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PubMed2006

Reproductive biology and mating system estimates of two Andean melocacti, Melocactus schatzlii and M. andinus (Cactaceae).

BACKGROUND AND AIMS: The genus Melocactus comprises 36 species of globose cacti with the most derived traits in the Cereeae tribe. It is the proper study system to examine what are the most derived reproductive strategies within that tribe. This study aims to characterize the reproductive biology and to estimate the mating system parameters of two Andean melocacti, Melocactus schatzlii and M. andinus. METHODS: The reproductive attributes of the two species were described, including floral morphology, anthesis patterns, floral rewards, floral visitors and visitation patterns. Levels of self-compatibility and autonomous self-pollination were estimated by hand-pollination experiments. Mating system estimates were obtained by conducting progeny array analyses using isozymes. KEY RESULTS: The flowers of the two species present the typical hummingbird-pollination syndrome. Despite their morphological resemblance, the two species differ in flower size, pollen and ovule production and anthesis pattern. Their main pollinator agents are hummingbirds, four species in M. schatzlii and one species in M. andinus. Both cacti are self-compatible and capable of self-pollination without the aid of pollen vectors. Population-level outcrossing rate was higher for M. schatzlii (t(m)=0.9) than for M. andinus (t(m)=0.4). At the family level, outcrossing rates for most mothers of M. schatzlii were higher (t(m)>0.8) than for M. andinus (t(m)<0.5). CONCLUSIONS: Although the two cacti are capable of selfing, M. schatzlii is a predominantly outcrossing species, while M. andinus behaves as a mixed-mating cactus. Hummingbirds are the only pollinators responsible for outcrossing and gene flow events in these species. In their absence, both melocacti set seeds by selfing. Based on its low population size, restricted distribution in Venezuela, low rates of floral visits, and high levels of inbreeding, M. andinus is considered to be an endangered species deserving further study to define its conservation status.

Animals↗
PubMed2003

Fig wasp dispersal and the stability of a keystone plant resource in Borneo.

The stability of interactions in remaining rainforest fragments is an issue of considerable concern for conservation. Figs are a pre-eminent tropical keystone resource because of their importance for wildlife, but are dependent on tiny (1-2 mm) species-specific wasps for pollination. To investigate fig wasp dispersal I trapped insects at various heights (5-75 m) in an isolated fragment (ca. 4500 ha) of Bornean rain forest. Fig wasps constituted the majority of captures above the canopy (pollinators 47%, non-pollinators 5%). However, genera were not evenly represented. There were 50% more species of monoecious fig pollinator than there were host species in the fragment, indicating some must have arrived from forests with different assemblages of figs at least 30 km away. Dioecious fig pollinators were poorly represented suggesting more limited dispersal, which could account for higher endemism and vulnerability to catastrophic disturbance in these figs. Diurnal activity and flight height also varied among genera. Most non-pollinating fig wasps were very rare.

Animals↗
PubMed2006

The effects of floral mimics and models on each others' fitness.

Plants that lack floral rewards may nevertheless attract pollinators by mimicking the flowers of rewarding plants. It has been suggested that both mimics and models should suffer reduced fitness when mimics are abundant relative to their models. By manipulating the relative densities of an orchid mimic Disa nivea and its rewarding model Zaluzianskya microsiphon in small experimental patches within a larger population we demonstrated that the mimic does indeed suffer reduced pollination success when locally common relative to its model. Behavioural experiments suggest that this phenomenon results from the tendency of the long-proboscid fly pollinator to avoid visits to neighbouring plants when encountering the mimic. No negative effect of the mimic on the pollination success of the model was detected. We propose that changes in pollinator flight behaviour, rather than pollinator conditioning, are likely to account for negative frequency-dependent reproductive success in deceptive orchids.

Adaptation, Physiological↗
PubMed2006

Sex in advertising: dioecy alters the net benefits of attractiveness in Sagittaria latifolia (Alismataceae).

The flowers and inflorescences of animal-pollinated dioecious plants are generally small and inconspicuous in comparison with outcrossing cosexual species. The net benefits of an attractive floral display may be different for dioecious compared to cosexual populations because dioecious species experience a more severe reduction in pollen delivery when pollinators forage longer on fewer individuals. Here, we develop a model that predicts the decrease in pollen delivery in dioecious relative to cosexual populations from female-female, female-male and male-male visit sequences as the number of individuals visited varies. To evaluate the predictions of our model we conducted a common garden experiment with dioecious and monoecious (cosexual) arrays of the insect-pollinated herb Sagittaria latifolia. We find that, although increasing the advertisements of floral rewards (i.e. increasing floral display) attracts more pollinators to individuals, the probability that these pollinators subsequently deliver pollen to neighbouring plants depends on sexual system. Because the number of individual plants visited per foraging trip did not increase significantly with floral display, the relative pollination success of dioecious versus monoecious populations decreases with increased floral display. We propose that this could explain why dioecy is strongly correlated with reduced floral display among angiosperm species.

Animals↗
PubMed1982

Sources, Fluxes, and Sinks of Nitrogen during Early Reproductive Growth of Maize (Zea mays L.).

A study was designed to (a) identify sources and sinks of N in the maize (Zea mays L.) shoot, by estimating net N fluxes for each of seven parts of the shoot, (b) determine effects of N entering the plant upon fluxes of N absorbed before reproductive growth, and (c) determine the effects of the opaque-2 gene on N fluxes in the maize shoot during early reproductive growth. Plants of a maize hybrid (Pioneer 3369A) and its opaque-2 counterpart (Pioneer L3369) were grown in a greenhouse using nutrient solution/sand culture, with NO(3) (-) as the N source during the vegetative growth phase. Beginning at the time of pollination, the same nutrient regime was continued, except that some plants received no N, and others received 3.75 millimolar (15)N as NO(3) (-)-N.Stalk and leaves were found to be primary N sources for the grain, while shank, husk, and cob acted first as N sinks, then as N sources during reproductive growth. Net fluxes of N for each plant part were estimated by calculating the first derivatives of regression equations used to fit data for N contents of each plant part as functions of time. All parts of the shoot were sinks for exogenous N (absorbed after pollination). Thirty-six days after pollination, the grain contained 60% endogenous N (absorbed before pollination) when 3.75 millimolar NO(3) (-)-N was supplied after pollination. Rates of total N influx to the grain were identical whether or not N was supplied in the nutrient solution during reproductive growth. At 36 days after pollination, less N had accumulated in the grain of the opaque-2 genotype, but otherwise there were no differences in N contents or dry weights of the shoots due to the opaque-2 gene. Absence of N from the rooting medium significantly affected N fluxes throughout the shoot during reproductive growth, but there were no detectable effects of the opaque-2 gene on N fluxes in parts of the plant other than the grain.

Journal Article↗
PubMed2004

An experimental evaluation of self-interference in Narcissus assoanus: functional and evolutionary implications.

Floral traits that reduce self-pollination in hermaphroditic plants have usually been interpreted as mechanisms that limit the genetic consequences of self-fertilization. However, the avoidance of sexual conflict between female and male function (self-interference) may also represent an important selection pressure for the evolution of floral traits, particularly in self-incompatible species. Here, we use experimental manipulations to investigate self-interference in Narcissus assoanus, a self-incompatible species with a stigma-height dimorphism in which the degree of spatial separation between sex organs (herkogamy) differs strikingly between the long- and short-styled morphs (hereafter L- and S-morphs). We predicted that weak herkogamy in the L-morph would cause greater self-pollination and hence self-interference. Experimental self-pollination reduced seed set when it occurred prior to, or simultaneously with, cross-pollination in the L-morph, but only if it occurred prior to cross-pollination in the S-morph. In the field, autonomous self-pollination was greater in the L-morph than the S-morph, but we found no evidence that self-interference reduced maternal or paternal fitness in either morph. One-day-old flowers of the L-morph have reduced stigma receptivity and hence exhibit protandry, whereas stigma receptivity and anther dehiscence are concurrent in the S-morph. This suggests that the two style morphs have alternative strategies for reducing self-interference: dichogamy in the L-morph and herkogamy in the S-morph. These results provide insight into the mechanisms that reduce sexual conflict in hermaphrodite plants and are of significance for understanding the evolution and maintenance of sexual polymorphisms.

Analysis of Variance↗
PubMedDate not supplied

[Sexual compatibility between two types of Hylocerus (Cactaceae)].

There are two types of pitahaya that are cultivated in Yucatan Peninsula of Mexico. They differ mainly in the skin color of the fruit, one of them has a red skin (Uqroo1), while the other has a light yellow skin (Uqroo2) both belong to Hylocereus undatus (Haworth) Britt. & Rose. The yellow skin pitahaya is the sweetest. The studies were conducted using the methods of self pollination and cross pollination, with direct crosses and reciprocal pollination in order to evaluate the effect related to the quantity of fruits that accomplish their growing process. Some characteristic parameters of fruits, thus obtained, were used to detect the possible xenic effect. The control samples were collected from naturally pollinated flowers. The experimental design used was completely random and the experiment was repeated fifteen times. The results revealed that the Uqroo1 turned out to be self-compatible, and their fruits reached one hundred percent of development. On the other hand, Uqroo2 was self-incompatible, that is, it did not accept self pollen. The control samples of both types reached the same weight, and the fruits of the Uqroo2 produced by cross pollination had the same or more weight than the control samples. Several parameters were positively correlated. The coefficient between the number of seeds and the fruit weight was r = 0.84. The highest correlation that was found (r = 0.97) in the fruit weight and the pulp weight within both types. The fruits obtained by cross-pollination maintained the characteristic of the female progenitor. It is suggest intercalate the yellow pitahaya plants with another types or species of pitahaya, other than the Uqroo1.

Cactaceae↗
PubMed2005

60 million years of co-divergence in the fig-wasp symbiosis.

Figs (Ficus; ca 750 species) and fig wasps (Agaoninae) are obligate mutualists: all figs are pollinated by agaonines that feed exclusively on figs. This extraordinary symbiosis is the most extreme example of specialization in a plant-pollinator interaction and has fuelled much speculation about co-divergence. The hypothesis that pollinator specialization led to the parallel diversification of fig and pollinator lineages (co-divergence) has so far not been tested due to the lack of robust and comprehensive phylogenetic hypotheses for both partners. We produced and combined the most comprehensive molecular phylogenetic trees to date with fossil data to generate independent age estimates for fig and pollinator lineages, using both non-parametric rate smoothing and penalized likelihood dating methods. Molecular dating of ten pairs of interacting lineages provides an unparalleled example of plant-insect co-divergence over a geological time frame spanning at least 60 million years.

Animals↗
PubMed2003

Olfactive detection of fig wasps as prey by the ant Crematogaster scutellaris (Formicidae; Myrmicinae).

In the species-specific and obligate mutualism between the fig (Ficus carica) and its pollinator (the fig wasps Blastophaga psenes), a third participant, the ant Crematogaster scutellaris, is a predator of the wasps. Here, we ask how ant workers can rapidly localise such prey, whose availability is limited in time and space. Using a Y-tube olfactometer, we tested ant response to odours emitted by different types of figs (receptive female, ripe female or male figs) and by fig wasps (pollinators or non-pollinators). We demonstrate that ants were significantly attracted only to odours emitted by pollinators, either alone or associated with odours of male figs (releasing wasps). Detection of prey odour by ants is an important trait that can explain their observed high rate of predation on pollinators, and could have important implications on the stability of the fig/fig wasp mutualism.

Animals↗
PubMed2003

Nectarless flowers: ecological correlates and evolutionary stability.

In animal-pollinated flowers, the pollinators cannot detect the presence of nectar before entering flowers, and therefore flowers may cheat by not producing nectar. An earlier model suggested that a mixed strategy of producing nectarful and nectarless flowers would be evolutionarily stable. Here we compare nectarless flowers as a cheating strategy with three competing hypotheses namely "visit-more-flowers", "cross-pollination enhancement" and "better contact". We collected field data on 28 species of plants to test some of the differential predictions of the hypotheses. Nectarless flowers were detected in 24 out of 28 plant species. Correlations of percent nectarless flowers with floral and ecological variables support the cheater flower hypothesis. We further model the cost-benefits of cheating and show that an evolutionary stable ratio of nectarless to nectarful flowers can be reached. The equilibrium ratio is mainly decided by factors associated with pollinator density and pollinator learning.

Animals↗
PubMed2006

Regulation of self-incompatibility by acetylcholine and cAMP in Lilium longiflorum.

Elongation of pollen tubes in pistils of Lilium longiflorum cv. Hinomoto after self-incompatible pollination was here found to be promoted by acetylcholine (ACh) and other choline derivatives, such as acetylthiocholine, l-alpha-phosphatidylcholine and chlorocholinechloride [CCC; (2-chloroethyl) trimethyl ammonium chloride]. Moreover, the elongation was promoted by neostigmine, a potent inhibitor of acetylcholinesterase (AChE; acetylcholine-decomposing enzyme) (EC 3.1.1.7.) and activities of this and choline acetyltransferase (ChAT; acetylcholine-forming enzyme) (EC 2.3.1.6.) in pistils were associated with self-incompatibility. The activity of ChAT was lower after self-incompatible as compared with cross-compatible pollination. Application of cAMP promoted ChAT activities in both cases, whereas activity of AChE in pistils after self-pollination was higher than that after cross-compatible pollination and was suppressed by cAMP in both cases. Furthermore, AChE activity was inhibited by treatment with neostigmine or heating. Our results indicate that the self-incompatibility with self-pollination is due to decrease of ACh and cAMP, causing reduction of ChAT and AC (adenylate cyclase) and concise elevation of AChE and PDE (cAMP phosphodiesterase), and therefore suppressed growth of pollen tubes.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1999

Pollen aperture heteromorphism. Variation in pollen-type proportions along altitudinal transects in Viola calcarata.

Some species produce pollen grains with different aperture numbers within a single individual (pollen aperture heteromorphism). In the pansy Viola diversifolia, aperture number is positively correlated with pollen germination speed, and negatively correlated with viability. In V. calcarata, young five-aperturate pollen grains germinate faster than four-aperturate ones. Heteromorphism could thus be favoured when pollination is unpredictable, as plants produce both very competitive and long-lived pollen grains. Depending on the efficiency of the pollinators, different proportions of pollen types will be optimal. In insect-pollinated species, such as V. calcarata, pollination efficiency generally decreases as elevation increases. We therefore expect a decrease in mean aperture number as altitude increases. This was found in four transects (out of six). Pollinator activity therefore has a potential impact on pollen morphology.

Plant Physiological Phenomena↗
PubMed2000

Cannabis (hemp) positive skin tests and respiratory symptoms.

BACKGROUND: We have noted several patients who had rhinitis and/or asthma symptoms when exposed to Cannabis plants in the summer months. Cannabis plants are common in the Midwest. OBJECTIVES: To examine whether Cannabis might be a clinically important allergen, we determined Cannabis pollination patterns in the Omaha area for 5 years, the prevalence of skin test positivity, and the association with respiratory symptoms. METHODS: Airborne Cannabis (and other weed) pollens were collected using a Rotorod air impactor, and pollen counts were done using a standardized protocol. RESULTS: Measurable Cannabis pollen count was not recorded until the last 2 weeks of July. Peak pollination typically occurred during mid- to late-August, and comprised up to 36% of the total pollen counts. Cannabis pollen was not observed after mid-September. To determine the prevalence of skin test positivity, we added Cannabis to the multi-test routine skin test battery. Seventy-eight of 127 patients tested (61%) were skin test positive. Thirty of the 78 patients were randomly selected to determine if they had allergic rhinitis and/or asthma symptoms during the Cannabis pollination period. By history, 22 (73%) claimed respiratory symptoms in the July through September period. All 22 of these subjects were also skin test positive to weeds pollinating during the same period as Cannabis (ragweed, pigweed, cocklebur, Russian thistle, marsh elder, or kochia). CONCLUSIONS: The strong association between skin test reactivity, respiratory symptoms, and pollination period suggests that Cannabis could be a clinically important aeroallergen for certain patients and should be further studied.

Air Pollutants↗
PubMed1997

Olea europaea airborne pollen in southern Spain.

BACKGROUND: Olea europaea pollen is one of the most abundant constituent pollens in Seville (southern Spain). It is responsible for many documented cases of pollinosis in the area. OBJECTIVE: To contribute to the useful knowledge of Olea europaea for allergists. METHODS: The number of Olea europaea pollen grains in the atmosphere was recorded during 8 consecutive years (1987-1994), using a Cour collector. RESULTS: The concentration of Olea europaea pollen was as high as 250 to 1015 grains/m3 only during 1 or 2 weeks in April and May. Overall annual production of O. europaea pollen alternated between years. The beginning of the main pollination period was related to the mean temperature of the preceding months (February and March). Pollination occurred when the mean temperature in both months was higher than 14 degrees C; conversely it was delayed when the mean temperature was lower. Main pollination period length depended upon both temperature and rainfall during this period: temperatures higher than 19.5 degrees C and absence of rainfall shortened the main pollination period, while lower temperatures (15 to 18 degrees C) together with rainfall rates above 100 mm lengthened it. CONCLUSIONS: Climatic variables such as preceding mean temperature and rainfall impact on pollen anthesis of Olea europaea affect onset and duration of pollination. A consideration of yearly cycles of pollen production as well as these variables should allow pollen forecasting.

Air Pollution↗
PubMed1997

Predominant tree aeroallergens of the Washington, DC area: a six year survey (1989-1994).

OBJECTIVE: A 6-year (1989 to 1994) aerobiologic survey of the Washington DC area was performed to identify predominant area tree pollens, atmospheric concentrations, and peak flowering periods. METHODS: Aeroallergen sampling was conducted using a volumetric rotating-arm impaction Rotorod sampler (Sampling Technologies, Inc, Los Altos Hills, California). RESULTS: The Washington DC pollen calendar may begin as early as January when pollen of the Cupresseacea, Aceracea, Pinaceae, and Betulaceae are observed in small amounts. February through June encompasses the major part of our tree season with considerable overlapping of pollination periods for various trees. The Ulmaceae have two distinct pollinating times with later flowering species of elm pollinating August through October coinciding with ragweed season. April is usually the month with the highest weekly average concentrations. Each year oaks contribute more than 50% of the total tree pollen count followed by pollen of the Pinacea, Cupresseacea, Moracea, and Betuleacea. Times for onset of pollination as well as peak atmospheric concentrations varied from year to year. High production years for some tree aeroallergens are low years for others. CONCLUSION: The Washington DC area is exposed to significant atmospheric concentrations of tree pollen from February through June. Establishing what area tree aeroallergens predominate with respect to their atmospheric concentrations and peak pollinating times is essential for the effective diagnosis and treatment of the tree-allergic patient.

Air Pollutants↗
PubMed2000

Plant invasions--the role of mutualisms.

Many introduced plant species rely on mutualisms in their new habitats to overcome barriers to establishment and to become naturalized and, in some cases, invasive. Mutualisms involving animal-mediated pollination and seed dispersal, and symbioses between plant roots and microbiota often facilitate invasions. The spread of many alien plants, particularly woody ones, depends on pollinator mutualisms. Most alien plants are well served by generalist pollinators (insects and birds), and pollinator limitation does not appear to be a major barrier for the spread of introduced plants (special conditions relating to Ficus and orchids are described). Seeds of many of the most notorious plant invaders are dispersed by animals, mainly birds and mammals. Our review supports the view that tightly coevolved, plant-vertebrate seed dispersal systems are extremely rare. Vertebrate-dispersed plants are generally not limited reproductively by the lack of dispersers. Most mycorrhizal plants form associations with arbuscular mycorrhizal fungi which, because of their low specificity, do not seem to play a major role in facilitating or hindering plant invasions (except possibly on remote islands such as the Galapagos which are poor in arbuscular mycorrhizal fungi). The lack of symbionts has, however, been a major barrier for many ectomycorrhizal plants, notably for Pinus spp. in parts of the southern hemisphere. The roles of nitrogen-fixing associations between legumes and rhizobia and between actinorhizal plants and Frankia spp. in promoting or hindering invasions have been virtually ignored in the invasions literature. Symbionts required to induce nitrogen fixation in many plants are extremely widespread, but intentional introductions of symbionts have altered the invasibility of many, if not most, systems. Some of the world's worst invasive alien species only invaded after the introduction of symbionts. Mutualisms in the new environment sometimes re-unite the same species that form partnerships in the native range of the plant. Very often, however, different species are involved, emphasizing the diffuse nature of many (most) mutualisms. Mutualisms in new habitats usually duplicate functions or strategies that exist in the natural range of the plant. Occasionally, mutualisms forge totally novel combinations, with profound implications for the behaviour of the introduced plant in the new environment (examples are seed dispersal mutualisms involving wind-dispersed pines and cockatoos in Australia; and mycorrhizal associations involving plant roots and fungi). Many ecosystems are becoming more susceptible to invasion by introduced plants because: (a) they contain an increasing array of potential mutualistic partners (e.g. generalist frugivores and pollinators, mycorrhizal fungi with wide host ranges, rhizobia strains with infectivity across genera); and (b) conditions conductive for the establishment of various alien/alien synergisms are becoming more abundant. Incorporating perspectives on mutualisms in screening protocols will improve (but not perfect) our ability to predict whether a given plant species could invade a particular habitat.

Animals↗
PubMed1997

Molecular organization of a gene in barley which encodes a protein similar to aspartic protease and its specific expression in nucellar cells during degeneration.

The nucellar cells of barley undergo progressive degeneration after ovule fertilization. This degeneration is a characteristic of programmed cell death. Increasing evidence has indicated that proteases are important regulators of programmed cell death in animals. We have cloned and characterized a barley gene which encodes an aspartic protease-like protein and is specifically expressed in nucellar cells during degeneration. The gene contains eight exons and seven introns and encodes a polypeptide of 410 amino acid residues. The deduced polypeptide is characterized by having two aspartic protease catalytic site motifs, the Asp-Thr-Gly-Ser in the N-terminal and Asp-Ser-Gly-Ser in the C-terminal region, and two other regions nearly identical to two regions of plant aspartic proteases. However, it shares < 20% overall sequence identity with the known plant aspartic proteases, and does not contain a 'prosequence' or a 'plant-specific insert' which are characteristics of plant aspartic proteases. We have named this aspartic protease-like protein 'nucellin'. In northern analyses nucellin transcripts were most abundant in ovaries 3-4 days after pollination, but only marginally detectable before pollination or 10 days after pollination. RNA in situ hybridization showed that before pollination the nucellin gene was expressed at a very low level only in a cluster of nucellar cells close to the embryo sac at the chalazal end, but after pollination it was highly expressed in most nucellar cells surrounding the entire embryo sac. Furthermore, no nucellin transcripts were detectable in anther, leaf, or root tissue. The temporal and spatial pattern of the nucellin gene expression is synchronal with nucellar cell degeneration and thus, nucellin may be involved with nucellar cell death.

Amino Acid Sequence↗
PubMed2004

The influence of floral display size on selfing rates in Mimulus ringens.

Pollinators often visit several flowers in sequence on plants with large floral displays. This foraging pattern is expected to influence the rate of self-fertilization in self-compatible taxa. To quantify the effects of daily floral display on pollinator movements and selfing, we experimentally manipulated flower number in four replicate (cloned) arrays of Mimulus ringens (Scrophulariaceae), each consisting of genets with unique combinations of homozygous marker genotypes. Four display classes (two, four, eight and 16 flowers) were present in each array. Pollinator visitation rate per flower and seed set per fruit were unaffected by display. However, flower number strongly influenced the frequency of within-plant pollinator movements, which increased from 13.8% of probes on two-flower displays to 77.6% of probes on 16-flower displays. The proportion of within-plant movements was significantly correlated with selfing (r = 0.993). The increase from 22.9% selfing on two-flower displays to 37.3% selfing on 16-flower displays reflects changes in the extent of geitonogamous self-pollination. We estimate that approximately half of all selfing on 16-flower displays resulted from geitonogamy. Selfing also varied dramatically among fruits within display classes. Nested ANOVA indicates that differences among flowers on two-flower ramets accounted for 45.4% of the variation in selfing, differences among genets accounted for 16.1% of the variation, and statistical and sampling error accounted for 38.5% of the variation. Differences among flowers within ramets may reflect the order of sequential floral probes on a display.

Crosses, Genetic↗