Investment In Sexual Reproduction Research Articles

The novel expression of clonality following whole-genome multiplication compensates for reduced fertility in natural autopolyploids.

Exploring the fitness consequences of whole-genome multiplication (WGM) is essential for understanding the establishment of autopolyploids in diploid parental populations, but suitable model systems are rare. We examined the impact of WGM on reproductive traits in three major cytotypes (2x, 3x, 4x) of Pilosella rhodopea, a species with recurrent formation of neo-autopolyploids in mixed-ploidy populations. We found that diploids had normal female sporogenesis and gametogenesis, high fertility, and produced predominantly euploid seed progeny. By contrast, autopolyploids had highly disturbed developmental programs that resulted in significantly lower seed set and a high frequency of aneuploid progeny. All cytotypes, but particularly triploids, produced gametes of varying ploidy, including unreduced ones, that participated in frequent intercytotype mating. Noteworthy, the reduced investment in sexual reproduction in autopolyploids was compensated by increased production of axillary rosettes and the novel expression of two clonal traits: adventitious rosettes on roots (root-sprouting), and aposporous initial cells in ovules which, however, do not result in functional apomixis. The combination of increased vegetative clonal growth in autopolyploids and frequent intercytotype mating are key mechanisms involved in the formation and maintenance of the largest diploid-autopolyploid primary contact zone ever recorded in angiosperms.

Nutrients Regulate the Effects of Arbuscular Mycorrhizal Fungi on the Growth and Reproduction of Cherry Tomato.

Arbuscular mycorrhizal fungi (AMF) colonize the rhizosphere of plants and form a symbiotic association with plants. Mycorrhizal symbionts have diversified ecological roles and functions which are affected by soil conditions. Understanding the effects of different AMF inoculation on plants under varied nutritional conditions is of great significance for further understanding the effects of the external environment regulating mycorrhizal symbiosis on plant phenotypic traits. In this study, the effects of four AMF inoculation treatments on the growth and reproductive performance of cherry tomato (Solanum lycopersicum var. cerasiforme) were investigated under three nutrient levels by pot experiment. It was found that the growth-promoting effect of AMF on cherry tomato decreased with nutrient reduction, and the effects of the same AMF inoculation treatment on cherry tomato were different at different nutrient levels. Nutrient levels and AMF had interactive effects on flower characteristics, fruit yield, resource allocation, and seed germination of the cherry tomato. In addition, AMF could promote sexual reproductive investment. Nutrient levels and AMF also affected the accumulation of nitrogen and phosphorus in cherry tomato, and there were significant differences among different AMF inoculation treatments. The results indicated that nutrient differences could affect the symbiosis between AMF and plants, and confirmed that there were differences in the effects of the four AMF inoculation treatments on the growth and reproductive traits of plants. The differences in growth and reproduction characteristics of cherry tomato between different AMF inoculation treatments at different nutrient levels indicated that the effects of AMF mycorrhizal on the traits of cherry tomato were regulated by nutrients.

Sexual reproduction trait expressions of grassland species along a gradient of nitrogen: phosphorus stoichiometry

AimsPlant investment in sexual reproduction is affected by nitrogen (N): phosphorus (P) stoichiometry. It has been suggested that an important adaptation to strong P limitation is reduced investment in sexual reproduction. We aim to investigate the specific influence of N:P on sexual reproduction performance within and between grassland species.MethodsEleven grassland species were selected in ten plots covering N limitation, co-limitation and P limitation. Nutrients in soil and above-ground biomass were determined, plus soil pH and soil moisture. A range of sexual reproduction traits were measured as a proxy for investment in sexual reproduction.ResultsAt the intraspecific level: compared with N-limited plots, in P-limited/co-limited plots, flowering time was later, flowering period in individuals was shorter, and number of flowers (inflorescences) per individual was smaller. At the interspecific level, in P-limited/co-limited plots, species had a significantly earlier flowering time and a longer seed stalk and seed panicle, than those in N-limited plots. However, flowering period was shorter and number of flowers (inflorescences) per individual was smaller under P limitation/co-limitation. Moreover, significant correlations between soil pH and soil moisture, and sexual reproduction performance of the selected grassland species were also found.ConclusionsP limitation/co-limitation restrict the sexual reproduction of grassland species, which may hamper their dispersal capacity. We recommend future studies further analyze the relationship between soil pH and N:P stoichiometry and the influence of soil pH, as well as soil moisture on sexual reproduction performance of grassland species in addition to analyzing N:P stoichiometry.

Density, parasitism, and sexual reproduction are strongly correlated in lake Daphnia populations.

Many organisms can reproduce both asexually and sexually. For cyclical parthenogens, periods of asexual reproduction are punctuated by bouts of sexual reproduction, and the shift from asexual to sexual reproduction has large impacts on fitness and population dynamics. We studied populations of Daphnia dentifera to determine the amount of investment in sexual reproduction as well as the factors associated with variation in investment in sex. To do so, we tracked host density, infections by nine different parasites, and sexual reproduction in 15 lake populations of D. dentifera for 3 years. Sexual reproduction was seasonal, with male and ephippial female production beginning as early as late September and generally increasing through November. However, there was substantial variation in the prevalence of sexual individuals across populations, with some populations remaining entirely asexual throughout the study period and others shifting almost entirely to sexual females and males. We found strong relationships between density, prevalence of infection, parasite species richness, and sexual reproduction in these populations. However, strong collinearity between density, parasitism, and sexual reproduction means that further work will be required to disentangle the causal mechanisms underlying these relationships.

Variation in growth, reproduction, and resource allocation in an aquatic plant, Vallisneria spinulosa: the influence of amplitude and frequency of water level fluctuations

Water level fluctuations (WLF), one of the most affected ecological drivers by climate change, are dominant forces controlling submerged macrophyte performance and distribution in freshwater ecosystems. Submerged macrophytes are prominent components of shallow lakes, predicting their response to WLF is therefore crucial for the management and conservation of these valuable and vulnerable ecosystems. We conducted an experiment in 15 outdoor mesocosms to explore the influence of WLF on the performance of Vallisneria spinulosa. We subjected V. spinulosa to WLF of two amplitudes and two frequencies, with stable water level as a control, and measured variations in 20 traits related with growth, sexual and asexual reproduction and resource allocation. Generally, compared with the control plants, fluctuations in water level adversely affected macrophyte biomass and growth, but increased both height and specific leaf area, which are helpful for adaptation of V. spinulosa to high-water level periods. Changes in the WLF frequency had little effect on the growth and reproduction of V. spinulosa plants apart from their leaf mass. In contrast, increased amplitude not only inhibited aboveground and root growth of V. spinulosa, but also decreased investment in sexual reproduction by influencing fruit production. V. spinulosa held a relatively stable allocation to overwintering asexual propagules in response to both components of WFL, which can maintain a capacity for clonal propagation following WLF. Moreover, as WLF amplitude increased, V. spinulosa invested a higher fraction of resources to belowground mass at the expense of their allocation to leaf mass. Our results suggest that shifts in WFL and especially magnified WLF amplitude due to climate change, may severely affect the growth and reproduction of submerged macrophytes with implications for other biota and the ecological state of shallow lakes.

Sexual reproduction traits of Holcus lanatus L. and Parnassia palustris L. in response to absolute and relative supply of nitrogen and phosphorus

Plant investment in sexual reproduction is affected by absolute and relative nitrogen (N) and phosphorus (P) supply. Reduced investment in reproductive traits has been suggested as an important adaptation to strong P-limitation. We experimentally tested how absolute and relative nutrient supply affected sexual reproduction traits of two grassland species.Seedlings of a common grass (Holcus lanatus) and an endangered forb (Parnassia palustris) were grown from seed from a dune area with low relative P-availability. Plants were grown in a full factorial experiment with three N:P supply ratios (5, 15, 45) and two absolute supply levels of N and P. After one year, a range of traits was measured as a proxy for investment in sexual reproduction. We found that N:P supply ratio did not affect sexual reproduction at low nutrient supply; at high nutrient supply, investment in sexual reproduction was significantly less at higher N:P supply ratios. For Holcus lanatus, N:P supply ratio 45 restricted the increase in sexual reproduction upon increasing nutrient supply. Parnassia palustris survival and flowering were low, especially at N:P supply ratio 15 (no results were available for P. palustris at N:P supply ratio 45 due to the high mortality).Our results highlight that at low nutrient supply N:P ratio rarely affected investment in sexual reproduction traits but at high supply low relative P-supply restricted plants’ sexual reproduction investment.

Evidencing the cost of sexual reproduction in the rotifer Brachionus plicatilis

Sex poses an immediate cost for monogonont rotifers, which combine exclusively asexual reproduction with periods of co-occurrence between asexual and sexual reproduction in their life cycle. Because sex is linked to dormancy, sexual daughters do not contribute to the current growth of a clonal genotype, as they only produce males or diapausing eggs. Therefore, the expectation under the all-else equal assumption (i.e., sexual and asexual females having equivalent life-history traits) is that female genotypes investing more in sexual daughters during the planktonic growing season will have slower rates of clonal growth. Here, we tested if these genotypes compensate for this greater investment in sex with higher fecundity and/or survival. We studied 45 genotypes (clones) of Brachionus plicatilis established from diapausing eggs isolated from sediments of ten brackish ponds in Spain. Using a life-table experiment, we estimated the investment in sexual reproduction of these genotypes and several life-history traits (lifespan, lifetime reproductive success, generation time and intrinsic growth rate). Results showed that there was a lack of correlation between sex-investment and any other life-history trait. Neither fecundity nor survival compensated the investment in sexual reproduction, so we conclude that the all-else-equal assumption holds and sex is costly in B. plicatilis.

Why outcross? The abandon-ship hypothesis in a facultative outcrossing/selfing fungal species

Most species able to reproduce both sexually and asexually (facultative sexual species) invest more in sexual reproduction in stressful environment conditions. According to the abandon-ship hypothesis, plasticity for investment in sexual reproduction may have been selected in these species, allowing unfit genotypes to generate progeny carrying new advantageous allelic combinations. We tested this hypothesis in Aspergillus nidulans, a fungus able to reproduce asexually, or sexually, by outcrossing and/or haploid selfing (i.e. fusion of genetically identical haploid nuclei, causing immediate genome-wide homozygosity). We crossed various strains of A. nidulans in a non-stressful environment and a stressful environment containing a non-lethal dose of fungicide. Without stress, crosses preferentially generated haploselfed fruiting bodies, whereas stressful conditions significantly increased the outcrossing rate. Our results strongly support the abandon-ship hypothesis and suggest that, for parents with low fitness, the costs of investing in sexual reproduction may be compensated by the production of fitter progeny carrying beneficial allele combinations. Similarly, the progeny generated by outcrossing was less fit than that produced by haploid selfing in non-stressful environments, but fitter in stressful conditions, suggesting that outcrossing may have short-term advantages in stressful environments in A. nidulans.

Sexual Dimorphism, Vegetative Growth and Reproductive Investment in the Rhizautoicous MossFissidens flaccidus(Fissidentaceae, Bryopsida)

Reproduction is one of the most important and expensive processes in the life history of plants. The cost commonly incurred by reproductive investment in plants with separate sexes may result in sexual dimorphism. Among bryophytes, sexual dimorphism has been observed in some sex-expressing dioicous species and in some sex-expressing monoicous species with a rhizautoicous sexual system. In the present study, we have investigated sexual dimorphism in morphological features and relative reproductive investments in sporophytic female, non-sporophytic female, sex-expressing male and non-expressing ramets in a population of the rhizautoicous Fissidens flaccidus. Morphometric analyses confirmed sexual dimorphism; gemmiform male ramets were smaller than the other ramet morphs, and exhibited greater sexual investment. Sexual reproductive investment was approximately 35% in males, 13% in non-sporophytic females and 25% in sporophytic females. Our results indicate trade-offs between reproductive investment and vegetative growth for both sexes in this species.

Daphnia invest in sexual reproduction when its relative costs are reduced.

The timing of sex in facultatively sexual organisms is critical to fitness, due to the differing demographic consequences of sexual versus asexual reproduction. In addition to the costs of sex itself, an association of sex with the production of dormant life stages also influences the optimal use of sex, especially in environments where resting eggs are essential to survive unfavourable conditions. Here we document population dynamics and the occurrence of sexual reproduction in natural populations of Daphnia magna across their growing season. The frequency of sexually reproducing females and males increased with population density and with decreasing asexual clutch sizes. The frequency of sexually reproducing females additionally increased as population growth rates decreased. Consistent with population dynamic models showing that the opportunity cost of sexual reproduction (foregoing contribution to current population growth) diminishes as populations approach carrying capacity, we found that investment in sexual reproduction was highest when asexual population growth was low or negative. Our results support the idea that the timing of sex is linked with periods when the relative cost of sex is reduced due to low potential asexual growth at high population densities. Thus, a combination of ecological and demographic factors affect the optimal timing of sexual reproduction, allowing D. magna to balance the necessity of sex against its costs.

Allocation to clonal and sexual reproduction and its plasticity in Vallisneria spinulosa along a water‐depth gradient

AbstractVariations in water level profoundly affect functional stability of freshwater ecosystems, as well as macrophyte growth and reproduction. Although the trade‐off between allocation to clonal and sexual reproduction in clonal plants can be influenced by a variety of environmental factors, whether variations of reproductive allocation (RA) in response to different environments are driven only by a size‐dependent effect (apparent plasticity) or whether RA can also change independently of plant size (true plasticity) is uncertain. We conducted an experiment in nine outdoor mesocosms (6400 L) to investigate the response of clonal and sexual reproduction and vegetative growth of a perennial submerged macrophyte Vallisneria spinulosa at water depths of 50, 100, or 150 cm. We evaluated size‐dependent and size‐independent effects of water depth on sexual and clonal RA. Deep water reduced vegetative size and sexual output (mass of fruits produced), but increased tuber production of V. spinulosa. There was an apparent trade‐off between reproductive modes in terms of biomass investment; plants in deep water allocated more resources into clonal propagation and reduced investment in sexual reproduction compared to plants in shallow or intermediate water. Slopes of allometric relationships (sexual vs. vegetative biomass and clonal vs. vegetative biomass) were significantly affected by water depth. Shifts in sexual RA in response to varying water depths were largely size‐dependent, but there were also size‐independent effects. In contrast, size‐independent effects were more important than effects of size changes in determining clonal RA. We concluded that V. spinulosa adapted to a water‐depth gradient by plastic trade‐offs between clonal propagation and sexual reproduction. Furthermore, a size‐independent effect on RA suggests a flexible reproductive strategy that could be critical for plant performance in changing aquatic environments.

Temporal patterns and processes of genetic differentiation of the Brachionus calyciflorus (Rotifera) complex in a subtropical shallow lake

Sympatric distribution and temporal overlap of cryptic zooplankton species pose a challenge to the framework of the niche differentiation theory and the mechanisms underlying the coexistence of potentially strong competitors. In this study, we collected Brachionus calyciflorus Pallas monthly from Lake Tingtang over the course of 1 year and clonally cultured them in the laboratory. Finally, 204 clones were established, and their nuDNA ITS1 and mtCOI sequences were analyzed. The phylogenetic relationships and GMYC model analyses revealed that B. calyciflorus was a species complex composed of three cryptic species. Cryptic species BcI-W, and BcII-S and Bc-SW underwent a clear seasonal succession. However, BcII-S and Bc-SW overlapped in June and July, and all the three cryptic species coexisted in November. Different preferences to water temperature might contribute to the seasonal succession. More investment in sexual reproduction accelerated the disappearance of cryptic species from the water column during the seasonal succession process. Differential responses in rate of population growth of the two overlapping cryptic species to increasing food level might reduce the intensity of competition between them and promote their coexistence over time. Differences in population growth rate partially resulted in the different relative abundances of the two overlapping cryptic species.

The influence of resource availability on flowering intensity in Zostera marina (L.)

The impact of resource availability on investment between asexual and sexual reproduction in seagrasses remains poorly understood. In this study, the effects of sediment nutrients and light availability on sexual and asexual reproduction in the seagrass Zostera marina (L.) were investigated. Field manipulations were combined with observational surveys to identify whether nutrient and light availability influenced flowering intensity of Z. marina in Chesapeake Bay, Virginia. A positive relationship between pore water ammonium and the percentage of flowering shoots was observed across locations with differing sediment nutrient types. In addition, short-term elevation of sediment nutrients increased the number of spathes per flowering shoot, but did not alter flowering shoot densities. Surveys around existing residential piers, used as observational surrogates for long-term shading, found seagrass directly below piers exhibited lower percentages of flower shoots than adjacent unshaded seagrass. In contrast, seasonal light reductions of seagrass did not significantly affect flowering intensity in experimental plots. Thus, increasing nutrient resources over both the seasonal and longer terms appeared to increase several aspects of investment in sexual reproduction, while only long-term reductions in shading decreased investment in sexual reproduction. Therefore, any factors which influence the duration and magnitude of nutrient and light resource availability to seagrass, may have important implications for the sustainability and resiliency of these valuable populations and the services they provide within increasingly threatened coastal systems.

Does fire affect the temporal pattern of trophic resource supply to pollinators and seed-dispersing frugivores in a Brazilian savanna community?

In tropical savannas, such as the campo cerrado in Brazil, fire plays an important role, affecting plant species’ life history. Since fire has the potential to modify the structure of savanna communities as a whole, it is expected that it may influence the resource supply for mutualists by altering the pattern of investment in sexual reproduction. We used an experimental approach to test if fire alters trophic resource availability to pollinators (nectar, pollen, and oil) and seed-dispersing frugivores (fleshy fruits) by altering the seasonality of reproductive phenophases in a savanna community. We sampled all individuals of 60 species that were common to both control and experimental fire treatments. Each month we recorded the number of reproductive individuals to test whether fire affected the temporal resource offered by the plant assemblage as a whole, and by each specific plant group supporting distinct groups of pollinators and seed-dispersing frugivores. We noticed that fire advanced the nectar, pollen, and fleshy fruit offered by the whole assemblage. Additionally, fire affected the temporal pattern of nectar and pollen available to various pollinator groups, and of fleshy fruits available to all seed-dispersing frugivores. In general, fire seems to have a neutral or even a positive effect on resource availability to mutualists. Nevertheless, there were differences in the availability of the resource utilized by each guild of mutualists.

De Novo Transcriptome Assembly and Sex-Biased Gene Expression in the Cyclical Parthenogenetic Daphnia galeata.

Daphnia species have become models for ecological genomics and exhibit interesting features, such as high phenotypic plasticity and a densely packed genome with many lineage-specific genes. They are also cyclic parthenogenetic, with alternating asexual and sexual cycles and environmental sex determination. Here, we present a de novo transcriptome assembly of over 32,000 D. galeata genes and use it to investigate gene expression in females and spontaneously produced males of two clonal lines derived from lakes in Germany and the Czech Republic. We find that only a low percentage (18%) of genes shows sex-biased expression and that there are many more female-biased gene (FBG) than male-biased gene (MBG). Furthermore, FBGs tend to be more conserved between species than MBGs in both sequence and expression. These patterns may be a consequence of cyclic parthenogenesis leading to a relaxation of purifying selection on MBGs. The two clonal lines show considerable differences in both number and identity of sex-biased genes, suggesting that they may have reproductive strategies differing in their investment in sexual reproduction. Orthologs of key genes in the sex determination and juvenile hormone pathways, which are thought to be important for the transition from asexual to sexual reproduction, are present in D. galeata and highly conserved among Daphnia species.

Demographic consequences of greater clonal than sexualreproduction in Dicentra canadensis.

Clonality is a widespread life history trait in flowering plants that may be essential for population persistence, especially in environments where sexual reproduction is unpredictable. Frequent clonal reproduction, however, could hinder sexual reproduction by spatially aggregating ramets that compete with seedlings and reduce inter‐genet pollination. Nevertheless, the role of clonality in relation to variable sexual reproduction in population dynamics is often overlooked. We combined population matrix models and pollination experiments to compare the demographic contributions of clonal and sexual reproduction in three Dicentra canadensis populations, one in a well‐forested landscape and two in isolated forest remnants. We constructed stage‐based transition matrices from 3 years of census data to evaluate annual population growth rates, λ. We used loop analysis to evaluate the relative contribution of different reproductive pathways to λ. Despite strong temporal and spatial variation in seed set, populations generally showed stable growth rates. Although we detected some pollen limitation of seed set, manipulative pollination treatments did not affect population growth rates. Clonal reproduction contributed significantly more than sexual reproduction to population growth in the forest remnants. Only at the well‐forested site did sexual reproduction contribute as much as clonal reproduction to population growth. Flowering plants were more likely to transition to a smaller size class with reduced reproductive potential in the following year than similarly sized nonflowering plants, suggesting energy trade‐offs between sexual and clonal reproduction at the individual level. Seed production had negligible effects on growth and tuber production of individual plants. Our results demonstrate that clonal reproduction is vital for population persistence in a system where sexual reproduction is unpredictable. The bias toward clonality may be driven by low fitness returns for resource investment in sexual reproduction at the individual level. However, chronic failure in sexual reproduction may exacerbate the imbalance between sexual and clonal reproduction and eventually lead to irreversible loss of sex in the population.

Can the life-history strategy explain the success of the exotic trees Ailanthus altissima and Robinia pseudoacacia in Iberian floodplain forests?

Ailanthus altissima and Robina pseudoacacia are two successful invasive species of floodplains in central Spain. We aim to explain their success as invaders in this habitat by exploring their phenological pattern, vegetative and sexual reproductive growth, and allometric relations, comparing them with those of the dominant native tree Populus alba. During a full annual cycle we follow the timing of vegetative growth, flowering, fruit set, leaf abscission and fruit dispersal. Growth was assessed by harvesting two-year old branches at the peaks of vegetative, flower and fruit production and expressing the mass of current-year leaves, stems, inflorescences and infrutescences per unit of previous-year stem mass. Secondary growth was assessed as the increment of trunk basal area per previous-year basal area. A. altissima and R. pseudoacacia showed reproductive traits (late flowering phenology, insect pollination, late and long fruit set period, larger seeds) different from P. alba and other native trees, which may help them to occupy an empty reproductive niche and benefit from a reduced competition for the resources required by reproductive growth. The larger seeds of the invaders may make them less dependent on gaps for seedling establishment. If so, these invaders may benefit from the reduced gap formation rate of flood-regulated rivers of the study region. The two invasive species showed higher gross production than the native, due to the higher size of pre-existing stems rather than to a faster relative growth rate. The latter was only higher in A. altissima for stems, and in R. pseudoacacia for reproductive organs. A. altissima and R. pseudoacacia showed the lowest and highest reproductive/vegetative mass ratio, respectively. Therefore, A. altissima may outcompete native P. alba trees thanks to a high potential to overtop coexisting plants whereas R. pseudoacacia may do so by means of a higher investment in sexual reproduction.

Reproduction of Daphnia pulex in a Northern Italy pond

This paper reports on the occurrence of Daphnia pulex in a small fishless water body of Northern Italy (Bodrio del pastore III) and describes its population dynamics. Bodrio is a typical water body originated by erosion from the old Po river-bed surface. During a three year study (2011-2013), D. pulex population showed an increase in density from spring to early summer, it declined in July-August and did not recover, presumably from ephippia, until the following spring. The seasonal dynamics was related to the species thermal tolerance and to invertebrate predation by Chaoborus that resulted in juvenile high mortality and in adaptive predator-avoidance cyclomorphosis. Seasonal variation was observed in the frequency of individuals, most juveniles, showing neckteeth. D. pulex population reproduces by cyclical parthenogenesis and showed a very early investment in sexual reproduction, independent of population density. Males and ephippial females appeared at the beginning of growth season before the density peak according to a typical feature of Daphnia populations from temporary habitats. This suggests a lower influence of the environmental factors on sex determination compared to populations inhabiting more permanent habitats. Lineages that produce males and ephippial females early in the season had lower growth rate than parthenogenetic ones but may preserve from selection pressure by predators a significant percentage of genetic variation linked to sex allocation so that evolution proceeds toward earlier and increased sexual reproduction. Our results suggest further investigation to verify whether the current population is the last remnant of a once much larger metapopulation eventually reduced by anthropogenic disturbances or if it represents the invasion of North American strains.

Low investment in sexual reproduction threatens plants adapted to phosphorus limitation

Plant species diversity in Eurasian wetlands and grasslands depends not only on productivity but also on the relative availability of nutrients, particularly of nitrogen and phosphorus. Here we show that the impacts of nitrogen:phosphorus stoichiometry on plant species richness can be explained by selected plant life-history traits, notably by plant investments in growth versus reproduction. In 599 Eurasian sites with herbaceous vegetation we examined the relationship between the local nutrient conditions and community-mean life-history traits. We found that compared with plants in nitrogen-limited communities, plants in phosphorus-limited communities invest little in sexual reproduction (for example, less investment in seed, shorter flowering period, longer lifespan) and have conservative leaf economy traits (that is, a low specific leaf area and a high leaf dry-matter content). Endangered species were more frequent in phosphorus-limited ecosystems and they too invested little in sexual reproduction. The results provide new insight into how plant adaptations to nutrient conditions can drive the distribution of plant species in natural ecosystems and can account for the vulnerability of endangered species.

Long-term nutrient enrichment differentially affects investment in sexual reproduction in four boreal forest understory species

The combustion of fossil fuels and associated warmer temperatures are causing a global increase in the availability of soil nutrients such as nitrogen. This will have pronounced effects on plants at northern latitudes that are adapted to low nutrient conditions. An experiment in northern Canada set up in 1990 has investigated the effects of long-term nutrient enrichment (fertilizer addition) and mammalian herbivore exclusion (fencing) on an understory plant community. We used this experiment to assess how 22 years of fertilization has affected investment in sexual reproduction in four herbaceous understory species. We measured reproductive output at the plot level (proportion of plants flowering) for four species (Mertensia paniculata, Epilobium angustifolium, Achillea millefolium and Festuca altaica) and at the individual plant level (biomass allocation to flower parts) for M. paniculata and E. angustifolium. Fertilization increased the probability of flowering for A. millefolium and resulted in a higher allocation of biomass to flower parts for E. angustifolium. Sexual reproduction in M. paniculata and F. altaica was largely unaffected by increased nutrient supply, and, as expected, herbivore exclusion had almost no effect on any species. Whereas plants in northern ecosystems currently reproduce mainly through clonal growth, rapidly changing environmental conditions and warmer temperatures will likely result in increased benefits of sexual reproduction. This could give a competitive advantage to species such as A. millefolium and E. angustifolium that increase investment in sexual reproduction when released from nutrient limitation.