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Timing of pollen arrival may affect the level of seeds fertilized by pollen from outside seed orchards, especially in seed orchards of Scots pine (Pinus sylvestris L.) established in southern Finland with stock from northern populations. We performed sequential pollination experiments with Scots pine pollen collected from seed orchard clones originating from southern and northern Finland and recipient strobili in clones originating from southern Finland. When southern pollen was introduced first, seeds were sired equally by northern and southern genotypes. When northern pollen was introduced first, northern genotypes were found in 75% of the resulting seeds. When both pollen types were introduced at the same time, the resulting seed crop was split almost equally between northern and southern genotypes. These results do not unconditionally support the idea that the first pollen grain in the pollen chamber always fertilizes the ovum; instead, they suggest a more complex way of competition between pollen grains. Le moment ou le pollen arrive peut affecter la quantite de graines fertilisees par le pollen provenant de l'exterieur des vergers a graines, particulierement dans les vergers a graines de pin sylvestre (Pinus sylvestris L.) etablis dans le sud de la Finlande avec du materiel provenant de populations nordiques. Nous avons realise des experiences de pollinisation sequentielle avec du pollen de pin sylvestre collecte dans des vergers a graines de clones originaires du sud et du nord de la Finlande et des strobiles recepteurs chez des clones originaires du sud de la Finlande. Lorsque le pollen provenant du nord etait introduit en premier, 75 % des graines produites correspondaient aux genotypes du nord. Lorsque les deux types de pollen etaient introduits en meme temps, les graines etaient reparties presque egalement entre les genotypes du nord et du sud. Ces resultats ne supportent pas inconditionnellement l'idee que le premier grain de pollen dans la chambre pollinique fertilise toujours l'ovule. Au contraire, ils laissent entrevoir un mecanisme plus complexe de competition entre les grains de pollen. [Traduit par la Redaction], Introduction While pollen competition that leads to nonrandom mating is well studied in angiosperms (Skogsmyr and Lankinen 2002; Bernasconi 2003), few experiments have focused on coniferous species such as Scots [...]

The late-nineteenth/early-twentieth century debate over homologous versus antithetic alternation of generations is reviewed. Supporters of both theories, at first, used Coleochaete as a model for the origin of land-plant life cycles. The early debate focused on the morphological interpretation of the sporophyte and on whether vascular cryptogams had bryophyte-like ancestors. The terms of the debate shifted after the discovery that the alternation of morphological generations was accompanied by an alternation of chromosome number. Supporters of homologous alternation now promoted a model in which land plants had been derived from an algal ancestor with an isomorphic alternation of haploid and diploid generations whereas supporters of antithetic alternation favored a model in which land plants were derived from a haploid algal ancestor with zygotic meiosis. Modern evidence that embryophytes are derived from charophycean green algae is more compatible with an updated version of the antithetic theory. Keywords Alternation of Generations * Apogamy * Apospory * Coleochaete * Dictyota * Embryophytes * Gametophyte * Sporophyte, Introduction For more than a century, theories of the 'antithetic' origin of sporophytes have been juxtaposed with theories of their 'homologous' origin. During this same period, there have been profound [...]

This study examines how the latitude of cultivation of Ginkgo biloba affects the timing of all phases of its sexual reproductive cycle, from pollination through germination. Seeds produced by trees growing in warm-temperate climates germinate earlier in the year than seeds produced in cold-temperate climates, and they have a longer period of time available for seedling establishment. The embryos of G. biloba seeds possess a temperature-dependent developmental-delay mechanism that allows seeds to survive winter by preventing premature germination in the fall. This and other cold-climate adaptations appear to have evolved within the genus Ginkgo during the early Cretaceous, when the Northern Hemisphere was undergoing dramatic cooling after a long period of stable, warm conditions. Ginkgo biloba seeds possess an odoriferous sarcotesta that attracts mammalian scavengers in Asia--most notably members of the Carnivora--presumably by mimicking the smell of carrion. Seeds cleaned of their sarcotesta germinated faster and at higher percentages than those with their sarcotesta intact, suggesting that animal dispersal plays an important role in promoting seedling establishment. During the Cretaceous, potential dispersal agents included mammals, birds, and carnivorous dinosaurs., Abstract Introduction Literature Review Pollination and Fertilization Germination Materials and Methods Results Discussion Evolutionary Implications Ginkgo Seed Dispersal Acknowledgments Literature Cited Introduction Ginkgo biloba L. is a large tree native [...]

Abstract: A total of 2561 slash pine (Pinus elliottii Engelm. var. elliottii) grafts were topgrafted in the winter of 2003 and evaluated in January of 2004. The objectives of this [...]

Abstract: Field trials established with clones and seedlings from the same families provide an opportunity for comparing full-sib family performance across propagule types. More than 1200 different clones together with [...]

Abstract: We studied flower stimulation in two young miniaturized seed orchards of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) in Oregon. In experiment 1, female and male flowering were substantially [...]

Abstract Introduction Gender-Biased Nectar Production (GBNP) in Dichogamous Plants Commonalities among Dichogamous Plants with GBNP GBNP is Male-Biased as Often as Female-Biased Nectar Production Biases Are Modest in Most Plants [...]

Soybean [Glycine max (L.) Merr.] seed protein is deficient in the essential sulfur-containing amino acids, methionine, and cysteine. Transgenic approaches to increase coding for these amino acids have not been particularly fruitful. Little is known about the relative importance of S stored in vegetative tissues for seed protein synthesis. This study was conducted to secure data on sulfur (S) uptake, distribution, and mobilization patterns in the reproductive phase of soybean grown under S sufficient conditions. Soybean plants were grown in hydroponic culture and pulsed with 3sS labeled S[O.sub.4] at several discrete stages during the reproductive phase of development. Sequential harvest of plants indicated where and how S is stored and mobilized during reproduction in soybean. Leaves supplied developing soybean seed with approximately 20% of its S requirement. Distribution of newly acquired S within plants changed through reproductive development; however, leaves mobilized S with a similar efficiency through R5.5. Expanding leaves take up disproportionately large quantities of S; however, leaf tissue seems dependent on newly acquired S, and is unable to utilize stored S[O.sub.4]. Pods play an important role in S storage and mobilization to seed. In contrast to the leaf fraction, expanding pods were able to utilize stored S. Pods and seeds seem dependent on mobilized S. This study demonstrates that developing soybean seeds are dependent on S that has been mobilized from other plant tissues., SOYBEAN SEED is an important source of dietary protein for humans and livestock; however, its protein contains low concentrations of the essential amino acids methionine and cysteine (Food and Agricultural [...]

Three quantitative trati loci (QTL) regions for the restoration of Owen CMS (cytoplasmic male sterility) in sugar beet (Beta vulgaris L.ssp. vulgaris) were identified through analysis of three populations segregating for genes restoring the fertility of cytoplasmic male sterile plants. Two large populations, A and B, were studied by means of 51 and 42 polymorphic and evenly distributed restriction fragment length polymorphism (RFLP) markers, respectively. A smaller population, C, was analyzed by use of six RFLP markers. Composite interval mapping in Population A detected a strong signal on linkage group IV that explained 79% of the phenotypic variation. More detailed analysis revealed the presence of two linked QTL on this chromosome. In Population B, a QTL that explained 72% of the phenotypic variation was detected at one end of linkage group III. Single-marker analysis of Population C resulted in significant signals for markers on linkage group IV, explaining 57% of the phenotypic variation. In each of the two large populations, what appeared to be minor alleles were also detected in the QTL regions., CYTOPLASMIC MALE STERILITY is a maternally inherited condition involving a plant's inability to produce functional pollen. It is commonly found in natural plant populations and is most frequently caused by [...]

Key Words female gametophyte, embryo sac, plant reproduction, Arabidopsis Abstract The plant life cycle alternates between a diploid sporophyte generation and a haploid gametophyte generation. The angiosperm female gametophyte is [...]

INGO MAIER (1) (*) CHRISTIAN HERTWECK (2) WILHELM BOLAND (2) Sexual reproduction in the large brown seaweeds of the Laminariales, commonly called kelp, involves signaling chemicals, or 'pheromones,' that induce [...]

The incidence of infection and reproductive success of Phoradendron californicum (desert mistletoe) on its host, Acacia gregii (catclaw), was quantitatively investigated in two localities of the Las Vegas Valley, Nevada, from March through November 1997. Similar patterns were detected between the two study sites. The abundance of Phoradendron was significantly positively correlated with age of Acacia trees, and more positively correlated with size. Phoradendron-infested trees were significantly older and larger, and had significantly lower diurnal and seasonal water potentials than adjacent uninfested trees. Phoradendron-infested trees were significantly more water-stressed than uninfested trees of similar age and size. Infested Acacia trees occurring on an extensive terrace surface were significantly more water-stressed than Acacia occurring along an intermittent wash during the dry summer season. Phoradendron canopy cover and fruit production were significantly larger on Acacia trees occurring along the wash than on the terrace. High levels of Phoradendron infestation greatly increased host-plant water stress, and low host-plant water potentials significantly reduced the canopy cover and fruit production of Phoradendron. However, characteristics of Phoradendron fruits were not significantly different between the two geomorphic surfaces. A combination of age, size and water status of Acacia trees largely influences the infection and reproductive success of Phoradendron in the Las Vegas Valley of southern Nevada., INTRODUCTION Parasitism occurs when one organism (parasite) benefits at the expense of the host organism. All Phoradendron spp. show some degree of parasitism or dependence on a host plant (Fisher, [...]

Horsenettle (Solanum carolinense. Solanaceae) plants possess the ability to bear both hermaphroditic and male flowers on the same plant, a breeding system referred to as andromonoecy. As part of an ongoing investigation into the evolution and maintenance of andromonoecy in horsenettle we conducted a field investigation that addressed the following questions: 1. Are fruit and seed production in horsenettle populations pollen limited? 2. Do pollen additions affect sex expression? 3. Is the size of the floral display or the percentage of flowers that are male associated with percentage fruit set, and therefore possibly related to the attraction of pollinators? We conducted pollen additions on 25 planks in each of two populations, and monitored 25 open pollinated control plants at each site. Mean percentage fruit set and seed set per fruit was significantly greater in the pollen addition treatment than in the control, which indicates that both populations were pollen limited. The percentage of flowers on a plant that were male was significantly greater in the pollen addition treatment than in the control, which suggests that pollen addition affects sex expression in horsenettle. Percentage fruit set did not correlate with total flower number or percentage of male flowers, which indicates that a larger floral display does not affect pollinator behavior in ways that influence female reproductive success. The results document the existence of pollen limitation in the two horsenettle populations studied and suggest that future studies should determine if male flower production influences male fitness or vegetative reproduction., INTRODUCTION The ability of individual plants to bear both male and hermaphroditic flowers characterizes the andromonoecious breeding system. Andromonoecy can be maintained in a population if plants that possess the [...]

In this study, we examined how foliar herbivory affected the relative allocation to male and female reproductive traits in a hermaphroditic plant. In two experiments, one in the greenhouse and the other in a growth chamber, leaves of full sibling plants of the annual wild radish, Raphanus raphanistrum, received one of four damage treatments to leaves (0, 25% [two types], or 50% leaf area removal). We controlled natural damage by Pieris rapae larvae through the use of clip cages. Measurements of both male and female reproductive characters were made on a series of flowers produced by each plant over its lifetime. We measured pollen production, pollen size, ovule number, ovule size, petal size, nectar production, and sugar content. Effects of herbivory on plant phenology were also assessed. At the end of the experiment, we quantified total flower production, fruit production, number of seeds and fruit, and seed and vegetative biomass. In general, male reproductive characters were more affected than female characters by herbivory. Leaf herbivory reduced pollen number and pollen size, whereas ovule size and number were not affected. Petal size, which we also classify more as a male trait, decreased with herbivory. Plants were generally able to completely compensate for herbivory in the total number of flowers and fruit they produced; however, fewer fruits were found in the heaviest damage treatment in the growth chamber experiment. We discuss alternative explanations for this pattern based on developmental constraints and adaptive responses. In summary, male fitness traits were much more strongly affected by herbivory than were female traits; full compensation in seed production after herbivory may come at the cost of male reproductive success in these hermaphroditic plants. Key words: allocation to male vs. female function; compensation; floral traits; foliar herbivory; male plant fitness; Pieris rapae; Raphanus raphanistrum; reproductive traits; wild radish., INTRODUCTION Foliar herbivory can affect plant fitness directly through changes in plant traits, and indirectly by altering pollinator visitation patterns to damaged plants (Strauss et al. 1996, Strauss 1997, Lehtila [...]

We studied resource allocation between sexual reproduction and clonal propagation in a perennial stoloniferous clonal plant, Potentilla anserina, an obligate outcrosser. We manipulated reproductive effort of Potentilla anserina either by hand-pollinating all flowers or by preventing pollination. To test the effect of resource-limiting conditions on resource allocation and reproductive output, we used a control and two levels of heavy metals (copper and nickel) to limit plant growth. The experiment was conducted as a 2 x 3 factorial design to reveal possible interactions between reproductive manipulation and resource limitation. Heavy metals decreased the total biomass of the plants and number of flowers and ramets produced. Only 50% of the plants grown with the higher level of heavy metals produced flowers. Pollination treatment interacted significantly with the heavy-metal treatment. In the metal control (no metals added) and lower heavy-metal treatment, there were no significant differences in total vegetative biomass between the two pollination treatments. Costs of reproduction in terms of subsequent flowering in the later season appeared to be clear, because the number of flowers per whole plant was lower if the plants were hand-pollinated and because the proportion of flowering ramets decreased due to hand-pollination. However, flowering may also be partly hormonally controlled. In contrast, hand-pollinated plants exposed to high concentrations of heavy metals tended to have greater biomass of vegetative plant structures and higher number of flowers compared to nonpollinated plants. Together, these results suggest that environmental factors may alter costs of reproduction but do not support the idea that these costs are more acute in resource (photosynthate)-limiting conditions. Key words: allocation; clonal plants; clonal propagation; compensatory flowering; costs and manipulation of reproduction; hand-pollination; heavy metals; Potentilla anserina; vegetative growth., INTRODUCTION One of the central concepts in life history theory is the principle of allocation of limited resources among competing activities (e.g., Cody 1966, Williams 1966, Reznick 1985). This competition [...]

This paper reports the results of a two-year field experiment on the determinants of fitness responses in Pinguicula vallisneriifolia (Lentibulariaceae), an endemic carnivorous plant of southeastern Spain. For the first time, in this experiment, we have considered irradiance as a factor, in combination with animal prey, for an array of natural field conditions. The goal was to determine how carnivory translates to fitness within different radiation regimes. For this, it was necessary to quantify an array of plant responses, such as survival, growth, reproduction (sexual and vegetative reproduction), as well as responses related to carnivory investment (leaf shape and mucilage secretion). Both irradiance and animal food supply proved to be important limiting factors for P. vallisneriifolia under field conditions. Plants clearly decreased in performance from the sunny habitat to the deep-shade one, with plants growing in the least irradiance registering the lowest values for all variables analyzed. The clearest response to prey was the production of axillary buds. Most vegetative and reproductive responses depended heavily on the initial biomass of the plant before the experiments, the largest plants bearing the most leaves, flowers, stolons, and axillary buds. A gradient from less to more mucilage secretion appeared from deep-shade to sunny habitat, and within each habitat from prey exclusion to prey addition levels. Trapped prey stimulated digestive secretions in a positive feedback (the more prey, the more mucilage secretion) under all irradiance conditions. The curled, more secretory leaves of the sunny plants, in comparison with the nearly flattened, less secretory leaves of the deep-shade plants, illustrate the constraints imposed by differing scenarios on the capture of both prey and photons. With nonlimiting water availability, more irradiance and prey results in more survival, growth, and sexual and vegetative reproduction. Nevertheless, it is not usual to find an optimum combination of resources (i.e., irradiance, prey, and water) available in the same microhabitat during the Mediterranean summer. The spatial uncoupling of limiting resources progressively increased towards the extremes of the irradiance gradient (sunny and deep-shade habitats, respectively), and therefore the dual photosynthetic and carnivore functions of P. vallisneriifolia leaves were not equally efficient in all habitats. These opposing resource gradients determined all vegetative and reproductive plant responses. The perennial character of this endemic plant, together with its vegetative form of propagation, allows the possibility of resisting extinction even in the absence of seedling recruitment or when vegetative growth is strongly limited. Key words: carnivorous plants; ecological heterogeneity; field experiment; growth and survival; irradiance; leaf shape; Lentibulariaceae; Mediterranean ecosystems; mucilage secretion; Pinguicula vallisneriifolia; prey capture; sexual and vegetative reproduction., INTRODUCTION Carnivorous plants use entrapped animal tissues for nutrition, reversing the normal animal-plant interaction and representing a great anomaly in the usual trophic order of life (Thompson 1981). These plants [...]

In many plant species with unisexual flowers, the female flowers lack pollinator rewards and are pollinated by visitors who mistake the female flowers for rewarding male flowers. Here we present the results of observations and experiments designed to investigate pollinator discrimination and its consequences for female reproductive success in two monoecious Begonia species pollinated by deceit. Male and female flowers of B. urophylla are similar in shape, but female flowers are smaller than male flowers, while in B. tonduzii, male and female flowers have strikingly different shapes, but their petaloid tepals are similar in total area. Flower visitors displayed marked discrimination against the rewardless female flowers of both species. Seven bee species were observed on B. urophylla, and for all species taken together the relative visitation rate to male flowers was 8.6 times that to female flowers. The bee Trigona fulviventris accounted for 95% of all visits to B. tonduzii and visited male flowers 15.4 times as often as female flowers. The flower visitors of B. urophylla varied significantly in their degree of discrimination against female flowers, with visitation rates to male flowers 3.7-21.8 times those to female flowers. The two most abundant flower visitors displayed the greatest discrimination against female flowers and, although they comprised nearly 54% of all visits, were responsible for only 15% of all visits to female flowers. Thus, the relative abundance of different flower visitors on B. urophylla is a poor predictor of pollinator importance. In both species the inflorescence sex ratio was male-biased early in the season and female-biased later. Hand-pollination experiments revealed that fruit set in B. tonduzii was pollinator limited both during peak and late flowering, with supplemental pollination having its greatest effect late in the season when male flowers were rare. In contrast, fruit set was only weakly affected by supplemental hand-pollination in B. urophylla. The significant pollinator limitation observed in B. tonduzii and the lack of it in B. urophylla are consistent with our observation that the visitation rate to female flowers was much higher in B. urophylla than in B. tonduzii, which was due in part to the lower level of pollinator discrimination against female flowers of B. urophylla. Our finding that female reproductive success is limited by pollinator visitation in B. tonduzii indicates an opportunity for the evolution of increased resemblance between male and female flowers in this species. Key words: Begonia; deceit pollination; floral display; fruit set; mimicry: monoecy; pollinator limitation; pollinator preference., INTRODUCTION Resemblance between male and female flowers has been observed for a number of plant species with unisexual flowers (Baker 1976, Bawa et al. 1982, Armstrong and Drummond 1986, Barfod [...]

We examined the influence of the leaf spot pathogen Cercospora kalmiae on reproductive success in self-fertilized vs. outcrossed progeny in the mountain laurel (Kalmia latifolia). To explore the interaction between disease incidence and mating system within natural populations of K. latifolia, we ascertained the correlation between disease intensity and two measures of plant reproductive success (proportional fruit set and seedling survival) and partitioned the correlation by pollination treatment (i.e., naturally pollinated, hand pollinated with outcrossed pollen, or self-pollinated). For outcrossed flowers, neither the number of fruits produced nor the performance of seedlings from these fruits was affected by the intensity of disease damage. However, for selfed flowers, both the number of fruits and the performance of seedlings were negatively correlated with disease damage on the maternal parent. Consequently, fungal infection on a maternal plant was associated with an increased proportion of outcrossed progeny produced by the host plant. Motivated by the observed correlation between disease and selfing, we performed a manipulative field experiment to examine the mechanism by which disease could influence the fitness consequences of different mating strategies. We hypothesized that intense C. kalmiae infection reduced K. latifolia resources by reducing photosynthetic leaf area and, consequently, enhanced abortion of self-fertilized fruits more than outcrossed fruits. We found that artificial leaf damage reduced outcrossed fruit set by 17% compared to controls. However, artificial leaf damage reduced selfed fruit set by 31% compared to controls. Similarly, artificial damage did not significantly affect infructescence abortion in outcrossed pollinations. However, for self-pollinated inflorescences, those subtended by damaged leaves experienced a 44% increase in infructescence abortion compared to controls. We conclude that resource limitation, here by leaf damage, can lower the production of self-fertilized seeds relative to outcrossed seeds, thus modifying a plant's mating system. Key words: hermaphrodite; Cercospora kalmiae; Kalmia latifolia; leaf spot pathogen; mating systems; mountain laurel; outcrossing; photosynthetic resources; seed production; self-fertilization., INTRODUCTION Fruit maturation is a dynamic process and may be influenced by many factors (Casper and Niesenbaum 1993). Among these, the source of pollen can affect which seeds will draw [...]

In his classic paper on the correlation between relatives, R. A. Fisher (1918) introduced the notion of 'dual epistacy' to account for deviations from linearity due to interactions between distinct [...]

In his monograph on plant speciation, Grant (1981) described several mechanisms by which the breeding behavior of hybrids could be stabilized, thus providing the potential for hybrid speciation. These include: [...]

It has been 30 years since Baker (1967) reemphasized in these pages the significance of what Stebbins (1957) had termed 'Baker's Law,' namely, that it is more likely for self-compatible [...]

We carried out phenotypic selection analyses to assess the relative importance of several floral traits, as well as microhabitat, in determining both male and female pollination success in a nonrewarding orchid (Cypripedium acaule Ait.) in two Nova Scotia populations. Fruit production in these one-flowered, cosexual plants was strongly pollen limited within a season: 100% of individuals set fruit following hand-pollination, but only 5% and 13% did so under natural circumstances in the two populations. Male and female reproductive success were highly correlated, with >90% of plants that received a pollinium also dispersing one. Despite very low visitation rates, the chance of a removed pollinium fertilizing another ovary was 36% and 51%, respectively, in the two populations. There was no evidence for selection acting differently, either through the two sexual functions or in the two populations. In contrast, the strength of directional selection on several traits differed among microhabitats within each population. Univariate and multivariate regressions indicated statistically significant directional selection acting on flower-opening date through male, female, and total (combined) pollination success in one population. For female, male, and total success in this population, we also detected correlational selection acting on opening date and flower height. There was also negative correlational selection acting on flower height and labellum length through female success. Microhabitats within the populations had a larger effect on both female and male success than did floral traits. In particular, the presence of ericaceous shrubs and an open canopy appeared to be closely linked with higher pollination rates. Key words: Bateman's rule; correlational selection; Cypripedium: deceit pollination; flower size; natural selection; Orchidaceae; phenology; plant height; pollen limitation; selection coefficient., INTRODUCTION The intuition that natural selection favors those floral dimensions and characteristics that result in precise pollen transfer is supported by at least two general patterns. First, most floral traits [...]

Maintenance and use of germplasm collections of Vicia species is difficult because of limited information on their mating systems. Polymorphism of seven enzyme systems in 31 accessions of 12 Vicia species were measured by isoelectric focusing to infer their mating system. To compare variability within and among accessions and between species, polymorphism indices were calculated by means of isozyme bands. All enzymes studied had polymorphic banding patterns. Twenty-eight accessions were variable for at least one of the seven enzymes, whereas three other accessions were uniform for all seven enzymes. Within-accession variation was larger than that among accessions in V. villosa Roth and V. villosa ssp. varia (Host) Corbiere, whereas within-accession variation was smaller than that among accessions of V. articulata Hornem., V. benghalensis L., V. cracca L., V. ervilia (L.) Willd., V. lutea L., V. narbonensis L., V. pannonica Crantz, V. peregrina L., and V. sativa L.. The results agreed with field tests which demonstrated that V. villosa and V. villosa ssp. varia are predominantly cross-fertilizing species, whereas the other species are mainly self-fertilizing. The use of isozyme bands to determine mating system proved to be accurate. In addition, this method is convenient because it utilizes a small seed sample and is inexpensive and easy to perform., SEVERAL Vicia species are of considerable economic importance as grain, green manure, cover, and forage crops. Management and use of germplasm collections of this genus has become difficult because of [...]

This study documents variation in the number of florets per flower head and the number of flower heads per flowering shoot for individuals of Solidago macrophylla, a perennial composite, on an elevational gradient in the White Mountains of New Hampshire, and asks if variation in floret distribution vs. plant insect attack predicts variation in reproductive success. Fifteen populations were censused over 2-3 yr to document the number of florets per head, the number of heads per shoot, aphid infestation and seedling emergence per flowering shoot. Additionally, levels of seed predation by tephritid flies were measured during the final year. Flowering shoots in populations at higher elevations produced significantly more florets per head and fewer flowering heads than flowering shoots in populations at lower elevations. Overall, populations at lower elevations produced more florets than populations at higher elevations. However, this difference in reproductive potential did not result in differential reproduction in either 1993 or 1994. Populations at higher elevations had fewer plants with aphids than populations at lower elevations. In 1993 neither aphid infestation levels nor floral life history traits predicted the mean number of emerging seedlings per shoot in the greenhouse. In 1994 the percent of flowering shoots per population with aphids was a significant negative predictor of the mean number of emerging seedlings per shoot in the greenhouse, whereas the number of seed predators per head per shoot was a significant positive predictor of the number of emerging seedlings. Floral life history traits did not predict reproduction in 1994. Finally, patterns of seedling emergence over the environmental gradient resulted in a greater opportunity for selection in lower vs. higher elevation populations., INTRODUCTION Life history traits have been shown to determine demographic processes in both theoretical (Cole, 1954; Lande, 1982; Caswell, 1989) and empirical studies (Bierzychudek, 1982; Kalisz and McPeek, 1992). While [...]

A key feature of self-incompatibility (SI) systems in plants is the mate availability or proportion of compatible matings in a population (Bateman 1952; de Nettancourt 1977). A mating is the [...]

Theoretical (e.g., Maynard Smith 1971; Lloyd 1979; Charlesworth and Charlesworth 1979, 1987, 1990; Lande and Schemske 1985; Campbell 1986) and empirical (e.g., see Charlesworth and Charlesworth 1987) studies have illustrated [...]

Leaf N concentration (LRN), stomatal conductance (g,), and grain-assimilate demand each affect the leaf [CO.sub.2]-exchange rate (CER) of winter wheat (Triticum aestivum L.) during grain fill. Although leaf CER, g,, and LRN decrease during this time, little research has been conducted to examine whether these decreases occur simultaneously or to determine the effects of grain development on these declines. This field study was conducted (i) to monitor changes in CER, LRN, and g, during winter wheat reproductive development, (ii) to examine the relationships between the rate and duration of CER and the rate and duration of grain rill, and (iii) to determine the effects of crop N status on the decline in LRN and CER during grain fill. Two early (Andy and Gore) and two medium (Northrup King Coker 9803 and Northrup King Coker 9835) maturing cultivars were grown with irrigation and two rates of spring-applied N (56 and 112 kg N [ha.sup.-1]) in 1994 and 1995. Cultivar ranking was similar for the date of inflorescence emergence, the initiation and termination of grain development, and the complete loss of green leaf area and flag-leaf photosynthetic activity. For all cultivars, flag-leaf CER and g, began to decrease near the beginning of grain rill, whereas LRN and leaf area index (LAI) began to decrease prior to grain rill. Rapid reductions in LRN and CER were found only after significant grain growth occurred, with the rate of decrease being relative to the cultivar ranking found for inflorescence emergence date. Averaged over cultivars and years, increasing the rate of spring-applied N increased LAI and LRN near inflorescence emergence by 37 and 24%, respectively but only delayed the complete loss of green leaf area by 2 to 3 d and had little effect on the duration of grain fill. Stage of grain growth had little effect on the loss of LRN and CER until the latter portion of grain rill, 'hen rapid reductions in these variables occurred. Increasing the rate (if spring-applied N did not significantly delay these decreases or extend the duration of grain rill., Winter wheat grain N originates from both the remobilization of vegetative tissue N and from the active uptake and assimilation of N during grain fill. Remobilized N is usually the [...]

For organisms with indeterminate growth, life history theory predicts that in environments where organisms experience high survival rates or gain fecundity with age or size, natural selection favors delayed maturity. In semelparous perennial plants the onset of reproduction is regulated by a threshold size for flowering. We tested this prediction by comparing sand dune populations of the facultative biennial herb Cynoglossum officinale. We collected data on flowering probability, survival, and growth rate in relation to plant size in two habitat types, open areas and poplar thickets, in Meijendel, The Netherlands, and in Holkham, England. Survival of established rosettes was highest in Holkham and lowest in open areas in Meijendel. Relative growth rates in Holkham were about three times as high as those in Meijendel. These findings agreed with the differences in threshold sizes found among the sites: the Holkham field population harbored higher threshold sizes than the Meijendel sites. We used the field data to compare optimal threshold sizes for flowering predicted by three existing models. All three models gave the same rank order for threshold sizes as found in the field: Meijendel open < Meijendel poplar thicket < Holkham. One model, which maximized population growth rate Λ, predicted optimal threshold sizes that agreed very well with threshold sizes found in the field. The predictions of the two other models, both maximizing [R.sub.0], were consistently lower than the threshold sizes observed in Meijendel, while their predictions for Holkham were too high. Key words: Cynoglossum officinale life history; facultative biennial; genetic variation; growth rate; hound's-tongue; optimization models; plant size and fitness; semelparous; survival; threshold size for flowering., INTRODUCTION The onset of reproduction is a key parameter in the life history of most organisms, and age and size at maturity are life history traits with a high impact [...]

The majority of outcrossing angiosperms have bisexual flowers, a condition from which self-pollination can evolve directly through the modification of self-incompatibility or other floral traits that prevent self-pollination. Indeed, theoretical [...]

Eastern gamagrass [Tripsacum dactyloides (L.) L.], a native, warm-season species, is a nutritious and palatable forage for grazing livestock. The grass has potential for rangeland and pasture improvement. This field study was conducted over 10 yr and one location to determine the reproductive characteristics of the various cytotypes of Tripsacum and identify methods for breeding agronomically superior cultivars. Intra- and interspecific crosses were made and evaluated between several Tripsacum cytotypes. Cytological and polymerase chain reaction-random amplified polymorphic DNA (PCR-RAPD) techniques were used to identify methods of reproduction and types of individuals generated. Results of the study identified two methods for facilitating horizontal gene flow among sexual and apomictic cytotypes. Materials with triploid and hexaploid constitutions were essential in the movement of sexual germplasm into apomictic tetraploids and of tetraploid germplasm into sexual diploids, respectively. Triploids and hexaploids were useful materials to introgress and transfer desirable alleles across species, cytotypes, and reproductive barriers. In addition, the generation of triploid and hexaploid genotypes will continue to exert major influences on Tripsacum evolution and speciation. This study identified additional methods and systems for improving Tripsacum germplasm by utilizing its distant relative maize (Zea mays L.) in a breeding or genetic evaluation program., Eastern gamagrass is a native warm-season, perennial bunchgrass and is often referred to as 'the grandad of grasses' (Martin, 1963). Historical references and early land survey records of settlers who [...]

Paspalum is a large genus that contains several important forage and turf grasses. Little or no information is available concerning the cytology and reproductive behavior of many of these species. The objectives of this study were to determine the cytology, method of reproduction, and fertility of accessions of eight different Paspalum species. Paspalum modestum Mez., P. monostachyum Vasey, P. repens Bergius, and one P. alcalinum Mez. accession were sexual diploids with 2n = 2x = 20 chromosomes. Meiosis was regular with primarily bivalent pairing. Even though P. modestum was sexual, the female gametophyte deteriorated in 43% of the ovules. Two P. alcalinum, one P. falcatum Nees, two P. paucifolium Swallen, three P. polyphyllum Nees, and one P. unispicatum (Scribn. et Merr.) Nash accessions were tetraploids with 2n = 4x = 40 chromosomes. During meiosis their chromosomes associated primarily as bivalents, quadrivalents, and univalents. Regardless of the species, all tetraploids were facultative aposporous apomicts. One P. alcalinum accession was a pentaploid with 50 chromosomes. Meiosis was irregular with the chromosomes associating as univalents, bivalents, trivalents, and quadrivalents. This accession reproduced as an obligate aposporous apomict. Seed set in P. modestum and P. monostachyum was very low but was high enough in the other species that they could be propagated by seed. These findings demonstrate the cytological and reproductive diversity within this large complex genus., According to Chase (1929), the genus Paspalum consists of more than 400 species. Essentially all are native to the Americas with the majority occurring in tropical and sub-tropical Central and [...]

The soybean [Glycine max (L.) Merrill] reproductive cycle represents more than 50% of the length of the total growth cycle. Immature embryo culture could be used to shorten this cycle. This study was conducted to develop an efficient technique to shorten the soybean reproductive cycle and to make it possible to develop recombinant lines from populations more rapidly. The importance of a pod pretreatment before embryo extraction, the effects of embryo age an germination rate, embryo position in the pod, and the composition of the germination medium (supplemented with sucrose or not) were analyzed to define an optimal technique. Plant recovery rate and genotype effects on germination were evaluated with 22 genotypes representing a broad genetic background. It was necessary to pretreat immature seed by exposing pods to 26 ° C for 4 d to induce germination. Best results (up to 100% germination) were obtained from embryos sampled at the end of lag phase of seed development (approximately 19 d after flowering). For three-seeded pods, the central embryos generally bad a higher germination rate than distal and proximal embryos (25 and 44 percentage points, respectively). Whatever the embryo position in the pod, adding sucrose significantly increased the germination of embryos sampled 14 to 18 d after flowering. Plantlets were obtained from 73% of the germinated embryos and the length of cycle win reduced from 130 to 140 d to 65 to 70 it. Average germination of the 22 genotypes was 80%; thus, this technique, paired with the single seed descent method, provides soybean breeders with a tool to develop lines quickly., The reproductive cycle represents more than 50% of the length of the total life cycle for soybean. In vitro culture of immature embryos has a number of basic and applied [...]

This study investigates the role played by showy structures in the reproduction of Lavandula stoechas L. (Lamiaceae), a self-compatible Mediterranean shrub with compact, head-like inflorescences that are terminated by a tuft of conspicuous pink bracts. Pollinator visitation rates to plants with bracts correlated positively with that of paired, treated shrubs with all their bracts removed and, overall, bractless and control plants had equivalent visitation rates. In experimentally split shrubs, however, a strong effect on pollinator choice was evident, and distant visitor approaches were most often to that side keeping the attractive organs. Fecundity was not depressed in plants with reduced visual displays, and neither was the amount of pollen dispersed per flower or the size of stigmatic loads. There were, however, more pollen tubes, on average, at the lowermost part of the style in controls (10.8 tubes/style) than in bractless shrubs (8.3 tubes/style). Small, nonsignificant declines in average seed size, germinability, and seedling mass were detected following bract removal. Data support the notion that bracts are not essential to seed production in mature, relatively dense Lavandula populations where bee pollinators are often in good supply, but may be all-important if plant density is extremely low, or during population establishment. The role of an amplified display in increasing average pollination distance and progeny quality in this species is discussed. Key words: fecundity; floral display; Lavandula; Lamiaceae; Mediterranean; outcrossing; pollinator attraction., INTRODUCTION Many aspects of animal-pollinated plant reproduction are influenced by the size of the floral display, including visitation rates and fecundity (e.g., Willson and Price 1977, Lack 1982, Gori 1983, [...]

Apomixis involves the parthenogenetic development of apomeiotic eggs. It has the potential of cloning plants through seed, and thus furnishes a unique opportunity in alfalfa breeding for developing superior cultivars with permanently fixed heterosis. Megasporogenesis of a meiotic mutant of alfalfa Medicago sativa subsp. falcata (L.) Arcang. (2N=2x=16), named PG-F9, that produced 2n second division restitution (SDR) and apomeiotic eggs at high frequencies, was cytologically analyzed by both stain-clearing and sectioning techniques. The restitutional 2n egg formation was mainly due to the omission of the second meiotic division. The absence of cytokinesis was also documented after a normal second meiotic division. The concurrent examination of integument growth, cell appearance, and nucleolus size associated with either the absence of degenerating meiotic products or aposporic initials in the ovules allowed the production of apomeiotic 2n megaspores to be ascribed to a diplosporic pathway. The mutant PG-F9 was grown in the field and in a growth chamber and the frequencies of normal, restitutional, and diplosporic cells were recorded under both environments. Restitutional 2n megaspore formation (dyads and triads with 2n chalazal megaspores) and the suppression or modification of meiosis leading to apomeiotic 2n megaspore production were influenced by environmental conditions. The frequency of normal tetrads was three times higher in the field (23.08%) than in the growth chamber (7.91%). The same trend was found for functional reduced chalazal megaspores. The frequency of restitutional cells was largely preserved in the two environments (51.92% in the field versus 50.31% in the growth chamber). The omission of normal meiosis resulting in diplosporic cells increased from 16.35% in the field to 26.27% in the growth chamber. The fertility of seed set and seeds per pod values of PG-F9 in controlled matings carried out in the field and in the growth chamber using different diploid and tetraploid pollen sources furnished information on 2n egg viability and partially supported the cytological results. The discrepancy observed indicated that some 2n megaspores were unable to develop into a functional embryo sac., The formation of 2n gametes (i.e., gametes with the somatic chromosome number) has been investigated both for studies of evolution (Stanford et al., 1972; Harlan and de Wet, 1975) and [...]

Many plant species seed at intervals of several years during their lifetime, with such reproduction often being synchronized over a large forest area and termed 'mast seeding' (Silvertown 1980). Mast [...]

Conflicting predictions have been made concerning the outcome of natural selection in obligately asexual populations. The general-purpose genotype hypothesis predicts that environmental fluctuations over time should eliminate asexual lineages that possess narrow ecological tolerances, and that therefore asexual populations should evolve to become more broadly tolerant of environmental variation than their sexually reproducing relatives. I tested this prediction by comparing the responses of a sexual and an asexual species of Erigeron (Asteraceae), E. philadelphicus and E. annuus, to four environmental treatments in a greenhouse experiment. Environmental treatments were created by varying the levels of competition from grass and the levels of shading that different individuals experienced. Overall, the treatment variables had roughly similar effects on both species. For both species, the presence of grass caused over 25% delays in the timing of bolting, and over 50% declines in biomass and the numbers of inflorescences produced. The effects of the shade treatment were entirely nonsignificant for both species. However, contrary to the prediction of the general-purpose genotype hypothesis, there were no significant differences in the magnitudes of these responses between the two species, which implies that asexual Erigeron individuals are no more general-purpose than sexuals. This lack of support for the general-purpose genotype hypothesis may indicate that biotic interactions such as competition, which are likely to promote the ecological specialization of lineages over generalist strategies, are more relevant in determining the evolution of niche width in these species., INTRODUCTION There is no doubt that sexual reproduction has come to dominate the life histories of plants, animals and fungi. Much of the morphological, structural and behavioral variation between groups [...]

Although mutualisms are often viewed as fragile constructs, subject to invasion by 'cheaters' that gain from the mutualism without providing compensating benefits, few studies have explored whether or not apparent cheating behavior by one player actually denies benefits to the other species. Panicled bluebells (Mertensia paniculata) experience high rates of nectar robbery by bumble bees (Bombus mixtus and B. frigidus) in the Wrangell Mountains of southcentral Alaska. Nevertheless, experimental prevention of nectar larceny in two seasons did not enhance components of female reproductive success (nutlet initiation, seed-set, and seed mass) or male success (pollen removal). Observational data show that the absence of a negative impact of nectar robbery is a consequence of bumble bee behaviors; the two bee species that rob mature flowers buzz-pollinate the same flowers at an earlier stage in floral development. The shift in bee behavior is driven by the presentation of different rewards at different times in the flowering period; young flowers contain pollen and older flowers produce nectar. Although flowers typically receive and donate pollen before most nectar is produced, the mature flowers producing a robbed nectar reward may nonetheless contribute to the reproductive success of bluebell plants. Flowers sequestered from pollinators in the early stage were still capable of initiating nutlets, demonstrating that older flowers can enhance female reproduction if pollinators are rare (when many early-stage flowers may go unvisited). Moreover, the removal of mature flowers reduced the visitation rate to early-stage flowers on the same plant. Because individual bumble bees switch frequently between nectar robbing and pollen collection, the nectar reward in mature flowers may act as a key enticement to pollinators, which then enhance plant reproduction by legitimately visiting early-stage flowers. Rather than representing a case of cheating behavior, nectar robbery may be an integral part of this plant-pollinator mutualism. Key words: bluebells; Bombus spp.; bumble bees; cheating behavior; floral color change; hermaphroditic plants; Mertensia paniculata; nectar robbery; plant-pollinator mutualism; pollen removal; reproductive success., INTRODUCTION Many ecologists have decried the scanty attention paid to mutualistic interactions (Risch and Boucher 1976, Boucher et al. 1982, Vandermeer 1984, Keddy 1990, Bronstein 1991). Past history seems to [...]

The form of angiosperm flowers is thought to have evolved in part via selection that excludes ineffective pollinators and increases the efficiency of pollen transfer by effective ones. In previous studies with the montane plant Ipomopsis aggregata, we documented pollinator-mediated selection on several aspects of floral form, including flower width. This character varies continuously within natural populations of I. aggregata, and individuals with wider flowers export more pollen per flower to surrounding plants. We previously showed that this component of phenotypic selection is due primarily to the per-visit effectiveness of hummingbirds, the most important pollinator in our study populations. Here we investigate mechanisms of differential visit effectiveness in greater detail. First, counts of pollen in unvisited flowers showed that pollen production itself increases with width. In aviary experiments, hummingbirds also removed a greater proportion of available pollen as width increased. We next videotaped visits to flowers that varied in width either naturally, or by experimental treatment, and found that hummingbirds inserted their bills more deeply into wider flowers. Finally, we directly manipulated how deeply birds could insert their bills, and found that more pollen was removed after deep insertion. Thus, several mechanisms appear to underlie selection on corolla width via visit effectiveness in pollen export. One involves a phenotypic correlation with pollen production; this underscores the value of experiments for untangling indirect from direct selection. Another mechanism involves direct selection due to the depth of insertion of a hummingbird's bill; this is rare evidence for one form of selection involving the 'fit' between pollinator and flower. Key words: flower shape and size; hummingbird; Ipomopsis; morphology; phenotypic correlation; pollen export and production; pollinator effectiveness; selection., INTRODUCTION Angiosperm flowers exhibit remarkable diversity in form. Floral morphology often serves to distinguish species (Grant 1949), and appears to correlate well in many cases with the morphology of prominent [...]

It is widely believed that desert annual plants maintain between-year seed banks, yet few field studies actually have measured the proportion of the viable seed bank that remains dormant through a season. Dormancy and germination fractions were quantified for a guild of winter annuals on a creosote flat in the Sonoran Desert for three years. Predictions from two types of theoretical models applicable to temporally variable environments were examined: (1) the evolution of life history traits promoting persistence in the face of temporal variation and (2) the role of temporal variation in mediating species coexistence. The density of ungerminated seeds was estimated by collecting soil samples after germination, but prior to new seed set. Seedlings were followed in nearby plots to estimate the density of germinated seedlings and their reproductive success. Long-term data collected from permanent plots over a 10-yr period were used to calculate temporal variation in reproductive success for each species. Species with higher temporal variation in reproductive success had lower germination fractions and smaller seeds, consistent with the theory that seed dormancy and large seed size are partially substitutable bet-hedging strategies. The data also suggested that this system possesses traits that are necessary for temporal variation to promote coexistence. First, between-year seed banks, necessary to buffer populations in unfavorable years, were documented for 17 species. Second, there was a strong tendency for year-to-year variation in germination fractions to vary among species. Finally, plants germinated more in years of higher reproductive success. We discuss how a correlation between germination and reproductive success enhances the role of temporal variance in success hierarchies in promoting species coexistence. Key words: desert annual plants; dormancy; field experiment; life history traits; predictive germination; reproductive success; seed banks; Sonoran Desert; spatial variation; species coexistence; temporal variation., INTRODUCTION It is widely assumed that desert annual plants have seed banks. However, close inspection of the literature (e.g., Nelson and Chew 1977, Freas and Kemp 1983, Reichman 1984, Price [...]

Hybridization and introgression are common phenomena in many plant and animal groups and have been proposed as important processes in evolution. Interspecific gene flow has received much attention not only [...]

Reproduction is closely tied to environmental conditions and the availability of resources, and thus typically varies with season. Consequently, perennial organisms that reproduce continuously are generally restricted to tropical regions with relatively aseasonal climates. The temperate marine alga Macrocystis pyrifera is a rare exception in this regard, as most individuals reproduce throughout the year in a seasonally variable habitat. Here we measure reproductive responses of the giant kelp Macrocystis during a period in which resources and environmental conditions fluctuated greatly and contrast these responses with those of the palm kelp, Pterygophora californica, a sympatric species that exhibits strictly seasonal reproduction. The quantity and quality of spore production tracked resource availability within and among years for Macrocystis, but not for Pterygophora. Reproductive allocation and spore standing stock in Macrocystis were negatively correlated with seawater temperature and positively correlated with the nitrogen content of adult plants. Macrocystis generally displayed two seasonally distinct peaks in spore production per year (winter and spring). The only disruption of this pattern coincided with a warmwater El Nino event. Although seawater temperature and the nitrogen content of adults were inversely related in Pterygophora, neither variable was significantly correlated with the quantity or quality of spore production in this species. Unlike Macrocystis, Pterygophora exhibited a well-defined reproductive season in which plants displayed a single broad peak in spore production that varied little in timing and magnitude among years, even during El Nino conditions. Spore C/N ratios remained relatively constant over time in both species, despite large seasonal fluctuations in C/N ratios of vegetative tissue of adults plants. Nonetheless, spore C/N ratios were positively correlated with seawater temperature in Macrocystis, but not in Pterygophora. Spore viability (swimming and germination) varied considerably, and often unpredictably, over time for both species. Our results support the general idea that environmental conditions and resources exert a much greater influence on the quantity and quality of reproduction in species that reproduce continuously than on the majority of species that are strictly seasonal in onset of reproduction. The differential responses of Macrocystis and Pterygophora may reflect their different morphologies and life-spans. Macrocystis is relatively short lived and may 'hedge its bets' by reproducing continuously rather than risk delaying reproduction. Conversely, since Pterygophora lives much longer, plants can afford to release spores only during times when the chances for reproductive success are predictably greatest because these plants are likely to reproduce again in subsequent years. Key words: algae; C/N ratio; El Nino; germination; kelp; Macrocystis pyrifera; Pterygophora californica, reproductive allocation; resource availability; seasonality; spore production; viability., INTRODUCTION Growth and reproduction generally reflect physical conditions of the environment and the availability of resources (Follett 1978, Bronson 1985, Munro et al. 1990, Adiyodi and Adiyodi 1993). Consequently, seasonal [...]

Key words.--Allozymes, apomixis, clonal variation, dandelions, multilocus genotypes, pollen flow, Taraxacum. Received October 24, 1993. Accepted September 19, 1994. The evolutionary potential of a population or species depends largely on [...]

Little is known about the reproductive ecology of aquatic angiosperms, despite their wide distribution and ecological importance. Surfgrass (Phyllospadix torreyi) is a clonal marine angiosperm that lives on turbulent rocky shores. Surfgrass exhibits a strongly female-biased sex ratio in flowering shoots throughout its distribution along the Pacific coast of North America. The ecological causes for this biased sex ratio were examined over 3 yr in a surfgrass population off Catalina Island in southern California, USA. Abundances, biomass, and C:N content of male and female flowering ramets were measured, and the reproductive phenology, reproductive losses to abortions, herbivore damage to fruits and seeds, and clonal survival and growth were quantified. Each year, a quarter of the vegetative ramets reproduced sexually and seed production in the population was prolific. The population sex ratio was female biased across the entire depth distribution of surfgrass, but males were more abundant deeper in the bed. Despite male rarity, pollen was abundant in the population, and virtually all ovules were fertilized, with few losses to abortions or herbivory before seed release. Potential female fitness (seeds produced) was highest at shallow depths where light availability was greatest and abortions were reduced. The spatial segregation of the sexes was not due to environmental sex lability but to greater ramification of female vs. male clones in shallow depths. Female flowering shoots had significantly higher biomass than males across water depth, despite no obvious cost in terms of vegetative growth, or advantage in terms of plant size. If current theory on sex allocation that the sex ratio should be biased toward the gender with the lower reproductive cost is true for surfgrass, then surfgrass provides an example of how a subtle resource allocation difference can result in a dramatic population bias. An alternative explanation for the female bias in surfgrass populations is greater male mortality due to significantly weaker attachment to the substratum. This study demonstrates the potential role hydrodynamics can play in aquatic plant reproduction and in structuring their populations., Key words: biomechanics; Phyllospadix; seagrass reproduction; sex ratio; surfgrass. INTRODUCTION Dioecious plants with sex chromosomes are predicted to have primary sex ratios (i.e., in seeds at the end of parental [...]

Intermediate selfing rates often are observed in populations of animal-pollinated plants (e.g., Aide 1985; Waller 1986). However, many theoretical studies did not predict the evolution of intermediate selfing, but rather [...]

The study of plant mating-system evolution has provided fertile ground for the interaction of theoretical and empirical workers. Extensive empirical work began with Darwin (1876) and has continued at an [...]

We conducted three experiments in which we applied additional hand pollination, flower removal, and leaf removal treatments in various combinations to Primula veris, a perennial spring-flowering rosette species. The purpose of the study was to determine whether the seed set of Primula veris was limited by pollen availability or by other resources, and whether there were measurable costs of reproduction. Hand pollination in the beginning of experiments significantly increased current seed set in only one of the three experiments. It also increased the next-year fruiting probability in that first experiment. In the second experiment, hand pollination did not significantly affect current seed set, but we nevertheless observed enhanced leaf growth in the treatment year and the two following years, and increased flowering frequency, fruiting frequency, and survival in the two following years. In the third experiment, after hand pollination we observed a higher net photosynthetic capacity of the leaves and, again, increased leaf growth in the treatment year and a higher flowering probability in the following year. The positive effect of hand pollination was even clearer when the leaves of the plants were removed at the beginning of the experiment. However, the treatment in which all the flowers were removed had effects on subsequent performance similar to those of the hand-pollination treatment, suggesting trade-offs. Thus, we did not observe any costs associated with reproduction after supplemental hand pollination; on the contrary, hand pollination resulted in increased survival, size, and reproduction of the plants in the subsequent years. Key words: compensation; cost of reproduction; Europe; perennial herb; plant reproduction; plant survival; pollination; Primula veris., INTRODUCTION In some outcrossing perennial plants, seed set may be controlled by pollination success (Bierzychudek 1981, Ayre and Whelan 1989, Lubbers and Lechowicz 1989, Jennersten 1991, Agren and Willson 1994). [...]

Females of dioecious plant species are expected to show greater trade-offs with other life history traits than males because of their high investment in reproduction. We investigated life history traits and resource allocation patterns for both males and females of the dioecious plant Silene latifolia, to document allocation both prior to and after reproductive investment. In addition, the impact of fruit production on subsequent allocation to reproduction and growth was investigated by varying the number of flowers pollinated on females. The mean date of first reproduction was the same for males and females. Early-flowering plants of both sexes invested less in leaf biomass than plants that delayed flowering. The percentage of flowers pollinated had a significant effect on how resources were allocated, and on the amount and timing of further flower production. Sexual dimorphism was observed in resource allocation patterns after, but not prior to, investment in reproduction. Overall, pollinated females were found to have more leaf biomass and invest nearly twice as much in reproduction as males, in spite of an apparent trade-off between leaf production and reproduction within both females and males. We conclude that sexual dimorphism in life history traits that affects resource acquisition causes the resource pool that is allocated to be variable, rather than static, thereby masking the underlying tradeoffs. Key words: dioecious; life history traits; sexual dimorphism; Silene latifolia; trade-offs., INTRODUCTION Traits affecting reproduction and survival will be bound together by physiological trade-offs, because allocation of limited resources to any one activity will occur at the expense of others (Cody [...]

The resources a plant invests in sexual reproduction are partitioned among multiple units, such as gametes within a flower, flowers within an inflorescence, and inflorescences on a plant. The manner [...]

In hermaphroditic plants, reproductive success is achieved through pollen donation (male success) and seed production (female success). Pollinators respond to variation in floral features, such as nectar quality, flower color, [...]

Pollination of flowering plants is followed by the germination of pollen, growth of pollen tubes, fertilization of ovules, and development of resulting embryos. Variation in performance during any of these [...]