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Species that propagate by sexual reproduction actively guard against the fertilization of an egg by multiple sperm (polyspermy). Flowering plants rely on pollen tubes to transport their immotile sperm to fertilize the female gametophytes inside ovules. In Arabidopsis, pollen tubes are guided by cysteine-rich chemoattractants to target the female gametophyte.sup.1,2. The FERONIA receptor kinase has a dual role in ensuring sperm delivery and blocking polyspermy.sup.3. It has previously been reported that FERONIA generates a female gametophyte environment that is required for sperm release.sup.4. Here we show that FERONIA controls several functionally linked conditions to prevent the penetration of female gametophytes by multiple pollen tubes in Arabidopsis. We demonstrate that FERONIA is crucial for maintaining de-esterified pectin at the filiform apparatus, a region of the cell wall at the entrance to the female gametophyte. Pollen tube arrival at the ovule triggers the accumulation of nitric oxide at the filiform apparatus in a process that is dependent on FERONIA and mediated by de-esterified pectin. Nitric oxide nitrosates both precursor and mature forms of the chemoattractant LURE1.sup.1, respectively blocking its secretion and interaction with its receptor, to suppress pollen tube attraction. Our results elucidate a mechanism controlled by FERONIA in which the arrival of the first pollen tube alters ovular conditions to disengage pollen tube attraction and prevent the approach and penetration of the female gametophyte by late-arriving pollen tubes, thus averting polyspermy. FERONIA prevents polyspermy in Arabidopsis by enabling pectin-stimulated nitric oxide accumulation at the filiform apparatus after the first pollen tube arrives, which disengages LURE1 chemoattraction to prevent late-arriving pollen tubes from entering the ovule., Author(s): Qiaohong Duan [sup.1] [sup.2] , Ming-Che James Liu [sup.1] [sup.3] , Daniel Kita [sup.1] [sup.4] [sup.7] , Samuel S. Jordan [sup.1] , Fang-Ling Jessica Yeh [sup.1] , Robert Yvon [...]

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 (1-4). 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., Species diversity is influenced both by overall nutrient availability and by nutrient stoichiometry--that is, how the ratio of available nutrients relates to their consumers' requirements (5). In terrestrial plant communities [...]

Sexual reproduction in non-vascular plants requires unicellular free-motile sperm to travel from male to female reproductive structures across the terrestrial landscape (1). Recent data suggest that microarthropods can disperse sperm [...]

Flowering sex ratios of d.ioecious plants are commonly male-biased but rarely female-biased. While greater costs of reproduction from females have been repeatedly demonstrated and explain male biases, male reproductive costs almost never exceed female costs, making the origins of female biases enigmatic. I investigated the seagrasses Phyllospadix scouleri and P. serrulatus (surfgrasses), which have some of the most extreme female-biased sex ratios documented (>90% female), to identify the mechanisms driving sex ratio bias. I developed sex-linked amplified fragment length polymorphism (AFLP) markers and applied them to three P. scouleri life stages at four sites to determine when during the life cycle sex ratio bias arises. Sex ratios were even among seedlings but became more female-biased at later life stages, indicating that sex ratios were driven by male-biased mortality. To identify when during the life cycle sex ratio bias developed, I examined sex differences in survival among seedlings and three aspects of reproductive costs that could potentially generate biased sex ratios under field conditions. No differences in seedling survival between the sexes were detected, and there was no evidence of substantial sex differences in costs of reproduction. I found no support for a trade-off between current and future reproduction or between reproductive investment and growth. Thus, costs of reproduction appear unlikely to drive sex ratio bias in surfgrass. Instead, small sex differences in growth and survival spread across the life cycle appear to be responsible for female-biased sex ratios and suggest that life history trade-offs other than reproductive costs drive sex ratio bias. Key words: cost of reproduction; dioecy; marine angiosperm; Olympic Peninsula, Washington, USA; Phyllospadix scouleri; Phyllospadix serrulatus; seagrass; seedling survivorship; sex-linked genetic marker; sex ratio.

Theory suggests that iteroparity may confer greater fitness than semelparity in situations in which temporal environmental variation is high and unpredictable. Variable age-specific mortality, density dependence, and other factors may also favor iteroparity over semelparity. Here, we empirically test the adaptive benefits of greater numbers of reproductive years in a study of reproductive schedules in an experimental population of a short-lived polycarpic perennial, Plantago lanceolata. A large experimental population was established that included four cohorts with similar genetic structure. Individuals were censused for mortality, size, and reproduction for seven years. Plants experienced variable numbers of reproductive years, but one or two years were most common (~46.7% of the population reproduced only once). The probability of flowering at least once prior to death was determined strongly by extrinsic, environmental or intrinsic but environmentally influenced variables, including early-life size, cohort, and block, but also varied with a number of interactions involving paternal lineage. Maternal effects explained small but significant components of the variance in the number of reproductive years among individuals in each cohort, while paternal effects were significant in only two cohorts. Number of reproductive years contributed significantly to fitness in this system, more so than all other variables tested, although most of the variation in relative fitness may be attributed ultimately to environmental influences. We suggest that the high proportion of each cohort composed of plants reproducing only once may be due to environmental constraints on either growth or size. Such environmental influences, particularly on early life size, may result in small but important indirect effects on fitness. Key words: inflorescence; iteroparity; Plantago lanceolata; reproductive schedule; reproductive timing; semelparity; Virginia, USA.

Development of theory has outpaced experimental tests for most maintenance of diversity mechanisms. Here we demonstrate how data from biodiversity--ecosystem functioning experiments can be used to determine the mechanisms that maintain plant species diversity. We hypothesized that grassland plant diversity is maintained by two classes of mechanisms: (1) equalizing mechanisms, which reduce asymmetric competition by reducing differences in monoculture biomass production among species in mixture, and (2) species interaction mechanisms, which increase overyielding by increasing niche partitioning and facilitation among species in mixture. Specifically, equalizing mechanisms reduce the coefficient of variation in monoculture biomass production among species in mixture. Species interaction mechanisms increase species overyielding in mixture, especially for low-biomass species. We tested these predictions with a seven-year data set from an experiment that varied grassland plant species evenness and richness. We used path analysis to model effects of these mechanisms on annual and multiyear changes in diversity. We found that diversity was frequently maintained by species interaction mechanisms and was infrequently maintained by equalizing mechanisms. Species interaction mechanisms maintained diversity by allowing the species that produced the least biomass in monoculture to benefit the most from species interactions in mixture. Equalizing mechanisms infrequently maintained diversity because asymmetric competition infrequently resulted in competitive exclusion. We propose that this mechanistic framework be used to better understand the specific processes that influence diversity. Key words: biodiversity; coexistence; complementarity; ecosystem function; net biodiversity effect; productivity.

A well-known, but largely untested, prediction in plant reproductive ecology is that dioecious taxa should produce larger, more, higher-quality, or better-defended seeds than cosexual taxa. Using a data set composed of 972 species in 104 families, representing the flora of the Tambopata Wildlife Reserve (Madre de Dios, Peru), we evaluated the first component of this prediction, examining ecological and evolutionary relationships between breeding system and mean seed size with two kinds of tests. First, we conducted cross-species analyses to determine whether species with different breeding systems differed significantly with respect to mean individual seed size. Second, we used a hypothesized phylogeny to identify pairs of the most closely related taxa or clades within the Tambopata community that differed with respect to breeding system. Comparing pair members allowed us to determine whether evolutionary divergence in breeding system (between taxa with unisexual vs. cosexual individuals) was consistently associated with evolutionary change in seed size. In both analyses, we controlled for potentially confounding effects of growth form by examining these relationships within woody and nonwoody taxa. Cross-species analyses revealed that dioecious species produced larger seeds than cosexual species among woody species, shrubs, lianas (each growth form analyzed separately), and all species pooled, but not among trees. Phylogenetically independent contrasts upheld the significant association between breeding system and seed size among woody taxa, lianas, and all taxa pooled, but not among shrubs. We discuss the implications of our findings for evolutionary hypotheses regarding associations between dioecy and seed size. Key words: angiosperms, breeding system, dioecy; monoecy; plant growth forms; rain forest; seed size.

Intraspecific variation in resistance to herbivory among genders and life-history phases of primary producers can significantly alter the ecological and evolutionary consequences of plant herbivore interactions. Seaweeds (macroalgae) with complex life histories have multiple distinct phases with associated variation in traits that can potentially lead to differences in resistance to consumers and provide a unique system in which to simultaneously test the effects of sex and life-history stage on herbivory. We tested the susceptibility to grazing of the three life-history stages and separate sexes of the chemically defended red alga Asparagopsis armata against the sea hare Aplysia parvula, and we related this to the plant quality traits of different stages and genders. Differences in nutrient content and halogenated secondary metabolites between life-history phases were highly sex dependent. Male gametophytes had a low concentration of secondary metabolites and the highest nutrient content. The highest secondary metabolite content was found within the female gametophyte, in the wall of the reproductive structures (cystocarps) that contain the microscopic carposporophyte phase. Feeding choices by A. parvula were consistent with differences in algal quality and defense and resulted in the haploid male gametophytes being the most preferred food type. The diploid carposporophyte found inside the chemically rich cystocarps was the least consumed life-history stage. Selective herbivory of male gametophytes by A. parvula is consistent with an observed shift in gametophyte sex ratio in the field from unity at the beginning of the reproductive season to female bias at the end. The variation in susceptibility to herbivory found between sex and life-history stages of A. armata represents the first example of sex-biased consumption in seaweeds and may contribute to the maintenance of complex life histories such as those found in red algae. Key words: algae; Aplysia parvula; Asparagopsis armata; chemical defense; dioecy; herbivory; heteromorphic life cycle; life history; plant-herbivore interaction.

Author(s): Wudan Yan [1] Nathan Lakey practically has to shout to be heard over the whirring machinery in the laboratory at Orion Biosains near Kuala Lumpur. One source of the [...]

Invasive species are a global threat to biodiversity and the functioning of natural ecosystems. Here, we report on a two-year experiment aimed at elucidating the combined and relative effects of three key controls on plant invasions: propagule supply, soil nitrogen (N) availability, and herbivory by native insects. We focus on the exotic species Lespedeza cuneata, a Rank 1 invasive species. Propagule supply and soil N-availability interacted to control the density and foliar cover of L. cuneata. In low N plots, density and foliar cover of L. cuneata were higher in the propagule addition plots than in the plots to which propagules were not added. Surprisingly, this interaction was significant only when the abundance of herbivores was experimentally reduced. This experiment provides evidence that native insect herbivores mediate the interactive effects of propagule supply and resources on invasion by a widespread invasive plant species. Key words: biological invasion; dispersal; herbivory; invasive species; Lespedeza cuneata; nutrients: plant-insect interactions.

The relationship between net primary productivity and biological diversity has been a central topic in ecology for several decades. The unimodal ('hump-back') relationship has been the most widely accepted for plants with the decrease in diversity at high productivity usually attributed to competitive exclusion. However, the relatively small species pool size under high productivity conditions may account for this pattern as well. Small species pool sizes for highly productive habitats are characteristic of temperate regions, where productive habitats for speciation and species migration have historically been rare. In contrast, productive habitats in the tropics have been relatively common during evolutionary history, resulting in large species pools. We hypothesize that evolutionary history contributes to the observed productivity--diversity relationship of plants, and that the productivity--diversity relationship differs between temperate and tropical regions. We investigated the productivity--diversity relationship patterns from 163 case studies throughout the world. Latitude described ~80% of the variation in the shape of the relationships. The unimodal relationship was found to dominate in the temperate zone, whereas the positive relationship was significantly more common in the tropics. We detected no influence due to methods of productivity measurement, but unimodal or positive productivity--diversity relationships were more likely within larger ranges of productivity. The length of the productivity gradient did not affect the latitudinal influence. In summary, the shape of the productivity--diversity relationship differs between temperate and tropical regions and the different evolutionary history of the local species pools is a probable cause for the difference. Key words: biodiversity conservation; generality of ecological rules; global diversity patterns; latitudinal gradient; macroecology; meta-study; plant biomass; plant species richness; primary productivity; productivity--diversity relationship; species pool; tropical ecology.

Central to the ecology and evolution of a broad range of plants is understanding why they routinely have submaximal reproduction manifested as low seed: ovule and fruit : flower ratios. We know much less about the processes responsible for low seed : ovule ratios than we do for fruit : flower ratios. Current hypotheses for low seed : ovule ratios are largely drawn from those for fruit : flower ratios, including proximate (ecological) causes of pollen limitation, resource limitation, and pollen quality, as well as the ultimate (evolutionary) hypothesis of 'bet hedging' on stochastic pollination. Yet, such mechanisms operating on fruit : flower ratios at the whole-plant level may not best explain low seed : ovule ratios at the individual-flower level. We tested each of these proximate and ultimate causes for low seed : ovule ratios using the specialized pollination mutualism between senita cacti (Pachycereus schottii) and senita moths (Upiga virescens). Seed : ovule ratios were consistently low (~0.61). Such excess ovule production by senita likely has a strong genetic component given the significant differences among plants in ovule number and the consistency in ovule production by plants within and among flowering seasons. Excess ovule production and low seed : ovule ratios could not be explained by pollen limitation, resource limitation, pollen quality, or bet hedging. Nevertheless, phenotypic selection analyses did show significant selection gradients for increased ovule number, suggesting that other evolutionary processes may be responsible for excess ovule production and low seed : ovule ratios. In contrast, low fruit : flower ratios at the whole-plant level were explained by an apparent equilibrium between pollen and resource limitation. Thus, mechanisms responsible for low fruit : flower ratios at the whole-plant level are not necessarily in accord with those of low seed : ovule ratios at the individual-flower level. This suggests that we may need to adopt a more pluralistic approach to seed : ovule ratios and consider alternative hypotheses, including a greater array of proximate and ultimate causes. Initial results of this study suggest that floral allometry, selection on correlated floral traits, stigma clogging with pollen grains, and style clogging with pollen tubes may provide promising avenues for understanding low seed : ovule ratios. Key words: bet hedging; Cactaceae; floral allometry; fruit : flower ratio; Pachycerus schottii; phenotypic selection; pollen limitation; pollen load; pollen quality; resource limitation; seed : ovule ratio; senita.

Pollination commonly limits seed production, as addition of pollen to stigmas often increases fecundity. This response is usually interpreted as evidence that plants' stigmas receive too few pollen grains to maximize ovule fertilization (quantity limitation); however, many genetic studies demonstrate that poor-quality pollen can also reduce seed production (quality limitation). We explore both aspects of pollen limitation theoretically with a dose-response model that incorporates a saturating negative-exponential relation of seed production to pollen receipt. This relation depends on aspects of ovule production, pollen import, pollen-pistil interactions and seed development, all of which can contribute to pollen limitation. Our model reveals that quantity limitation is restricted to the lowest range of pollen receipt, for which siring success per pollen grain is high, whereas quality limitation acts throughout the range of pollen receipt if plants do not import the highest-quality pollen. In addition to pollinator availability and efficiency, quantity limitation is governed by all post-pollination aspects of seed production. In contrast, quality limitation depends on the difference in survival of embryos sired by naturally delivered pollen vs. by pollen of maximal quality. We briefly illustrate the distinction between these two components of pollen limitation with results from the mistletoe Tristerix corymbosus. Our model also shows that the standard pollen-supplementation technique neither estimates the total intensity of pollen limitation nor distinguishes between its quantity and quality components. As an alternative, we propose a methodological protocol that requires both measurement of seed production following excess pollination with only outcross pollen and quantification of the dose-response relation of seed output to pollen receipt. This method estimates both the total extent of pollen limitation and its two components. Finally, we consider the influences on quantity and quality limitation, which reveals that quantity limitation probably occurs much less often than has been inferred from pollen-supplementation experiments. These interpretations suggest that an expanded perspective that recognizes the fecundity consequences of pollination with poor-quality pollen would promote ecological understanding of pollen limitation. Key words: plant reproduction; pollen limitation; pollen quality; pollination; seed production; supplemental pollination; Tristerix corymbosus.

Given the occurrence of mixed mating systems among plants, a general mechanism explaining the evolution and maintenance of this condition is needed. Although numerous theoretical models predict mixed mating to be evolutionarily stable, conditions favoring intermediate selfing are often stringent and have limited applicability. Here we investigated the role of vegetative herbivory, a ubiquitous biotic factor limiting plant reproduction, in the mating system expression of Impatiens capensis (Balsaminaceae), a species with an obligate mixed-mating system (individuals produce both selfing, cleistogamous, and facultatively outcrossing, chasmogamous flowers). Herbivory reduced proportional chasmogamous reproduction partially, but not entirely, through a reduction in plant size and the strength of this effect varied among replicates. Herbivory decreased geitonogamous selfing in chasmogamous flowers via several mechanisms including reduced chasmogamous flower display size and pollinator visitation rate and altered pollinator composition. Overall, herbivory caused a decrease in whole-plant outcrossing, indicating that the effects of herbivory on proportional chasmogamous reproduction, which favor selfing, outweigh the effects on chasmogamous outcrossing rate, which favor outcrossing. Not only do our findings unravel the mechanisms underlying herbivore-mediated changes in the mating system, but they also point to the role of natural enemies in contributing to the maintenance of a mixed mating system. Key words: Impatiens capensis; inbreeding; mating system; outcrossing; plant-pollinator interactions; vegetative herbivory.

Population context should influence pollination success and selection on floral display in animal-pollinated plants because attraction of pollinators depends not only on the characteristics of individual plants, but also on the attractiveness of co-occurring conspecifics. The insect-pollinated herb Primula farinosa is polymorphic for inflorescence height. Natural populations may include both long-scaped plants, which present their flowers well above the soil surface, and short-scaped plants, with their flowers positioned close to the ground. We experimentally tested whether seed production in short-scaped P. farinosa varied with local morph frequency and surrounding vegetation height. In tall vegetation, short-scaped plants in polymorphic populations produced more fruit and tended to produce more seeds than short-scaped plants did in monomorphic populations. In low vegetation, population composition did not significantly affect fruit and seed output of short-scaped plants. The results suggest that long-scaped plants facilitate short-scaped plants in terms of pollinator attraction and that the facilitation effect is contingent on the height of the surrounding vegetation. The documented facilitation should contribute to the maintenance of the scape length polymorphism in ungrazed areas where litter accumulates and vegetation grows tall. Key words: alternative reproductive strategies; facilitation; floral display; plant height; pollination; positive interactions; predation; Primula farinosa.

Pollination by animals is critical to sexual reproduction of most angiosperms. However, little is known about variation in pollination service to single plant species. We report results of a long-term study Ipomopsis aggregata, a semelparous montane herb whose flowers are visited by hummingbird and insect pollinators as well as 'floral larcenists.' We censused flower visitors over seven summers at permanent study sites separated by several hundred meters, and counted pollen delivered to flowers on a subset of plants observed for visitation. The species composition of the community of visitors varied significantly across years and within the flowering season; sites varied significantly only in the magnitude of parallel annual changes in the visitor community. Rates of flower visitation fluctuated over an order of magnitude or more. Variation in mean stigma pollen load among plants flowering in the same site and year was explained by a causal path model in which visitation rates by pollinators and larcenists had linear positive and negative effects, respectively. A simplified model including only pollinators explained almost as much variance as did the full model. However, qualitatively different parameter estimates were produced by an analogous causal model based on population means across site-year combinations. Discrepant results from within- and between-population levels of analysis suggest that pollen receipt is influenced by environmental factors that vary among sites and years, as well as by pollinator visit rates. We present a heuristic causal model that includes such factors, and we note its implications for ecological and evolutionary studies of pollination. Key words: field study; floral larcenists; floral visitation rates; flower-visitor community; hummingbirds; insects; Ipomopsis aggregata; long-term study; path analysis; plant population dynamics, pollen delivery; pollination services; structural equation modeling.

We analyzed seed production of mountain beech (Nothofagus solandri var. cliffortioides) forest along an elevational gradient in New Zealand from 1020 to 1370 m (treeline) for the years 1973-2002. We used seed production data from nine elevations and a site- and species-specific net carbon (C) availability model from two elevations (1050 m and 1340 m) to examine how three variables (temperature, soil moisture, and net C availability) during three key periods (resource priming, flowering primordia development, and flowering) influence seed production. These three strongly interrelated variables have all been considered determinants of seed production but have not previously been tested together in a single analysis. Seed production increased over the 30-year period, with the greatest increases at high elevations; this increase was driven by a greater frequency of intermediate-sized seeding years. We then determined how temperature, soil moisture, and net C availability determined seeding, and examined whether temporal trends in the seeding data could be linked to similar temporal trends in temperature, soil moisture, or net C availability. High seed production was related to cool summers with high soil moisture during resource priming, warm summers during flower primordia development, and low net C availability during flowering. Positive temporal trends in temperatures during the period of flower primordia development accounted for the increase in seed production, suggesting that increasing temperatures are promoting more frequent seed production at high elevations. Key words: carbon dioxide; evergreen; global change; masting; montane; mountain beech; New Zealand; reproduction; respiration; soil moisture; temperature; warming.

Current understanding of the extent, causes for, and consequences of variation in nutrient composition in plants is limited. Important questions to be addressed include to what extent nutrients covary, how flexible nutrient ratios are within a population or species, how reproduction influences nutrient ratios, and how much the ratios of nutrients to mass and nutrients to each other change through ontogeny. This information is needed to assess the physiological and ecological consequences of plant nutrient composition and to what extent plants function as balanced systems in acquisition and allocation of resources. We studied the variation in nutrient stoichiometry (i.e., the ratio between contents of different nutrients within a plant) in relation to three factors: (1) environmental availability of nitrogen, (2) plant size, and (3) reproductive status. We investigated these questions in 11 populations of the carnivorous plant Pinguicula vulgaris in northern Scandinavia. Dry mass and N and P content were measured for reproductive and vegetative portions of flowering individuals and for winter buds corresponding to four reproductive states: control reproductive individuals, experimentally vegetative individuals (from which flower buds were removed), adult vegetative individuals, and individuals below the threshold size for reproduction. [N], [P], and to a lesser extent, N and P content were positively related to soil N, but not to prey capture. Nutrient stoichiometry was also size dependent; in general, small plants were relatively enriched in N and relatively depleted in P compared to larger plants. Reproductive status affected not only size, but also nutrient stoichiometry of the resulting winter bud. Winter buds derived from reproductive individuals had a higher [N] and lower [P] than those of the different types of nonreproductive individuals. Our findings indicate that studies of nutrient stoichiometry in plants must go beyond links between environmental and plant nutrient concentrations to consider internal processes such as growth and reproduction. Key words: carnivorous plant; Pinguicula vulgaris; plant nutrient stoichiornetry; plant size; reproductive status; Scandinavia; size dependence; soil nutrient availability.

Sympatric plant species with similar flowering phenologies and floral morphologies may compete for pollination, and as a consequence potentially influence each other's reproductive success and mating system. Two likely competitors are Mimulus ringens and Lobelia siphilitica, which co-occur in wet meadows of central and eastern North America, produce blue zygomorphic flowers, and share several species of bumble bee pollinators. To test for effects of competition for pollination, we planted experimental arrays of Mimulus ringens, each consisting of genets with unique combinations of homozygous marker genotypes. In two arrays we planted mixtures of Mimulus and Lobelia, and in two additional arrays we planted Mimulus without a competitor for pollination. Bumble bee pollinators frequently moved between Mimulus and Lobelia flowers in the mixed-species arrays, with 42% of plant-to-plant movements being interspecific transitions. Pollinator movements between species were associated with a reduction in the amount of conspecific pollen arriving on Mimulus stigmas. The presence of Lobelia led to a significant 37% reduction in the mean number of Mimulus seeds per fruit. In addition, Mimulus had a significantly lower rate of outcrossing in the mixed-species arrays (0.43) than in the 'pure' arrays (0.63). This is the first study to demonstrate that competition for pollination directly influences outcrossing rates. Our work suggests that in self-compatible populations with genetic load, competition for pollination may not only reduce seed quantity, but may also lower seed quality. Key words: Bombus fervidus; competition for pollination; field experiment; improper pollen transfer; Lobelia siphilitica; mating system; Mimulus ringens; outcrossing rate; seeds per fruit; seed set; pollen loss; visitation rate.

Optimal Defense Theory predicts that plants exposed to herbivory should allocate more resources to produce costly secondary metabolites in tissues with higher fitness values. To increase plant resistance, the secondary metabolites must have a negative impact on the preference and/or performance of herbivores. We tested the hypotheses that induction of secondary metabolites (phlorotannins) in a brown seaweed in response to grazing by herbivorous gastropods will differ between seaweed tissues with different fitness values (basal stipes and annual shoots), and that the subsequent change in food value will affect the fitness (growth and fecundity) of the gastropods. Induction of phlorotannins was significant in both tissue types but was more pronounced in basal stipes, which have a higher fitness value. Basal tissues also had significantly higher constitutive defense levels than did apical tissues. No effects of algal tissue type or grazing history on the growth rate of the gastropods were detected. However, the number of viable eggs was significantly lower for gastropods feeding on basal shoots, and there was a significantly lower proportion of viable eggs produced by gastropods that were offered previously grazed seaweed tissues. The results show that induced resistance, and its variation among different plant parts, can have significant negative effects on herbivore performance that may reduce future herbivore pressure and thus enhance plant fitness. Key words: Ascophyllum nodosum; chemical defense; consumption; egg production; fecundity; fitness; growth; Littorina obtusata; phlorotannins; reproduction; resistance; within-plant variation.

1 Monocarpy in facultative biennials can be favoured by selection when there is a more than proportional increase in fitness with size. The possible contributions of larger reproductive output and higher offspring quality to such an increase were investigated in the facultative biennial plant Digitalis purpurea. Straw mass (rosette leaves and flowering stem excluding fruits and seeds) was determined for 100 individuals of varying size and correlated with the number of flowers and seeds per flower to examine whether sex-allocation is size dependent. 2 To determine whether maternal size influences offspring growth, and whether this effect is more pronounced in the presence of competition, seeds from 32 maternal plants were grown alone, and with one, two or four competitors. 3 Total seed number increased proportionally with size. Seed quality, measured as seed size, germination percentage and speed also increased with maternal size. The combined fitness measures of total seed mass (seed number x seed size), number of seedlings (seed number x germination percentage) and total female fitness (seed number x germination percentage x mean offspring dry mass after 14 weeks) all increased disproportionally with size. 4 Sex-allocation was size dependent, with large plants emphasizing the female function. 5 Offspring dry mass after both 8 and 14 weeks of growth was strongly influenced by competition, whereas the effect of maternal size was significant only at the first harvest date. Competition did not accentuate the effects of maternal size. 6 The results support that monocarpy exists in D. purpurea because of increased offspring quality rather than a disproportionate advantage in seed output of large individuals. Key-words: delayed reproduction, maternal size-effects, monocarpy, offspring quality, seed size variation

Variable seed production may have important consequences for recruitment but is poorly documented for frugivore-dispersed tropical trees. Recruitment limitation may also be a critical spatial process affecting forest dynamics, but it is rarely assessed at the scale of individual trees. Over an 11-yr period, we studied the consequences of variable seed production for initial seedling recruitment in three shade-tolerant tree species (Quararibea asterolepis, Tetragastris panamensis, and Trichilia tuberculata) on Barro Colorado Island, Panama. We measured annual seed production for a permanent sample of focal trees and censused annual new seedling establishment within a restricted dispersal neighborhood of each tree. We analyzed temporal and spatial variability in recruitment and compared recruitment limitations among species. Annual seed production in Quararibea and Tetragastris fluctuated widely, whereas Trichilia had more consistent seed production across years. Within species, trees were synchronized in seed production, and synchrony appeared partly influenced by El Nino climatic events. Seedling recruitment varied temporally and spatially. At the population scale, all species had greater recruitment in productive seed years, and individual trees had differing contributions to this temporal pattern. At the focal-tree scale, recruitment patterns differed among species. Quararibea and Tetragastris trees with higher average seed production recruited more seedlings in their local neighborhoods than did less fecund trees. In contrast, Trichilia seedling recruitment did not increase with seed crop size, suggesting negative density dependence. At the tree neighborhood scale, no species showed evidence of density dependence in first-year survival. Comparatively, recruitment was more seed-limited in Quararibea and Tetragastris and more establishment-limited in Trichilia. Overall, our results indicated that: (1) variable seed production influenced seedling recruitment both temporally and spatially, and (2) species differed in limitations to recruitment. Key words: Barro Colorado Island, Panama; density dependence; Quararibea asterolepis; recruitment limitation; seed production; seedling demography; Tetragastris panamensis; Trichilia tuberculata; tropical tree demography.

Propagule dispersal in seaweeds is a process influenced by a variety of biological and physical factors, the complexity of which has hindered efforts to understand colonization, persistence, post-disturbance recovery, and dynamics of algal populations in general. In view of this limitation, we employ here modifications to an existing turbulent-transport model to explore the mechanics of nearshore macroalgal spore dispersal and its relationship to coastal hydrodynamic conditions. Our modeling efforts focus on four example species of seaweed whose reproductive propagules span a wide range in sinking speed and height of release above the sea floor: the giant kelp Macrocystis pyrifera, the erect fucoid Sargassum muticum, the small filamentous brown alga Ectocarpus siliculosus, and the flaccid red alga Sarcodiotheca gaudichaudii. Results indicate that both propagule sinking speed and release height can affect dispersal distance substantially, but that the influence of these biological parameters is modulated strongly by the intensity of turbulence as dictated by waves and currents. In rapid flows with larger waves, it is primarily fluid dynamic processes, in particular current velocities, that determine dispersal distance. Additional simulations suggest that patterns of spore dispersal are highly skewed, with most propagules encountering the sea floor within a few meters to hundreds of meters of their parents, but with a sizeable fraction of spores also dispersing as far as kilometers. Such model predictions imply a much greater potential for longer range dispersal than has typically been assumed, a finding with important implications for understanding the demographics of algal populations and for predicting levels of connectivity among them. Key words: Ectocarpus siliculosus; eddy diffusivity; flow; macroalgae; Macrocystis pyrifera; propagule; release height; Sarcodiotheca gaudichaudii; Sargassum muticum; sinking speed; turbulence; vertical mixing.

Masting, the intermittent production of large flower or seed crops by a population of perennial plants, can enhance the reproductive success of participating plants and drive fluctuations in seed-consumer populations and other ecosystem components over large geographic areas. The spatial and taxonomic extent over which masting is synchronized can determine its success in enhancing individual plant fitness as well as its ecosystem-level effects, and it can indicate the types of proximal cues that enable reproductive synchrony. Here, we demonstrate high intra- and intergeneric synchrony in mast seeding by 17 species of New Zealand plants from four family across >150 000 [km.sup.2]. The synchronous species vary ecologically (pollination and dispersal modes) and are geographically widely separated, so intergeneric synchrony seems unlikely to be adaptive per se. Synchronous fruiting by these species was associated with anomalously high temperatures the summer before seedfall, a cue linked with the La Nina phase of El Nino--Southern Oscillation. The lone asynchronous species appears to respond to summer temperatures, but with a 2-yr rather than 1-yr time lag. The importance of temperature anomalies as cues for synchronized masting suggests that the timing and intensity of masting may be sensitive to global climate change, with widespread effects on taxonomically disparate plant and animal communities. Key words: abiotic factors; Chionochloa; cross-correlation; Dacrydium; El Nino--Southern Oscillation; Elaeocarpus; masting; New Zealand; Nothofagus; Phormium; synchrony; temperature.

Plant reproductive strategies may evolve from fitness trade-offs between seed dispersal and seedling establishment. Small crops of large seeds generally are not dispersed as far as large crops of small seeds, but large seeds contain more reserves for seedling establishment. However, selection pressures imposed on these traits may vary among environments. This study examined the extent and consequences of environmental variation in the seed dispersal strategy of a fleshy-fruited plant, the common chokecherry (Prunus virginiana). From 1996 to 1998, P. virginiana fruit crop and seed traits were measured for plants sampled in moist riparian or dry slope habitats in western Montana. The consequences of variation in P. virginiana location, seed size, and seed number for seed dispersal were estimated from 1996 to 1999 by collecting seeds in seed traps. In all years, P. virginiana produced larger crops of smaller seeds in riparian than in slope habitats. Reproductive biomass was lower for plants on moisture-limited slopes than for similarly sized plants in riparian habitats. However, P. virginiana on slopes increased seed size rather than seed number in a year with relatively high levels of precipitation, suggesting that large offspring size may play a more important role than seed number in this environment. Environmental variation in P. virginiana reproductive traits may contribute to differences in seed dispersal patterns. Frugivores removed greater numbers of seeds from plants with large fruit crops and preferentially consumed relatively small seeds within sites (particularly in slope habitats). In riparian habitats, seed deposition by frugivores was greater away from rather than under P. virginiana canopies. In contrast, seed deposition on slopes was greatest under canopies. Thus, the production of many small seeds may be an adaptive response to increase seed dispersal in the riparian environment, where dispersal may be more important than seed size for successful offspring recruitment. Key words: common chokecherry; environmental variation; fruit removal; plant reproductive strategies; Prunus virginiana; seed dispersal; seed size vs. number.

1 For 3 years, I examined the effects of fragmentation on pollination of an endemic, euglossine bee-pollinated, epiphytic orchid, Catasetum viridiflavum, on 10 islands created during the construction of the Panama Canal and at five sites in nearby large tracts of mainland forest. 2 I investigated the viability of pollinia over time, availability of pollinators and male and female reproductive success (measured as removal of pollinaria and fruit set, respectively) at different sites. 3 Viability of pollinia declined dramatically over time, although some remained at least partially viable for up to 60 days. Bees moved between trapping stations at different sites within a day, and viable pollen therefore could have been transferred between populations. 4 Although euglossine bees were equally frequent in fragments and continuous forest, those recorded on islands were visitors from mainland sites, and not island residents. 5 Neither male nor female reproductive success were significantly different between island and mainland forest types in 1997. The higher reproductive success in certain sites within both forest types throughout the flowering season could not be explained by variation in overall population floral display. Larger inflorescences had higher male and female reproductive success. 6 In 2 of 3 years, plants on islands had significantly lower fruit set than plants on mainland sites. Female reproductive success differed dramatically across years and sites. 7 The low fruit set in 1996 and 1998 on islands in comparison with mainlands, and the observation that bees are not island residents, conform with expectations of physical isolation of forest patches. In spite of the evidence of fragmentation in this system, patterns of pollinator behaviour and of reproductive success suggest significant connectedness among sites. This 3-year study shows that a single year study may not have highlighted the complexity of the system. Key-words: Barro Colorado Island, epiphytic orchid, euglossine bee, forest fragmentation, plant reproduction

Competition for pollination has been hypothesized to select for the divergence of floral traits between species and populations. A primary prediction of this hypothesis is that the strength of competition for pollination, mediated by variation in plant abundance, should directly influence the strength of selection on floral traits. To test this prediction, I examined the relationships between multiple components of plant abundance and pollination, reproductive success, and phenotypic selection via female fitness on four floral traits in artificial and natural populations of the hummingbird-pollinated Ipomopsis aggregata. In the artificial arrays, I manipulated the absolute density and interspersion of neighboring I. aggregata and a competitor for pollination (Castilleja linariaefolia). I also measured natural variation in the absolute and relative density of these two species within a 2.5-m radius of focal I. aggregata plants in three natural populations. The strength of competition for pollination in the I. aggregata--C. linariaefolia system was only weakly influenced by local plant abundance. Both the absolute density and interspersion of plants in the arrays significantly influenced at least one component of I. aggregata's pollination and reproductive success, but the effects were not consistent across these components. For example, the treatment groups that received more conspecific pollen were not the same ones that set more seeds/fruit. Within the natural populations, variation in relative and absolute plant density influenced two components of I. aggregata's pollination and reproductive success, but only in one to two populations per component. As would be expected from these inconsistent effects of plant abundance on pollination and reproduction, the strength of selection on floral traits of I. aggregata in both the arrays and natural populations was also only weakly dependent on abundance. Previous studies have indicated (1) that self-incompatible species such as I. aggregata should experience strong, abundance-dependent effects on pollination, and (2) that variation in plant abundance at a local scale should have a stronger effect on pollination than variation at a larger spatial scale. In contrast, my results suggest that the effect of plant abundance on pollination cannot be easily predicted from simple diagnostic traits such as breeding system or spatial scale. Key words: Castilleja linariaefolia; competition; density; floral traits; Ipomopsis aggregata; natural selection; phenotypic selection; pollination.

The effects of dichogamy on plant pollination and reproduction are examined, specifically the form of protandry, in which the emergence of the stigma follows pollen presentation.

Research indicates that germination and emergence are more important in plant succession than seedling survival. Seed mass was inversely related to litter effects. Data were obtained from observations of a four-year-old annual plant community in the Mediterranean region.

1 A long-term experiment was established in 1990 in which seeds of 54 native species, not originally present at the site, were sown into a fertility x disturbance matrix established in unproductive limestone grassland at the Buxton Climate Change Impacts Laboratory (BCCIL). The objective was to examine the roles of productivity and disturbance as major factors controlling the invasibility of plant communities, and to identify the functional characteristics of successful invaders in response to different types of invasion opportunity. The results of the first 2 years of the study have already been published. 2 After 2 years, invasion was strongly promoted by disturbance and less so by increased fertility. Three years later the cover of invaders had declined over most of the matrix, and the greatest cover of sown species was where the highest levels of fertility and disturbance coincided. However, no part of the fertility--disturbance matrix was immune to invasion and the area of the matrix occupied by each of the sown species that successfully established was unique. Abundance of invaders was reduced by low soil pH. 3 The identity and distribution of the successful invaders changed as the early stages of invasion gave way to a later stage of consolidation. After 2 years regenerative traits (seed mass and germination characteristics) were the best predictors of success. After 5 years these traits were unrelated to success of the invaders, the most successful invaders were perennial grasses, and no single trait was a good predictor of invasiveness. 4 Our results are consistent with the hypothesis that invasions are promoted by an increase in the availability of resources, either through addition of extra resources or a reduction in their use by the resident vegetation. Key-words: BCCIL, disturbance, fertility, functional types, herbivory, invasibility, limestone grassland, plant traits, seed size

The resource allocation method is used to create a predictive model of reproduction rates in plants, both vegetative and sexual, within the framework of their respective evolutionary costs. Trade-offs between ramet and seed production within given environments are examined.

Research shows that sexual Taraxacum officinale dandelions have no advantage over nonsexual, or apomictic, dandelions in competitive environments. Competition was found to reduce growth to an equal extent in both sexual and apomictic plants.

Research on Ranunculus reptans, a clonal herb, shows that allocation to vegetative reproduction shifts to sexual reproduction with increasing density. Thus, intraspecific competition plays a key role in R. reptans evolutionary processes, as it affects selection and genetic drift within the population.

Research shows that shoot reproductive status for Rhododendron lapponicum is dependent on shoot size, or shoot leaf area; shoot age; and concentrations of phosphorus and nitrogen. No variation in mean age for reproductive onset was found for differences in altitude.

Research shows a link between population size and inbreeding coefficients in the rare perennial plant Arnica montana. Positive correlations were also found between population size and effective alleles, polymorphic loci proportions and expected heterozygosity.

The effects of nectar robbers on plants and their mutualistic pollinators are poorly understood due, in part, to the paucity of studies examining male reproductive success in nectar-robbed plants. Here we measured the effects of a nectar-robbing bumblebee, Bombus occidentalis, on realized male reproductive success (seeds sired) in a hummingbird-pollinated plant, Ipomopsis aggregata. To determine the effects of nectar robbing on paternity, we used a series of experimental populations of plants containing a known allozyme marker. In each population, we experimentally controlled the levels of nectar robbing on each I. aggregata plant by cutting a hole in the corolla with dissecting scissors and removing nectar with a micro-capillary tube. We measured hummingbird-pollinator foraging behavior and fruit and seed production (maternal function) for each plant. We then genotyped seeds for the allozyme marker to determine the number of seeds sired by plants with known levels of robbing. Heavy nectar robbing (> 80% of flowers robbed) significantly reduced the number of seeds sired, as well as the number of seeds produced due to pollinator avoidance of heavily robbed plants. Total plant reproduction, both male and female contributions, were reduced by 50% due to high levels of robbing. To date, no other studies have measured the effects of nectar robbing on realized male function (number of seeds sired). Ours is the first study to demonstrate that robbing can simultaneously decrease realized male reproductive success as well as female reproductive success, and that the effects are incurred indirectly through pollinator avoidance of robbed plants. Key words: Bombus occidentalis; hummingbird-pollinator behavior; Ipomopsis aggregata; male function; nectar robbing, effect on plant reproductive success; Rocky Mountain Biological Laboratory (Colorado, USA); siring success.

Genetic variation in photosynthetic traits within populations provides the potential for evolution, but few studies relate phenotypic variation in these traits to variation in fitness. We tested the prediction that a lower photosynthetic rate reduces fecundity and survivorship by comparing wild-type (WT) Amaranthus hybridus family lines to those having a single-gene mutation that confers resistance to atrazine (R) and lowers the rate of photosynthetic carbon assimilation. Wild-type and R family lines with nearly uniform nuclear genomes were used to minimize the confounding effects of other loci. We established experimental populations in agricultural and one-year-old field plots and measured chlorophyll fluorescence, gas exchange, and the fecundity and survivorship of WT and R genotypes for two generations. The R genotype had a lower efficiency of electron transport through photosystem II, which translated into a 20-30% decrease in photosynthetic rate at light levels above 400 (mu)mol*m(super -2)*s(super -1). Compared to the WT, the R genotype also had lower water-use efficiency, higher specific leaf area, and greater leaf nitrogen concentration on a mass, but not area, basis. In five of six replicate populations, the R genotype had lower fecundity than the WT in the first generation. Survivorship of seed over winter was similar for the two genotypes, but survivorship of R seedlings during early establishment was lower than the WT in the agricultural field. The consistent pattern of selection against the R genotype during vegetative growth stages suggests that a lower photosynthetic rate reduces fitness. This selection, paired with heritable variation for photosynthetic traits within populations, provides a more complete scenario for the evolution of photosynthetic traits. Key words: Amaranthus hybridus; atrazine resistance; genotype frequency; selection for photosynthesis; water-use efficiency.

1 Theoretical models indicate that coexistence of diploid and polyploid individuals in sympatric populations is unlikely when mating is random among cytotypes and hybrids are inviable. However, coexistence may be facilitated by prezygotic isolating mechanisms that reduce intercytotype mating and increase assortative mating. 2 We examined the ecological factors regulating intercytotype mating in Chamerion (formerly Epilobium) angustifolium by measuring floral morphology, flowering synchrony and insect foraging preferences in a mixed population within a diploid-tetraploid contact zone. We also calculated the minimum rate of betweencytotype mating from estimates of the frequency of triploid offspring. 3 Diploids had significantly shorter and narrower petals as well as shorter styles than tetraploids. Inflorescences were significantly taller in tetraploids than diploids, but the mean number of open flowers per inflorescence did not differ. Diploid and tetraploid flowering periods overlapped by 51%, with diploid stems flowering earlier. 4 In a plot of 20 diploid and 28 tetraploid stems that were flowering simultaneously, only 26% of all bee flights were between flowers on different stems. Of the total flights between inflorescences, only 15% were between different cytotypes. The combined effects of flowering asynchrony and insect foraging reduced the opportunities for intercytotype mating from 49% expected if mating is random to about 2% of the total number of pollinator flights. 5 A computer simulation indicated that the deficiency of pollinator flights between cytotypes was due largely to the spatial structure of cytotypes and limited pollinator flight distances within the observation plot. The frequency of triploid offspring produced during the period when both cytotypes were in flower was 6.6%, similar to the proportion of flights observed between flowers on different cytotypes (4%). 6 The results indicate that flowering phenology and insect behaviour (as influenced by clonal structure) have a significant effect on prezygotic mating isolation and triploid production, and may contribute to the maintenance of mixed cytotype populations in Chamerion angustifolium. Keywords: fireweed, phenology, pollinator behaviour, polyploidy, reproductive isolation, triploids

1 We monitored flowering and fruiting of individual male and female plants of Oemleria cerasiformis over a 6-year period in a population in western Canada, and calculated fruit set (percentage of pistils maturing) and reproductive effort (RE) (gram of reproductive tissue per gram of leaf). 2 Over 6 years, male O. cerasiformis had on average much lower total RE, but much higher RE at flowering, than females. 3 In males, strong correlations between RE and light suggested that investment in reproduction was largely determined by light levels. There were strong positive correlations of RE between years, with no evidence of periodic fluctuations. 4 In females, in contrast to males, RE at flowering was not related to light. However, fruit set was strongly correlated with light. Flowering RE and fruit set were uncorrelated in females, indicating that these are affected by different factors. 5 Correlations of RE between years in females, although often significant, were lower than in males, indicating that RE fluctuates more between years in females than in males and may respond to past levels of RE. Flowering may reflect adjustments in response to past reproduction, or may be controlled by resources other than light. Fruit set was not significantly related to previous RE. 6 The greater total RE of females and their limited ability to adjust fruit set are probably major factors contributing to the greater mortality rates of females and the male-biased sex ratios in O. cerasiformis. Keywords: control of flowering, dioecious plants, fruit set, resource allocation

To determine how character mapping using phylogenetic trees has been used for analysis of plant breeding system evolution and plant-pollinator interaction, a study has been carried out. An additional focus was determining how the macroevolutionary approaches extended understanding of plant reproductive biology farther than insights from studies of microevolutionary processes.

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 [...]

1 The advantages of guerrilla and phalanx growth for the guerrilla Elymus lanceolatus ssp. lanceolatus and phalanx E. l. ssp. wawawaiensis were evaluated over 2 years in two taxon mixtures with a range of densities of each subspecies and under two levels of watering. 2 Ramet numbers and biomass of the guerrilla subspecies were higher than those of the phalanx grass in the first year but in the second year declined greatly, while the phalanx grass showed no change in biomass and an increase in ramet numbers. High neighbour densities affected the phalanx subspecies more strongly than the guerrilla subspecies in the first year, but in the second year there were few differences between subspecies. Biomass of the guerrilla grass remained greater than that of the phalanx grass but ramet numbers were similar in the second year. 3 For both subspecies in both years, probability of flowering decreased at higher neighbour densities, indicating adaptation for competitive ability. In the first year, biomass was more strongly reduced by densities than flowering was, but in the second year, when crowding was apparently greater, flowering was more severely affected. 4 Genet survival was high and similar for both subspecies. 5 The presumed advantage of guerrilla subspecies in exploiting open space was supported. The guerrilla grass exploited resources more quickly in the first year by faster growth and greater ramet production, but its biomass, ramet numbers and rhizome growth, and thus its advantage, were reduced in the second year. 6 The phalanx subspecies had slower growth, produced more ramets in later years, and delayed flowering until later years. Although less able to exploit open resources, it appeared adapted to more stressful conditions, and may be able to exploit temporal resource pulses more effectively. Keywords: clonal growth, competition, Elymus lanceolatus, resource patches, sexual reproduction, vegetative reproduction

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 [...]

1 Phenology and reproduction were studied in three populations of the cleistogamous herb Oxalis acetosella during three growing seasons, in order to see how the balance between chasmogamous (CH) and cleistogamous (CL) reproduction varies with temporal and spatial environmental variation and with plant size. The numbers of CH and CL flower buds, flowers, immature capsules and mature capsules were counted per ramet, ramet sizes were estimated, and mature capsules were collected for seed counts. 2 Both CH and CL flower numbers were positively correlated with ramet size expressed as leaf number, but the correlation was much stronger in the CL phase. CL flower production also varied significantly between years and sites. Thus, CL production in O. acetosella was not independent of resources and climatic variation. 3 When the effects of year and site were taken into account, the probability of an individual flower developing into a mature fruit was not higher in the CL phase than in the CH phase. 4 CL production was affected by fertilization success in the CH phase. Ramets with one or more CH flowers left unfertilized generally produced more CL buds than ramets with all their CH flowers fertilized. The former group also tended to have more seeds per CL capsule. 5 Since reproductive success in the two phases varies in different temporal and spatial patterns, cleistogamy in O. acetosella is considered to be a bet-hedging strategy optimizing reproductive output in fluctuating environments. 6 The findings of this study are in conflict with the general view on cleistogamy as a fail-safe mechanism for back-up seed production, unaffected by variations in resource supply and environmental conditions. Keywords: chasmogamous, reproductive rate, resources, spatial variation, temporal variation

1 The effect of supplementary feeding on growth and reproduction of three carnivorous plants species was investigated over a 6-year period. Pinguicula alpina, P. villosa and P. vulgaris populations growing at two altitudes in a subarctic environment were fed with fruit flies (Drosophila melanogaster). 2 Fed plants increased in size relative to control plants during the first years. Subsequently a stable size difference between feeding levels was established. The weight of the over-wintering part was higher in fed plants than in control plants. 3 The flowering frequency (i.e. proportion of plants in a population carrying flowers) was also higher in the fed plants. The proportion of flowering plants increased in the feeding treatment compared to control plants during more-or-less the whole experimental feeding period (5-6 years). Seed production also increased slowly in response to feeding. 4 No feeding effect on nitrogen and phosphorus concentrations in seeds and overwintering parts was found. 5 In most characteristics the high-altitude populations were less responsive than populations growing at low altitude. In the high-altitude population reproduction failed repeatedly, suggesting that seed output may be more dependent on abiotic factors than on resource availability in cold environments. 6 Pinguicula villosa and P. vulgaris used the new resources the same summer for increased leaf rosette growth and current reproduction, showing these species to be income breeders, while the third species (P. alpina) allocated a larger proportion to storage and future reproduction, characteristic of a capital breeder. Keywords: capital breeder, carnivorous plant, income breeder, nutrients, Pinguicula, resource allocation

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 [...]

1 We studied the relationships between population size, reproduction and population growth rate in 23 populations of the rare, short-lived plant Gentianella germanica. We also investigated a possible correlation of population size effects with environmental variation in climate, topography, soil, vegetation, and management. To ascertain whether the differences between populations have a genetic basis, we grew 20 seed families from each of the populations in a common garden experiment. 2 In 1993, population sizes ranged from 40 to 5000 flowering plants in the field populations (geometric mean 386). Plants in small populations had fewer seeds per fruit and fewer seeds per plant than plants in larger populations, whereas seed mass was independent of population size. From 1993 to 1995 population size decreased in most populations (mean annual population growth rate 0.876), and this decrease was larger in small populations than in large populations. 3 In the common garden the positive correlation between the number of surviving plants per planted seed and original population size increased steadily over time. After 17 months there were significantly more flowering plants and more flowers per planted seed for seeds from large populations than for those from small populations. 4 Although environmental variables accounted for significant variation in population growth rate and plant performance both in the field and in the common garden, effects of population size detected in stepwise multiple regressions were not confounded with environmental effects. 5 We conclude that the reduced performance observed in plants from smaller populations was explained by genetic effects rather than by habitat quality, although pollinator limitation may have contributed to fitness reductions in the field. The Observed patterns suggest further reductions of population sizes in Gentianella germanica in the future, especially in already small populations. Our study lends support to the view that genetic problems are a major concern in plant conservation. Keywords: common garden study, population size, demography, rare species, reproduction