plants were slower or less likely to produce regenerative structures (protonemata or shoots) and produced fewer regenerative tissue areas or structures. The ability and the timeline to reproduce sexually and regenerate clonally were unaffected by an inorganic nutrient amendment. However, when leaves subtending the sporophyte were removed, the sporophytes were less likely to mature, tended to take a longer time to mature, and were smaller compared to sporophytes from shoots with a full complement of upper leaves. Our fi ndings indicate that plants investing in sexual reproduction suffer a cost of decreased clonal regeneration and indicate that sporophyte maturation is resource-limited, with upper leaves contributing to the nutrition of the sporophyte. This study represents only the second explicit experimental demonstration of a trade-off between sexual and asexual reproduction in bryophytes.

1. Two competing hypotheses relating to thermostress were proposed to understand skewed sex ratios in Syntrichia caninervis, a reproductive investment hypothesis and a wildfire selection hypothesis. 2. Nearly all shoots from both sexes remained viable (regenerated in culture) following exposure to 120 °C for 30 min, thus setting a new upper thermotolerance record for adult eukaryotic organisms for a minimum 30 min exposure time. 3. Males regenerated faster than females, produced more biomass, and suffered less fungal attack than females. Findings support the wildfire selection hypothesis.

Premise of the study Free-living sperm of mosses are known to be partially desiccation tolerant. We hypothesized that mature moss antheridia should also tolerate desiccation and that rehydration to partial turgor (prehydration) or rehydration to full turgor (rehydration) before immersion in water is required for full recovery from any damaging effects of prior desiccation. Methods Bryum argenteum (silvery-thread moss) was grown in continuous culture for several months, produced mature perigonia (clusters of antheridia), and these were subjected to a slow rate of drying (∼36 h from full turgor to desiccation) and equilibration with 50% relative humidity. Perigonia were prehydrated (exposed to a saturated atmosphere) or rehydrated (planted upright in saturated media) for 0, 45, 90, 135, 180, and 1440 min, then immersed in sterile water. Time to first sperm mass release, number of antheridia releasing sperm masses, and the integrity of the first sperm mass released were assessed. Key results Rehydration of dried antheridia for at least 3 h before immersion in water resulted in antheridia functioning similar to control undried antheridia. Compared with rehydration, prehydration was not effective in the recovery of antheridia from desiccation. Conclusions For the first time, moss antheridia are shown to be fully desiccation tolerant at a functional level, capable of releasing fully functional sperm following a slow drying event provided the antheridia are allowed to rehydrate at least 3 h before immersion in water.

Summary 1 When the two sexes compete so intensively that one of them may be consistently excluded from patches of habitat, how can they coexist in the population as a whole? 2 To address this question, we constructed a population model capable of simulating the dynamics of sex-specific life-history stages within frequently disturbed patches and across a multipatch system strongly influenced by extinction and colonization (metapopulation). 3 We parameterized the model based on the dioecious bryophyte Marchantia inflexa, attempting to capture sufficient biological realism for the results to be quantitatively comparable with natural patterns. 4 In nature, M. inflexa spreads by tissue extension and dispersal of asexual propagules within patches or sexual spores between patches. Females have faster tissue expansion and males greater production of asexual propagules. Some patches and even entire populations lose males or, more rarely, females. 5 In the model, males were often eliminated by competition from individual patches, but both sexes almost always persisted in the metapopulation (as in nature), with females typically predominating. Male advantage during patch filling and spores produced and dispersed where males (the fugitive sex) had not yet been eliminated kept both sexes in the model system. 6 Similar mechanisms may maintain both sexes in other systems, particularly small, highly disturbed populations where life-history traits and mortality differ between the sexes.

Female plants of the moss Syntrichia caninervis are more common than male plants and are found in more thermally stressful habitats than male plants. We hypothesized that this distribution pattern is due to a more favorable regeneration response of females to thermal stress compared to that of males. Hydrated leaves from four genotypes of both sexes of S. caninervis were exposed for 60 min under lighted conditions to temperatures of 20, 30, 35, 40, and 45°C. Leaves were allowed to regenerate on native sand under recovery conditions (12-h photoperiod, 20°C lighted, and 8°C dark) for 56 days, and over this period, protonemal emergence, growth rate, and shoot production were assessed. Leaves exposed to higher heat shocks produced protonemata significantly later, exhibited significantly reduced growth rates over the course of the experiment, and produced fewer shoots but did not differ in the probability of producing a shoot. Males tended to produce protonemata earlier than females at the highest thermal stress, whereas females tended to produce protonemata earlier under control conditions. Female leaves regenerated at twice the rate of male leaves, producing twice the area of protonemal cover; this gender difference was lessened at the highest thermal stress. Female leaves regenerated significantly more shoots than males, with each sex exhibiting different peaks of shoot production depending on the thermal stress. No interaction effect was detectable between gender and stress treatment. While females had a more favorable regeneration response relative to males, thermal stress diminished this difference, thus suggesting that our hypothesis was not supported.

Spatial variation in population sex ratios is common in bryophytes, but the ecological correlates of this variation are not well documented. The dioecious desert moss Syntrichia caninervis presents an example of this variation occurring at the regional scale (kilometers) as well as the microscale (centimeters). Here, our goal is to correlate variation in plant traits and sex expression levels to relevant ecological variation, and specifically to investigate whether spatial segregation of the sexes (SSS) exists at the level of the patch. Five sporophytic patches of S. caninervis were sampled at 10 cm intervals along a transect extending from shrub understory into the exposed intershrub region, thus representing a stress gradient of light intensity and moisture availability. Along a gradient from understory to intershrub microsites, individual plant length and biomass declined significantly, with plants under the canopy twice as large as those in the more exposed microsites. Sex expression declined...

Disparate sex ratios are a widespread pattern in dioecious bryophytes, with female‐biased ratios especially prevalent in arid environments. The absence of male plants in environments experiencing high desiccation pressure prompted the hypothesis that male plants may be less desiccation tolerant than female plants in the desert moss Syntrichia caninervis. This hypothesis was investigated by exposing detached leaves to consecutive wet/rapid‐dry treatments and monitoring viability, protonemal emergence time, shoot production, growth rate of secondary protonemata, and microbial infection frequency over a 56‐d period. The desiccation treatment consisted of exposure of mature 1‐yr‐old leaves to zero, two, four, and six wet/rapid‐dry cycles. Hydrated leaves were then allowed to regenerate. Desiccation stress level was significantly correlated to reduced protonemal emergence, reduced growth rates, and reduced shoot production. Female detached leaves produced protonemata more quickly, and these protonemata grew tw...

Local competition for space across a wide array of taxa typically involves three mechanisms that we denote here as expansion (spreading into unoccupied habitat), lottery (replacing dead competitors), and overgrowth (encroaching on competitors along zones of contact). By formulating and analysing a simple, general model incorporating these features, we identify ecological conditions and life-history features that lead to stable coexistence or competitive exclusion (with or without initial-condition dependence) and gain insight by linking these to case studies in the literature. We demonstrate the importance of contact inhibition, a little-studied feature of overgrowth, and we show how life-history tradeoffs may influence and be influenced by local competition for space. The general model we present can help indicate whether local interactions are sufficient to explain patterns of coexistence or exclusion and can serve as the foundation for more specific, realistic models of spatial competition.

Spatial segregation of the sexes in bryophytes has been implicated as the primary reason for the lack of sporophyte production in many dioicous bryophyte populations. Additionally, sex-specific microhabitat specialization by dioicous bryophytes may influence population sex ratios and the maintenance of sexually dimorphic traits. We examined habitat use of female and male M. inflexa in two populations in Trinidad and 10 populations in the U.S.A. to determine whether the sexes were spatially segregated within populations and if the sexes specialized on different microhabitats. Populations differed in habitat characteristics, sex ratios varied among populations, and populations consisted mainly of single-sex or non-sex-expressing patches of plants. Despite the fact that Marchantia inflexa is sexually dimorphic, female and male plants used areas of similar substrate, humidity, wind speed, and exposure within and among populations. In U.S.A. populations, males were found in areas with more open canopy...

Marchantia inflexa, a dioecious thallose liverwort, is sexually dimorphic in clonal expansion traits. We used selection analyses to measure the magnitude and direction of selection on clonal fitness to uncover possible mechanisms for the maintenance of preadult sexually dimorphic characters. We planted replicates of genotypes of female and male M. inflexa in two light environments in a greenhouse and measured morphological and phenological characters associated with growth and asexual reproduction. Timing to onset of asexual reproduction and plant size early in development were under sex-specific selection in a low light environment. Additionally, females exhibited a sex-specific cost of plasticity in the timing of their onset of asexual reproduction in high light. Selection on asexual fitness tended to shift traits toward monomorphism rather than sexual dimorphism, whereas the expressed phenotype of females was congruent with patterns of selection acting on sexual fitness. We detected negative trade-offs between asexual and sexual fitness components in females in one light environment. Opposing selective forces acting on asexual and sexual fitness components may explain how sexual dimorphisms persist in the face of selection for monomorphism in the preadult phase.

Ten sporophytic populations of Syntrichiacaninervis contained an average of 22 individualscm−2, with a sex ratio of 7.9 Female:1 Male: 3.1 Nonexpressing(N = 300). In each of the populations, female individuals outnumberedmale individuals. A representative population size of 50 × 25cm was estimated to contain 27,250 organically distinct individualplants. Given the wide disparity in reproductive investment in this dioeciousspecies, sex-specific traits were investigated at the level of the individualinbiomass, total stem length, number of ramets, number of branches, length ofannual growth interval, length of longest ramet, age, number of inflorescences,number of ramets expressing sex, and consecutive seasons of sex expression. Theonly significant sex dimorphism recorded was in consecutive seasons of sexexpression, with nonsporophytic female individuals exhibiting a higherfrequencythan males. However, nonexpressing individuals had lower biomass, shorter totalstem length, fewer branches, and shorter ramets than males and females, andfewer ramets than female individuals. When the biomass of female and maleindividuals was controlled for inflorescence number, no significant differencesbetween the sexes in biomass were found. There appears to be a threshold sizefor sex expression, with all individuals above 2.0 mg dry weightexpressing sex (N = 108). Biomass and total stem length are strongpositive correlates (r = 0.88), and individual biomass is a betterpredictor of the number of inflorescences produced per individual than is stemlength (r = 0.85 vs. r = 0.69, respectively). Independent of stemlength, individual biomass had a positive and significant relationship withinflorescence number; however, independent of individual biomass, stem lengthwas not associated with inflorescence number. Overall sex expression was 0.74(individual level) and 0.65 (ramet level). The functional sex ratio wasassessedat the inflorescence level, and ranged from 9.7♀:1♂, to14.9♀:1♂ over the most recent four years. Fertilization frequencywas 0.69 (individual level) and 0.34 (perichaetial level). Over the last threeyears, 63% of all fertilized perichaetia resulted in an abortivesporophyte.

The desert moss Syntrichia caninervis exhibits one of the most skewed sex ratios in the plant kingdom, with female individuals far outnumbering male individuals (exceeding 14♀:1♂). The "cost of sex hypothesis" derives from allocational theory and predicts that the sex which is most expensive should be the rarer sex. This hypothesis, which, as considered here represents the realized cost of sexual reproduction, is contingent upon two assumptions that are explored: (1) that male sex expression is more expensive than female sex expression, and (2) that sexual reproduction is resource limited. Using inflorescence biomass and discounting sperm, male sex expression was found to be in the neighborhood of one order of magnitude more expensive than female sex expression, and this difference is reflected in higher numbers of gametangia per male inflorescence, presence of paraphyses in male inflorescences, and a much longer developmental time for male inflorescences. The realized cost of female reproduction from two communities dominated by S. caninervis was found to be lower than the realized cost of male sexual reproduction. Resource-limited reproduction was assessed by determining the frequency of sporophyte abortion, the age distribution of sporophyte abortions, and patterns of sporophyte abortion that may be density dependent. Among ten sexually reproducing populations, abortive sporophytes occurred at a frequency of 0.64. Abortive sporophytes averaged 8% the mass of mature sporophytes, and cohort sporophytes from the same individual female were found to abort in a density-dependent pattern. We conclude that the two assumptions, upon which the cost of sex hypothesis depends, are supported.

Unisexual, female- or male-biased populations are common among some clonal plants. Within and among populations, the relative frequencies of males and females can be influenced by sex-specific demographic patterns that, in turn, can be a consequence of life-history characteristics. The objectives of this study were to describe (1) population sex-ratio patterns among habitat patches along a river, and (2) sex-specific patterns of and correlations among life-history clonal traits including: growth rates, number of meristematic tips and asexual reproduction in the dioecious liverwort, Marchantia inflexa. In Trinidad, a section of a stream was surveyed for the occurrence of female and male sex expressing thalli among habitat patches, and habitat characteristics (canopy openness and patch size) were recorded. The numbers of female and male inflorescences were obtained also. Of the 209 patches observed in the field, 83% did not contain sex expressing thalli, 9% contained thalli of both sexes, and the rest contained only female- (4%) or male-expressing (4%) thalli. Sex expression was less common among small patches, and there was a tendency for sex expression to be less likely among patches with the lowest canopy openness. The proportion of male inflorescences among the bisexual patches ranged from 0.22 to 0.80. In a greenhouse, we planted gemmae (asexual propagules) from field-collected isolates: ten female and eight male. On six occasions, we harvested replicates of each isolate to estimate isolate trait means. Females grew faster, produced more meristematic tips and had lower levels of asexual reproduction than males. Number of meristematic tips was negatively correlated with asexual reproduction and positively correlated with growth rate. These sex-specific patterns may lead to the high frequency of single sex patches as well as biased adult population sex ratios that are observed in the field.

The moss Syntrichia caninervis is the dominant soil bryophyte in a blackbrush (Coleogyne ramosissima) community in the southern Nevada Mojave Desert, with a mean cover of 6.3%. A survey of the 10-ha study site revealed an expressed ramet sex ratio of 14 / :1 ? (N 5 890), with 85% of ramets not expressing sex over their life span, and an expressed population sex ratio of 40/ :2 ? :1 /? (female : male : mixed-sex, N 5 89), with 52% of populations not expressing sex. A greater incidence of sex expression was associated with shaded microsites, higher soil moisture content, and taller ramets. Shaded microsites had higher surface soil moisture levels than exposed microsites. In the exposed microhabitat, surface soil moisture was positively correlated with ramet height but not with sex expression. Male ramets and populations were restricted to shaded microhabitats, whereas female ramets and populations were found in both shaded and exposed microhabitats, suggesting gender specialization. The rarity of mature sporophytes, found in 0% of the ramets sampled and in only 3% of the populations, is probably due to the rarity of mixed-sex populations. We hypothesize that mixed-sex populations are rare because of factors relating to male rarity and that the differential cost of sex expression reduces the clonal growth capacity of male individuals.