Production Of Asexual Propagules Research Articles

Rainfall and gemmiferous shoots influence asexual reproduction in two tropical mosses

Background: For some bryophytes, asexual reproduction may be the primary means of population survival, which can be affected by rainfall and moss colony features. Questions and / or Hypotheses: We investigated i) how gemma output differed in two tropical epiphytic mosses with mainly asexual and sexual-asexual reproduction; ii) how is the pattern of gemmae production through an annual interval; and iii) whether gemma production in both species is correlated with rainfall and colony features (shoot density, number of gemmiferous shoots, and sexual structures) per shoot and area (cm2). Studied species / data description /Mathematical model: Calymperes afzelii Sw. and Syrrhopodon incompletus Schwägr. Study site and dates: The sampling was conducted every two months for a year at Agua Blanca State Park in Tabasco, Mexico. Methods: Squares were used to record the gemma production per shoot and cm2, the number of gemmiferous shoots, and shoots with sexual structures. Daily mean precipitation was obtained from a meteorological station. We analysed the effect of rainfall and colony features on gemmae production at the shoot and cm2 levels using generalized linear models. Results: C. afzelii produced gemmae more constantly than S. incompletus. Gemma production is higher during months of high rainfall. The rainfall and number of gemmiferous shoots are suitable predictors of gemma production. Conclusions: Our results exemplify how rainfall and gemmiferous shoots influence the production of asexual propagules in two mosses with different reproductive strategies in the same tropical environment. This information is essential to understand the population dynamics of tropical mosses.

Bacidia gigantensis (Ramalinaceae), a new species with homosekikaic acid from the north shore of Lake Superior in Ontario, Canada

Bacidia gigantensis, a green to greenish-brown, sorediate, crustose to microsquamulose lichen is described as new to science. It is corticolous on mature Thuja occidentalis trees throughout Sleeping Giant Provincial Park on the Sibley Peninsula along the north shore of Lake Superior, Ontario. The species is unusual within Bacidia due to the production of asexual propagules and homosekikaic acid. Placement in Bacidia is based on the characters of the sexual reproductive structures (biatorine apothecia with a true exciple, Bacidia-type asci, and sigmoid, acicular, ascospores), ITS sequence data and molecular phylogenetic analyses of mtSSU sequence data. The latter also inferred a relationship to Bacidiopsora, a tropical genus that has been proposed for synonymy with Bacidia and includes other species with similar chemistries.

GEMMA CUP-ASSOCIATED MYB1, an Ortholog of Axillary Meristem Regulators, Is Essential in Vegetative Reproduction in Marchantiapolymorpha.

A variety of plants in diverse taxa can reproduce asexually via vegetative propagation, in which clonal propagules with a new meristem(s) are generated directly from vegetative organs. A basal land plant, Marchantia polymorpha, develops clonal propagules, gemmae, on the gametophyte thallus from the basal epidermis of a specialized receptacle, the gemma cup. Here we report an R2R3-MYB transcription factor, designated GEMMA CUP-ASSOCIATED MYB1 (GCAM1), which is an essential regulator of gemma cup development in M.polymorpha. Targeted disruption of GCAM1 conferred a complete loss of gemma cup formation and gemma generation. Ectopic overexpression of GCAM1 resulted in formation of cell clumps, suggesting a function of GCAM1 in suppression of cell differentiation. Although gemma cups are a characteristic gametophyte organ for vegetative reproduction in a taxonomically restricted group of liverwort species, phylogenetic and interspecific complementation analyses support the orthologous relationship of GCAM1 to regulatory factors of axillary meristem formation, e.g., Arabidopsis REGULATOR OF AXILLARY MERISTEMS and tomato Blind, in angiosperm sporophytes. The present findings in M.polymorpha suggest an ancient acquisition of a transcriptional regulator for production of asexual propagules in the gametophyte and the use of the regulatory factor for diverse developmental programs, including axillary meristem formation, during land plant evolution.

The double role of pigmentation and convolute leaves in community assemblage of Amazonian epiphytic Lejeuneaceae

BackgroundEpiphytic bryophyte communities in the Amazon forest show a vertical gradient in species composition along the trunk of the host trees. The investigation of species traits related to this pattern has focused on the physiology of selected taxa with a clear preference for one of the extremes of the gradient. Although some species are indeed only found on the tree base or in the outer canopy, the vertical gradient is composed mainly by the variation in the abundances of species with a broader occurrence along the height zones. Therefore, this study approaches the differences among community assemblages, rather than among species, to test the role of morphological and dispersal traits on the establishment of the vertical gradient in species composition.MethodsA character state matrix was built for 104 species of the family Lejeuneaceae recorded as epiphytes in the Amazonian terra firme forests, and six binary traits supposed to influence species occurrence: dark pigmentation on leaves; ability to convolute leaves when drying; possession of thickened cell walls; reproduction mode (monoicous or dioicous); occurrence of asexual reproduction; and facultative epiphyllous habit. Based on a previous dataset on community composition along the vertical gradient, trait occurrences in random draws of the metacommunity was compared to trait occurrences in field data, in order to detect significant deviations in the different height zones.ResultsFour out of the six traits tested showed significantly higher or lower occurrence in the species composition of canopy and/or understory communities. Traits related to high dispersal ability did not vary much along the vertical gradient; although facultative epiphylls were overrepresented on tree base. Dark pigmentation and convolute leaves were significantly more frequent in the canopy communities, but also significantly less frequent in communities at the base of the tree.DiscussionDark pigmentation and convolute leaves seem to be advantageous for the establishment in the canopy zones. They may, respectively, prevent light damage and allow longer periods of photosynthesis. Interestingly, these traits occur randomly along the trunk, but are wiped out of communities on the tree base. In the relatively deep shade of the first meters of the understory, they possibly hamper net carbon gain, the first by darkening the leaf surface and the second by delaying desiccation—which can be damaging under high temperatures and low light. The fact that production of asexual propagules is not overrepresented in the most dynamic microenvironment along the gradient, the canopy, challenges current views of bryophyte life strategy theory.

Effects of initial propagule size and water depth on Butomus umbellatus L. growth and vegetative propagation

Over the last century, flowering rush (Butomus umbellatus L.: Butomaceae) has escaped its native Eurasian range and has become a problematic species in parts of North America. As an aquatic invasive species, flowering rush has degraded wetlands in introduced areas and has interfered with human water usage. Although experimental work has been published regarding the reproductive biology of the species, we found few manipulative experiments aimed at testing ecological attributes of this species in the literature. The research reported here demonstrates that flowering rush is capable of aggressive clonal growth and propagation, whether from vegetative rhizome buds or from fragments of rhizomes themselves. This species was capable of growth along a depth gradient from zero to 132 cm and showed an ability to adjust biomass allocation along that gradient; however, biomass and asexual propagule production declined at depths beyond approximately 50 cm. The combination of regrowth from relatively small propagules, ability to tolerate depths of greater than one meter, and plasticity of biomass allocation along habitat gradients make this species a potential threat in many aquatic and wetland habitats in its introduced range. However, certain aspects of its biomass allocation strategies may enhance chemical control for plants growing at greater depths or those regenerating from rhizome buds, both of which tend to have greater S:R biomass ratios.

Species delimitation and phylogeography of the Pectenia species-complex: A misunderstood case of species-pairs in lichenized fungi, where reproduction mode does not delimit lineages

The main goal of this work was to study species boundaries in the genus Pectenia and elucidate the biogeographic history of the four currently accepted species. To accomplish this, we included 92 specimens across the range of Pectenia in Europe and northern Africa. We used three nuclear loci and assessed species circumscription using two Bayesian coalescent-based methods and the Bayes Factor approach. We reviewed the value of reproductive mode and other morphological features as predictors of monophyletic groups. Our results suggest that the production of asexual propagules and sexual structures are not characterizing monophyletic groups. The genus includes two morphologically well-characterized main lineages, where one lineage is composed by two sub-lineages that are with a case of cryptic speciation explained by a biogeographic pattern. We suggest treating the two lineages as two species, which are characterized by lobe structure: Pectenia plumbea and P. atlantica. Both of these species include samples with asexual propagules and apothecia, and thus do not correspond to any of the earlier morphologically defined species. The results of the biogeographic analysis indicate that the Mediterranean basin is the most likely ancestral distribution area of P. plumbea, whereas P. atlantica probably originated in Macaronesia.

Reproductive allocation between the sexes, across natural and novel habitats, and its impact on genetic diversity

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.

Gemma output in the liverwort Lophozia ventricosa (Dicks.) Dumort: spatial variation, density dependence, and relationships among production components

Although gemma production is common among liverworts, and thought to play a key role in their population dynamics, quantitative data on numbers produced at shoot and colony levels, or on spatial variation in these numbers, are very sparse. Here we investigate gemma output of a boreal and arctic liverwort species, Lophozia ventricosa, at populations in Trøndelag, a boreal region of central Norway, and in arctic tundra on Svalbard. Production parameters investigated include colony size, shoot density, number of gemmae per shoot, proportion of shoots gemmiferous, and gemmiferous shoot density. Colony-level output was calculated as the product of the number of gemmae per shoot, colony size, and gemmiferous shoot density. Nested analysis of variance, used to spatially partition variance in these gemma-production components, reveals that the vast majority of the variation lies at the measurement level, i.e. among shoots within colonies or among colonies within plots. The only significant difference between the two geographic areas is that in boreal sites shoots tend to produce slightly more gemmae, and form larger, denser, colonies. This translates to somewhat higher colony-level output in boreal, compared to arctic, sites. Evaluation of a structural equations model reveals intricate patterns of relationship among the production components and provides strong evidence of negative density dependence of shoot-level production. We argue that explicit evaluation of size–number tradeoffs, allometric scaling of production with shoot size, and detailed studies of genetic versus phenotypic effects on production levels, are necessary to understand how asexual propagule production is shaped by selection on life histories.

Coelomycete Fungi in the Clinical Lab

Most human mycoses are incited by fungi that replicate by the production of asexual propagules (usually called conidia), which are readily dispersed throughout nature and also in vitro. Fungi that are acquired in this manner include a diversity of yeasts and dermatophytes, as well as those whose acquisition is primarily pulmonary, such as the thermally dimorphic primary pathogens, and several opportunistic genera such as Aspergillus, Fusarium and others. Recent reports, however, indicate an increasing number of infections, ranging from superficial to systemic, that are due to coelomycetous fungi. In these fungi, the asexual spores are produced within fruiting bodies referred to as a conidiomata. As these conidia are less frequently airborne, the method of acquisition is commonly by traumatic implantation of plant material or by a diversity of contaminated fomites, rather than by inhalation. These infections are also more commonly seen in immunocompromised individuals. In this work, we have attempted to provide a historial overview as well as the current taxonomy for this group of fungi, an up-to-date assessment of the scope of infections caused by various coelomycetous genera, their clinical entities, useful tools for isolation and identification, and general guidelines for the appropriate management and treatment of these mycoses.

Asexual propagules as an adaptive trait for epiphylly in tropical leafy liverworts (Lejeuneaceae)

Many links between form and function are described in the context of adaptation. Several morphological and life-history traits in the leafy liverwort family Lejeuneaceae (Marchantiophyta) have been hypothesized to be adaptations for living on the surface of leaves of vascular plants (epiphylly). There have been, however, no rigorous tests of these hypotheses. Using a recently published phylogeny of Lejeuneaceae and trait data from published monographs, I tested the correlations of putative adaptive traits with the incidence of epiphylly. Both cross-species and phylogenetic-based analyses of trait data were performed to distinguish the patterns of shared evolutionary history from independent origins of putatively adaptive traits. The rates of transitions between different combinations of character states were also calculated to determine whether traits were more likely to evolve in the presence of epiphylly. Only one trait, production of asexual propagules, was correlated with epiphylly in the phylogenetic-based analysis. The rate of transition to asexual propagules was also significantly higher in the presence of epiphylly. Other traits correlated with epiphylly appeared to be the results of shared evolutionary history among sister taxa and therefore not due to adaptive evolution. The present study distinguished production of asexual propagules from other traits as a key adaptive response to living on the leaf surface. No other putative "adaptive" traits to epiphylly showed evidence of being specific adaptation to epiphylly. The results highlight the importance of phylogenetically controlled methods in determining an adaptive function of traits.

Turion production and nutrient reserves in Potamogeton crispus are influenced by sediment nutrient level

The influence of sediment nutrient content on asexual propagule production in plants is poorly understood, especially in submersed macrophytes. To improve the understanding of turion (an aboveground asexual propagule) production, Potamogeton crispus L. was planted in 2 experimental conditions that differed in their levels of sediment nutrients. After 10 wk of growth, sediment nutrient level had significantly impacted the plants' vegetative and reproductive traits. Most vegetative trait measures of P. crispus (e.g. leaf mass fraction and stem mass fraction) were higher when plants were grown in nutrient-rich sediment compared with plants grown in nutri- ent-poor sediment. Reproductive trait measures (e.g. turion mass fraction and individual turion biomass) were higher in plants grown in nutrient-poor sediment compared with plants grown in nutrient-rich sediment. Plants grown in nutrient-rich sediment produced a larger number of small turions ( 100 mg) and stored more total nonstructural carbohydrate (the major proportion of which was starch) in them. Path analysis revealed that total plant biomass (strong positive effect), leaf and stem biomass (weak negative effects) had direct effects on total turion biomass, which consequently affected turion size and number. Moreover, ramet number and mean shoot height also had weak but direct effects (both negative effects) on turion size and number. These results demonstrate that sediment nutrient content mediates plant vegetative traits and can subsequently affect turion production and reserves in P. crispus.

Cellular differentiation in moss protonemata: a morphological and experimental study.

Previous studies of protonemal morphogenesis in mosses have focused on the cytoskeletal basis of tip growth and the production of asexual propagules. This study provides the first comprehensive description of the differentiation of caulonemata and rhizoids, which share the same cytology, and the roles of the cytoskeleton in organelle shaping and spatial arrangement. Light and electron microscope observations were carried out on in vitro cultured and wild protonemata from over 200 moss species. Oryzalin and cytochalasin D were used to investigate the role of the cytoskeleton in the cytological organization of fully differentiated protonemal cells; time-lapse photography was employed to monitor organelle positions. The onset of differentiation in initially highly vacuolate subapical cells is marked by the appearance of tubular endoplasmic reticulum (ER) profiles with crystalline inclusions, closely followed by an increase in rough endoplasmic reticulum (RER). The tonoplast disintegrates and the original vacuole is replaced by a population of vesicles and small vacuoles originating de novo from RER. The cytoplasm then becomes distributed throughout the cell lumen, an event closely followed by the appearance of endoplasmic microtubules (MTs) in association with sheets of ER, stacks of vesicles that subsequently disperse, elongate mitochondria and chloroplasts and long tubular extensions at both poles of the nucleus. The production of large vesicles by previously inactive dictysomes coincides with the deposition of additional cell wall layers. At maturity, the numbers of endoplasmic microtubules decline, dictyosomes become inactive and the ER is predominantly smooth. Fully developed cells remain largely unaffected by cytochalasin; oryzalin elicits profound cytological changes. Both inhibitors elicit the formation of giant plastids. The plastids and other organelles in fully developed cells are largely stationary. Differentiation of caulonemata and rhizoids involves a remarkable series of cytological changes, some of which closely recall major events in sieve element ontogeny in tracheophytes. The cytology of fully differentiated cells is remarkably similar to that of moss food-conducting cells and, in both, is dependent on an intact microtubule cytoskeleton. The disappearance of the major vacuolar apparatus is probably related to the function of caulonema and rhizoids in solute transport. Failure of fully differentiated caulonema and rhizoid cells to regenerate is attributed to a combination of endo-reduplication and irreversible tonoplast fragmentation. The formation of giant plastids, most likely by fusion, following both oryzalin and cytochalasin treatments, suggests key roles for both microtubules and microfilaments in the spatial arrangement and replication of plastids.

Persistence of the sexes in metapopulations under intense asymmetric competition

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.

Asexual Reproduction of Phytophthora capsici as Affected by Extracts from Agricultural and Nonagricultural Soils

ABSTRACT Formation of sporangia and zoospores in species of Phytophthora is known to be influenced by soil microbial and chemical composition. In Phytophthora capsici, the study of the relationship of soil chemical composition to production of sporangia and zoospores has been limited. P. capsici is a soilborne pathogen of a wide array of vegetable crops, including chile pepper (Capsicum annuum) in New Mexico. Production of sporangia and zoospores by P. capsici was evaluated in extracts of soils from three different environments in New Mexico: (i) agricultural environments with a long history of chile pepper cropping and occurrence of P. capsici (CP), (ii) agricultural environments with no history of chile pepper cropping and no occurrence of P. capsici (Non-CP), and (iii) nonagricultural environments consisting of forests and rangelands (Non-Ag). There was a significant difference in production of P. capsici asexual propagules, expressed as natural log (number of sporangia x number of zoospores), among the three environments (P = 0.0298). Production of propagules was 9 to 13% greater in Non-Ag than in CP or Non-CP environments. Stepwise multiple discriminant analysis and canonical discriminant analysis identified the edaphic variables Na, pH, P, organic matter content, and asexual propagule production as contributing the most to the separation of the three environments. Two significant (P < 0.0001) canonical discriminant functions were derived with the first function, accounting for approximately 75% of the explained variance. Based on the two discriminant functions, approximately 93, 86, and 89% of observations in CP, Non-CP, and Non-Ag environments, respectively, were classified correctly. Soils from agricultural and nonagricultural environments differentially influence production of sporangia and zoospores in P. capsici, and soil samples could be effectively classified into agricultural and nonagricultural environments based on soil chemical properties and the production of asexual propagules by P. capsici in soil extracts.

Geographic and phylogenetic evidence for dispersed nuclear introgression in a daphniid with sexual propagules

The role of among-species gene flow in eukaryotic evolution remains controversial. Putative hybrid lineages are common in water fleas, but their ecological success is often associated with polyploidy and the production of asexual propagules. Advanced hybrid lineages with sexual propagules are expected to be geographically restricted because their successful dispersal is contingent on overcoming fertility complications, assimilation by parent taxa, and competition with parent taxa. Here we provide evidence that a diploid lineage of Daphnia has been formed by introgression between distantly related species and attained a broad distribution (Nearctic) despite its requirement for sexual propagules. The evidence is based on geographical discordance, phylogenetic discordance, recombinant genotypes and additive genotypes of the nuclear internal transcribed spacer regions (ITS) and mitochondrial DNA. Additive genotypes also provided evidence of hybridization between introduced European Daphnia and North American Daphnia. We argue that the unique biology of Holarctic lacustrine water fleas and the spatial separation of lineages during Pleistocene glaciation have promoted hybridization and its evolutionary consequences.

The balance between sexual and asexual reproduction in plants living in variable environments

Abstract The balance between sexual and asexual propagule production is studied in an evolutionary model where plants produce the two kinds of propagules in genetically determined proportions. The male function of plants producing asexual propagules can be varied, and the sexual and asexual propagules carry different probabilities to turn into new reproductive individuals. These fitnesses may vary over years. The evolution of the population’s reproductive system is studied assuming modifier alleles with small effects. In this setting a balanced, mixed reproductive system can evolve, but only if the difference in fitness between the sexual and asexual propagules varies over years. When the two kinds of propagules are very similar to each other, as is often the case with sexual and asexual seed formation, evolution will tend towards a state dominated by the one or the other reproductive system.

The ecology of subdivided populations of a clonal freshwater bryozoan in southern England

Data on patterns of incidence, physicochemical properties of sites, transplant experiments and patterns of reproduction provide insights into the ecology of subdivided populations of the freshwater bryozoan. Cristatella mucedo. Collectively, these data indicate that C. mucedo is distributed as a metapopulation composed of highly clonal sub-populations in the Thames Valley region. Canonical discriminant function analysis of data on water chemistry and site size indicated that physicochemical variables did not discriminate between sites in which C. mucedo was present and absent suggesting that suitable sites are present but unoccuppied as would be expected in a metapopulation. The establishment of transplanted colonies in a previously unoccuppied site provides further evidence that suitable but unoccuppied sites are present in the region. Apparent extinction and colonization events in local populations are consistent with expected dynamics of sub-populations within a metapopulation. Generally low proportions of colonies producing larvae, a short phase of sexual activity, non-detection of sexual activity in many populations, and simultaneous and similar production of asexual (statoblasts) and sexual (larvae) propagules indicate that populations in the Thames Valley region invest predominantly in clonal replication. These high levels of clonality may contribute to metapopulation dynamics by increasing the likelihood of local extinction when populations are challenged by adverse biotic or abiotic conditions. Notable r-selected traits such as rapid clonal growth and massive production of asexual propagules represent a viable ecological strategy for freshwater bryozoans since the relative isolation of habitats allows highly clonal populations to persist through metapopulation dynamics at the regional scale.

There's More to a Mushroom than Meets the Eye: Mating Studies in the Agaricales

Mating studies and related research are used in discussions of the following subjects: 1) long-distance mating phenomena, including strain-specific ability to dikaryotize mates; 2) the “biological species concept;” 3) clamp connection suppression in certain long-distance dikaryotization; 4) discrepancies between in vivo and in vitro mating behavior; 5) independent evolutionary rates of various characters; 6) occurrence and retention of amphithallism; and 7) the role of asexual propagule production in the mushroom life-cycle. Examples are drawn from several genera of Agaricales.

There's more to a mushroom than meets the eye: Mating studies in the Agaricales

Mating studies and related research are used in discussions of the following subjects: 1) long-dis- tance mating phenomena, including strain-specific ability to dikaryotize mates; 2) the biological species concept; 3) clamp connection suppression in certain long-distance dikaryotization; 4) discrepancies be? tween in vivo and in vitro mating behavior; 5) inde- pendent evolutionary rates of various characters; 6) occurrence and retention of amphithallism; and 7) the role of asexual propagule production in the mush- room life-cycle. Examples are drawn from several gen- era of Agaricales.