Genetic diversity and geographic differentiation in Tacca chantrieri (Taccaceae): an autonomous selfing plant with showy floral display

BACKGROUND AND AIMS: Despite considerable investment in elaborate floral displays, Tacca chantrieri populations are predominantly selfing. It is hypothesized that this species might possess considerable spatial or temporal variation in outcrossing rates among populations. To test this hypothesis, genetic variability and genetic differentiation within and among T. chantrieri populations were investigated to find out if they are in agreement with expectations based on a predominantly inbred mating system. METHODS: Genetic diversity was quantified using inter-simple sequence repeats (ISSR) in 303 individuals from 13 populations taken from known locations of T. chantrieri in China, and from one population in Thailand. KEY RESULTS: Of the 113 primers screened, 24 produced highly reproducible ISSR bands. Using these primers, 160 discernible DNA fragments were generated, of which 145 (90.62 %) were polymorphic. This indicated considerable genetic variation at the species level. However, there were relatively low levels of polymorphism at population levels, with percentages of polymorphic bands (PPB) ranging from 8.75 % to 55 %. A high level of genetic differentiation among populations was detected based on different measures (Nei's genetic diversity analysis: G(ST) = 0.5835; AMOVA analysis: F(ST) = 0.6989). Furthermore, based on levels of genetic differentiation, the 14 populations clustered into two distinct groups separated by the Tanaka Line. CONCLUSIONS: High levels of differentiation among populations and low levels of diversity within populations at large spatial scales are consistent with earlier small-scale studies of mating patterns detected by allozymes which showed that T. chantrieri populations are predominantly selfing. However, it appears that T. chantrieri has a mixed-mating system in which self-fertilization predominates, but there is occasional outcrossing. Significant genetic differences between the two distinct regions might be attributed to vicariance along the Tanaka Line. Finally, possible mechanisms of geographic patterns based on genetic differentiation of T. chantrieri are discussed.     

New glycosides of the campesterol derivative from the rhizomes of Tacca chantrieri

Seven new glycosides of the campesterol derivative (24R,25S)-ergost-5-ene-3beta,26-diol (1-7) were isolated from the rhizomes of Tacca chantrieri (Taccaceae). Their structures were determined by extensive spectroscopic analysis, including 2D NMR data, and a few chemical transformations.     

Spirostanol saponins from the rhizomes of Tacca chantrieri and their cytotoxic activity

The rhizomes of Tacca chantrieri have been analysed for steroidal saponin constituents, resulting in the isolation of four new spirostanol saponins (1-4), along with one known saponin (5); their structures were elucidated on the basis of extensive spectroscopic analysis, including 2D NMR, and the results of hydrolytic cleavage. The isolated compounds were evaluated for their cytotoxic activity against HL-60 human promyelocytic leukemia cells.     

The pollination biology of Burmeistera (Campanulaceae): specialization and syndromes

The floral traits of plants with specialized pollination systems both facilitate the primary pollinator and restrict other potential pollinators. To explore interactions between pollinators and floral traits of the genus Burmeistera, I filmed floral visitors and measured pollen deposition for 10 species in six cloud forest sites throughout northern Ecuador. Nine species were primarily bat-pollinated (84-100% of pollen transfer); another (B. rubrosepala) was exclusively hummingbird-pollinated. According to a principal components analysis of 11 floral measurements, flowers of B. rubrosepala were morphologically distinct. Floral traits of all species closely matched traditional ornithophilous and chiropterophilous pollination syndromes; flowers of B. rubrosepala were bright red, lacked odor, opened in the afternoon, and had narrow corolla apertures and flexible pedicels, which positioned them below the foliage. Flowers of the bat-pollinated species were dull-colored, emitted odor, opened in the evening, and had wide apertures and rigid pedicels, which positioned them beyond the foliage. Aperture width appeared most critical to restricting pollination; hummingbirds visited wide flowers without contacting the reproductive parts, and bats did not visit the narrow flowers of B. rubrosepala. Aperture width may impose an adaptive trade-off that favors the high degree of specialization in the genus. Other floral measurements were highly variable amongst bat-pollinated species, including stigma exsertion, calyx lobe morphology, and pedicel length. Because multiple species of Burmeistera often coexist, such morphological diversity may reduce pollen competition by encouraging pollinator fidelity and/or spatially partitioning pollinator's bodies.     

Evolution and homology of bird pollination syndromes in Erythrina (Leguminosae)

Erythrina L. (Leguminosae: Phaseoleae) is a pantropical genus of over 100 species, all of which are either hummingbird or passerine pollinated. Phylogenetic hypotheses based on morphological and chloroplast DNA restriction site characters suggest that shifts from passerine to hummingbird pollination have occurred a minimum of four times in the genus. In hummingbird-pollinated species the inflorescences are held upright, the flowers are arranged radially along the axis, and the narrow standard petal is conduplicately folded to form a pseudotube. In most of the passerine-pollinated species, the inflorescences are held horizontally, the flowers are secund, and the standard petal is open so that the nectar and androecium are easily visible and accessible. Nectar amino acid concentrations and sucrose to hexose ratios are closely associated with pollination mode. Despite the general resemblance in flower and inflorescence morphology among species with the same pollination type, homology assessment reveals that petal morphology and size, and calyx and pollen morphology differ. Morphological characters, even if comprising modifications associated with adaptive pollination systems, therefore provide useful phylogenetic information.     

Predicting the pathway to wind pollination: heritabilities and genetic correlations of inflorescence traits associated with wind pollination in Schiedea salicaria (Caryophyllaceae)

The transition from biotic to abiotic pollination was investigated using Schiedea, a genus exhibiting a remarkable diversity of inflorescence architecture associated with pollination biology. Heritabilities and genetic correlations of inflorescence traits were estimated in gynodioecious Schiedea salicaria (Caryophyllaceae), a species that has likely undergone a recent transition to wind-pollination. Using a partial diallel crossing design, significant narrow-sense heritabilities were detected for inflorescence condensation (h2 = 0.56 to 0.68 in the two sexes) and other traits related to the extent of wind pollination in Schiedea species. Heritabilities were generally higher in hermaphrodites than in females. Strong genetic correlations may constrain the evolution of some inflorescence traits that facilitate wind pollination, such as simultaneous shortening of inflorescence length and elongation of the subtending internode. The presence of significant narrow-sense heritabilities for traits associated with wind pollination suggests, however, that selection for more effective wind pollination in the windy, pollinator-limited environments where S. salicaria grows could lead to the evolution of the highly condensed inflorescences characteristic of other wind-pollinated species of Schiedea.     

The mating game: pollination and fertilization in flowering plants

Recent work has revealed signaling molecules that control pollination, including small peptides that mediate pollen recognition and glycoproteins that support pollen tube growth. The polarized growth of pollen tubes requires a calcium-mediated signal cascade, and cues derived from the haploid and diploid ovule cells guide pollen tubes to the eggs.     

Pollen morphology in relation to floral types and pollination syndromes in Pedicularis (Orobanchaceae)

Floral diversification in the genus Pedicularis (Orobanchaceae) is remarkable among flowering plants. In this genus, floral morphology and pollinator behavior are closely co-adaptive. In the current paper, pollen grains of 23 representative species of Pedicularis mainly from North America, with two species from Japan and two species from China, whose pollination ecology was previously studied, were examined using light microscopy and scanning electron microscopy. Two pollen aperture types and three kinds of exine ornamentation were recognized among these species. In addition, pollen data from previous and the current studies of Pedicularis were integrated and analyzed, together with some pollination characters. There was a significant association between pollen aperture types and corolla types, as well as between pollination syndromes and corolla types. However, there was no association of exine ornamentations with corolla types. The relationships and evolution of this genus were discussed with regards to pollen morphology, corolla types and pollination syndromes.     

The effect of timing of pollination on the mating system and fitness ofKalmia latifolia (Ericaceae)

Plant mating systems are known to vary within species and some immediate ecological factors have been found to be associated with the geographic distribution of selfing. The environmental condition of the maternal plant may influence the production of selfed seed relative to outcrossed seed. This study investigated the effect of late pollination on the mating system of Kalmia latifolia, a long-lived perennial shrub. A 2 × 2 experimental design was used to determine whether reproductive success declines over the course of the flowering season and whether there was an interaction between pollination time (early vs. late in the season) and pollen type (self-fertilized vs. outcrossed). An interaction of this sort would indicate context-dependent fitness of selfed seeds compared to outcrossed seeds and, thus, show an ecological influence over a plant's mating system. Relative fitness was assessed in terms of female reproductive success. Timing of pollination did not affect abortion of outcrossed seeds; however, delay in pollination increased abortion of selfed seeds by 34.7%. Thus, it appears that plants selectively aborted selfed seeds rather than outcrossed seeds and this selection was more intense at the end of the season. An ecological factor such as time of pollination may affect the mating system of K. latifolia.     

Flower morphology, pollination biology and mating system of the complex flower of Vigna caracalla (Fabaceae: Papilionoideae)

Background and Aims

Vigna caracalla has the most complex flower among asymmetrical Papilionoideae. The objective of this study was to understand the relationships among floral characteristics, specialization, mating system and the role of floral visitors under different ecological contexts.

Methods

Five populations were studied in north-western Argentina, from 700 to 1570 m a.s.l. Anthesis, colour and odour patterns, stigmatic receptivity, visitors and pollination mechanism were examined and mating-system experiments were performed.

Key Results

The petals are highly modified and the keel shows 3·75–5·25 revolutions. The sense of asymmetry was always left-handed. Hand-crosses showed that V. caracalla is self-compatible, but depends on pollinators to set seeds. Hand-crossed fruits were more successful than hand-selfed ones, with the exception of the site at the highest elevation. Bombus morio (queens and workers), Centris bicolor, Eufriesea mariana and Xylocopa eximia trigger the pollination mechanism (a ‘brush type’). The greatest level of self-compatibility and autonomous self-pollination were found at the highest elevation, together with the lowest reproductive success and number of pollinators (B. morio workers only).

Conclusions

Self-fertilization may have evolved in the peripheral population at the highest site of V. caracalla because of the benefits of reproductive assurance under reduced pollinator diversity.Key words: Fabaceae, Vigna caracalla, asymmetry, breeding system, complex flowers, elevational gradient, pollination     

蒟蒻薯属(薯蓣科)植物DNA条形码研究

蒟蒻薯属(Tacca)植物种间在形态上差别不大,导致分类上存在一定的困难.DNA条形码是一种利用短的DNA标准片段来鉴别和发现物种的方法.本研究利用核基因ITS片段和叶绿体基因trn H-psbA,rbcL,matK片段对蒟蒻薯属6个种的DNA条形码进行研究,对4个DNA片段可用性,种内种间变异,barcode gap进行了分析,采用Tree-based和BBA两种方法比较不同序列的鉴定能力.结果显示:单片段ITS正确鉴定率最高,片段组合rbcL+matK正确鉴定率最高.支持CBOL植物工作组推荐的条码组合rbcL+matK可作为蒟蒻薯属物种鉴定的标准条码,建议ITS片段作为候选条码.丝须蒟蒻薯Tacca integrifolia采自西藏的居群与马来西亚居群形成了2个不同的遗传分支,且两者在形态上也存在一定的差异,很可能是一个新种.     

利用传粉综合征预测:长瓣兜兰模拟繁殖地欺骗雌性食蚜蝇传粉

在花部进化受传粉者主导这一经典理论影响下,传粉综合征一直被认为是被子植物对应于某些特定传粉者的标志,因此,可以利用传粉综合征来预测传粉者。近年来,这种对应和预测受到多因素影响,以及花部进化理论和传粉者泛化理论的冲击。在本研究中,我们选择长瓣兜兰Paphiopedilum dianthum作为实验材料,来探讨传粉综合征与传粉者的关系以及利用前者预测后者的有效范围。长瓣兜兰具有的一系列特征,同其他依靠假繁殖地欺骗食蚜蝇传粉的兜兰种类相似,包括倒盔状唇瓣,较大的中萼片以及花瓣上的黑色突起和睫状毛,而且长瓣兜兰同这些种类有很近的亲缘关系和相似的生境。根据传粉综合征概念,长瓣兜兰应该是由食蚜蝇传粉,通过模拟繁殖地来欺骗传粉者。为了检验这些预测,我们对长瓣兜兰进行了传粉生物学研究。长瓣兜兰是自交可亲和的物种,不存在自动自交授粉现象,必须依靠昆虫传粉才能结实。结果表明,雌性黑带食蚜蝇Episyrphus balteatus是长瓣兜兰的主要传粉者,并且这种兜兰是通过模拟繁殖地来欺骗食蚜蝇传粉的。根据本实验结果,我们认为传粉综合征只是对应于不同的传粉选择压力而不是简单对应于传粉者种类,而使用传粉综合征预测时还需要考虑生境和演化历史等因素对花部形态的影响,这样才可能得到有效的结果。     

Demographic analysis of delayed mating in mating disruption: a case study with Cryptophelbia illepida (Lepidoptera: Tortricidae)

Laboratory-derived life tables were used to determine the effect of delaying mating of adult female koa seedworm, Cryptophlebia illepida (Butler) (Lepidoptera: Tortricidae), 4 and 6 d on population growth rates. Leslie matrices were developed from the life tables and used to project the effects for approximately four generations. Delay of mating caused a decrease in population growth rate and also resulted in asynchronous population cycling between control (1-d delay) and the delayed treatments. By the fourth generation, the control population began to increase 10 and 14 d before the 4- and 6-d delay treatments, respectively. Increasing the mortality of females during the first 7 d of adult life resulted in a greater reduction of the populations where mating was delayed than in the control populations. This result suggests that even at relatively low levels of natural enemy mortality, there is a synergistic effect when mating is delayed. The implications of these effects on mating disruption management programs are discussed.     

From pollination byLepidoptera to selfing: The case ofDianthus glacialis (Caryophyllaceae)

Pollination of the alpine herbDianthus glacialis was studied in a population in the Swiss Alps in 1991 and 1992. Only one insect species,Zygaena exulans (Lepidoptera), was observed to visit the flowers ofD. glacialis. Pollen loads onZ. exulans indicate that it is an effective pollinator ofD. glacialis. In 1991,Z. exulans frequently visited flowers ofD. glacialis. However, in 1992 almost no visits could be observed. Despite the occurrence of pollinators and the conspicuous flowers ofD. glacialis, there are strong indications that this plant is mainly selfing: (1) anthesis of individual flowers is short (c. one and a half days), (2) protandry, although pronounced in otherDianthus spp., is absent, (3) nectar production is low, (4) odour production is weak, (5) seed production by spontaneous selfing is high, (6) seed set in emasculated flowers is extremely low and (7) the seed/ovule ratio is distinctly higher inD. glacialis than in outcrossing plants.—Selfing inD. glacialis could have evolved under a shortage of pollinators during the glaciation periods. Present levels of cross-pollination byZ. exulans have apparently not been sufficient to reverse the pollination mechanism ofD. glacialis from selfing to outcrossing.     

Predicting phenotype from patterns of annotation

MOTIVATION:Predicting the outcome of specific experiments (such as the growth of a particular mutant strain in a particular medium) has the potential to allow researchers to devote resources to experiments with higher expected numbers of 'hits'. RESULTS: We use decision trees to predict phenotypes associated with Saccharomyces cerevisiae genes on the basis of Gene Ontology (GO) functional annotations from the Saccharomyces Genome Database (SGD) and other phenotypic annotations from the Yeast Phenotype Catalog at the Munich Information Center for Protein Sequences (MIPS). We assess the methodology in three ways: (1) we use cross-validation on the phenotypic annotations listed in MIPS, and show ROC curves indicating the tradeoff between true-positive rate and false-positive rate; (2) we do a literature-search for 100 of the predicted gene-phenotype associations that are not listed in MIPS, and find evidence for 43 of them; (3) we use deletion strains to experimentally assess 61 predicted gene-phenotype associations not listed in MIPS; significantly more of these deletion strains show abnormal growth than would be expected by chance.     

Nonrandom mating in Clarkia gracilis (Onagraceae): a case of cryptic self-incompatibility

In plants capable of both self-fertilization and outcrossing, the selfing rate depends on the proportion of self pollen in pollen loads and on the relative postpollination success of self pollen in siring offspring. While the composition of pollen loads is subject to unpredictable variation, paternity success of self vs. outcross pollen following pollen deposition may be controlled by maternal plants. This study examined postpollination paternity success in Clarkia gracilis ssp. sonomensis, in which deposition of self pollen is common. Pure loads of self and outcross pollen produced similar numbers of mature seeds, but equal mixtures of self and outcross pollen yielded more than three times as many outcrossed offspring as selfed offspring. The finding that the paternity success of self pollen depends on whether it is in competition with outcross pollen helps to explain an earlier finding that the selfing rate in experimental populations was highest when pollinator activity was lowest. Cryptic self-incompatibility allows paternity by self pollen when outcross pollen is unavailable.