Large Clones on Cliff Faces: Expanding by Rhizomes through Crevices

Background and Aims Large clones of rhizomatous plants are found in many habitats, but little is known about whether such clones also occur on cliff faces where environmental conditions are extremely harsh and heterogeneous. Methods Using molecular (intersimple sequence repeat, ISSR) markers, the genotypic composition of a cliff-face population of Oxyria sinensis in Sichuan, China, was investigated. Key Results The 98 O. sinensis ramets sampled belonged to 12 different genotypes (clones). The three most frequent clones were represented with 45, 22 and 12 ramets, respectively; the remaining nine were represented with only one to five ramets. The three largest clones spanned at least 2·7 m in the vertical direction and 4·6-6·9 m in the horizontal direction on the cliff face. Conclusions On the cliff face, large clones of O. sinensis are formed by rhizomes growing along the crevices. Expansion by rhizomes may help O. sinensis to exploit the patchy resources and support establishment and growth of new ramets. Moreover, rooted ramets connected by rhizomes may effectively reduce the susceptibility of O. sinensis to rock fall and erosion and thus greatly improve the chances for long-term survival. The multi-clone structure indicates that sexual reproduction is also important for the long-term persistence of O. sinensis populations on cliff

Sex and the Single Gametophyte: Revising the Homosporous Vascular Plant Life Cycle in Light of Contemporary Research

Homosporous vascular plants are typically depicted as extreme inbreeders, with bisexual gametophytes that produce strictly homozygous sporophytes. This view is promulgated in textbook life cycles despite ample evidence that natural populations of most species regularly outcross. We review research on a variety of mechanisms, including genetic load, asynchronous production of eggs and sperm, and pheromonal control of gamete production, that actively promote heterozygosity in ferns and lycophytes. Evolution of the land plants cannot be reconstructed without accurate depictions of the unique life cycle that has helped make ferns the second most diverse lineage of vascular plants on Earth. With revised illustrations and definitions, we provide scientists, educators, and students with a contemporary understanding of fern and lycophyte reproduction, revealing them as evolutionarily dynamic and exploiting a wide range of mating systems

Photographic analysis of field-monitored fern gametophyte development and response to environmental stress

Premise: Ferns differ from seed plants in possessing a life cycle that includes a small, free-living, seemingly vulnerable gametophyte stage in which sexual reproduction occurs. Most research on the response of fern gametophytes to environmental stress has been conducted on gametophytes grown in culture or harvested from natural habitats and subsequently manipulated and tested in laboratory experiments. We present a fixed-distance photographic methodology for monitoring longevity of gametophytes and their response to environmental stress in natural, undisturbed habitats over their life spans. Methods: We present methodology for non-invasive monitoring of growth and development in response to environmental factors, using programmed, fixed-distance photography, coupled with computer analyses allowing qualitative and quantitative comparisons. We tracked growth rates and stress responses of individual gametophyte plants to seasonal changes in a temperate climate. Results: Gametophytes and young sporophytes survived freezing and drought in temperate habitats, as we document through photographs and growth measurements. Gametophyte growth was suspended during the cold season and resumed the following spring. Individual gametophytes survived for up to nearly three years with retention of the ability to produce sporophytes. Discussion: Life histories of fern gametophytes in temperate habitats are more similar to those in tropical habitats than previous research has suggested. They survive and maintain reproductive capacity over several growing seasons, allowing extended opportunity for outbreeding. The application of photographic monitoring of additional species and habitats has great potential for a more complete understanding of the ecology of reproduction in homosporous vascular plants. Keywords: fern gametophytes; photographic monitoring; reproductive strategies; winter stress

Sichtbare und unsichtbare Grenzen der Fiederzwenke

Seit Mitte des 20. Jahrhunderts wecken die hellgrünen Kolonien der Fiederzwenke im Nationalpark die Neugier der Forscher. Wie schnell wachsen sie? Wie alt werden sie? Woher kommen sie? Profitieren sie vom globalen Klimawandel

Allelic configuration and polysomic inheritance of highly variable microsatellites in tetraploid gynodioecious Thymus praecox agg

Polyploidy plays a pivotal role in plant evolution. However, polyploids with polysomic inheritance have hitherto been severely underrepresented in plant population genetic studies, mainly due to a lack of appropriate molecular genetic markers. Here we report the establishment and experimental validation of six fully informative microsatellite markers in tetraploid gynodioecious Thymus praecox agg. Sequence data of 150 microsatellite alleles and their flanking regions revealed high variation, which may be characteristic for polyploids with a reticulate evolutionary history. Understanding the patterns of mutation (indels and substitutions) in microsatellite flanking-sequences was a prerequisite for the development of co-dominant markers for fragment analyses. Allelic segregation patterns among progeny arrays from ten test crosses revealed tetrasomic inheritance in T. praecox agg. No evidence of frequent double reduction was detected. Polymerase chain reaction (PCR) based dosage effects allowed for precise assignment of allelic configuration at all six microsatellite loci. The quantification of allele copy numbers in PCR was verified by comparisons of observed and expected gametic allele frequencies and heterozygosities in test crosses. Our study illustrates how PCR based markers can provide reliable estimates of heterozygosity and, thus, powerful tools for breeding system and population genetic analyses in polyploid organism

Sex-ratio variation and spatial distribution of nuclear and cytoplasmic sex-determining genes in gynodioecious Thymus praecox across altitudinal gradients

ABSTRACT Background: Females and hermaphrodites co-exist in populations of gynodioecious plant species. Gynodioecy often depends on persistent polymorphisms for both cytoplasmic male-sterility (CMS) genes and nuclear restorers of male fertility. Questions: How do ecological gradients affect population sex ratio? Is sex-ratio variation attributable to variation in the nuclear-cytoplasmic genetic composition of populations? Is there spatial covariation between CMS types and nuclear restorer alleles among populations? Study system: Late-successional populations of gynodioecious Thymus praecox, a species widespread in the European Alps and distributed from subalpine to alpine altitudes. Methods: We surveyed sex-ratio variation of adults along altitudinal gradients. We used offspring sex ratios from open pollination in natural populations and from controlled crosses within and among populations to estimate the diversity and spatial distribution of sex-determining alleles. Results: The proportion of hermaphrodites decreased with increasing altitude. However, offspring sex ratios were constant across altitudes, indicating similar cytonuclear genetic diversity at contrasting adult sex ratios. Sex-determining alleles were geographically widespread, but significantly higher proportions of hermaphrodites produced by withinpopulation crosses compared with those among populations indicated locally adjusted restorer frequencies. Balancing selection may act on sex-determining genes. Our findings further point to a role for environment-dependent selection via the relative maternal fitness of females and hermaphrodites in maintaining the altitudinal sex-ratio variation

Population genetic consequences of the reproductive system in the liverwort Mannia fragrans

Ecological factors affecting reproduction and dispersal are particularly important in determining genetic structure of plant populations. Polyoicous reproductive system is not rare in bryophytes; however, to date, nothing is known about its functioning and possible population genetic effects. Using the liverwort Mannia fragrans as a model species, the main aims of this study were to separate the relative importance of the components of the polyoicous reproductive system and to assess its consequences on the genetic structure of populations. High sex expression rates increasing with patch size and strongly female-biased sex ratios were detected. Additional input into clonal growth after production of sex organs was found in males compared to females. Similar clonal traits of the rare bisexual and asexual plants and preference toward newly colonized patches suggest that selection prefers colonizers that first develop organs of both sexes, hence ensuring sexual reproduction when no partner is present. Despite frequent spore production, ISSR markers revealed low genetic diversity, probably resulting from the effective clonal propagation of the species and frequent crossing between genetically identical plants. The presence of numerous rare alleles and unique recombinant haplotypes indicates occasional recombination and mutation. Effective spreading of new haplotypes is probably hampered however by large spore size. Since populations are small and isolated, such haplotypes are probably continuously eliminated by genetic drift. These results suggest that although both sexual and asexual reproductions seem to be effective, asexual components of the reproductive system play a greater role in shaping the genetic composition of the population

Multilocus dataset reveals demographic histories of two peat mosses in Europe-1

<p><b>Copyright information:</b></p><p>Taken from "Multilocus dataset reveals demographic histories of two peat mosses in Europe"</p><p>http://www.biomedcentral.com/1471-2148/7/144</p><p>BMC Evolutionary Biology 2007;7():144-144.</p><p>Published online 22 Aug 2007</p><p>PMCID:PMC2018716.</p><p></p>ing haplotypes are marked with black dots and lines connecting haplotypes denote one mutational change. Well-differentiated clades are shown within red, green and blue ellipses. Letters on the map have the colour of the corresponding genetic clade