SIZES OF NATURAL MICROGAMETOPHYTE POPULATIONS IN PISTILS OF PHLOX DRUMMONDII

The numbers of microgametophytes in the stigmas of the outcrossing Phlox drummondii were determined in 19 natural populations. Microgametophyte numbers per stigma ranged from 0 to over 40 in each population. The number of flowers per plant, distance to the nearest-neighbor, and number of plants within 1 m of the focal plants explained about 23% of the variation in microgametophyte numbers within 2 of the populations. The mean number per stigma across all populations was 14.34; and the mean number per population varied from 7.77 to 19.52. Given that there are 3 ovules per flower, there was an average of 4.73 microgametophytes per ovule. Sixty-nine percent of all pistils contained more than 3 microgametophytes, thereby presenting an opportunity for intergametophytic competition.     

华山新麦草开花物候期观测和自然种群基因流的间接估测

华山新麦草（Psathyrostachys huashanica keng)为我国特有种,仅分布在陕西华山。通过对自然种群传粉物候期观测发现,华山新麦草的传粉高峰期与海拔有一定关系。海拔每升高200m,传粉物候期就推迟2－3d;海拔差异超过500m的亚种群,传粉物候期就不会出现重叠。同时应用等位酶分析技术和E－统计分析间接估测华山新麦草自然种群的基因流（Nm）,其值较一般风媒传粉植物低。通过华山新麦草资源状况、生长环境的调查以及移栽试验的观察,认为该物种稀的主要原因之一 可能是其生存竞争能力弱,最终被迫生长在其它物种所不能生存的环境。     

EFFECTS OF PARENTAGE AND SIZE OF THE POLLEN LOAD ON PROGENY PERFORMANCE IN CAMPANULA AMERICANA

To examine the effects of maternal and paternal parentage and the size of the pollen load on seed size and weight and on progeny performance we conducted a controlled crossing experiment using a natural population of Campanula americana. We found that seed size was positively correlated with early seedling performance for all but one of traits we measured (days to emergence), but was not significantly correlated with any of the later vegetative measures or reproductive output. We detected significant effects due to the maternal parent for the vegetative traits days to emergence, days to first leaf, and final plant height, as well as total seed weight, and mean seed weight per fruit. Significant paternal effects were found for all of the seedling traits except number of leaves after vernalization. The progeny from fruits receiving high pollen loads significantly outperformed the progeny from fruits receiving low pollen loads for the traits days to first and second leaf, numbers of leaves after vernalization, and days to first flower. These results not only demonstrate the importance of parentage and seed weight on progeny performance, but also indicate that variations in the size of the pollen load may be important in seedling establishment in natural populations.     

SEXUALITY, INCOMPATIBILITY, SIZE VARIATION, AND PREFERENTIAL POLYANDRY IN NATURAL POPULATIONS AND CLONES OF SELLAPHORA PUPULA (BACILLARIOPHYCEAE)

The capitate and rectangular demes of the freshwater epipelic diatom Sellaphora pupula (Kütz.) Mereschk. are dioecious, the first such report for any freshwater diatom. Sexual differentiation, which is probably determined genetically, involves recognition at the cell surface as well as differences in gamete behavior (one gametangium produces an active "male" gamete, the other a passive "female" gamete). In culture, successful sexual reproduction occurs only when compatible clones are mixed. All cells of a clone behave identically in interclonal crosses, being either male or female, regardless of the stage of the life cycle, in contrast to the sequential hermaphroditism of centric diatoms. Males and females have identical frustule morphology. As in other diatoms, there is an upper size threshold for sexual reproduction, below which cells become progressively easier to sexualize. In culture, sexual interactions occur in cells much smaller than those ever seen in natural populations, so that in nature the sexual size range is effectively open. Natural populations almost always contain sexualizable cells; often, most of the cells are below the upper sexual size threshold. Male gametangia are, on average, slightly larger than females in the capitate deme, which may be produced by preferential polyandry, depleting the population of males and making them younger at mating. Rarely, selfing occurs producing zygotes, but these abort before producing initial cells. The sizes of the gametangia and initial cells are correlated but this does not invalidate the use of "cardinal points" of the life cycle in taxonomy. No interbreeding occurs between the rectangular and capitate demes. However, when males of one deme are mixed with females of the other, there is a stimulation of activity, as during the early stages of pairing in compatible intrademic crosses.     

AERODYNAMICS OF WIND POLLINATION IN SIMMONDSIA CHINENSIS (LINK) SCHNEIDER

Wind tunnel analyses of Simmondsia chinensis (Link) Schneider or “jojoba” were conducted to quantify the behavior of airborne pollen grains around individual branches and leaves and near individual carpellate flowers. Field data (wind velocity) were used to ensure a correspondence between wind tunnel and natural conditions. Based upon the visualization of individual pollen grain trajectories, it is concluded that pollen deposition on stigmatic surfaces is influenced by large-scale aerodynamic patterns, generated by foliage leaves, and small-scale airflow patterns, formed around and by floral parts and stigmas. Leaves are seen to deflect airborne pollen grains into trajectories that can intersect ambient airflow at 90° angles, showering decumbent carpellate flowers with pollen. Similarly, flowers can deflect pollen upward and downwind, toward other flowers. The extent of floral bract and sepal recurvature is shown to influence the extent of pollen deposition by determining the characteristic airflow pattern around stigmas. Available evidence concerning the relatively recent evolutionary transition to anemophily in Simmondsia is interpreted within the context of morphological adaptations and exaptations favoring wind pollination.     

POLLEN FLOW AND FECUNDITY IN POPULATIONS OF LITHOSPERMUM CAROLINIENSE

Stigmatic pollen loads of pin and thrum forms of distylous Lithospermum caroliniense (Walt.) MacMill. generally have very large proportions of incompatible pollen grains. Assortative pollination probably results from large components of self-pollination rather than geitonogamous pollinations, because pollen loads of large and small individuals are the same, although large individuals would be expected to experience more geitonogamous pollinator flights than small individuals. The distylous reproductive system appears relatively insensitive to changes in pollinator activity and preferential pollen flow between pins and thrums cannot be demonstrated. In contrast to the relatively uniform proportions of pin and thrum pollen on stigmas, absolute pollen loads vary substantially in different years and localities. Extremely low fecundity, which appears to be characteristic of this species, may result in part from lack of pollinator activity. However, even under optimal conditions for pollination, fecundity is less than 20%. Although L. caroliniense appears to have an inefficient pollination system, intrinsic low fecundity may represent a more critical feature of the life history.     

EFFECTS OF SOIL NITROGEN ON POLLEN PRODUCTION,POLLEN GRAIN SIZE,AND POLLEN PERFORMANCE IN CUCURBITA PEPO (CUCURBITACEAE)

To determine the effects of soil nitrogen on pollen production, pollen size, and pollen performance, two cultivars of zucchini (Cucurbita pepo) were grown under two nitrogen regimes in an experimental garden. The two cultivars were true breeding for alternative alleles for a one gene trait, ovary color. The soil nitrogen treatment had a significant effect on most measures of reproductive output through the female function. The nitrogen treatment did not affect the number of staminate flowers per plant but did have an effect on the number of pollen grains per staminate flower and the mean pollen grain size. A pollen mixture experiment revealed that pollen produced by plants in the high nitrogen treatment sired significantly more seeds than pollen from low nitrogen plants. Moreover, we found that the high nitrogen pollen sired even a greater percentage of seeds in the region of the fruit (ovary) previously shown to be fertilized by the fastest growing pollen tubes. Thus, the difference in the number of seeds sired by pollen from the two nitrogen treatments is due to differences in pollen performance. We conclude that spatial heterogeneity in soil nitrogen can influence the paternity of seeds in a plant population.     

DISC ELECTROPHORETIC STUDY OF POLLEN PROTEINS FROM NATURAL POPULATIONS OF BETULA POPULIFOLIA IN NEW JERSEY

Pollen proteins from individual trees of eight natural populations of B. populifolia Marsh. located in diverse physiographic provinces of New Jersey were separated by disc electrophoresis with 7 % acid and basic acrylamide gels. Specific stains and substrates for detecting general proteins, esterase, and leucine aminopeptidase isoenzymes were utilized. Average Rp values, 95 % confidence intervals, and percentage similarity values were calculated. Dendrograms were constructed to illustrate protein similarity among populations. The effects of increasing the concentration of protein samples subjected to electrophoresis and storage of pollen (4 C over 16 months) were investigated. After statistical analysis we concluded that: each protein system investigated revealed different amounts of intra- and interpopulation variation, different population ranking (determined by amount of variation), and different population similarity groupings; conclusions based on the comparisons of numbers of protein bands were not always valid; disc electrophoretic data revealed information about natural selection and gene flow; the effect of increasing pollen protein concentration was quantitative; with storage pollen proteins increased in overall positive charge.     

ALLOPOLYPLOIDY IN NATURAL AND CULTIVATED POPULATIONS OF PORPHYRA (BANGIALES,RHODOPHYTA)1

To confirm whether allopolyploidy occurs in samples of previously identified Porphyra yezoensis Ueda, P. tenera Kjellm., and P. yezoensis × P. tenera from natural and cultivated populations, we examined these samples by using PCR‐RFLP and microsatellite analyses of multiple nuclear and chloroplast regions [nuclear regions: type II DNA topoisomerase gene (TOP2), actin‐related protein 4 gene (ARP4), internal transcribed spacer (ITS) rDNA and three microsatellite loci; chloroplast region: RUBISCO spacer]. Except for the ITS region, these multiple nuclear markers indicated that the wild strain MT‐1 and the cultivated strain 90‐02 (previously identified as P. yezoensis × P. tenera and cultivated P. tenera, respectively) are heterozygous and possess both genotypes of P. tenera and P. yezoensis in the conchocelis phase. Furthermore, gametophytic blades of two pure lines, HG‐TY1 and HG‐TY2 (F₁ strains of MT‐1 and 90‐02, respectively), were also heterozygous, and six chromosomes per single cell could be observed in each blade of the two pure lines. These results demonstrate that allopolyploidy occurs in Porphyra strains derived from both natural and cultivated populations, even though ITS genotypes of these strains showed homogenization toward one parental ITS.     

THE RELATIONSHIPS BETWEEN SEASONAL VARIATION IN LIGHT INTENSITY,RAMET SIZE,AND SEXUAL REPRODUCTION IN NATURAL AND EXPERIMENTAL POPULATIONS OF ASTER ACUMINATUS (COMPOSITAE)

We conducted experiments to evaluate the effects of different patterns of seasonal light availability on ramet size and sexual reproduction in the understory herb, Aster acuminatus. In April 1982, 200 potted rhizomes were divided equally between a high light and a shaded site. Twice during the growing season subsets of pots were reciprocally transferred between the sites, resulting in eight different light treatments. There was significant variation among treatments in mean ramet weight (0.41–1.21 g), height (15.0–23.4 cm), number of flowers (0.4–7.9) and percentage of ramets flowering (14–95). Periods of high light increased ramet height, weight, rhizome production and flowering, but high light earlier in the season increased ramet height more than did high light later in the season, while high light later had pronounced effects on the other three traits. Measurements taken in nine natural patches experiencing different patterns of seasonal light availability are consistent with the experimental results. The results provide new insights into the general phenomenon of size-dependent reproduction in herbs and illustrate how the phenology of biomass allocation can affect growth and reproduction.     

WIND POLLINATION,SELF-INCOMPATIBILITY,AND ALTITUDINAL SHIFTS IN POLLINATION SYSTEMS IN THE HIGH ANDEAN GENUS ESPELETIA (ASTERACEAE)

Altitudinal changes in breeding and pollination systems of tropical montane plants were studied in 13 species of Espeletia growing in the Venezuelan Andes from 2,000 to 4,300 m. Hand pollination tests showed that all species were strongly self-incompatible. The four species found only above 4,000 m had up to 10% median seed set in self-pollinated heads, which was significantly higher than the lower elevation species. Nine species were insect-pollinated, with large bees the major pollinator group. An endemic páramo hummingbird, Oxypogon guerinii, was an important visitor of E. schultzii in three populations examined. Experimental bagging experiments showed that the four high elevation species were wind-pollinated, further evidenced by the lack of pollinator visits and markedly different capitulum morphologies. Open-pollinated seed set in two wind-pollinated species, E. spicata and E. timotensis, was strongly dependent on the population's flowering density, which varied significantly from year to year. The shift from insect to wind pollination in Espeletia can be related to the low pollinator availability at high elevations in the Andes, protection of the capitula from snow and daily frosts, and the extremely long flowering periods of individual heads.     

THE MOTION OF WINDBORNE POLLEN GRAINS AROUND CONIFER OVULATE CONES: IMPLICATIONS ON WIND POLLINATION

Comparisons are presented between the three-dimensional airflow patterns created around and by a scale model of a conifer ovulate cone and the trajectories of windborne pollen grains around Picea, Larix, and Pinus ovulate cones. Three general components of the airflow pattern around an ovulate cone model are 1) doldrum-like eddies, rotating over the adaxial surfaces of cone scales and directed toward attached ovules, 2) airflow spiralling around the cone axis along cone scale orthostichies and parastichies, and 3) a complex pattern of vortices (“umbilicus”) directed toward the leeward surface of the ovulate cone. The observed trajectories of pollen grains around cones of Picea, Larix, and Pinus conform to two of these three airflow components: 1) pollen grains are seen to roll along cone scales toward the distal scale margin and to become reentrained in airflow directed backward toward attached ovules, and 2) pollen grains passing around the cone are deflected into the “umbilicus” airflow pattern, where they either settle on or impact with cone scales (approach trajectories), or where they approach the leeward cone surface but are deflected away by airflow passing under the cone (Z-shaped trajectories). Vectoral analyses of pollen grain motion reveal a complex pattern of trajectories influenced by boundary layer conditions defined by ovulate cone geometry and ambient airflow speed. Wind tunnel studies of ovulate cones subtended by leaves and stem indicate that leaves circumscribing the cone act as a snowfence, deflecting windborne pollen toward the cone. Vectoral analyses of airflow patterns and pollen grain trajectories close to ovulate cones indicate that wind pollination in conifers is a non-stochastic aerodynamic process influenced by cone-leaf morphology and the behavior of pollen grains as windborne particles.     

VARIATION IN POLLEN FLOW WITHIN AND AMONG POPULATIONS OF IPOMOPSIS AGGREGATA

Pollen dispersal is a major component of gene flow in plant populations. It can influence microevolution within and among populations as well as the evolution of floral characters that affect dispersal. Most previous studies have relied on point estimates to characterize dispersal distances, even though there is likely to be substantial intrapopulational and interpopulational variation. We measured variation in pollen dispersal for the hummingbird-pollinated herb Ipomopsis aggregata (Polemoniaceae), using powdered fluorescent dyes to estimate pollen movement. Analysis of 5–6 natural populations in each of three years indicated that mean and mean squared distances of pollen dispersal, measured over the reproductive lifespan of individual plants, varied more than threefold among populations and years. Dispersal distances also shifted over the season within a given population. Unlike the variation among populations, these seasonal changes were associated in part with changes in flower density. The mean distance of pollen dispersal from an individual plant was unrelated to the date of first flowering, but did reflect two floral characters. Plants with higher variance in stamen length across flowers delivered pollen farther on average, as predicted by computer simulations of pollen carryover. Plants with lower mean stamen lengths also delivered pollen farther. Such effects of plant characters on pollen dispersal are a critical prerequisite for dispersal to evolve in response to its effects on fitness.     

POLLEN AND GENE DISPERSAL: THE INFLUENCES OF COMPETITION FOR POLLINATION

Pollinators that forage indiscriminately can transfer pollen from one species to another, reducing the amount that reaches conspecific flowers. I present evidence that the presence of another plant species visited by the same pollinators can also reduce pollen dispersal distances and outcrossing. This has the potential to influence gene flow and reproductive success. Pollen carryover and movement patterns were measured for the shared insect pollinators of Stellaria pubera and Claytonia virginica in North Carolina. Bee flies deposited similar amounts of Stellaria pollen on a series of pistillate Claytonia flowers as on a series of pistillate Stellaria flowers. In arrays of potted plants, flies and solitary bees visited most flowers on a plant before leaving and then flew to a nearby plant chosen independently of species; 95% of moves were to one of 12 nearest neighbors. These measures of pollen carryover and movement patterns were used in a set of computer simulations to predict pollen dispersal distances. The simulations suggested that C. virginica substantially reduces outcrossing and pollen flow in S. pubera. These predictions were tested by tracking dye movement from anthers in populations of potted plants. Addition of C. virginica reduced the mean squared distance moved by dye to receptive S. pubera flowers by 23% and reduced the amount of dye moved by 51%. The estimated pollen component of gene flow was also much lower in a natural population of 5. pubera mixed with C. virginica than in the synthetic single-species populations.