Inter-and intraspecific variation in fern mating systems after long-distance colonization: the importance of selfing

<p>Abstract</p> <p>Background</p> <p>Previous studies on the reproductive biology of ferns showed that mating strategies vary among species, and that polyploid species often show higher capacity for self-fertilization than diploid species. However, the amount of intraspecific variation in mating strategy and selfing capacity has only been assessed for a few species. Yet, such variation may have important consequences during colonization, as the establishment of any selfing genotypes may be favoured after long-distance dispersal (an idea known as Baker's law).</p> <p>Results</p> <p>We examined intra-and interspecific variation in potential for self-fertilization among four rare fern species, of which two were diploids and two were tetraploids: <it>Asplenium scolopendrium </it>(2n), <it>Asplenium trichomanes </it>subsp. <it>quadrivalens </it>(4n), <it>Polystichum setiferum </it>(2n) and <it>Polystichum aculeatum </it>(4n). Sporophyte production was tested at different levels of inbreeding, by culturing gametophytes in isolation, as well as in paired cultures with a genetically different gametophyte. We tested gametophytes derived from various genetically different sporophytes from populations in a recently planted forest colonized through long-distance dispersal (Kuinderbos, the Netherlands), as well as from older, less disjunct populations.</p> <p>Sporophyte production in isolation was high for Kuinderbos genotypes of all four species. Selfing capacity did not differ significantly between diploids and polyploids, nor between species in general. Rather selfing capacity differed between genotypes within species. Intraspecific variation in mating system was found in all four species. In two species one genotype from the Kuinderbos showed enhanced sporophyte production in paired cultures. For the other species, including a renowned out crosser, selfing capacity was consistently high.</p> <p>Conclusions</p> <p>Our results for four different species suggest that intraspecific variation in mating system may be common, at least among temperate calcicole ferns, and that genotypes with high selfing capacity may be present among polyploid as well as diploid ferns. The surprisingly high selfing capacity of all genotypes obtained from the Kuinderbos populations might be due to the isolated position of these populations. These populations may have established through single-spore colonization, which is only possible for genotypes capable of self-fertilization. Our results therewith support the idea that selection for selfing genotypes may occur during long-distance colonization, even in normally outcrossing, diploid ferns.</p

Biomechanical properties of the terrestrial mosses Pleurozium schreberi (Brid.) Mitt. and Pogonatum japonicum Sull. &amp; Lesq. along altitudinal gradients in northern Japan

Altitudinal gradients along mountain slopes provide valuable opportunities to study variation in plant traits in response to changes in environmental conditions along such  gradients. This study focused on biomechanical traits of two moss species, the more or less horizontally growing Pleurozium schreberi and the erect-growing Pogonatum japonicum, along altitudinal gradients on two mountains in Hokkaido, northern Japan. We measured stem diameter in two directions to determine the second moment of area I, used three-point bending tests with free stem ends to determine the slope of the force-deflection curve dF/dx, and used these data to calculate Young’s modulus and flexural rigidity of the stems. Both species showed much variation in all traits among replicates in the samples at each altitude. Environmental variation associated with altitude had more effect on the biomechanical traits of P. japonicum than on those of P. schreberi. Stems of P. japonicum were thicker (larger I) than those of P. schreberi and had a larger Young’s modulus and flexural rigidity. Stems tended to become thinner (lower second moment of area) and less rigid (lower flexural rigidity) at increasing altitude in both species

Data from: Dispersal versus environmental filtering in a dynamic system: drivers of vegetation patterns and diversity along stream riparian gradients

1. Both environmental filtering and dispersal filtering are known to influence plant species distribution patterns and biodiversity. Particularly in dynamic habitats, however, it remains unclear whether environmental filtering (stimulated by stressful conditions) or dispersal filtering (during re-colonization events) dominates in community assembly, or how they interact. Such a fundamental understanding of community assembly is critical to the design of biodiversity conservation and restoration strategies. 2. Stream riparian zones are species-rich dynamic habitats. They are characterized by steep hydrological gradients likely to promote environmental filtering, and by spatiotemporal variation in the arrival of propagules likely to promote dispersal filtering. We quantified the contributions of both filters by monitoring natural seed arrival (dispersal filter) and experimentally assessing germination, seedling survival and growth of 17 riparian plant species (environmental filter) along riparian gradients of three lowland streams that were excavated to bare substrate for restoration. Subsequently, we related spatial patterns in each process to species distribution and diversity patterns after 1 and 2 years of succession. 3. Patterns in initial seed arrival were very clearly reflected in species distribution patterns in the developing vegetation and were more significant than environmental filtering. However, environmental filtering intensified towards the wet end of the riparian gradient, particularly through effects of flooding on survival and growth, which strongly affected community diversity and generated a gradient in the vegetation. Strikingly, patterns in seed arrival foreshadowed the gradient that developed in the vegetation; seeds of species with adult optima at wetter conditions dominated seed arrival at low elevations along the riparian gradient while seeds of species with drier optima arrived higher up. Despite previous assertions suggesting a dominance of environmental filtering, our results demonstrate that nonrandom dispersal may be an important driver of early successional riparian vegetation zonation and biodiversity patterns as well. 4. Synthesis: Our results demonstrate (and quantify) the strong roles of both environmental and dispersal filtering in determining plant community assemblies in early successional dynamic habitats. Furthermore, we demonstrate that dispersal filtering can already initiate vegetation gradients, a mechanism that may have been overlooked along many environmental gradients where interspecific interactions are (temporarily) reduced

Data from: Early plant recruitment stages set the template for the development of vegetation patterns along a hydrological gradient

1. Recruitment processes are critical components of a plant's life cycle. However, in comparison with later stages in the plant life cycle (e.g. competition among adults), relatively little is known about their contribution to the regulation of plant species distribution. Particularly little is known about the individual contributions of the three main recruitment processes—germination, seedling survival, and seedling growth—to community assembly, while quantitative information on these contributions is essential for a more mechanistic understanding of the regulation of plant species distribution and biodiversity. 2. Riparian zones along streams provide a globally-relevant case study for evaluating the importance of the different stages of plant recruitment. The natural hydrological gradients of stream riparian zones are currently being restored after a period of worldwide habitat degradation. To identify how recruitment contributes to vegetation patterns and biodiversity in riparian zones, we carried out field experiments at restored lowland streams. We quantified the germination of introduced seeds, and survival and growth of introduced seedlings of 17 riparian plant species across a gradient from the stream channel to upland. 3. The hydrological gradient of riparian zones acted as a strong environmental filter on all three recruitment processes, through imposing an abiotic limitation (excess water) at low elevations and a resource limitation (water shortage) at higher elevations. Other variables, such as soil organic matter content and nutrient availability, only affected recruitment marginally. 4. Species-specific patterns of environmental filtering initiated niche segregation along the riparian gradient during all three recruitment processes, but particularly during germination and seedling growth. These recruitment niches appeared strongly related to indicator values for adult distribution optima, suggesting that at least some riparian plant species may have evolutionary adaptations that promote recruitment under favourable hydrological conditions for adult growth and reproduction. 5. Our results suggest that strong environmental filtering during germination and seedling growth plays an important role in determining later adult distributions, by forming the spatial template on which all subsequent processes operate. In addition to well-known mechanisms, such as competitive exclusion at the adult stage, environmental filtering during early recruitment stages already strongly affect plant distribution and diversity

Seed arrival, recruitment and presence in vegetation along riparian gradients

11 worksheets with data on seed arrival, experimentally studied recruitment processes (germination, seedling survival and seedling growth), and natural developing vegetation (worksheets 3-7), model predictions of seed arrival and recruitment processes (worksheets 8-11), abiotic variables (worksheet 2) and description of column headers (worksheet 1)

Fraaije et al. mesh bags control experiment

Two worksheets containing data on a control experiment which tested the effect of mesh bags on germination, with the data in worksheet 1, and description of column headers in worksheet 2

Fraaije et al. field experiments

Eight worksheets with data on experimentally studied recruitment processes (germination, seedling survival, and seedling growth: worksheet 1-3), re-structured for multivariate analyses (worksheet 4-6), soil parameters (worksheet 7) and description of column headers (worksheet 8)