Pollen and resource limitation in a gynodioecious species

Differences between plant sex morphs in pollen or resource availability may affect their relative fitness and thereby the sex ratio of dimorphic species. In gynodioecious species, in which hermaphroditic and female plants coexist, a variety of factors (e.g., hermaphrodite self-fertility or rarity or pollinator discrimination against females) might be expected to lead to stronger pollen limitation in females than in hermaphrodites. On the other hand, females have been found to be superior compared to hermaphrodites in low-nutrient conditions. The effects of supplemental hand-pollination and resource addition on the reproductive output of the self-fertile gynodioecious perennial Geranium sylvaticum (Geraniaceae) were tested for several populations that differ in their female frequency (4.4-23.0%). Both pollen and resource availability limited fruit set and the number of seeds produced per plant; however, seed set (i.e., the number of seeds produced per fruit) was limited only by resources. Because pollen limitation in females did not correlate with female frequency, our results suggest that pollen limitation in females does not depend on the frequency of the pollen-producing hermaphrodites. Furthermore, because pollen and resource availability limited reproductive output of both sex morphs, these factors may not contribute significantly to maintenance and evolution of gynodioecy in G. sylvaticum.     

不同居群准噶尔无叶豆果实和种子特性及种子萌发差异

研究准噶尔无叶豆(Eremosparton songoricum) 6个居群间果实和种子特性及种子萌发差异, 以揭示异质生境下准噶尔无叶豆果实和种子的生态适应机制。结果显示: 居群间准噶尔无叶豆的植株距离(F = 2.34, p = 0.03)和植株冠幅(F = 8.49, p < 0.01)存在显著差异, 沙漠北缘E、F居群和沙漠腹地C居群(受人类干扰剧烈)的植株距离和植株冠幅高于沙漠腹地A、B、D居群; 居群间准噶尔无叶豆果实和种子的长度、宽度、厚度、重量存在显著差异, 居群E、F和C的大部分参数显著高于其他沙漠腹地居群; 居群间果实多子性(F = 6.96, p < 0.01)也存在显著差异, 居群C的果实多子性最高((32.50 ± 4.79)%); 萌发结果表明, 居群间新鲜的成熟种子萌发不存在显著差异, 且萌发率都低于15%; 所有居群的大部分种子都存在物理性休眠现象, 人为划破种皮能显著提高种子萌发率, 但在低温(15/5 ℃)条件下, 所有居群的种子萌发率都较低, 说明低温抑制了种子萌发; 经人为划破种皮解除物理休眠后, 种子的休眠没有完全释放, 居群C、E和F (大种子居群)的种子萌发率显著高于居群A、B和D (小种子居群) (F = 30.77, p < 0.01), 说明准噶尔无叶豆种子不仅存在物理性休眠现象, 也可能存在生理休眠现象。不同程度的种子复合休眠可能是准噶尔无叶豆不同居群适应古尔班通古特沙漠的重要生存策略。     

沙丘稀有种准噶尔无叶豆花部综合特征与传粉适应性

植物花部特征进化与传粉适应性一直是进化生态学领域关注的核心问题之一。以古尔班通古特沙漠自然生长的准噶尔无叶豆为对象,对其花部特征和传粉特性进行了野外观察和室内的分析研究。结果表明:种群花期历时21 d,花序花期历时7-12 d,单花花期一般3 d,若遇阴雨天气,花期可延长1-2 d,整个花期龙骨瓣一直保持闭合状态。单花10枚花药在旗瓣微张时已全部完成散粉。准噶尔无叶豆主要靠分泌花蜜、鲜艳的花色以及旗瓣基部的黄色辐射状纹理结构吸引传粉者。准噶尔无叶豆花期的有效传粉者为4种蜂类昆虫,它们的平均访花频率为(7.75±0.57)次·花^-1·d^-1,访花高峰期表现为三峰型: 13:00-14:00,16:00-17:00和19:00-20:00。准噶尔无叶豆人工套袋实验表明该种为自交亲和型,主动自交少见,生殖成功依赖传粉者。胚珠成功受精至果实完全成熟阶段存在自交衰退,柱头角质层结构和花粉刷结构是准噶尔无叶豆在进化过程中形成的减少自交,倾向异交的机制。     

花粉和资源限制对青阳参坐果率的影响

以生长于自然种群的青阳参植株为材料进行补充授粉试验,以人工种植的青阳参植株为材料进行资源限制试验,探讨花粉和资源限制对青阳参坐果率的影响.结果表明:自花授粉、天然授粉和异株异花授粉植株的结实率分别为1.7％、2.25 ％和24％,花粉来源对青阳参坐果存在显著影响;补充施肥和不补充施肥植株的坐果率分别为5.12％和3.1...     

Seed development in the rare cold desert sand dune shrub Eremosparton songoricum and a comparison with other papilionoid legumes

No study has yet been carried out on seed development in a cold desert sand dune papilionoid legume. Thus, our primary aims were to (i) monitor seed development in the cold desert sand dune species Eremosparton songoricum from the time of pollination to seed maturity, and (ii) compare seed development in this species with that in other species of papilionoid legumes. Fruit and seed size, mass and seed moisture content, and seed imbibition, germination, desiccation tolerance and water retention during development (pollination to seed maturity) were monitored in the papilionaceous shrub E. songoricum in the Gurbantunggut Desert of northwest China. The duration of seed development was 40 days. Seeds reached physiological maturity 28 days after pollination (DAP), at which time 58% of them germinated and they had developed desiccation tolerance. Seeds became impermeable 36–40 DAP, when their moisture content was about 10%. The final stage of maturation drying occurred via loss of water through the hilum. The developmental stages and their timing (DAP) in seeds of E. songoricum are generally similar to those reported for other papilionaceous legumes with a water‐impermeable seed coat (physical dormancy). In general, the developmental features of seeds with water‐impermeable coats at maturity do not appear to be specific to habitat or phylogeny.     

Genetic load,nutrient limitation,and seed production in Lupinus texensis (Fabaceae)

The interaction of mating system and nutrient limitation in determining seed production was investigated in the annual, self-compatible plant Lupinus texensis (Fabaceae). Abortion of developing seeds is a major factor limiting seed production in natural populations (17-28%). Selfing rates are generally low (0.02-0.21), suggesting that deleterious recessive genes may be maintained at significant levels in natural populations. The average inbreeding depression associated with seed development is δ = 0.24. Nutrient limitation reduced seed output across experimental treatments by a factor of 0.22 through decreased production of inflorescences, flowers, and ovules, and by a factor of 0.29 through increased abortion of fruits and of seeds within fruits. Competition for resources among fruits increased the frequency of seed abortion. Moreover, a greater proportion of selfed seeds were aborted as the overall abortion rate increased. Estimates of genetic load may therefore only be appropriate if undertaken in the field, and inbreeding depression may vary from year to year simply due to changes in environmental conditions rather than to underlying genetic changes in populations. The existence of inbreeding depression and the high frequency of abortions suggest that selective abortion favoring outcrossed progeny occurs in natural populations of L. texensis.     

RAPD and morphological analysis of the rare plant species Vicia pisiformis (Fabaceae)

The amount and pattern of genetic variation was surveyed in two Swedish and three Czech populations of the rare perennial forest plant Vicia pisiformis. This species has a mainly easterly-continental European distribution and has few and small populations in Sweden. It is classified as 'vulnerable' on the Swedish Red Data list. Seeds from natural populations were collected and grown under controlled conditions in growth chambers. The variation was estimated in growth and fecundity traits and with Random Amplified Polymorphic DNA, RAPD. Low inter- and intra-population variation in RAPD-markers was found using 11 primers, with a similarity index (Wetton) for the families of 0.98. In contrast, multivariate analysis of variance showed significant morphological differences within and between populations. Also in the univariate ANOVAs, a number of the traits showed significant between-and/or within population differentiation. Cluster analysis for the morphological traits and RAPDs (UPGMA) did not structure the variation of families in accordance with their geographical distance. A Mantel test based on comparisons between Mahalonobfs and Jaccard distance for morphological and RAPD data, respectively, did not reveal any significant correlation between the two matrices. It is concluded that if a genetic conservation program is to be applied on Vicia pisiformis , different sampling strategies are needed to capture morphological vs RAPD variation. This is, to our knowledge, the first investigation that compares RAPD and morphological variation in a threatened plant species.     

A rare new species of Polhillia (Genisteae,Fabaceae)

The new species Polhillia ignota Boatwr. is described. This species is known only from two collections, one between Vredenburg and Saldanha and the other close to Porterville. The new species is most similar to P. obsoleta, which is known only from a few localities around Worcester, in its narrow, sericeous leaflets and flowers of equal size, but differs in its flattened mature leaves with larger leaflets (up to ± 12 mm long), longer pseudo-peduncles (up to ± 15  mm long), denser inflorescences (with up to four flowers), shorter pedicels (1–2 mm long) and non-auriculate wing- and keel petals.     

Pollen limitation in three sympatric species ofVaccinium (Ericaceae) in the Upper Ardennes, Belgium

The reproductive success of three co-flowering species ofVaccinium (V. myrtillus, V. vitis-idaea andV. uliginosum) was studied in one heathland of the Upper Ardennes, Belgium, during three years (1988–1990). The purpose was to examine whether pollen limitation, flower position and flowering phenology may influence patterns of fruit set in these three sympatric species. I quantified fruit and seed set following supplementary hand-pollinations and compared this to natural fruit set. On the same plants, I also quantified fruit and seed set in relation to the spatial position of the flowers on the ramet and their temporal sequence of blooming. Hand-pollination had no significant effect on fruit set inV. vitis-idaea andV. uliginosum, but significantly increased seed number per fruit in 1989. InV. myrtillus both fruit and seed set were increased by supplementary pollination, but significantly in only one year. Analyses of position effects revealed that the fruits in the lower positions in the ramet did not mature preferentially and did not contain more seeds inV. uliginosum and inV. vitis-idaea. Flowering phenology also had no significant effect for these species. InV. myrtillus hand-pollinated flowers showed a seasonal decline in seed number, and control (naturally pollinated) flowers showed a seasonal increase in fruit set. Fruit and seed set appear to be pollen-limited rather than resource-limited inV. uliginosum. In the two other species, unfavorable weather (frosts) could be a more important cause of low fruit and seed set.     

Pollen limitation in the endangered Chinese endemic species Sinocalycanthus chinensis

Pollen limitation negatively impacts endangered and endemic plants with small fragmented populations, such as Sinocalycanthus chinensis, an endangered plant endemic to China. In this study, we analyzed the pollen limitation of the S. chinensis Damingshan (DMS) population in 2006, 2009, and 2010, and crossed plants with mates separated by different distances, both within and between populations. The DMS population exhibited strong pollen limitation in fruit set, seed set, and seeds per fruit in 2006, 2009, and 2010. The average accumulated pollen limitation (for fruit set times seeds per fruit) was 0.510 ± 0.180. Progeny crossed with pollen from intermediate neighboring plants within the same population (separated by 30–50 m from pollen recipients) had the lowest fitness. No optimal outcrossing distance was found within the DMS population. Progeny from crosses with the Shunxiwu (SXW) and Daleishan (DLS) populations performed relatively better, while those from crosses with Qingliangfeng (QLF) and Longxushan (LXS) populations performed worse. Compared with average reproductive success, outbreeding depression was found in progeny from crosses with the LXS and QLF populations. Reproductive success from pure self‐pollination indicated S. chinensis is self‐compatible. Geitonogamous selfing increased reproductive success. Based on geitonogamous selfing, the proportion of selfed offspring was relatively high. These results provide basic references for the conservation of this species.     

Pollen limitation and fruit abortion in a declining rare tree,the Eurasian yew (Taxus baccata L.): A reproductive cost of ecological marginality

Populations of rare tree species such as the dioecious and anemophilous yew (Taxus baccata) are especially prone to extinction if they occupy marginal habitats. This is the case of yew populations growing in Mediterranean mountains under dry climate and a severe anthropogenic disturbance regime, which show insufficient regeneration. We examined two of the likely mechanisms driving this population decline. The study was conducted in a central Spanish yew population in 2005 and 2006. On one hand, we tested for the effect of the amount of pollen received by female flowers by means of a pollen addition experiment. On the other hand, we tested for the effect of initial fruit set on abortion and mature fruit production. Finally, we evaluated the effect of the spatial arrangement of male and female yew trees on realized fecundity. The success of fertilization and fruiting in the experimental population was pollen-limited. Female trees aborted ca. 70% of the fruit set in both years and treatments. Fruit set was significantly influenced by the females' neighbourhood, with fecundity decreasing exponentially with distance to the nearest male in both years. Overall, our results indicate that factors associated with ecological marginality have a strong influence on yew performance.     

准噶尔无叶豆片断化居群的遗传变异及克隆多样性

准噶尔无叶豆(Eremosparton songoricum)是豆科无叶豆属小半灌木, 既能开花结实进行有性繁殖, 又可以靠根茎进行无性克隆繁殖, 为国家三级保护植物, 在中国仅片断化分布于新疆古尔班通古特沙漠局部区域。本文采用ISSR分子标记对采自古尔班通古特沙漠腹地及边缘的7个准噶尔无叶豆自然居群共148个个体进行了遗传变异和克隆多样性分析。8个引物共扩增出84个位点, 其中77个为多态性位点, 物种水平上的多态位点百分比PPB为91.67％, Nei's基因多样性指数I为0.3192, Shannon信息指数H为0.3540; 居群水平上的多态位点百分比PPB为58.45％, Nei's基因多样性指数I为0.2248, Shannon信息指数H为0.3270。居群间的遗传分化系数G_ST为0.2978。AMOVA分析表明, 有31.88%的遗传变异存在于居群间, 表明居群间存在显著的遗传分化。克隆多样性分析表明, 居群水平上, 居群G的Simpson多样性指数和均匀度指数最高, 分别为0.9400和0.9885; 居群E最低, 分别为0.8457和0.9021。物种水平上, Simpson多样性指数为0.9858, 均匀度指数为0.9673。本研究结果表明, 和其他荒漠植物相比, 准噶尔无叶豆表现出较高的遗传变异水平和克隆多样性, 这主要与该物种兼性生殖的繁育方式及多克隆起源有关; 而居群间产生了显著的遗传分化则主要由于人为干扰引起的生境片断化和居群减小而导致的基因交流障碍所致。遗传变异水平和遗传结构的研究将为分析准噶尔无叶豆致濒原因及进化潜力提供重要资料, 对该物种保护具有指导意义。     

Two new species of Mimosa (Fabaceae) endemic to Bolivia

Two new species ofMimosa are described:M. woodii (sect.Mimosa), from the central Andean valleys of Bolivia, andM. suberosa (sect.Habbasia), from Serranía Huanchaca in the Noel Kempff National Park in the north east of Santa Cruz Department in eastern Bolivia. The affinities of each are discussed, their distributions mapped, and both species are illustrated.     

Pollen production in anemophilous species of the Poaceae family in Tetouan (NW Morocco)

Total pollen production per inflorescence and per square meter were studied in anemophilous species of the Poaceae family, to determine the relative contribution of each species to the total load of pollen released and to identify the species with the highest potential pollen emission. This was done by calculating the number of pollen grains per flower and per inflorescence and by estimating the density of inflorescences in an area of one square meter. Pollen production per inflorescence varied between 12,000 and 15 million grains, often being higher in the perennial species. Mountainous, grassland, riverside, and littoral areas contributed similarly to the amount of pollen grain production per square meter. Species such as Gaudinia fragilis, Hordeum murinum, Lolium rigidum, and Trisetaria panicea, with high pollen records, were found in all the studied areas. Aerobiological analysis will be undertaken to determine the main pollen season of Poaceae species. The results obtained are of great importance for respiratory health management in this region.     

Spatial effects and rare outcrossing events in Medicago truncatula (Fabaceae)

In order to elucidate the mechanisms underlying the large amount of RAPD polymorphism found in 1990 in a population of the selfing annual Medicago truncatula GAERTN. (Fabaceae), we have analysed most of the individuals (n = 363) from the same population 6 years later using microsatellite loci. We confirm the result of the earlier study, namely that this population is very polymorphic and highly subdivided, with approximately 37% of the variance distributed among subpopulations, only 50 m apart one from another. We use standard F-statistics analyses, linkage disequilibria, minimum spanning network, multilocus assignment tests and spatial autocorrelation analyses to test the hypotheses that spatial structure and outcrossing events are involved in maintaining the large amount of genetic diversity at the level of each subpopulation. Interestingly, fine-scale spatial structure could be observed in only one subpopulation suggesting that other mechanisms are acting elsewhere. To the best of our knowledge, this is the first study of fine spatial genetic structure in a predominantly selfing species.     

Pollen diversity and its implications to the systematics of Poecilanthe (Fabaceae,Papilionoideae, Brongniartieae)

The small South-American genus Poecilanthe has a striking morphological diversity in leaf type, inflorescence, seed morphology and chemical composition. Recent phylogenetic work also shows that Poecilanthe is paraphyletic. Despite the importance of palynology to better understand morphological diversity and potentially inform evolutionary analyses, the pollen morphology of Poecilanthe and most of its close relatives is unknown. This study uses light and electronic microscopy to describe the pollen morphology of eight species of Poecilanthe and the four related genera Ormosia, Harpalyce, Clathrotropis and Cyclolobium. We found pollen grains colpate only in four species of Poecilanthe and Harpalyce brasiliana and colporate pollen grains in the other four Poecilanthe species and the other related genera (Ormosia, Clathrotropis and Cyclolobium). An identification key for pollen of all species is provided. Using principal component analyses (PCA) we found that pollen grains of the Poecilanthe have considerable diversity. However, only limited correspondence between the PCA clusters and the Poecilanthe clades was found, suggesting that pollinic characters do not reflect evolutionary history in this group.