FLORAL DISPLAY IN PHYLA INCISA: CONSEQUENCES FOR MALE AND FEMALE REPRODUCTIVE SUCCESS

The inflorescences of Phyla incisa consist of flowers in two phases: younger, nectar-containing flowers that have yellow corolla throats and older, nectar-lacking flowers that have dark purple corolla throats. Observations of pollinator visitation patterns to both natural and manipulated inflorescences were made to determine the role of each flower phase in pollinator attraction. The effect of older-phase flowers on male and female reproductive success was determined by comparing stigmatic pollen loads and estimates of pollen removal from inflorescences having different numbers of these flowers. The pollinators of Phyla selected larger inflorescences more often than expected based upon the size distribution of inflorescences available to them. Both younger- and older-phase flowers contributed to the attraction of pollinators, but the latter were less effective in this function. The presence of older-phase flowers significantly increased the visitation rate to inflorescences and the amount of pollen removed but had little effect on pollen deposition on stigmas. The lack of correspondence between pollen deposition and pollinator-visitation rate was not due to stigma saturation, since stigma loads varied greatly. The data indicate that the deposition of pollen on stigmas in this species is a relatively stochastic process, whereas pollen removal from inflorescences occurs at a much more regular rate. Old-phase flower retention appears to contribute to reproductive success through increased pollen donation when pollinator activity is high and may also increase the probability of seed set when pollinators are rare.     

POPULATION STRUCTURE ALONG A STEEP ENVIRONMENTAL GRADIENT: CONSEQUENCES OF FLOWERING TIME AND HABITAT VARIATION IN THE SNOW BUTTERCUP,RANUNCULUS ADONEUS

Few studies have determined how gene flow and selection interact to generate population genetic structure in heterogeneous environments. One way to identify the potential role played by natural selection is to compare patterns of spatial genetic structure between different life cycle stages and among microenvironments. We examined patterns of spatial structure in a population of the snow buttercup (Ranunculus adoneus), using both adult plants and newly emerged seedlings. The study population spans a steep environmental gradient caused by gradual melting of snow within a permanent snowbed. Early-melting sites are characterized by denser vegetation, more fertile soils, and a longer growing season than late-melting sites tens of meters away. The flowering time of R. adoneus is controlled entirely by time of snowmelt, so the contiguous population is phenologically substructured into a series of successively flowering cohorts, reducing the opportunity for direct pollen transfer between early- and late-melting sites. For four highly polymorphic enzyme loci in this tetraploid species, there was subtle, but statistically significant, genetic differentiation between early, middle, and late-melting cohorts; adults usually showed greater differentiation among snowmelt zones than did seedlings. At two loci in adults and one locus in seedlings, homozygotes were more common than predicted at Hardy-Weinberg equilibrium, even when assuming maximum levels of double reduction during meiosis. This pattern suggests the occurrence of self-fertilization and/or population substructure. To determine how spatial isolation and phenological separation each contribute to genetic substructure, we used bivariate regression models to predict the numbers of allele differences between randomly paired individuals as a function of meters separation in space and days separation in flowering time. For newly emerged seedlings, we found that spatial separation was positively associated with genetic difference, but that the additional contribution of phenological separation to genetic difference was not significant. This implies that seeds and/or pollen move effectively across the snowmelt gradient, despite differences in flowering time. As was true for seedlings, spatial separation between paired adults contributed to greater genetic difference, but for a given spatial separation, the genetic difference between adult plants was reduced by phenological separation. This result implies that postemergence selection is favoring at least some seeds that migrate across the snowmelt gradient. Directional gene flow across the snowmelt gradient probably results from a genetic source-sink interaction, that is, the colonization of ecologically marginal late-melting sites by high quality seeds produced by the larger subpopulation in early-melting sites. Effective gene flow from high to low quality microenvironments is likely to impede adaptation to late-melting locations.     

REPRODUCTIVE SUCCESS OF FUCUS VESICULOSUS (PHAEOPHYCEAE) IN THE BALTIC SEA

Marine organisms colonizing brackish habitats such as the Baltic Sea must cope with the negative effects of low salinities on reproductive success because these may reduce gamete viability and/or increase polyspermy. Reproductive characteristics of the marine seaweed Fucus vesiculosus L. were studied in several brackish habitats, particularly in the northern Baltic Sea, to understand its ability to reproduce where few other marine species survive. Polyspermy and fertilization success were variable at the boundary of the continuous distribution of F. vesiculosus in the Baltic Sea, and polyspermy was high (10%–30%) when fertilization was successful. A strong female bias (80%–86%, ca. 5.5:1) was found at the northernmost limit of Baltic F. vesiculosus. Electrophysiological studies showed that many eggs have a high input resistance (519 ± 150 MΩ[mean ± SE, n = 14] at Drivan, 1995), which may be helpful in preventing polyspermy in this brackish habitat. The polyspermy block remains sodium-dependent in the northern Baltic. Sperm bound quickly to northern Baltic eggs in natural water, but fertilization was delayed compared to marine F. vesiculosus. A subset of northern Baltic eggs studied during an optimal reproductive period (7–11 July 1995) had a membrane potential (E_m) of ca. −100 mV and an effective fertilization potential (FP) of ca. 2 min with a plateau of −25 mV, but repolarized too rapidly for the FP to be protective. Pronuclear migration and cell wall secretion occurred more slowly in Baltic than in marine zygotes. The reproductive success of theseboundary populations may be dependent upon windows of opportunity when there are favorable combinations of the levels of salinity, water motion, population density, and sex ratio. These factors and the short duration of the reproductive season in the northern Baltic Sea may result in reproductive failure in some years.     

PHENOLOGY AND REPRODUCTIVE ALLOCATION IN ANDROPOGON SCOPARIUS (GRAMINEAE) POPULATIONS IN COMMUNITIES OF DIFFERENT SUCCESSIONAL STAGES

Successional populations of Andropogon scoparius in Franklin Township, Somerset County, New Jersey, were compared as to their phenology and reproductive allocation. Field data from six populations in old-fields ranging in age from 2 to 40 years indicated significant differences in both phenology and reproductive effort (ratio of reproductive to total shoot biomass). Mean date of first anthesis was consistently later with increasing age of the old-field, and the later the first anthesis date for a population, the lower was the reproductive effort. Population data on mean maximum height and seed weight showed no relation to successional age. Greenhouse experiments on three of the populations revealed that most of the field differences were attributable to local habitat effects on phenotypic expression. The possibility of some genetic differentiation paralleling successional age was raised by the consistent (though sometimes statistically not significant) differences between the early (3-yr) and late (40-yr) successional populations in date of first anthesis and in reproductive effort under two light intensities and uniform greenhouse conditions.     

REPRODUCTIVE SUCCESS AND INFLORESCENCE SIZE OF CALOPOGON TUBEROSUS (ORCHIDACEAE)

Reproductive success of Calopogon tuberosus, which produces no nectar, was investigated in relation to inflorescence size and dispersion pattern. Mean inflorescence size was 2.56 (range 1–10). A bagging experiment showed that insects are required for pollen transfer and that fruits are produced from self-, geitonogamous, and cross-pollinations; fruit set was not 100%. Fruit set of nonmanipulated plants was limited by the number of pollinator visits. Reproductive success increased with increasing inflorescence size, although not above theoretical predictions. However, the probability of producing no fruit or contributing no pollinia decreased with increasing inflorescence size since sequential flowering increased the probability of a pollinator visit to the inflorescence over the blooming period. Large inflorescences did not provide a greater pollinator attraction than small ones, because inflorescences only presented a few open flowers at a time. In addition, flowers on plants growing in clumps of 2–8 plants had a higher probability of setting fruit, apparently because of increased pollinator attraction. Although there are obvious selective advantages for large inflorescences, the sequential flowering habit, and low resource availability may reduce the advantages of large inflorescence size at our study site.     

VARIATION IN MALE REPRODUCTIVE INVESTMENT AND MALE REPRODUCTIVE SUCCESS IN WHITE SPRUCE

An experimental population composed of ramets of white spruce clones was studied to determine the influence of different levels of clonal male reproductive investment on clonal male reproductive success, where the male reproductive success of different clones in the population was defined as the proportion of the seed crop sired by each clone. We present a multilocus estimation procedure which provides unbiased estimates of the proportion of seed sired by each parental genotypic class from pollen gamete frequency data, whenever gametic segregation frequencies are known. Significant linear and quadratic components were found for the relationship between the number of male cones produced and the estimated proportion of the seed crop sired. A clone that produced an exceptionally large number of male cones, however, did not have the greatest male reproductive success. In general, the results support an assumption made in theoretical models of selection on mating system modifiers regarding the relationship between male investment and male reproductive success. They also support the hypothesis that male reproductive success in wind-pollinated species continues to increase substantially with increasing male reproductive investment.     

AUTOGAMY AND COMPETITION FOR POLLINATORS IN HEPATICA AMERICANA (RANUNCULACEAE)

Hepatica americana is one of the earliest flowering vernal herbs in the deciduous forests of piedmont North Carolina. Unlike most other members of the spring wildflower community, its flowers are nectarless and autogamous. The number of insect visits a flower receives varies markedly through the blooming season and is lowest when H. americana is in full bloom. Potential for outcrossing as measured by the seed set of emasculated flowers follows the same pattern. The mid-season decline in insect-pollination is most likely the result of competition with Erythronium umbilicatum, which flowers concurrently with H. americana and is much more attractive to the solitary bees that are the principal early season pollen vectors. Because of this competitive disadvantage, seed set of H. americana in piedmont North Carolina would be pollination-limited if the flowers were not autogamous. Autogamy may also be favored by flowering early in the spring before pollinators are available. Opportunities for outcrossing in H. americana are primarily the result of protogyny and blooming earlier than competitors.     

BREEDING SYSTEM EVOLUTION IN LEAVENWORTHIA: BREEDING SYSTEM VARIATION AND REPRODUCTIVE SUCCESS IN NATURAL POPULATIONS OF LEAVENWORTHIA CRASSA (CRUCIFERAE)

Populations of Leavenworthia crassa (Cruciferae) studied for 3 years exhibited among- and within-population genetic variation for a suite of floral and reproductive traits (flower width, petal length, anther position, ability to set seeds in the absence of pollinators, time to first flowering) associated with breeding system. We used electrophoretic markers to show that a population with small, monomorphically colored flowers with introrse anthers had a significantly lower outcrossing rate (t = 0.03) than did a population with larger, polymorphically colored flowers with extrorse anthers (t = 0.33). In the more-outcrossing population the correlation between higher maternal plant outcrossing rate and the suite of six traits approached significance (P < 0.067), with greater petal size, greater flower width, and reduced ability to set seeds in the absence of pollinators contributing significantly. Plants in selfing populations had a generally higher reproductive success, with a higher number of flowers per plant, a smaller proportion of unfertilized ovules, a smaller proportion of fertilized ovules aborted, a higher rate of fruit set, and overall a larger number of seeds matured than did plants from the more outcrossing populations. Pollen limitation did not appear to account for lower reproductive success in outcrossing populations. Resource limitation did not differ substantially between populations. However, within-ovary patterns of fertilization, abortion, and seed weight were significantly less random in outcrossing populations than in selfing populations, suggesting that differential gamete and embryo success may be responsible for lower reproductive success in outcrossing populations.     

FACTORS INFLUENCING THE REPRODUCTIVE SUCCESS OF IPOMOEA PES-CAPRAE (CONVOLVULACEAE) AROUND THE GULF OF MEXICO

The reproductive biology of Ipomoea pes-caprae, a pantropical beach morning glory, was studied at five sites around the Gulf of Mexico. The primary pollinators were Xylocopa species (carpenter bees) which dispersed pollen up to 90 m. Exclusion experiments demonstrated that ants feeding on extrafloral nectaries increased seed set but did not protect seeds from predation by the bruchid beetle Megacerus. The water-dispersed seed and long-range dispersal of pollen may function to counter the sporophytic incompatability mechanism of the plant; populations exhibit a large neighborhood size. Key reproductive factors in the life cycle of I. pes-caprae are the long-range pollen flow and mass germination of water-dispersed seeds.     

THE EFFECT OF FLOWER PRODUCTION ON MALE REPRODUCTIVE SUCCESS IN WILD RADISH POPULATIONS

Flower production is the major determinant of pollen yield and an important component in pollinator attraction. Consequently differences among plants in flower production are expected to have a substantial impact on their relative success at fathering seed. We examined this prediction using one natural and three structured populations of wild radish. We found that a plant's relative success at fathering seed on another plant in the population (male fertility) increased with flower production. Nonetheless, the increase in fertility exhibited a diminishing marginal gain, with the relationship varying among populations. The relationship between the estimates of total number of seeds sired and flower production varied substantially among the populations examined, ranging from a weakly linear to strongly negative quadratic. Not surprisingly, the spatial structure of the population with respect to seed yield had a powerful effect on the total number of seeds sired because male fertility decreased exponentially with intermate distance. This exponential relationship occurred in all populations examined. Other covariates important to male fertility were flower color, time, the specific identity of the male parent, and male by female interaction. The identity of the male parent consistently accounted for a large portion of the variation in male fertility, indicating that other unmeasured features of the plant influenced its success.     

GENETIC CONSEQUENCES OF AUTOPOLYPLOIDY IN TOLMIEA (SAXIFRAGACEAE)

Although there is an extensive literature on the genetic attributes of allopolyploids, very little information is available regarding the genetic consequences of autopolyploidy in natural populations. We therefore addressed the major predicted genetic consequences of autopolyploidy using diploid and tetraploid populations of Tolmiea menziesii. Individual autotetraploid plants frequently maintain three or four alleles at single loci: 39% of the 678 tetraploid plants exhibited three or four alleles for at least one locus. Heterozygosity was also significantly higher in autotetraploid populations than in diploid populations: H_° = 0.070 and 0.237 in diploid and tetraploid Tolmiea, respectively. Most of the genetic diversity in T. menziesii is maintained within populations (ratio of gene diversity within populations to mean total genetic diversity = 0.636). The total genetic diversity due to differentiation between the two cytotypes is only 0.055. Such a low degree of differentiation between cytotypes would be expected between a diploid and its autotetraploid derivative. Most diploid and all tetraploid populations examined are in genetic equilibrium. Diploid and tetraploid Tolmiea share three or four alleles at six of eight polymorphic loci. This suggests that either autotetraploid Tolmiea was formed via crossing of genetically different diploids (perhaps via a triploid intermediate) or autopolyploidy occurred more than once in separate individual plants, followed by later crossing of autotetraploids.     

濒危植物南川升麻生殖特性的研究

研究了南川升麻的生殖生物学特性,并探讨了其致濒的原因。南川升麻只分布在中国四川省金佛山地区,仅１个居群,个体总数６０００￣８０００株,其中开花植株约占１９％左右;花序圆锥状,花期８月中至１０月初,１１月中下旬果实成熟。南川升麻雌雄异熟,表现为大约花谢７ｄ后柱头才发育成熟;自然条件下可正常受精,但频率低,结籽率平均仅为５．８％￣７．０％,可授期内人工异株授粉,结籽率可提高到２８．０％;胚乳核型,种子     

REPRODUCTIVE PHENOLOGY OF LAMINARIA SACCHARINA (L.) LAMOUR. (PHAEOPHYTA) AT THE SOUTHERN LIMIT OF ITS DISTRIBUTION IN THE NOTHWESTERN ATLANTIC OCEAN1,2

Laminaria saccharina (L) Lamour. Sporophytes were monitored monthly from October 1982 to September 1983 to investigate reproduction phenology and relationshiops to growth paatterns aaat its southern limit of distribution in the northwest Atlantic Ocean (Long Island Soundd). Plants exhibited an annual growth pattern. Growth raate, bladelehgth, maximum width, area, stiipe lehgth an wet weight swhoed the same seasonal pattern and reached maximum values between May and June. Only blade thickness continued to increase tthrooughout the ovservation period. Blade dissintegration occurred dduring August and September. Reproductive sporophytes occurred throughout the observation period; the greatest frequency of appearance occurred in October (43.8%) and June (37.8%). The blade area covered by sori ranged from 2.4% (Janaury) to 6.1% (August). Meiospore release under laboratory conditions was maximum in May and minimum in July. No meio-spores were released in August Sporulation was not correlated with meristematic growth of nitrogen content How ever, reproductive plants were generally larger and thicker throughout the sporulation period, and had a greater carbort content is spring than nonreproductive plants. Fecundity and reproductive success of female gametophytes were maximum in spring and minimum in winter. The growth of early sporophyte stages in the laboratory was greatest in early spring; however, juvenile macroscopic stages were hardly observed in the field during summer months due to warm water temperatures. “Over-summering” of gamelophytes and / or microscopic sporophytes may account for the annual cycle of Laminaria at its southern limit of distribution.     

LIFETIME REPRODUCTIVE SUCCESS,SELECTION, AND THE OPPORTUNITY FOR SELECTION IN THE WHITE-TAILED SKIMMER PLATHEMIS LYDIA (ODONATA: LIBELLULIDAE)

We present estimates of lifetime reproductive success in Plathemis lydia, a territorial dragonfly. We partition the opportunity for selection into multiplicative episodes using the techniques of Arnold and Wade (1984a, 1984b) and measure selection on several morphological and behavioral characters. For both sexes, variance in survivorship was the largest contribution to variance in lifetime reproductive success. Covariance effects are also strong for both sexes, suggesting considerable non-independence of episodes. Opportunity for selection calculated on a daily basis did not approximate analogous values determined from lifetime reproductive success. Phenotypic characters for which we investigated selection included body mass, hind wing length, first date of reproduction, and (for males) an index of territorial aggressiveness. We failed to find any significant direct targets of selection in either males or females. However, the combined effects of direct and indirect selection on early reproduction were significant for males, acting primarily through increased survivorship and increased time per day spent at the pond. Similarly, females present earlier in the season had shorter interclutch intervals. Partitioning of selection acting on male hind wing length and on aggressiveness reveals relationships between selective episodes, possibly indicative of phenotypic trade-offs between natural and sexual selection through male-male competition for females. Division of selection into episodes is a useful technique for identifying the source of selection. However, ordering effects can bias results, except when episodes occur in strictly chronological sequence. We present a method for circumventing this difficulty.     

REPRODUCTIVE ECOLOGY OF CARYA (JUGLANDACEAE): PHENOLOGY,POLLINATION, AND BREEDING SYSTEM OF TWO SYMPATRIC TREE SPECIES

Observations and experiments on both shagbark (Carya ovata; 2n = 32) and mockernut (C. tomentosa; 2n = 64) hickories in a New Jersey forest were performed over a 2-year period to determine the mechanisms operating both to maintain reproductive fidelity and to regulate fruit initiation. Phenological observations indicated significant differences between the species for almost all vegetative and reproductive characters examined; however, a large amount of overlap was also observed. Pollination experiments indicated that pollen limitation is not a significant factor in reducing fruit set in these anemophilous species. Pollen-ovule ratios ranged from 1 to 25 × 10⁶. Pollen was 80–90% viable at time of shedding. The large surface area of vegetative structures (e.g., leaves) at the time of pollination may retard the flow of pollen into and out of the canopy and thus increase self-pollination. A full diallel cross, replicated 5 times, was made among 8 trees (4 trees of each species) to characterize combining ability and compatibility relationships. All trees were found to be both geitonogamous and xenogamous to varying degrees. A high frequency of putative interploidal cross-compatibility was also observed. Fruits from these interspecific crosses were found to be germinable. Observations on individual trees suggested that dichogamy may help to reduce selfing and promote outcrossing in this breeding system. While most trees exhibited a temporal separation of genders, the trait was found to be quite plastic (i.e., trees switched between protogyny and protandry between years). Pistillate flowers were receptive for all trees within a species during the same general time period; however, pollen shedding varied considerably among trees and between years. Both species appear to be utilizing a broad array of mechanisms in order to maintain reproductive fidelity and adequate fruit set.     

CONTROL OF IN VITRO SEPAL DEVELOPMENT OF EXCISED FLORAL BUDS OF AQUILEGIA (RANUNCULACEAE)

Excised floral buds of Aquilegia formosa Fisch. were grown on a coconut-milk medium containing the minerals and vitamins of Murashige and Skoog, sucrose, and kinetin. The plant growth regulators indoleacetic acid (IAA, 0.5 mg/liter) and gibberellic acid (GA, 2.0 mg/liter) were added singly and in combinations; both were omitted from the control medium. The addition of GA to the basal medium was required to support sepal development on flowers at all phases of development. The formation of stomatal complexes in the epidermis of the sepals occurred only in the presence of GA. Sepals grown in the presence of GA also contained trichoblasts and developing trichomes, while none were formed in the absence of GA. The role of IAA in the development of these idioblasts was not clear but it appeared to have no effect. The hormones GA and IAA had different effects on the growth of the sepals. In the presence of GA the sepals increase in length until comparable with sepals grown in vivo. However, the sepals remained small when GA was omitted from the medium. Upon closer examination of this effect, it was determined that there was a direct proportionality between an increase in cell number in the epidermis and an increase in sepal length. The role of the two hormones in increasing epidermal cell length in sepals was distinct and separate. Exogenous IAA had no effect upon cell division but was required for cell elongation, while GA was required for cell division and had no effect on cell elongation. The GA effect in promoting cell division in the sepals was substantiated by use of autoradiography. If the buds were grown on media with GA, twice as many epidermal cells along the central file incorporated significant amounts of tritiated thymidine. The cell cycle of the epidermal cells of the GA-treated sepals was ca. 8.7 hr in duration and ca. 13.0 hr if GA was deleted from the medium.     

DISTRIBUTION,SEASONALITY AND REPRODUCTIVE PHENOLOGY OF BANGIA ATROPURPUREA (RHODOPHYTA) IN RHODE ISLAND,U.S.A.1

Forty-seven sites along the Rhode Island coastline were sampled on a seasonal basis for the presence of the red alga Bangia atropurpurea (Roth) C. Ag. This species was found to be widely distributed, occurring at 94% of the hard, stable substrates sampled. Bangia populations were most, widespread in the winter (71% of sites) and least frequent in the summer (29% of sites). At one location, three high intertidal populations (average height 101 cm) and three low intertidal populations (average height 14 cm) were sampled monthly for two years. The upper intertidal populations appeared in September and persisted until at least May, whereas the lower populations were ephemeral, appearing for only a few months in late winter. The high intertidal populations were present on 85% of the sampling dates white the lower ones were observed on 25% of the sampling dates. Upper intertidal filaments reproduced exclusively by asexual monospores unlike those of the lower populations which were largely sexual. The maximum diameter of asexual and carpogonial filaments was 120 and 250 nm, respectively. Monosporagenesis was strongly correlated to temperature whereas gametogenesis was strongly correlated to photopriod.     

THE INFLUENCE OF FLOWER COLOR ON OUTCROSSING RATE AND MALE REPRODUCTIVE SUCCESS IN IPOMOEA PURPUREA

Experimental populations of the annual plant, Ipomoea purpurea, composed of individuals belonging to two flower color morphs were studied to determine the effect of flower color on outcrossing rate and reproductive success as a male parent. Analyses of parent and offspring genotypes show that the pigmented and white morphs outcross at similar rates, but that the white morph is favored as a pollen donor. The result suggests that the dynamics of selection occurring at the locus coding for white versus pigmented flowers are more complex than previously believed. Factors such as frequency-dependent outcrossing rates and epistatic effects of the white allele may be operating. The results also suggest that pollinator observations are unreliable indicators of the actual mating system.