Structure and dynamics of natural populations of polyploid trilliums

To confirm predominant self-pollination in natural populations ofTrillium apetalon (2n=4x=20, SSUU), chromosome constitutions of endosperms (2n=30, SSSUUU) fertilized in nature were analyzed for the patterns of H-segments of cold-treated chromosomes. The endosperms were of two kinds: homo-constitutions in which three chromosomes in each of the ten sets of homologues were of the same patterns of H-segments and hetero-constitutions in which one chromosome in a set of three homologous chromosomes was different from the other two. Out of 30 endosperms, 27 (90%) were of homo-constitutions and only three (10%) were of hetero-constitutions. Since the population consisted of various homokaryotypes in which each of the ten pairs of homologous chromosomes was homozygous for the patterns of H-segments, the endosperms of homo-constitutions were the result of self-pollination, and those of hetero-constitutions were from cross-pollination. Due to pollination tests conducted in two natural populations, many good seeds were found in the fruits from both open-pollinated flowers and those covered with cotton-bags. In striking contrast, no good seeds were found in the fruits from flowers castrated and pollinated in the open-air. An additional evidence of predominant self-pollination and occasional cross-pollination was given by analyzing spatial distribution of plants of various karyotypes in a population.     

Life History Studies on the Genus Trillium (Liliaceae) I. Reproductive Biology of Four Japanese Species

Abstract Four Japanese Trillium (Liliaceae) species which are representative perennial herbs of the temperate deciduous forests— Trillium kamtschaticum (2x), T. apetalon (4x), T. tschonoskii (4x) and T. smallii (6x)—were studied for their reproductive characteristics, e.g., patterns of reproductive resource allocation and reproductive output.
In spite of the differences in ploidy levels (from 2x to 6x), all four species showed very similar reproductive traits. It became evident that in response to the increase in reproductive allocation to total reproductive organs (RA), the number of seeds produced per plant (P_N) clearly increased. This trend is well in accord with the relationship found in four North American species and also several temperate woodland perennial herbs which occur in closed, stable and predictable environments, and possess typical xenogamous breeding systems. Although there is no conspicuous trend between ploidy levels and P_N, one of the significant differences noted in this study was in seed weight, which ranged from 2.93 mg in diploids, to 3.42–3.45 mg in tetraploids, and to 4.47 mg in hexaploids.     

The pollination ecology of Gentiana cruciata (Gentianaceae) -specifics of a Bulgarian population in comparison to Dutch populations

This study deals with the pollination ecology of a population Gentiana cruciata in the Vitosha Mts., SW Bulgaria. Fortyeigth % of flowers bagged at bud stage developed into fruits. Flowers in the investigated population was visited actively by insects. Halictus bees constituted 34.5% of all insect visits. Visits by bumblebees (mainly Bombus hortorum) constituted 18.9% of all insect visits. All open-pollinated flowers set fruit capsules and their seed set was high. The pollination biology of this population (at the south-westem part of the distributional range of the species) is compared to that of populations in The Netherlands (at the north-western margin of the distribution range of the species).     

濒危植物焕镛木的兼性无融合生殖

2001～2002年连续两年在广西环江木论和广西罗城大黄泥的2个焕镛木(Woonyoungia septentrionalis(Dandy)Law)自然种群中,对单性异株的濒危植物焕镛木进行繁育系统测定,对即将开花的雌花花蕾分别进行套袋、套网、人工授粉处理,并用自然授粉雌花作对照,其座果率和结实率统计结果表明:自然授粉、人工授粉、套袋和套网处理的花均能结实,但它们的座果率和结实率存在较大的差异.在两个种群中,人工授粉和自然授粉的总结实率(PERS)均比套袋和套网处理的高,其中人工授粉的最高,套网处理的最低.由此可见,焕镛木既能通过有性生殖方式结实,又能通过无融合生殖方式结实,而且这两种生殖方式获得的种子均能萌发成幼苗,由此断定,焕镛木的繁育系统为兼性无融合生殖.这是首次报道木兰科植物存在无融合生殖现象.     

濒危植物焕镛木的兼性无融合生殖

2001—2002年连续两年在广西环江木论和广西罗城大黄泥的2个焕镛木(Woonyoungia septentrionalis (Dandy) Law)自然种群中,对单性异株的濒危植物焕镛木进行繁育系统测定,对即将开花的雌花花蕾分别进行套袋、套网、人工授粉处理,并用自然授粉雌花作对照,其座果率和结实率统计结果表明：自然授粉、人工授粉、套袋和套网处理的花均能结实,但它们的座果率和结实率存在较大的差异。在两个种群中,人工授粉和自然授粉的总结实率(PERS)均比套袋和套网处理的高,其中人工授粉的最高,套网处理的最低。由此可见,焕镛木既能通过有性生殖方式结实,又能通过无融合生殖方式结实,而且这两种生殖方式获得的种子均能萌发成幼苗,由此断定,焕镛木的繁育系统为兼性无融合生殖。这是首次报道木兰科植物存在无融合生殖现象。     

The role of frugivorous birds in fruit removal and seed germination of the invasive alien Cotoneaster franchetii in central Argentina

Many invasive plant species have fleshy fruits that are eaten by native frugivorous birds which disperse their seeds and may facilitate their germination, playing an important role in plant invasion success. The fleshy‐fruited shrub Cotoneaster franchetii (Rosaceae) is an important invasive alien in the mountainous regions of central Argentina. To determine the role of avian frugivorous in fruit removal of this species, we conducted a frugivore exclusion experiment including bagged and unbagged branches in 75 plants of C. franchetii. At the end of the dispersal period, we compared the percentage of missing fruits (removed by birds + naturally dropped) in unbagged branches with the percentage of naturally dropped fruits in bagged branches. To assess whether any mechanism acting on seeds during their passage through bird guts (de‐inhibition by pulp removal and/or seed scarification) affects seed germination of this species, we compared percentage and speed of germination among seeds obtained from faeces of the native frugivorous Turdus chiguanco, from manually de‐pulped fruits, and from intact fruits. The percentage of missing fruits per shrub in unbagged branches was significantly higher than the percentage of naturally dropped fruits in bagged branches, suggesting that frugivorous birds play an important role in fruit removal of C. franchetii in the study area. Seeds from bird faeces and from manually de‐pulped fruits germinated in higher percentage and faster than seeds from intact fruits. Germination percentage and speed of seeds from manually de‐pulped fruits were significantly higher than those of gut‐passed seeds. These results indicate that T. chiguanco increases and accelerates seed germination of C. franchetii through pulp removal, but not through seed scarification. Overall, our findings indicate that native frugivorous birds facilitate the dispersal and germination success of C. franchetii, likely playing an important role in its invasion throughout the mountainous region of central Argentina.     

Conservation implications of the reproductive ecology of Agalinis acuta (Scrophulariaceae)

Reproductive ecology of Agalinis acuta was investigated by examining potential for self-fertilization before and at anthesis, reproductive output from outcrossed vs. selfed matings, and effects of browsing, plant size, and conspecific plant density on seed and fruit production. These features of a plant species can provide indirect information pertinent to conservation such as patterns and maintenance of genetic diversity, risk associated with inbreeding depression, and changes in pollinator abundance or effectiveness. The species is self-compatible, with 97% of selfed flowers setting fruit; pollinators were not required for reproduction. However, seed set in self-pollinated fruits averaged 17-20% less than that in open-pollinated fruits. Geitonogamous and facilitated selfing are possible throughout anthesis and autonomous selfing is possible late in anthesis as corollas abscise. Delaying self-pollination until after outcrossing opportunities likely limits selfing rates and thus reduces risks associated with inbreeding but allows reproduction in absence of pollinators. Supplementing pollen on open-pollinated flowers yielded no additional seed set over controls. Neither early-season browsing of primary stems nor conspecific plant density had significant effects on number of fruits per plant, on fruit size, or on number of seeds from open-pollinated flowers. Currently, reproduction appears to be high (about 2400 seeds/plant), and future risks due to lack of genetic diversity are likely low.     

A comparative study of the reproductive character and genetic diversity of an autogamous Tylophora matsumurae and its progenitor Tylophora tanakae (Apocynaceae-Asclepiadoideae)

Reproductive character and genetic diversity were investigated for an autogamous species of Tylophora matsumurae endemic to the Ryukyu Islands and its progenitor species T. tanakae. Approximately one-fourth of bagged flowers set fruits in T. matsumurae, although no fruits were obtained from bagged flowers in T. tanakae. In situ pollen tube germination was observed with high frequency in all five populations examined in T. matsumurae. Furthermore, in T. matsumurae, anther sacs were not dehisced even at anthesis. These results suggest the highly autogamous nature of T. matsumurae. No allozymic variation was detected in all seven populations examined in T. matsumurae. The phenogram constructed using the neighbor-joining method based on Nei's unbiased genetic distance indicated that T. matsumurae clustered with the Okinoerabu Island population of T. tanakae. The estimated outcrossing rate of four populations of T. tanakae varied from 0.18 to 0.59. It is probable that T. matsumurae had been derived from the predominantly self-pollinating population of T. tanakae, and rapidly enlarged its distribution area.     

A Study on Pollination Biology of Paeonia suffruticosa subsp. spontanea (Paeoniaceae)

Field observation on pollination in three populations of Paeonia suffruticosa subsp. spontanea in southern Shanxi Province showed that five species of bees in two families and four species of beetles were engaged in pollination. Examination on bodies of these in sects under SEM, and seed set produced by controlled insect-pollination indicated that the bees, especially the species in the genus Andrena were main pollinators and the beetles except those of small size were only fluctuating vectors. Flowers of this taxon are scented and nonectariferous. Flowers attracted bees and beetles mainly by pollen. A study on seed-set in the three populations revealed considerable variation within and among populations. The plants were no apomict and autogamy, but geitonogamy sometimes could produce mature seeds (x＝ 2.86 seeds per carpel). In the population with less flowers (less than 40 flowers), natural seed-set (x＝3.88) was close to the seed-set produced by hand cross-pollination (x = 3.21), but in the population with more flowers(near 100 flowers) natural seed-set (x＝ 2.48) was lower than that by hand cross-pollination (x = 3.21). The seed-set was low for both natural and artificial cross-pollination with only about one forth of ovules developing into seeds.     

矮牡丹传粉生物学的初步研究

对山西省南部矮牡丹3个居群连续两年的野外观察和实验研究表明,共有5种蜂和4种甲虫参 与矮牡丹的传粉。电镜观察和人工控制昆虫传粉试验证明,蜂类,特别是地蜂类是矮牡丹的主要传粉 者,而甲虫类只是一种不稳定的传粉者。矮牡丹花无蜜液,但可散发气味,主要以花粉吸引昆虫。矮牡 丹不存在无融合生殖,也没有自动自花结实现象,但同株异花能产生少量种子,具微弱的自交性。在花 少的居群中自然结实率与人工异交结实率近相等。矮牡丹的结实率低,平均只有近1／4的胚珠发育成种子。     

FACTORS LIMITING FRUIT AND SEED PRODUCTION OF A TEMPERATE SHRUB,STAPHYLEA TRIFOLIA L. (STAPHYLEACEAE)

Staphylea trifolia L., the bladdernut, is a self-incompatible temperate woodland shrub that flowers in May in Illinois. Factors limiting reproduction were studied at four levels: 1) Seeds/fruit. Seed production in open-pollinated fruit was frequently limited by too few fertilized ovules. Seed production in hand-cross-pollinated fruit was limited by resources or dispersal constraints: seed abortion rates were higher in hand-cross-pollinated fruits than in open-pollinated fruits. 2) Fruits/flower and 3) fruits/inflorescence. The number of fruits set and matured per flower and per infloresence in the open-pollinated treatment was limited by the number of flowers naturally cross-pollinated. In hand-cross-pollinated inflorescences, fruit set was not limited by resources even though fruit set was ten times greater than in the open-pollinated treatment. Evidence that resources limited fruit maturation in the hand-cross-pollinated inflorescences was equivocal. In hand-cross-pollinated flowers, fruit set was lowest when cold nights followed pollination, suggesting that cool temperatures limited postpollination physiological processes. 4) Fruits/individual. Early-flowering individuals matured fewer fruits than later-flowering individuals. Within the latter group, fruit production increased with plant size, although a relatively small individual matured the maximum number of fruits. Flowering phenologies and size of individuals varied among patches, resulting in differential reproductive success of patches.     

Self-pollination of Asarum caulescens Maxim. (Aristolochiaceae) in Japan

Abstract Observations in two populations of Asarum caulescens belonging to sect. Asarum indicate that inbreeding predominates becuase (1) no effective pollinator was observed, (2) bagged flowers set fruits with well-swollen seeds, and (3) the behaviour of filaments, changing from recurved to straight posture, results in direct deposition of pollen grains on the stigmas. This result agrees with reports on three other species of sect. Asarum in Europe and North America. We suggest that species of sect. Asarum diverged from an autogamous ancestor.     

Elevation-related variation in the population characteristics of distylous Primula nivalis affects female fitness and inbreeding depression

The population characteristics of distylous species are highly sensitive to stochastic natural selection pressure.Therefore,populations growing under different environmental conditions may vary in floral morph ratios,potentially affecting female fitness and leading to inbreeding depression.However,the variation in offspring quality among populations as a result of inbreeding depression is poorly understood in distylous species.This study investigates variations in plant density,seed mass,seed viabilityfemale fitness,and post-dispersal inbreeding depression in both sexual morphs(long-styled and shortstyled plants)of the distylous Primula nivalis that were subjected to different pollination treatments along an elevational gradient from 1657 to 2704 m a.s.l.Population characteristics(morph plant density and ratio)and fruit set were significantly affected by sexual morph and elevation.Plant density and fruitset frequencies were lower for short-styled than for long-styled plants at 2704 m a.s.l.The seeds from the cross-pollinated flowers of both morphs were higher in quality than those of self-pollinated flowers.The female fitness of seeds from cross-pollinated flowers of both morphs was higher than that of seeds from open-pollinated and self-pollinated flowers.The female fitness of seeds from long-styled flowers was higher than that of seeds from short-styled flowers at all elevations.Inbreeding depression increased with elevation among plants with short-styled flowers but not among those with long-styled flowers.Variation in the elevation-dependent mating system might influence female fitness and affect inbreeding depression in both floral morphs.In conclusion,the low quality of seeds from short-styled flowers at high elevations might decrease short-styled flower frequency,affecting population characteristics.     

Long-term variation in seed mass and seed production in populations of Paris quadrifolia

Seed production of the perennial herb Paris quadrifolia L. (Liliaceae) was investigated in five populations in northern Poland. The long-term seed production per square metre differed significantly among populations and years. Moreover, throughout the 7-year study period, 30% of both whole ripe fruits and seeds alone were predated. Variation in seed mass per fruit in both space and time was significant. Throughout the 7-year study, nearly all the marked individuals produced fruits once every 2 years. The most frequent break between fruiting was 2 years and the longest was 5 years. Only the mean seed mass in fruits of the same individual varied significantly over subsequent years. In the five populations, the number of ovules, number of seeds in the fruit and seed mass varied significantly between populations. However seed/ovule ratio did not differ in fruits in the five populations. The seed mass/number trade-off in fruits was strongly partially correlated when the effect of total seed mass was considered. Breeding experiments suggest that P. quadrifolia has a substantial capacity for both inbreeding and outbreeding. There were no significant differences in the seed/ovule ratio, seed number or seed mass in fruits produced from bagged or control flowers. However, both seed/ovule ratio and number of seeds were significantly lower in fruits from emasculated flowers.     

Forest association and phenology of wild coffee in Kibale National Park, Uganda

A study on the forest association and phenology of wild coffee ( Coffea canephora Pierre) was conducted in Kibale forest, Uganda. Nested quadrats were used to enumerate tree species, including coffee and herbaceous plants associated with forest and coffee stands. A total of 150 coffee trees was marked along transects and monthly scans carried out to score for fruits, flowers, leaves and leaf insect damage. Pre- and post-dispersal predation levels and coffee yield estimates were made by examining fruits from trees, forest floor and seasonal fruit falls into demarcated plots. In the forest, wild coffee stands are associated with low-quality forest types in terms of timber species (about 10.5 canopy species/study site) and low stocking densities of trees ≥ 50 cm d.b.h. (average 38 trees ha⁻¹ for each site) and poor forest regeneration. In the forest, wild coffee reproductive phases overlap with ripening, coinciding with flower bud and flower production. The variable peak ripening season falls between November and April. The wild coffee yields are generally low (average of 3.5 intact fruits 16 m⁻² month⁻¹), with low insect fruit/seed damage (4–19%) but high levels of wastage due to monkeys, bats and birds.     

FLOWER,FRUIT AND SEED ABORTION IN TROPICAL FOREST TREES: IMPLICATIONS FOR THE EVOLUTION OF PATERNAL AND MATERNAL REPRODUCTIVE PATTERNS

Flower, fruit and immature seed abortion was studied in seven self-incompatible species of trees in a tropical lowland semideciduous forest. The species showed considerable variability in fruit and seed set and the rate at which flowers and fruits were aborted. The amount of flower and fruit abortion also varied over time within species. Small samples of open-pollinated flowers in three species showed adequate amounts of pollen on the stigma, but it could not be determined whether the pollen was compatible or incompatible. In a species with multiseeded fruits, the aborted fruits contained significantly fewer seeds than those retained on the plant. Position of fruit within the inflorescence and of seed within the ovary also had a marked effect on abortion: fruits and seeds at certain positions had a higher probability of abortion than those at other positions. Experiments to test the effect of pollen source on abortion were inconclusive. The factors underlying abortions were evaluated in the context of three mutually non-exclusive hypotheses. It is concluded that selection for increased pollen dispersal and uncertainty in paternity of the zygotes are major factors underlying abortions.     

Frugivory and seed dispersal by redwings Turdus iliacus in southwest Iceland

We studied consumption of wild fruits by redwings Turdus thacus coburnt at two sites on the southwest coast of Iceland, just prior to the autumn migration During this period the principal study site offers c 800000 fruits ha⁻¹ most of these are of Empetrum nigrum (c 90% of fresh weight), but fruits of Vaccimum uliginosum. Arctostaphylos uva-ursi, Vaccimum myrtillus and Rubus saxatilis are also present Redwings regularly consumed the fruits of all these species except R saxatilis At both study sites E nigrum fruits were the most important component of the redwing diet (70 - 80% of fruits ingested), followed by V uliginosum (c 20%) Neither species was consumed as predicted on the basis either of overall relative abundance of fruits or of relative frequency of occurrence of fruiting plants in two hundred 0 3 m² plots In another forty 0 3 m² plots, the number of E nigrum fruits consumed over a seven-day penod was not significantly correlated with the number of fruits initially present Empetrum nigrum seed width is positively correlated with fruit size, and the mean width of seeds in droppings suggests that redwings prefer large E nigrum fruits (which have a higher pulp-to-seed weight ratio) to small E nigrum fruits Despite the predominance of E nigrum, redwing droppings tend to contain a mix of seeds of different species, the most frequent combination being E nigrum and V uliginosum     

Mating system parameters at hierarchical levels of fruits, individuals and populations in the Brazilian insect-pollinated tropical tree, Tabebuia roseo-alba (Bignoniaceae)

For many tree species, mating system analyses have indicated potential variations in the selfing rate and paternity correlation among fruits within individuals, among individuals within populations, among populations, and from one flowering event to another. In this study, we used eight microsatellite markers to investigate mating systems at two hierarchical levels (fruits within individuals and individuals within populations) for the insect pollinated Neotropical tree Tabebuia roseo-alba. We found that T. roseo-alba has a mixed mating system with predominantly outcrossed mating. The outcrossing rates at the population level were similar across two T. roseo-alba populations; however, the rates varied considerably among individuals within populations. The correlated paternity results at different hierarchical levels showed that there is a high probability of shared paternal parentage when comparing seeds within fruits and among fruits within plants and full-sibs occur in much higher proportion within fruits than among fruits. Significant levels of fixation index were found in both populations and biparental inbreeding is believed to be the main cause of the observed inbreeding. The number of pollen donors contributing to mating was low. Furthermore, open-pollinated seeds varied according to relatedness, including half-sibs, full-sibs, self-sibs and self-half-sibs. In both populations, the effective population size within a family (seed-tree and its offspring) was lower than expected for panmictic populations. Thus, seeds for ex situ conservation genetics, progeny tests and reforestation must be collected from a large number of seed-trees to guarantee an adequate effective population in the sample.     

Observations on the Reproductive Biology of Miconia calvescens DC (Melastomataceae), an Alien Invasive Tree on the Island of Tahiti (South Pacific Ocean)1

Miconia calvescens DC (Melastomataceae) is a dominant invasive species in the tropical oceanic island of Tahiti (French Polynesia, South Pacific Ocean), where it was introduced as an ornamental plant. Whereas this small tree is sparse in its native range of Central America, it has spread in Tahiti into a wide variety of habitats including native wet forests. The remarkable success of this invasion is due in great part to prolific reproduction: a mature tree can bear up to 220 inflorescences with an average of 1330 flowers/inflorescence, 208 fruits/infructescence and 195 seeds/fruit. Two and a half years of phenological observations in a highly invaded site indicated that three major peaks of flowering occur/year over brief periods: flower anthesis lasted a few days and pollen grain germination suggested a short stigmatic receptivity of only a few hours; no pollinators were observed foraging on flowers during our survey; the production of fruits containing viable seeds in bagged inflorescences showed that self-fertilization can occur; pollen-ovule ratio (log P/O = 2.68) suggested facultative xenogamy; bagged isolated flowers to test for autogamy and style cutting to learn whether apomixis occured or not were not conclusive. The flowering phenology and the breeding system of M. calvescens enable this plant to build up rapidly successful populations from even a single propagule on the island of Tahiti and on other sites of introduction. The vegetation structure of Polynesian native forests compared to Neotropical rain forests probably plays an important role in determining the reproductive success of M. calvescens and could provide a complementary explanation of the biological invasion processes in tropical oceanic islands.     

Pollen tube growth and self-incompatibility in three Ziziphus species (Rhamnaceae)

Self-incompatibility and synchronous protandrous dichogamy have previously been reported in Ziziphus species. In this work, we conducted a comparative analysis of fluorescence microscopy observations of pollen tube growth following controlled cross pollinations of emasculated flowers and self-pollinations of non-emasculated flowers in three Ziziphus species, Z. jujuba, Z. mauritiana and Z. spina-christi, with the aim to determine the type of the self-incompatibility system of each species. In addition, to test whether autonomous self-pollination, parthenocarpy or agamospermy occurs, flowers were emasculated (or not) and covered. Fruit set and seed viability were monitored. The presence of binucleate pollen grains and the cessation of pollen tube growth in the style suggest that the self-incompatibility system operating in the studied Ziziphus species is gametophytically controlled. Controlled self-pollination in Z. mauritiana resulted in fruits that dropped off before maturation, whereas in Z. spina-christi the flowers dropped off one or two days after pollination. Following controlled self-pollination, small fruits lacking viable seeds were obtained in Z. jujuba, probably due to the stimulus provided by pollination (stimulative parthenocarpy). In the cultivar Tamar of Z. jujuba, the relatively high percentage of seedless fruits obtained in emasculated bagged flowers without hand pollination suggests that this cultivar can set seedless fruits without any pollination stimulus.