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Sex ratio variation is common among organisms with separate sexes. In bryophytes, sex chromosome segregation at meiosis suggests a balanced progeny sex ratio. However, most bryophyte populations exhibit female-biased phenotypic sex ratios based on the presence of reproductive structures on gametophytes. Many bryophyte populations do not form sexual organs, and genotypic sex ratio variation in such populations is mostly unknown. We tested sex expression, and phenotypic and genotypic sex ratios against environmental parameters in natural populations of the unisexual wetland moss Drepanocladus lycopodiodes at 11 sites in each of three regions in southern Sweden. We identified sex in 660 individual ramets, based on sexual structures, when present, or with a specifically designed molecular marker, when absent. All regions exhibited a female bias in phenotypic and genotypic sex ratios. Sex ratio biases and sex expression differed between regions. Sex ratios were less female-biased in larger patches. Wetter patches exhibited a stronger female bias in genotypic sex ratio and lower sex expression. This is the first evidence of environmental effects on genotypic sex ratio in mosses. A higher frequency of females in wet patches could be due to higher female resource demands for sporophyte production or higher male sensitivity to wetness. A higher incidence of females than males in moister sites aligns with female flowering plants, but differs from reproductive bryophytes in drier environments. Taken together with previous results, our data indicate that sex ratio variation and its drivers differ among species, their life histories and environments.

In the Baltic area, the long-lived dioicous wetland moss Drepanocladus turgescens (T.Jensen) Broth. produces sporophytes rarely and at irregular intervals. Based on surveys of sporophyte occurrences at 13 sites in two regions in northern Gotland (Sweden) during three to five years, we ask: (1) Is sporophyte formation associated with precipitation and a precipitation index that considers the dry periods during July-August of the preceding year, when gametangia are formed and fertilization occurs? (2) Does the estimated spore output suffice for the species’ long-term persistence of the (Northern) European population species? In one of the study regions, where D. turgescens occurs in depressions, sporophyte formation was associated with the two precipitation parameters. In the other study region, with relatively higher precipitation and exposed occurrences on a slightly sloping bedrock with very little accumulated soil, no such association existed. We suggest that this lack of weather effects results from that the exposed rock habitat requires longer continuously wet periods than the depression habitat to allow for gametangia initiation and development, and fertilisation. Average spore production for six spore capsules, from three Gotland localities was 181,000. Based on the sporophyte counts during the survey years, we estimated the total reproductive output as 411.5 million spores in 2013, and 42.5 million in 2015, in the two respective study regions. Taken together with data on haplotype patterns and considering observations on recent colonisations, we argue that such a relatively low and episodic regional spore production is sufficient to maintain global populations of long-lived species, even if these occur in specialized and geographically restricted habitats.

Sex ratio variation is commonly observed in natural populations of many organisms with separate sexes and genetic sex determination, including bryophytes. Most bryophyte populations exhibit female-skewed expressed adult sex ratios, generally inferred from counts of sexually mature plants. For the rarely sexually reproducing perennial dioicous moss Drepanocladus lycopodioides, we showed that a female bias also exists in the genetic adult sex ratio, using a specifically designed molecular sex-associated marker. Here, we investigated whether the meiotic spore sex ratio contributes to the observed bias in genetic adult sex ratio in natural populations. Earlier attempts to study meiotic sex ratios have involved commonly cultivated ruderals that rapidly express sex in the laboratory. We established single-spore cultures from field-collected sporophytes from these populations and used the marker to assess the sex of individual sporelings. Spore germinability was (near) complete, and mortality among sporelings was virtually absent. The true meiotic sex ratio did not differ from equality, but strongly differed both from the observed genetic sex ratios in the natural adult populations, and from the European scale genetic sex ratio. We conclude that the biased population sex ratios in this species arise at life cycle stages after spore germination. Sexual dimorphism may selectively favour female proliferation during some phase of gametophyte development. Based on methodological progress, we successfully used a perennial study species with rare sexual reproduction, which significantly broadens the life history spectrum investigated in bryophyte sex ratio studies.

Sex identification before sexual maturity is notoriously difficult in plants with separate sexes, but is crucial to address many life history related issues. To study the performance of the two sexes in the rarely sexually reproducing dioecious moss Drepanocladus turgescens a molecular sex marker is needed. The female-targeting marker previously developed for D. trifarius and D. lycopodioides amplifies for a few D. turgescens males, which can thus not be distinguished from females. In a significant addition to the earlier developed method we sequenced the portion successfully amplified by the primers PT-3f and PT-3r for six females and three males. Differences between males and females were revealed at five sequence positions. Examination of a total of fourteen females and seven marker amplifying males confirm that females and such males differ consistently at these positions. The usefulness of a previous protocol for moss sex identification is thus extended to another dioecious moss by the addition of a step where a portion of the sex-correlated region is sequenced.

Hedenas, L. & Bisang, I. 2019. Are the remains of the Central European population of Drepanocladus turgescens genetically distinct from Scandinavian populations? – Herzogia 32: 209–218.The wetland moss Drepanocladus turgescens occurs in interglacial refugia in both mountains and lowlands of Europe. It is relatively frequent in Scandinavia, but due to habitat deterioration, it has severely declined in Central Europe. We compare haplotype variation based on the nuclear markers ITS (1+2) and gpd, and the plastid rpl16 in 103 samples from both Scandinavia and Central Europe, including the Alps. The Central European population harbours five haplotypes that are unknown in NW Europe. It is genetically similar to southern Scandinavian populations, but differs clearly from the populations in the Scandinavian mountain range and on Svalbard. Despite that D. turgescens has disappeared from many lowland localities in Central Europe, haplotype numbers and diversity do not differ from values in Scandinavia. Central European nucleotide diversity is slightly lower than in Scandinavian populations. The high number of private haplotypes in a limited sample and the still high genetic diversity suggest that conservation measures in Central Europe are motivated. We suggest assessing the spatial and temporal genetic variation in Central Europe, to identify the regions with the highest genetic diversity, and those which genetic diversity has been lost compared to records from the beginning of the 20th Century. This will allow well-targeted and efficient conservation actions.

Summary: The evolution of island syndromes has long served as a model to understand the mechanisms accounting for phenotypic differentiation. Combining literature data with actual observations, we determine whether typical syndromes such as the loss of dispersal power and the bias towards self-compatibility (Baker's law) apply to vagile organisms, using bryophytes as a model. The life-history traits (LHTs) observed in oceanic island floras were statistically different from those observed on continents, evidencing the evolution of island syndromes. In contrast, LHTs of continental and continental island floras were similar, pointing to differences in migration intensity between continents, continental islands and oceanic islands. The proportion of bisexual species was significantly higher on oceanic islands than on continents. A significant proportion of species that are unisexual or bisexual on continents shifted towards exclusive bisexuality on oceanic islands, suggesting that Baker's law applies to bryophytes. The underlying mechanisms, however, probably differ from in situ selection for selfing. The proportion of species producing specialized asexual diaspores, which are assumed to play a role in short-distance dispersal (SDD), was higher on oceanic islands than on continents. The proportion of species producing spores, which are involved in long-distance dispersal (LDD), exhibited the reverse trend, suggesting a shift in the prevalent reproductive strategy to favour SDD on oceanic islands. Approximately 50% of the species, however, maintained the ability to produce sporophytes on oceanic islands, and the relative frequency of fertile shoots within collections of four model species was even higher on islands than on continents. Synthesis. Bryophytes exhibit typical island syndromes, indicating that migration rates between oceanic islands and continents are not sufficient to prevent the effects of genetic drift and contradicting the view that the sea does not impede migration in the group. Significant shifts in life-history traits (LHTs) towards increased production of specialized asexual diaspores and decreased sporophyte production on oceanic islands indeed point to a global loss of long-distance dispersal (LDD) ability. The maintenance of traits characteristic for LDD in a large number of species has, however, substantial consequences for our understanding of island plant evolution, and in particular, for our vision of islands as evolutionary dead ends. © 2013 British Ecological Society.

The moss Drepanocladus trifarius (F. Weber & D. Mohr) Broth. ex Paris was used as a model species for a first evaluation of whether male and female haplotype patterns based on a combination of the nuclear molecular markers ITS and gpd, and the chloroplast rpl16 are congruent or not. In 23 female and 23 male shoots from specimens sampled in Northern and Central Europe, sex was determined either by the presence of sexual branches or by a recently developed molecular marker. Analysis of molecular variance (AMOVA) showed that a small (6%) and almost significant (p = 0.066) fraction of the variation within the data is due to differences between the genders and that the haplotype diversity is higher among females than among males. No significant differences in haplotype variation were found among geographical regions. The near significant differences between females and males, despite low variation in ITS and rpl16, in this first study ever of potential differences in haplotype variation between genders of dioecious mosses suggests that further investigations of more specimens and more variable molecular markers should be performed. Such studies could potentially reveal patterns of relevance to understanding, for example, immigration routes and to pin-point refugial areas of different significance to the respective genders.

Premise of research. Maintenance of dioecious and monoecious sexual systems at nearly equal frequencies, infrequent sexual expression, and distinctly female-skewed sex ratios among the dioecious species are reproductive characteristics of bryophytes, which are otherwise unusual among embryophytes. Most sex ratio assessments to date have relied on gametophytes forming sexual organs, and how these reflect genetic genders is largely unresolved.Methodology. For the European wetland moss Drepanocladus lycopodioides, we ask whether the adult expressed sex ratio is more strongly female biased than the “true” population sex ratio based on genetically male and female plants, i.e., whether males exhibit a lower sex expression rate than females (shy males). We assess expressed sex ratio on the basis of sex expression in individually scored herbarium specimens. We directly and on a large geographic scale assess nonexpressed sex ratio, for the second time in a moss, by sexing individual shoots from nonexpressing speci...

The habitat of the pleurocarpous moss Drepanocladus trifarius is commonly described as mineral-rich wet fens. We sampled individual D. trifarius shoots at 214 pre-defined randomly distributed spots in an area of ca 15 km2 in a sloping fen in central–western Sweden. We assessed the habitat variation of the sampling spots in this area by means of a multi-variate analysis (DCA) based on the species identity of the ten shoots adjacent to D. trifarius, and by indicator values for light availability and substrate moisture, acidity, and nutrient availability of the associated species. Both approaches indicated that D. trifarius occurred in well lit and constantly moist, wet or submerged places. Most spots were weakly acid to sub-neutral, but some spots had distinctly acid conditions. Generally the spots were nutrient-poor, but a few were nutrient- rich. DCA revealed gradients from relatively wet, sub-neutral to basic towards drier and more acid habitats, and from nutrient-poor to -richer environments. The species obviously exhibits a broader than expected niche width with respect to substrate acidity and nutrients. We suggest that succession, disturbance, or climatic factors may explain the species’ occurrences in different habitats.

Background: We recently demonstrated that dwarf male plants are much more common among mosses than hitherto thought. Dwarf plants, producing functional male sexual organs occur in 10–20% of the moss species worldwide. Aims: We investigated how an inadvertent omission of dwarf males affects estimates of male sex expression rates and sex ratios. Methods: We recorded frequencies of specimens with female-expressing plants, male-expressing normal-sized and/or dwarf plants, and sporophytes in herbarium material of five model species from Macaronesia. We analysed how frequency estimates of male occurrence and sex ratios were affected by excluding dwarf males. Results: Occurrence of dwarf males was positively associated with sporophyte formation. When dwarf males were excluded, male mate availability was missed in 51–61% of specimens (in 74–76% of sporophyte-containing specimens). Specimen-level sex ratio was balanced in material with sporophytes in the three species exhibiting male dwarfism, but strongly female ...

Dwarf males occur in several animal groups but are unique to mosses among the green land plants. Mosses, with more than 50% unisexual species and common fertilisation distances in the range of a few decimetres, have evolved various means to cope with potential problems to successfully achieve fertilisation and to ensure sporophyte production and sexually produced diaspores. We explore the abundance of different kinds of extreme female-biased sexual size dimorphism in homocostate pleurocarpous mosses. Based on direct observations and literature information, we investigated the large-scale geographical distribution of this phenomenon, and whether male dwarfism was associated with family position. Almost 60% of 1737 species with information about sexuality are dioecious, and males are known in 769 dioecious species. Dwarf males occur in 178 of these (23%), and are considered obligate in 113 species (63% of 178). We thoroughly examined a subset of 162 species. Among these 72 species (44%) form dwarf males, but only 18 species (25% of 72) produce obligate dwarf males. We conclude that especially facultative male dwarfism is much overlooked among dioecious mosses. The distribution of dioecious species and dwarf males among the latter was related to family membership, but showed little correlation with geographic area. Male dwarfism thus appears useful as a taxonomic character to define bryophyte families. We estimate that between roughly one quarter and almost half of dioecious pleurocarpous moss species exhibit male dwarfism, and the majority of these (75%) form dwarf males facultatively. Male dwarfism in mosses is suggested to have evolved as a result of (1) competing selective pressures of the cytoplasmic and nuclear genomes, (2) competition between the sexes, (3) selection for reduced fertilisation distances, or a combination of these. The associated niche shift of the males may also provide these with a suitably humid and nutrient-rich habitat.

Dioecious plants, including many bryophytes, rarely exhibit discernible sexual dimorphism before sexual maturity. Because many species and populations of dioecious bryophytes do not express their sex, it remains mostly unresolved whether expressing individuals reflect the ratios of genetically male and female plants. The present study assesses the population sex ratio of the wetland moss Pseudocalliergon trifarium in central and northern Europe. For the first time in a bryophyte, we estimate the sex ratio in a population by assessing directly both expressing and non-expressing plants. Expressed gender ratio was assessed from herbarium specimens. Single shoots from non-expressing specimens were sexed using a recently developed molecular sex marker. On the basis of the female and male frequencies in these two data sets and the overall proportion of expressing specimens, we estimate the European population sex ratio to be 1.93 : 1 (female/male). Expressed, non-expressed, and population sex ratios are not significantly different from each other, suggesting that gender differences in rates of sex expression cannot account for the female bias. Earlier studies of P. trifarium failed to reveal gender-specific growth rates or pre-zygotic reproductive costs. Gender differences at the spore to protonemal stage, in mortality, or niche preferences could potentially explain the uneven sex ratio. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 132–140.

Evidence is accumulating that significant amounts of substances can move internally in ectohydric bryophytes, which lack specialized structures for internal water movement. This potential for resource translocation is likely to affect the productivity in individual shoot sections. We tested whether annual growth intervals in the pleurocarpous moss Pseudocalliergon trifarium were performing as independent units by comparing the biomass of annual increments within individual shoots from 13 populations from northern and central Sweden. Pseudocalliergon trifarium has a distinct shoot architecture with discrete annual segments and is therefore well suited to study annual biomass allocation patterns. Mass of the most recent growth interval was directly correlated with segment mass of at least two preceding years. The strength of the relationship between current growth and four consecutively older annual increments decreased linearly with age of the annual segments, suggesting that correlations within shoots were the result of resource translocation rather than of among-year correlations in local environmental factors. Our data suggest that interconnected segments are physiologically integrated, and that size relationships between successive increments are relatively independent of environmental conditions. We conclude that annual growth intervals cannot be considered as independent assimilatory units. Internal resource transfer across annual segments may buffer variation in external availability of or internal demands for resources, and has implications for the understanding of growth patterns and reproductive investments in ectohydric bryophytes.

A fundamental assumption in life-history theory is that reproduction is costly. Higher reproductive investment for fruits than for flowers may result in larger costs of reproduction in females than in males, which is often used to explain male-skewed sex ratios in unisexual seed plants. In contrast, bryophytes have predominantly female-biased sex ratios, suggested to be a product of a higher average cost of sexual reproduction in males. Empirical evidence to support this notion is largely lacking. We investigated sex-specific reproductive effort and costs in the unisexual moss Pseudocalliergon trifarium that has a female-dominated expressed sex ratio and rarely produces sporophytes. Annual vegetative segment mass did not differ among male, female, and non-expressing individuals, indicating that there was no threshold-size for sex expression. Mean and annual mass of sexual branches were higher in females than in males, but branch number per segment did not differ between sexes. Prefertilization reproductive effort for females was significantly greater (11.2%) than for males (8.6%). No cost for sexual branch production in terms of reduced relative vegetative growth or decreased investment in reproductive structures in consecutive years was detected. A higher realized reproductive cost in males cannot explain the unbalanced sex ratio in the study species.

We investigated the cost of sporophyte production in the moss Dicranum polysetum both by examining patterns of growth and reproduction in unmanipulated shoots and by experimentally manipulating sexual reproduction. The estimated proportion of total carbon investment allocated to sexual reproduction in sporophyte-producing shoots over the study period was 74.8%. Unmanipulated shoots that aborted all sporophytes had a significantly higher growth in the top shoots than shoots that produced sporophytes. In sporophyte-producing shoots, total apical growth decreased proportionately with the number of sporophytes. Experimental prevention of sporophyte development resulted in significantly higher total apical growth of the gametophytes. Shoots where current perichaetia were lacking when marked had a mass increase in the top shoots similar to manipulated sporophytic shoots whereas sporophytic control shoots grew significantly less than these two categories. The difference between control shoots and manipulated shoots in the mass of vegetative apical growth was mainly because of different length increments whereas mass per unit length was similar between groups. The probability to reproduce sexually in the year after the manipulation, and the biomass allocated to this reproduction, were not affected by the experimental treatment.

Infraspecific genetic diversity is generally underestimated in biodiversity assessments. We use haplotype patterns based on the nuclear gpd and plastid rpl16 to examine whether genetic diversity is related to geography, gender, habitat and/or frequency of sexual reproduction in Drepanocladus lycopodioides. This moss is restricted to western Eurasian semi-natural and natural habitats and decreases in frequency in many parts of Europe. Haplotype diversity differs among three regional populations (Öland, Gotland, Stockholm archipelago) in its South Swedish Baltic core distribution area and is positively affected by patch size. The regional populations differ from each other genetically and haplotype variation is unequally partitioned between the genders, most likely a result of immigration history and limited equalizing effects of sexual reproduction. In a Holocene context, the regional populations of Öland and Gotland display evidence of a decrease or bottleneck, and immigration into both regions. We suggest that higher haplotype diversity in Gotland and Öland and lack of migration to the Stockholm archipelago may be an effect of longer colonization history of the former, and niche pre-emption in the natural habitats of the latter. The Baltic population is representative for the genetically relatively homogeneous European population, and D. lycopodioides displays low ITS variation compared with other European mosses. In a conservation context it is relevant that the three regional populations are not interchangeable. It is of concern that three populations within the species’ core distribution are vulnerable. Our results strongly suggest that infraspecific genetic diversity must be considered in the management of the species at the continental level.

We investigated biomass allocation patterns in sporophyte-bearing and non-sporophytic plants of the perennial moss Dicranum polysetum Sw. from southern Sweden by comparing dry masses of various reproductive and vegetative plant modules. Assessing parental vegetative biomass is critical in bryophytes due to continuous decay of basal shoot portions. We propose a method to estimate the photosynthetically active gametophyte biomass at the onset of the current sporophyte cycle retrospectively. With this measure for vegetative plant size, the proportional investment in reproductive structures, reproductive effort, was 16% when sporophytes were produced, and 1.3% when perichaetia remained unfertilized. In sporophytic plants, vegetative apical growth and reproductive output (measured both as dry mass and sporophyte number) were positively correlated, and reproductive effort was inversely related to the mass of the annual segment preceding sporophyte initiation. The development of mature sporophytes was n...