Abstract: Bateman’s principle states that male fitness is usually limited by the number of matings achieved, while female fitness is usually limited by the resources available for reproduction. When applied to flowering plants this principle leads to the expectation that pollen limitation of fruit and seed set will be uncommon. However, if male searching for mates (including pollen dissemination via external agents) is not sufficiently successful, then the reproductive success of both sexes (or both sex functions in hermaphroditic plants) will be limited by number of matings rather than by resources, and Bateman’s principle cannot be expected to apply. Limitation of female success due to inadequate pollen receipt appears to be a common phenomenon in plants. Using published data on 258 species in which fecundity was reported for natural pollination and hand pollination with outcross pollen, I found significant pollen limitation at some times or in some sites in 159 of the 258 species (62%). When experiments were performed multiple times within a growing season, or in multiple sites or years, the statistical significance of pollen limitation commonly varied among times, sites or years, indicating that the pollination environment is not constant. There is some indication that, across species, supplemental pollen leads to increased fruit set more often than increased seed set within fruits, pointing to the importance of gamete packaging strategies in plant reproduction. Species that are highly self-incompatible obtain a greater benefit relative to natural pollination from artificial application of excess outcross pollen than do self-compatible species. This suggests that inadequate pollen receipt is a primary cause of low fecundity rates in perennial plants, which are often self-incompatible. Because flowering plants often allocate considerable resources to pollinator attraction, both export and receipt of pollen could be limited primarily by resource investment in floral advertisement and rewards. But whatever investment is made is attraction, pollinator behavioral stochasticity usually produces wide variation among flowers in reproductive success through both male and female functions. In such circumstances the optimal deployment of resources among megaspores, microspores, and pollinator attraction may often require more flowers or more ovules per flower than will usually be fertilized, in order to benefit from chance fluctuations that bring in large number of pollen grains. Maximizing seed set for the entire plant in a stochastic pollination environment might thus entail a packaging strategy for flower number or ovule number per flower that makes pollen limitation of fruit or seed set likely. Pollen availability may limit female success in individual flowers, entire plants (in a season or over a lifetime), or populations. The appropriate level must be distinguished depending on the nature of the question being addressed.

Abstract: Interpopulation gene flow in plants is mediated by a combination of pollen and seed dispersal. The effectiveness of pollen and seeds in bringing about gene flow depends upon the mode of inheritance of the genetic marker. For nuclear and paternally inherited markers, gene flow occurs in both pollen and seed. For maternally inherited markers, genes are only dispersed in seeds. As a result, levels of population differentiation under drift-migration equilibrium are expected to differ for markers with contrasting modes of inheritance, and the extent of such differences should be related to the relative levels of pollen and seed migration among populations. A model is developed that relates expected values of population differentiation (Fst) for nuclear, paternally and maternally inherited markers, to pollen and seed migration rates. The model is used to estimate the relative rates of seed and pollen flow in six species of plants where Fst values are available for both nuclear and maternally inherited markers. Estimates of (pollen flow/seed flow) range from four in wild barley to 200 in oaks, and this pattern of variation is consistent with the reproductive characteristics of the species concerned.

Abstract: Flowering plants have evolved various stratagems to prevent inbreeding and promote outcrosses. One such mechanism, gametophytic self-incompatibility, provides a genetic barrier to self-fertilization, and in the simplest cases is controlled by the highly polymorphic S locus. Growth of a pollen tube in the style is arrested when the S allele carried by the pollen matches one of the two S alleles carried by the pistil. Putative S allele proteins of the pistil have been identified in several solanaceous species based on their co-segregation with S alleles, and they have been shown to be ribonucleases. So far, there has been only correlative or indirect evidence for the claim that these S allele-associated proteins (S proteins) are involved in recognition and rejection of self pollen. Here we show that inhibition of synthesis of S3 and S2 proteins in Petunia inflata plants of S2S3 genotype by the antisense S3 gene resulted in failure of the transgenic plants to reject S3 and S2 pollen. We further show that expression of the transgene encoding S3 protein in P. inflata plants of S1S2 genotype confers on the transgenic plants the ability to reject S3 pollen. The self-incompatibility behaviour of the pollen was not affected by the transgene in either set of experiments. Taken together, these findings provide direct in vivo evidence that S proteins control the self-incompatibility behaviour of the pistil.

Abstract: Many angiosperms employ self-incompatibility systems to prevent inbreeding. The simple genetics of such systems have made them attractive models of plant cellular communication. Implicit in the single locus genetics is that only one or a few gene products are necessary for recognition and rejection of incompatible pollen. Results in the sporophytic system of the Brassicaceae suggest that different S-locus products are responsible for the pollen and pistil parts of the recognition and rejection response. In solanaeceous plants, which have a gametophytic self-incompatibility system, the S locus product responsible for the pollen portion of the interaction has not been identified, but ribonucleases encoded by the S-locus (S-RNases) are strongly implicated in the style part of the recognition and rejection reaction. In Nicotiana alata, pollen recognition and rejection occur if its S-allele matches either S-allele in the style. The putative stylar S-RNase is abundant in the transmitting tract, and pollen rejection may be related to action of S-RNase on pollen RNAs. Efforts to understand the molecular basis for pollen recognition and rejection have been limited by the lack of a system for manipulating and expressing S-RNases. Here we use the promoter of a style-expressed gene from tomato to obtain high levels of S-RNase expression in transgenic Nicotiana. Recognition and rejection of N. alata pollen S-alleles occur faithfully in the transgenic plants. Our results show that S-RNases alone are sufficient for pollen rejection in this system.

Abstract: Two Arabidopsis thaliana genes, QRT1 and QRT2, are required for pollen separation during normal development. In qrt mutants, the outer walls of the four meiotic products of the pollen mother cell are fused, and pollen grains are released in tetrads. Pollen is viable and fertile, and the cytoplasmic pollen contents are discrete. Pollination with a single tetrad usually yields four seeds, and genetic analysis confirmed that marker loci segregate in a 2:2 ratio within these tetrads. These mutations allow tetrad analysis to be performed in Arabidopsis and define steps in pollen cell wall development.

Abstract: The LAT52 gene of tomato is expressed in a pollen-specific manner. It is shown that LAT52 encodes a heat-stable, glycosylated protein that traverses the secretory pathway when expressed in a baculovirus expression system. The LAT52 protein shows some similarity with Kunitz trypsin inhibitors and with pollen proteins from maize, rice and olive, but the biological function of these pollen proteins is unknown. To test whether the LAT52 protein plays an important role during pollen development, tomato plants were transformed with an antisense LAT52 gene driven by the LAT52 promoter. Because the LAT52 gene is expressed gametophytically, only 50% of the pollen of the primary transformants would be expected to express the antisense construct. Selfprogeny of 19 of the primary transformants showed the predicted 3:1 segregation for a single locus insertion of the linked kanamycin-resistance gene. However, the self-progeny of the other 32 primary transformants showed a 1:1 segregation pattern and could not transmit the linked kanamycin-resistance gene through the male. A subset of these 1:1 segregation class plants was examined in detail. The pollen showed lower levels of LAT52 mRNA and LAT52 protein when compared with wild-type. In vitro, approximately 50% of the pollen grains appear to hydrate abnormally; this anomaly is not present when the same pollen grains are incubated in a medium with higher water potential. In vivo pollination experiments showed that the growth of around 50% of the pollen tubes is arrested in the style. The 3:1 segregation class plants showed no significant differences from untransformed control plants. Taken together, the results show a direct correlation between the reduced expression of LAT52 protein and abnormal pollen function, and suggest that the LAT52 protein plays a role in pollen hydration and/or pollen germination.

Abstract: . 1The behaviour and activity patterns of Apis mellifera and of five species of Bombus were analysed in relation to climatic variables and nectar quality on three varieties of unsprayed cultivated raspberry (Rubus idaeus) in eastern Scotland. 2Stages of floral morphology and reward were similar for the three varieties: young flowers offered both nectar and pollen, but medium and old flowers offered nectar only, in diminishing quantities. 3A wide range of insects visited raspberry flowers, but bees were dominant, bumblebees being responsible for about 60% of all visits and honeybees making up most of the remaining percentage. All bees had substantial pollen deposited on their bodies during visits, though few specifically collected it. 4Bombus spp. were found to favour young (receptive) flowers strongly, especially early in the morning when pollen was most abundant: whilst Apis visited unselectively. Bumblebees also foraged over substantially longer periods of the day, and in poorer weather, some being present at most times of observation; and they foraged more quickly in terms of flower visits per minute. 5Bombus carried more pollen on their bodies than Apis, and also deposited more pollen on raspberry stigmas, with B.lapidarius and B.terrestris being particularly effective and also being the most abundant species. All bumblebees also foraged over a longer range, moving between canes and rows more frequently than did honeybees. 6Bumblebees are therefore likely to be substantially more important as pollinators of raspberries than are honeybees, especially as raspberries though moderately self-fertile may exhibit metaxenia. Reasons why Bombus may be the preferred pollinator in most sites of raspberry cultivation are discussed, together with implications for present and future growers.

Abstract: From a pollen tube cDNA library of Petunia inflata, we isolated clones encoding a protein with structural features and biochemical properties characteristic of receptor-like kinases. It was designated PRK1 for pollen receptor-like kinase 1. The cytoplasmic domain of PRK1 is highly similar to the kinase domains of other plant receptor-like kinases and contains nearly all of the conserved amino acids for serine/threonine kinases. The extracellular domain of PRK1 contains leucine-rich repeats as found in some other plant receptor-like kinases, but overall its sequence in this region does not share significant similarity. Characterization of a gene encoding PRK1 revealed the presence of two introns. During pollen development, PRK1 mRNA was first detected in anthers containing mostly binucleate microspores; it reached the highest level of mature pollen and remained at a high level in in vitro-germinated pollen tubes. The recombinant cytoplasmic domain of PRK1 autophosphorylated on serine and tyrosine, suggesting that PRK1 may be a dual-specificity kinase. Monospecific immune serum to the recombinant extracellular domain of PRK1 detected a 69-kD protein in microsomal membranes of pollen and pollen tubes. The characteristics of PRK1 suggest that it may play a role in signal transduction events during pollen development and/or pollination.

Abstract: The phenological relationships between nesting behavior of a specialist, solitary bee, Dieunomia triangulifera, and the flowering of its primary pollen source, Helianthus annuus, were studied for 3 yr at a site in northeastern Kansas, which contained between 50 000 and >150 000 nests. Activity patterns of D. triangulifera are closely synchronized with pollen availability on nearby sunflower plants in three ways: (1) each year, D. triangulifera became active within days of the beginning of the local sunflower bloom, and the emergence schedule of the entire population at the nest site was timed such that all females had constructed nests and were collecting pollen at peak bloom; (2) over a season the greatest numbers of provisioning females were active at peak bloom, when pollen was most abundant; and (3) over the day, females made more trips, each of which took less time when pollen was most abundant on nearby flowers than when it was scarce. Between seasons, female reproductive success varied positively with the availability of H. annuus pollen. When pollen was abundant, and the population at the nest site was low, °3 times more cells were provisioned than the following year when the bee population was high and pollen abundance declined. Furthermore, 20 pollen—collecting bee species (10 specialists and 10 generalists), besides D. triangulifera, used an estimated 68% of the available sunflower pollen at this site. These data suggest that resource limitation is important in shaping patterns of provisioning behavior in D. triangulifera. Other behaviors presumably related to reproductive success were variable and suggest resources were not limiting: (1) all females did not forage on each day, even at peak bloom; (2) variance in both trip durations and the numbers of trips made per day was large; and (3) females produced far fewer eggs in their lifetime than apparently possible. We suggest that the apparently conflicting evidence for resource limitation may be explained by a physiological limit on the rate of egg production; in such a case, the effects of resource limitation, while clearly important, might not be the primary factor limiting reproductive output. Female D. triangulifera benefit by being synchronized with their resource. Daily and seasonal synchrony enable females to collect a greater amount of pollen during shorter foraging trips. The translates into higher mean reproductive success and, at the population level, allows more females to be supported by the pollen produced from nearby plants. In short, those females that are synchronized with the sunflower bloom effectively increase their own resource availability. This phenomenon may be general, especially in short—lived organisms, i.e ., the evolution of specialization may be associated with fitness benefits based on synchrony with a preferred food source.

Abstract: We identified a tobacco stigma-specific gene, designated STIG1. The STIG1 gene is developmentally regulated and expressed specifically in the stigmatic secretory zone. We used a chimeric STIG1-GUS gene to show that the stigma-specific STIG1 gene expression pattern is controlled primarily at the transcriptional level. We constructed a stigma-specific cytotoxic gene by fusing the STIG1 gene 5' regulatory region with the coding sequence of the Bacillus amyloliquefaciens barnase gene, to assess the role of the stigmatic secretory zone in the pollination process. Pistils of transgenic STIG1-barnase tobacco plants undergo normal development, but lack the stigmatic secretory zone and are female sterile. Pollen grains germinate on the ablated 'stigmatic' surface, but are unable to penetrate the transmitting tissue of the style. Application of stigmatic exudate from wild-type pistils to the ablated surface increases the efficiency of pollen tube germination and growth and restores the capacity of pollen tubes to penetrate the style. Our data demonstrate the importance of the stigmatic secretory zone in the pollination process and provide an approach to identify compounds produced by the stigma that are critical for successful pollination and fertilization to occur.

Abstract: 1 Pollen diagrams from four peatbogs and a marshland located in the Atlantic and Mediterranean zones of north-central Spain are described, and their correlation is used to define a Holocene pollen reference sequence for the region. 2 Two main variants may be defined for the reference sequence: a northern variant, characterized by the predominance of deciduous trees, corresponds to sites under Atlantic temperate and moist climatic influence and a southern variant, with lower deciduous tree diversity, corresponds to sites under Mediterranean and continental climatic conditions. A vegetation gradient from the Atlantic to the Mediterranean side may be inferred from the pollen analysis. 3 A compilation of 14C dated pollen diagrams from the northern Iberian Peninsula is used to plot maps for the Holocene spread of the principal tree genera. 4 Quercus, Corylus, Alnus, Taxus and Pinus had a wide distribution in the northern Iberian Peninsula during pre-Holocene times, as patchy refugia situated at medium elevations. They spread from these refugia at different times depending on climatic, geomorphological and successional conditions. Fagus, Abies and Carpinus could have spread through the Pyrenees. 5 Anthropogenic disturbance at the range limit of Fagus, Abies and Carpinus is probably responsible for their present geographical distribution. 6 The present-day Pinus silvestris forests growing in the Iberian Cordillera, southern Pyrenees and Cantabrian Cordillera have a local origin and may constitute the Mediterranean mountain pine forest altitudinal zone, not previously described for the Iberian Peninsula.

Abstract: Selection favouring an outcrossing plant's ability to sire seeds generally promotes floral characters that increase (1) the frequency of pollinator visits, (2) the number of pollen grains dispersed to other plants by each pollinator and (3) the probability of a pollen grain successfully fertilizing an ovule after reaching a stigma. Flowers influence pollen dispersal and fertilization probabilities by determining the pattern of pollen removal during a series of visits (dispensing schedule). We model male reproductive success to identify optimal dispensing schedules, which characteristically involve monotonic increases in the proportion of remaining pollen removed during successive visits. These schedules balance the benefits of restricted removal, which counteracts the diminishing returns associated with animal pollination (e.g. pollinator grooming, local mate competition), with the advantages of increased removal to avoid time-dependent losses in fertilization ability (e.g. pollen precedence, declining viability). Because pollinator availability mediates this balance, the most effective dispensing schedule allows dynamic adjustment of removal to the prevailing frequency of visits experienced by individual plants. As an example of such dynamic removal we demonstrate that the dispensing mechanism ofLupinus sericeus flowers allows facultative adjustment of removal to the interval between visits. Because optimal control of pollen removal can increase a plant's mating opportunities by an order of magnitude, dispensing mechanisms should be a common component of floral design.

Abstract: A developmental analysis of pollination responses in Arabidopsis implicates pollen as well as stigma maturation factors in the acquisition of reproductive function. In the anther, competence of pollen to germinate and to produce pollen tubes in situ occurred late in development. In the pistil, competence to support pollen germination and tube growth extended over a broad developmental window, and abundant as well as efficient pollen tube development was observed on pistils at anthesis and for a period of 1–2 days prior to flower opening. In contrast, pollen tube growth on immature pistils was found to proceed at low efficiency, at reduced growth rates, and with lack of directionality. Based on the pattern of pollen tube growth at different stages of pistil maturation, temporally regulated signals emanating from specialized cells of the pistil are inferred to be operative in each of the four identified phases of pollen tube growth. In the stigma and the stylar transmitting tissue, these signals directed the path of intra-specific pollen tubes as well as pollen tubes from another cruciferous genera, Brassica. By contrast, in the ovary, signaling by the ovule was effective only on intra-specific pollen tubes and was thus identified as the basis of inter-specific incompatibility. Furthermore, the acquisition of reproductive function was found to involve, in addition to the induction of a variety of stimulatory signals, a heretofore unrecognized developmental restriction in the capacity of epidermal surfaces of the flower to support pollen tube growth.

Abstract: Introduction Virtually all applications of Quaternary pollen analysis, whether ecological, climatological, archeological, or stratigraphic, are ultimately concerned with inferring temporal changes in vegetation composition from pollen assemblages. Stratigraphic changes in pollen assemblages are assumed to record changes in vegetation composition, which in turn provide information about changes in species distribution, prevailing climate, human activities, and cultural resources. Within certain spatial and temporal realms, spatially separated sites contain similar stratigraphic changes in pollen assemblages. These similarities form the basis for classical pollen-stratigraphic zonation, and for chronostratigraphic correlation when independent evidence (e.g., radiocarbon dates) indicates that the zones are contemporaneous among nearby sites. The synchroneity derives from the pollen sequences at the individual sites having recorded the same or similar changes in vegetation composition. The interest in studying pollen sequences that record past vegetational changes has led Quaternary palynologists to seek sedimentary deposits with good pollen preservation, and stable, continuous, datable deposition. Preservation must be sufficiently good that most pollen grains can be reliably assigned to morphotypes corresponding to extant plant taxa at or below the family level. A stable depositional environment is required to ensure that changes in pollen assemblages can be attributed to vegetational changes rather than depositional episodes. Continuous, independently datable records are desirable for an uninterrupted record of vegetational changes at a site, for comparison of records among sites, and for linking the pollen record to other kinds of data (paleontologic, paleoclimatic, geologic, archeologic, biogeographic). Quaternary palynologists bring additional criteria to bear in evaluating pollen records and potential sampling sites.

Abstract: To determine the effects of soil phosphorus on pollen production, pollen grain size, phosphate concentration per pollen grain, and the siring ability of pollen, two cultivars of the common zucchini (Cucurbita pepo) were grown under two soil phosphorus conditions in an experimental garden. Overall, soil phosphorus availability had a significant effect on reproductive output through the female function and on traits affecting the male function of plants (staminate flower production, pollen production per flower, and pollen grain size). In addition, pollen produced by plants in the high phosphorus soils had a higher phosphate concentration than pollen produced by plants in the low phosphorus soils. A pollen mixture experiment revealed that pollen produced by plants in the high phosphorus treatment sired significantly more seeds than pollen produced by plants in the low phosphorus treatment. This study showed that growing conditions such as soil phosphorus can influence the size of a pollen grain and its chemical composition, which, in turn, can affect its ability to sire mature seeds.

Abstract: Summary Two particle samplers for ambient air. situated together: a static size–selective bio–aerosol sampler (SSBAS) and a Burkard pollen and spore trap were compared in sampling intact birch pollen grains through one flowering period of Betula (a total of 44 days). The SSBAS trapped pollen grains three times more efficienily than the Burkard trap, but the variations in pollen counts were significantly correlated. In contrast, birch pollen antigenic activity and the pollen count in the Burkard samples were not closely correlated. The antigenic concentration was occasionally high both before and after the pollination period. There was a high birch pollen antigenic activity in particle size classes where intact pollen grains were absent, even on days when the pollen count was very low. Correspondingly, on days with high birch pollen counts in the air, pollen antigenic activity was on several occasions low. indicating that pollen grains were empty of antigenic material. The small particle size classes are especially important to allergic, patients because they are able to penetrate immediately into the alveoli and provoke asthmatic reactions. Therefore, aerobiological information systems based on pollen and spore counts should be supplemented with information concerning antigenic activities–in the air.

Abstract: Flavonols are essential for pollen germination and tube growth in petunia and can be supplied by either the pollen or stigma at pollination. HPLC analysis and a sensitive bioassay demonstrated that both pollination and wounding induce flavonol accumulation, especially kaempferol, in the outer cell layers and exudate of the stigma. Pollination and wounding induced nearly identical flavonol kinetics and patterns of accumulation in the same target tissue, suggesting that they share elements of a common signal transduction pathway. The wound response was systemic, because kaempferol accumulated in the stigma when distal tissues, such as the corolla, stamens, or sepals, were wounded. We have exploited the germination requirement for flavonols and the high level of kaempferol that accumulates after wounding to enhance plant fecundity. Seed set was significantly increased by mechanically wounding the corolla and stamens prior to the application of pollen to the stigma. A reproductive role for a plant secondary metabolite and the specific function of stigmatic kaempferol are discussed from an evolutionary perspective.

Abstract: Background: To determine the cross-reacting antigens of kiwi fruit and other foods and pollen, we investigated 22 patients allergic to kiwi fruit: 10 with severe systemic reactions and 12 with localized symptoms confined to oral and pharyngeal mucosa (oral allergy syndrome). Seven patients with birch pollen allergy who tolerated kiwi fruit were included as a control group. Methods: All patients were evaluated by skin testing and RAST; three patients were evaluated by RAST inhibition assays. Results: Prick tests showed positive reactions to kiwi fruit in all patients, whereas specific IgE to kiwi fruit could be demonstrated only in patients with generalized severe symptoms. Surprisingly, all 22 patients with clinical kiwi allergy showed positive prick test results and elevated IgE to birch pollen. Clinically, all complained of rhinitis during birch pollen season. Many patients showed sensitization to grass and mugwort pollen. Also, food allergy was found to be associated with kiwi allergy: we found strong reactions to apple and hazelnut; moderate reactions to carrot, potato, and avocado; and weak reactions to wheat and rye flour, pineapple and papaya, and their enzymes bromelain and papain. RAST inhibition studies revealed cross-reacting antigens between birch pollen and kiwi fruit. Interestingly, patients with birch pollen allergy without clinical signs of kiwi allergy had positive prick test reactions to kiwi. Patients with kiwi allergy showed higher concentrations to birch pollen IgE compared with patients with isolated birch pollen allergy. Conclusions: Our results indicate that kiwi allergy is a new manifestation of birch pollen–associated food allergy and is mediated by cross-reacting antigens in the kiwi fruit. Kiwi allergy can be expected in patients with birch pollen allergy exhibiting high levels of IgE to birch pollen. (J ALLERGY CLIN IMMUNOL 1994;94:70-6.)

Abstract: Starch was cytologically localized and biochemically assayed in different anther cell layers of Lilium cv. Enchantment during pollen development and its presence was correlated with anther growth. Two phases could be distinguished: the first, the growth phase, extends from the beginning of meiosis to the vacuolated microspore stage and corresponds to maximum increase in anther size and weight. During this period, microspores lack amyloplasts and starch is degraded in the outer staminal wall layers. The tapetum does not contain starch reserves but accumulates a PAS-positive substance in its vacuole. The second phase, the maturation phase, begins with the late vacuolated microspore stage and lasts until pollen maturation. Anther growth is slowed during this phase. A wave of amylogenesis/ amylolysis occurs first in the late vacuolated-microspores and young pollen grains and, next, in the staminal envelopes. In the pollen grain, the cytoplasm of the vegetative cell is filled with starch, but amyloplasts are not detected in the generative cell. When pollen grains ripen, amylaceous reserves are replaced with lipids. In the staminal envelopes, the second amylogenesis is particularly evident in the endothecium and the middle layers; the peak of starch is reached at the young bicellular pollen grain stage; starch disappears from the anther wall early during the maturation phase. The wave of amylogenesis/amylolysis occurring in the staminal envelopes during the maturation phase is peculiar to Lilium. It is interpreted as a sudden increase in carbohydrate level caused by lower anther needs when the growth is completed. Staminal envelopes may act as a physiological buffer and regulate soluble sugar level in the anther. Stages of anther growth correlate with starch content variations and this suggests that during the growth phase, products of starch hydrolysis in the staminal envelopes may be consumed partly by anther cell layers and partly by microspores.

Abstract: Bees (superfamily Apoidea, order Hymenoptera) represent one of the major success stories in evolution. With about 20,000 species in 11 families (Michener 1979), they are twice as diverse as birds. All species, except cleptoparasites (cuckoos), construct nests and provision cells with pollen and concentrated nectar (honey), the sole food of both larvae and adults. This niche is otherwise occupied only by a few vespid wasps.

Abstract: In most higher plants sexual interactions are mediated by animal pollinators that affect the number and differential reproductive success of mates. The number and sex of breeding individuals in populations are central factors in evolutionary theory, but the quantitative effect of plant population size on pollinator-mediated mating is understudied. We investigated variation in pollen removal (male function) and fruit set (female function) among flowering populations of different size of two bumblebee-and one butterfly-pollinated, rewardless, pollen-limited, hermaphroditic orchid species in Sweden. As the amount of pollen removed from plants by insects (either absolute or proportional) increased, so did the number of pollinations, whereas the proportions of plants with different pollinator-designated functional sex (male, female, hermaphrodite) depended primarily on the ratio between the amount of fruit set and pollen removed within populations. A larger population size was found to have several effects: (1) the total numbers of pollinia removed and fruits set increased; (2) the proportion of pollen removed from plants decreased; (3) the proportion of flowers pollinated decreased in the butterfly-but was not affected in the bumblebee-pollinated species; (4) the ratio between fruits set and pollinia removed increased linearly in the bumblebee-pollinated species but reached a maximum at c. 80 individuals in the butterfly-pollinated species; (5) the numbers of pollinator-designated pure male and hermaphrodite individuals increased; and (6) the variance in pollinium removal, but not fruit set, increased among individuals. These findings empirically verify the basic importance of population size for the mating structure of outcrossing plants, and indicate that selection for female sexual traits is reinforced when population size is smaller while selection for male sexual traits is reinforced when population size is larger.

Abstract: There is a body of evidence which suggests that the frequency of atopic diseases—particularly those induced by pollen allergens (rhinoconjunctlvitis and/or bronchial aslhma)—^is increasing because of interaction with air pollution; in fact, atopic diseases have become more common during the past two decades 11-3], Irritant gases and airborne matter have both adjuvant activity for specific IgE production against common allergens in experimental animals and enhancing effects on allergic symptoms in sensitized subjects [4-6]. This trend is also evident in ihe Mediterraneans, where the climate, characterized by mild winters and dry summers, facilitates the growing of a characteristic vegetation with the production of various types of allergenic pollen, some of which are different from those of central and northern Europe [7]. However, in the context of the Mediterranean area, several concurrent climatic and geographical factors promote the growth of various vegetations with many wind-pollinating plant families and species. As a result, the frequency of allergic sensitization to pollen is different, for example, between northern Italy on the one hand, with a continental and rather middle European climate, where allergy to grass pollen is more important, and southern Italy on the other hand, with a Mediterranean sub-tropical climate, where Parietaria is the major cause of pollinosis and OHve is responsible for many sensitizations [8]. The pollinosis situation in the northern Mediterranean area is halfway between the typical Mediterranean situations and that of central Europe. In the latter area, and particularly in the southern part of France, mean annual pollen counts show that grass pollen and Cupressaceae pollen are the most frequent causes of pollinosis. Some Mediterranean pollen types, such as Oleaceae, Platanus or Parietaria^ are also of importance. Plantain is also represented in relatively large amounts [9].

Abstract: 1 In order to identify the mode and intensity of fertility selection in a heterostylous population under severe pollinator limitation, morph composition and intraand intermorph pollen loads, fruit and seed set were investigated in an isolated population of the endangered, heterostylous species Primula sieboldii. 2 Seventy-six genets were classified as either of the pin or thrum morph on the basis of measurements of stigma-anther separation and relative anther height, except for one genet that exhibited a short homostylous phenotype. There was a 1:1 ratio of pin and thrum plants in the population. 3 Measurements of stigmatic pollen load indicated that legitimate pollination (i.e. by the opposite morph) was extremely limited. Female fertility was generally low but varied significantly among style morphs and among genets within morphs. The pin morph showed significantly higher fertility than the thrum morph. High fruit and seed set was recorded for the short homostyle. 4 Legitimate pollination by hand resulted in a significant increase in fruit and seed set except for the homostyle where high spontaneous seed set already occurred. Intragenet pollination or illegitimate (i.e. intramorph) pollination resulted in no seed set. 5 It was concluded that pollen limitation is largely responsible for the low female fertility of plants in the population. Under severe pollinator limitation, it is possible that the self-fertile homostyle will have a selective advantage and will spread in the population.

Abstract: The hypothesis that most of the pollen collected by forest-floor moss polsters originates from local sources (i.e. trees growing within a 20-m radius) was tested by comparing pollen and forest inventory data from 30 plots in three extensively forested regions. Within each region, plots were located in forest stands similar in composition to regional forests (matrix sites) as well as in patches differing substantially from regional forests (patch sites). Scatter plots and regression analyses indicated that between 25 and 90% of the tree pollen in the assemblages originated from trees growing beyond the 20-m forest-sampling radius. Most of the extraneous pollen was from taxa that were regionally abundant in forests, and highly productive of well-dispersed pollen (...)