Abortion occurs during double fertilization and ovule development in Paeonia ludlowii

Paeonia ludlowii (Stern & Taylor) D.Y.Hong, an endangered species, is indigenous to Tibet, China and propagated only by seed under natural conditions. Its natural reproduction is constrained by low fecundity. Excess seed abortion is a key factor restricting its natural reproduction, cultivation, introduction, and protection. Understanding the specific origin and occurrence of aborted ovules is important for the protection of offspring. Using serial sectioning analysis, we studied the process of pollination and fertilization of P. ludlowii and examined the characteristics of aborted ovules, developmental differences after flowering of normal and aborted ovules, and their ratios at different positions in P. ludlowii ovaries. During pollination, fertilization, and seed development, ovule abortion was frequent, with a random abortion position. There were three types of abortion, namely, abnormal pistil, sterile ovules, and embryo and endosperm abortions. Of these, embryo and endosperm abortions could be divided into early abortion and middle abortion. The early aborted ovules stopped growing on day 12, the endoblast and endosperm in the embryo sac aborted gradually. Furthermore, the shape of the embryo sac cavity changed. The volume of aborted ovules was significantly different from that of fertile ovules. At ripening, the external morphology of different types of aborted seeds was significantly different. The possible reasons for the abortion of the ovules are also discussed.

Fertilization and Soil Nutrients Impact Differentially Cranberry Yield and Quality in Eastern Canada

High berry yield and quality of conventionally and organically grown cranberry stands require proper nutrient sources and dosage. Our objective was to model the response of cultivar “Stevens” to N, P, K, Mg, Cu, and B fertilization under conventional and organic farming systems. A 3-year trial was conducted on permanent plots at four production sites in Quebec, Canada. We analyzed yield predictors, marketable yield, and fruit quality in response to fertilization and soil properties. Cranberry responded primarily to nitrogen fertilization and, to a lesser extent, to potassium. Berry yield was closely related to the number of fruiting uprights (r = 0.92), berry counts per fruiting upright (r = 0.91), number of reproductive uprights (r = 0.83), and fruit set (r = 0.77). Nitrogen increased berry yield nonlinearly but decreased berry firmness, total anthocyanin content (TAcy), and total soluble solids content (°Brix) linearly, indicating a trade-off between berry yield and quality. Fertilizer dosage at a high-yield level ranged between 30 and 45 kg N ha−1 in both conventional and organic farming systems. Slow-release fertilizers delayed crop maturity and should thus be managed differently than ammonium sulfate. Berry weight increased with added K. Redundancy analysis showed a close correlation between marketable yield, berry quality indices, and soil tests, especially K and Ca, indicating the need for soil test calibration.

No Effect of Selective Maturation on Fruit Traits for a Bird-Dispersed Species, Sambucus racemosa

Selective abortion, also called selective maturation, is a phenomenon wherein maternal plants selectively mature ovules that have the potential to grow into higher-quality fruits, such as those that contain more seeds. We hypothesized that the effects of selective maturation on fruit traits could be influenced by the dispersal mechanism. However, to date, limited studies have been conducted on selective maturation in bird-dispersed fruits. Unlike self- or wind-dispersed species, bird-dispersed species would not selectively mature fruits that contain more seeds because they are not preferred by birds. Here, we investigated the effect of selective abortion on the fruit traits of a bird-dispersed species, elderberry (Sambucus racemosa L. subsp. kamtschatica). We performed a flower-removal experiment. Half of the inflorescences on each individual tree were removed for the treatment group, whereas the control group was not manipulated. We found that the flower-removed trees showed higher fruit sets, suggesting the existence of resource limitation. The number of seeds per fruit did not increase by the experimental treatment. Additionally, the control individuals did not produce larger fruits. The lack of effects on fruit traits supported our hypothesis that the effect of selective maturation on fruit traits may differ among species with different dispersal mechanisms.

Plant traits moderate pollen limitation of introduced and native plants: a phylogenetic meta-analysis of global scale

The role of pollination in the success of invasive plants needs to be understood because invasives have substantial effects on species interactions and ecosystem functions. Previous research has shown both that reproduction of invasive plants is often pollen limited and that invasive plants can have high seed production, motivating the questions: How do invasive populations maintain reproductive success in spite of pollen limitation? What species traits moderate pollen limitation for invaders? We conducted a phylogenetic meta-analysis with 68 invasive, 50 introduced noninvasive and 1931 native plant populations, across 1249 species. We found that invasive populations with generalist pollination or pollinator dependence were less pollen limited than natives, but invasives and introduced noninvasives did not differ. Invasive species produced 3× fewer ovules/flower and >250× more flowers per plant, compared with their native relatives. While these traits were negatively correlated, consistent with a tradeoff, this did not differ with invasion status. Invasive plants that produce many flowers and have floral generalisation are able to compensate for or avoid pollen limitation, potentially helping to explain the invaders' reproductive successes.

Mechanisms of mast seeding: resources, weather, cues, and selection

546 I. 546 II. 547 III. 548 IV. 552 V. 554 VI. 556 VII. 558 VIII. 558 IX. 559 559 References 559 SUMMARY: Mast seeding is a widespread and widely studied phenomenon. However, the physiological mechanisms that mediate masting events and link them to weather and plant resources are still debated. Here, we explore how masting is affected by plant resource budgets, fruit maturation success, and hormonal coordination of cues including weather and resources. There is little empirical support for the commonly stated hypothesis that plants store carbohydrates over several years to expend in a high-seed year. Plants can switch carbohydrates away from growth in high-seed years, and seed crops are more probably limited by nitrogen or phosphorus. Resources are clearly involved in the proximate mechanisms driving masting, but resource budget (RB) models cannot create masting in the absence of selection because some underlying selective benefit is required to set the level of a 'full' seed crop at greater than the annual resource increment. Economies of scale (EOSs) provide the ultimate factor selecting for masting, but EOSs probably always interact with resources, which modify the relationship between weather cues and reproduction. Thus, RB and EOS models are not alternative explanations for masting - both are required. Experiments manipulating processes that affect mast seeding will help clarify the physiological mechanisms that underlie mast seeding.

Developmental plasticity, genetic assimilation, and the evolutionary diversification of sexual expression in Solanum

PREMISE OF THE STUDY

For over a century, it has been hypothesized that selection can convert an environmentally induced phenotype (i.e., plasticity) into a fixed (constitutively produced) phenotype, a process known as genetic assimilation. While evidence of assimilation is accumulating, the role of plasticity generally and assimilation specifically in evolutionary diversification has rarely been examined from a comparative phylogenetic perspective. •

METHODS

We combined experimental analyses of plasticity with ancestral state reconstructions to examine the evolutionary dynamics of sexual expression in two well-characterized sections (Acanthophora and Lasiocarpa) in Solanum subgenus Leptostemonum. We examined sexual expression phenotypes and the proportion of staminate flowers produced under contrasting resource conditions in 10 species and combined these data with previous studies. •

KEY RESULTS

Staminate flower production was phenotypically plastic for nine of 14 species and unaffected by treatment in five species. Two of the nonplastic species bore few staminate flowers, and three constitutively produced large numbers of staminate flowers. For individuals and species producing staminate flowers, these flowers occurred in a distinctive architectural pattern that was qualitatively the same in both plastic and nonplastic species. Parsimony and Bayesian reconstructions demonstrate that plasticity is ancestral among the species studied. •

CONCLUSIONS

Plasticity has been lost independently in sections Acanthophora and Lasiocarpa, and the consequence of its loss results in evolutionary diversification of sexual expression. In section Acanthophora, loss of plasticity represents a reversion to production of predominantly hermaphroditic flowers. In contrast, the fixed production of staminate flowers in Lasiocarpa has the hallmarks of evolution via genetic assimilation.

Selective seed abortion induced by nectar robbing in the selfing plant Comastoma pulmonarium

• Self-pollination often provides plants with the benefit of reproductive assurance; thus, it is generally assumed that species' interactions that alter floral attractiveness or rewards, such as nectar robbing, will have little effect on the seed production of selfing species. We challenge this view with experimental data from Comastoma pulmonarium, a selfing annual experiencing a high ratio of nectar robbing in the Qinghai-Tibet Plateau. • We manipulated robbing (robbed or netted) and pollination mode (hand-selfed or hand-outcrossed) in a factorial design and measured the number of developing ovules and mature seeds, together with seed weight and seed germination, in each treatment. • Robbing decreased the number of mature seeds, but not the number of developing ovules, suggesting a negative influence of robbers through indirect effects via selective seed abortion. We found no evidence for early-acting inbreeding depression, but found later-acting inbreeding depression. Our data also suggested that later-acting inbreeding depression of progeny from robbed flowers could be reduced in comparison with that from unrobbed flowers. • We suggest that nectar robbing can have both negative and positive effects on the quantity and quality, respectively, of progeny produced in selfing plants, and challenge the view that robbing has no effect on selfing species.

Reproductive compensation in the evolution of plant mating systems

Reproductive compensation, the replacement of dead embryos by potentially viable ones, is known to play a major role in the maintenance of deleterious mutations in mammalian populations. However, it has received little attention in plant evolution. Here we model the joint evolution of mating system and inbreeding depression with reproductive compensation. We used a dynamic model of inbreeding depression, allowing for partial purging of recessive lethal mutations by selfing. We showed that reproductive compensation tended to increase the mean number of lethals in a population, but favored self-fertilization by effectively decreasing early inbreeding depression. When compensation depended on the selfing rate, stable mixed mating systems can occur, with low to intermediate selfing rates. Experimental evidence of reproductive compensation is required to confirm its potential importance in the evolution of plant mating systems. We suggest experimental methods to detect reproductive compensation.