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PubMed2002

The formation and function of plant volatiles: perfumes for pollinator attraction and defense.

Plants synthesize and emit a large variety of volatile organic compounds with terpenoids and fatty-acid derivatives the dominant classes. Whereas some volatiles are probably common to almost all plants, others are specific to only one or a few related taxa. The rapid progress in elucidating the biosynthetic pathways, enzymes, and genes involved in the formation of plant volatiles allows their physiology and function to be rigorously investigated at the molecular and biochemical levels. Floral volatiles serve as attractants for species-specific pollinators, whereas the volatiles emitted from vegetative parts, especially those released after herbivory, appear to protect plants by deterring herbivores and by attracting the enemies of herbivores.

Adaptation, Physiological↗
PubMed1999

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.

Cell Polarity↗
PubMed2002

Elaeolenchus parthenonema n. g., n. sp. (Nematoda: Sphaerularioidea: Anandranematidae n. fam.) parasitic in the palm-pollinating weevil Elaeidobius kamerunicus Faust, with a phylogenetic synopsis of the Sphaerularioidea Lubbock, 1861.

A new nematode, Elaeolenchus parthenonema n. g., n. sp., is described from the palm-pollinating weevil Elaeidobius kamerunicus Faust. The new genus is placed in the Anandranematidae n. fam., which, together with the genus Anandranema Poinar et al., 1993, is characterised by nematodes having only a single autotokous generation in the insect host. This is the first report of a member of this superfamily reproducing only parthenogenetically. The development of E. parthenonema and its effect on the weevil host is discussed, along with a phylogenetic synopsis of the families of the Sphaerularioidea Lubbock 1861. The Beddingiidae n. fam. is proposed for Beddingia Blinova & Korenchenko, 1986, comprising the original Deladenus parasites of Hymenoptera that possess both free-living and parasitic amphimictic generations in their life-cycles. This family is considered to have the most primitive type of development in the superfamily.

Animals↗
PubMed2003

Environmental biology: heat reward for insect pollinators.

In neotropical forests, adults of many large scarab beetle species spend most of their time inside the floral chambers of heat-producing flowers, where they feed and mate throughout the night and rest during the following day, before briefly flying to another flower. Here we measure floral temperatures in Philodendron solimoesense (Araceae) in French Guiana and the respiration rates of Cyclocephala colasi beetles at floral and ambient temperatures, and show that the the beetles' extra energy requirements for activity are 2.0-4.8 times greater outside the flower than inside it. This finding indicates that heat produced by the flower constitutes an important energy reward to pollinators, allowing them to feed and mate at a fraction of the energy cost that would be required outside the flower.

Animals↗
PubMed2002

Male fitness of oilseed rape (Brassica napus), weedy B. rapa and their F(1) hybrids when pollinating B. rapa seeds.

The likelihood that two species hybridise and backcross may depend strongly on environmental conditions, and possibly on competitive interactions between parents and hybrids. We studied the paternity of seeds produced by weedy Brassica rapa growing in mixtures with oilseed rape (B. napus) and their F(1) hybrids at different frequencies and densities. Paternity was determined by the presence of a transgene, morphology, and AFLP markers. In addition, observations of flower and pollen production, and published data on pollen fertilisation success, zygote survival, and seed germination, allowed us to estimate an expected paternity. The frequency and density of B. napus, B. rapa, and F(1) plants had a strong influence on flower, pollen, and seed production, and on the paternity of B. rapa seeds. Hybridisation and backcrossing mostly occurred at low densities and at high frequencies of B. napus and F(1), respectively. F(1) and backcross offspring were produced mainly by a few B. rapa mother plants. The observed hybridisation and backcrossing frequencies were much lower than expected from our compilation of fitness components. Our results show that the male fitness of B. rapa, B. napus, and F(1) hybrids is strongly influenced by their local frequencies, and that male fitness of F(1)hybrids, when pollinating B. rapa seeds, is low even when their female fitness (seed set) is high.

Brassica napus↗
PubMed1999

Genomic coalescence in a population of laxmannia sessiliflora (Angiospermae, anthericaceae): an association of lethal polymorphism, self-pollination and chromosome number reduction

A population of Laxmannia R. Br. (Angiospermae, Anthericaceae) near Collie, Western Australia, combines the taxonomically significant sessile inflorescences of L. sessiliflora Dcne. (n = 4) and the derived breeding system of L. ramosa Lindl. (n = 4). It exhibits a polymorphism for seed-aborting lethal equivalents, significant levels of self-pollination and a chromosome polymorphism in which a haploid genome with n = 3 is most frequent. Allozyme analysis indicates that the population is either of hybrid origin or one that has uniquely diverged from a phylogenetic link between the two species. The population is considered to represent a natural demonstration of the phenomenon of genomic coalescence as modelled by James (1992, Heredity, 68, 449-456) in which devices which reduce the number of independently segregating supergenes heterozygous for recessive lethals are elevated to high frequencies by inbreeding. The population also suggests a mechanism whereby dysploid chromosome number reduction may be promoted by natural selection in natural population systems.

Journal Article↗
PubMed1999

History can be more important than 'pollination syndrome' in determining the genetic structure of plant populations: the case of aconitum lycoctonum (Ranunculaceae)

The Aconitum lycoctonum complex is a widespread yellow-flowered group of species found in central and southern Europe. Because of extreme morphological variability, the systematics of this group is confusing, and hybridizations among taxa are often hypothesized. To determine whether hybridization, realized mating system within populations or colonization from different Pleistocene refugia might explain some of the morphological variation, the genetic structure of 19 populations from central and southern Europe was studied using starch gel electrophoresis and 10 enzyme loci, of which eight were polymorphic. A pattern typical of an outcrossing species was expected because A. lycoctonum flowers are adapted to pollination by long-tongued bumblebees. However, heterozygosity was very low (between 0.031 and 0.150), which is atypical of either widespread or outcrossing species. The inbreeding coefficient, FIS, also suggested inbreeding in more than half the populations. Analysis of molecular variance showed that 31% of the genetic variation is found among populations, again suggesting inbreeding. A neighbour-joining tree based on Reynolds's genetic distance showed a clear separation between the central/eastern European populations and the samples from the Iberian peninsula and Alpes Maritimes. These data are consistent with the hypothesized refugia and the phylogeographical histories of several European forest trees. The genetic identity of all populations was very high, suggesting that all investigated populations belong to the same species despite high morphological variability. Hybridization was not supported by the data.

Journal Article↗
PubMed2000

Genetic structure in the nonrewarding, bumblebee-pollinated orchid Calypso bulbosa.

Among- and within-population variation at neutral loci is governed by an interaction between stochastic processes and gene flow. A previous study of pollen dispersal in which the transfer of individually marked pollinia was monitored, indicated not only that populations of the nonrewarding, bumblebee-pollinated orchid Calypso bulbosa are connected by substantial levels of gene flow, but also that seed production may be the result of self-fertilization to a considerable extent. We examined the genetic structure of 21 C. bulbosa populations in northern Sweden by F-statistics analyses of variation at three polymorphic allozyme loci. Four populations each consisted of two or three distinct patches, which also allowed us to evaluate among-patch differentiation. The inbreeding coefficient over all loci within populations was high (FIS=0.283). F-statistics indicated that the level of genetic differentiation among patches within populations varied among populations. FST among patches within populations ranged between -0.021 and 0.119 and was significantly different from zero in two of the populations. There was low to moderate genetic differentiation among populations (FST=0. 072). A Mantel test indicated a positive correlation between geographical and genetic distances among populations, but this correlation was dependent on the difference in allele frequencies between the southernmost population sampled and all other populations. Self-fertilization and substructuring within sampling units (within patches and populations) may have contributed to the high inbreeding coefficients observed in many C. bulbosa populations. Long-distance seed and pollen dispersal may account for the low to moderate genetic differentiation among populations.

Animals↗
PubMed2000

Pollination in the marine realm: microsatellites reveal high outcrossing rates and multiple paternity in eelgrass Zostera marina.

The mating system was examined in two annual populations of eelgrass (Zostera marina), a marine angiosperm displaying subaqueous pollination. Multilocus genotyping using microsatellite DNA markers allowed the assessment of the pollen source based on single progeny as units of observation. Outcrossing was detectable by the presence of non-maternal alleles at one or more of the loci. In outcrossing cases, three microsatellite alleles were present in unripe seeds, consisting of both maternal alleles and the paternal allele composing the triploid primary endosperm. In ripe seeds, only the diploid embryonal genotype was amplifiable by PCR. Two intertidal populations situated in the German Wadden Sea were almost entirely outcrossing (t +/- SE 0.96 +/- 0.03, N=60 and 0.97 +/- 0.029, N=37). Because of the high polymorphism displayed by the eight chosen microsatellites, representing a total of 69 and 76 alleles, the likelihood of erroneously inferring selfing was small (alpha=0.0026 and 0.0007). In order to study the correlation of paternity, the coefficient of relatedness was determined within sibships. Relatedness (r +/- SE) was calculated as 0.357 +/- 0.059 and 0.343 +/- 0.037, indicating multiple paternities within inflorescences. Small amounts of tissue (< or = 0.1 mg) such as the developing seeds of recently fertilized ovules, were sufficient for PCR-amplification. Hence, PCR-based methods, such as multilocus microsatellite genotyping, allow the detection of pollen origin early in the development of progeny. They will be useful to distinguish postfertilization processes such as selective abortion and germination from other prefertilization determinants of plant mating systems.

Crosses, Genetic↗
PubMed1997

Phylogeography and host association in a pollinating seed parasite Greya politella (Lepidoptera: Prodoxidae).

Inferring the historical context of ecological diversification is an important step in understanding the way that population-level processes result in a diversity of species and interactions in communities. We performed a phylogeographic analysis of mitochondrial DNA haplotypes from the pollinating seed parasite Greya politella (Lepidoptera: Prodoxidae) in order to determine the degree to which populations were structured according to geographical location and host-plant association. Ninety-eight individuals were sampled from 29 locations ranging from southern California to western Idaho. Restriction-site variation in 87 individuals (27 populations) was screened by digestion with 11 endonucleases, followed by Southern blotting; 38 restriction-site positions were mapped by double digests. Haplotypes were further defined by generating fragments 251 bases in length via PCR, screening them for sequence variation using denaturing gel gradient electrophoresis (DGGE), and sequencing the resulting variants. Parsimony analysis of the resulting 12 restriction-site and 15 sequence haplotypes indicated strong geographical structuring of populations: (i) most populations were monomorphic for haplotype; (ii) haplotypes from California and the Pacific Northwest (Oregon, Washington and Idaho) formed robust monophyletic groups. Population structure was significant both within and between the two regions, as reflected by NST. Patterns of host-plant association and haplotype phylogeny suggest that populations have recently undergone host-plant shifts in many different parts of the species range, although the direction and number of host shifts cannot be determined at the present level of sampling resolution.

Animals↗
PubMed2003

Genetic analysis of spatial foraging patterns and resource sharing in bumble bee pollinators.

Conservation biologists, evolutionary ecologists and agricultural biologists require an improved understanding of how pollinators utilize space and share resources. Using microsatellite markers, we conducted a genetic analysis of space use and resource sharing at several spatial scales among workers of two ecologically dissimilar bumble bee species (Bombus terrestris and B. pascuorum) foraging in an urban landscape (London, UK). At fine scales, the relatedness of workers visiting small patches of flowers did not differ significantly from zero. Therefore, colonies shared flower patches randomly with other colonies, suggesting that worker scent-marks deterring visits to unrewarding flowers have not evolved as signals benefiting nestmates. To investigate space use at intermediate scales, we developed a program based on Thomas & Hill's maximum likelihood sibship reconstruction method to estimate the number of colonies utilizing single sites. The average number of colonies (95% confidence limits) sending workers to forage at sites of approximately 1 ha in area was 96 colonies (84-118) in B. terrestris and 66 colonies (61-76) in B. pascuorum. These values are surprisingly high and suggested that workers travelled far from their colonies to visit the sites. At the landscape scale, there was little or no genetic differentiation between sites. We conclude that urban habitats support large bumble bee populations and are potentially valuable in terms of bumble bee conservation. In addition, bumble bee-mediated gene flow in plants is likely to occur over large distances and plant-bumble bee conservation requires landscape-scale action.

Alleles↗
PubMed2003

Flexible mating: cross-pollination affects sex-expression in a marine clonal plant.

Many functionally hermaphroditic plants have evolved mechanisms to reduce interference between the sex functions and to optimize reproductive output. In addition to physical mechanisms such as the spatial (herkogamy) and temporal (dichogamy) separation of male and female functions, plasticity in sex expression by means of mate-recognition (flexible mating) could be important in plants with variable access to cross-pollen. This applies particularly to clonal plants because of their modular growth form. We experimentally tested for the effects of pollen source and vegetative neighbourhood on instantaneous sex ratio and seed production in the self-compatible clonal marine angiosperm Zostera marina L. To this end, we exposed the (monoecious) flowering shoots to self and cross-pollen and to neighbourhoods of their own and a mix of foreign vegetative shoots. Flowering shoots that had been exposed to cross-pollen showed (1) a significantly lower female/male ratio at peak flowering, evidence for mate-recognition, and (2) a significantly higher seed set by the end of the season. Both effects were independent of the genetic composition of their vegetative neighbourhood. The results suggest that Z. marina maintains a cryptic self-incompatibility system not previously described for angiosperms with sub-aqueous pollination. In Z. marina, and possibly other self-compatible clonal plant species, mate-recognition could be a means of increasing the out-crossing probability for flowering shoots with central positions within their clone.

Biological Evolution↗
PubMed2004

Cretaceous flowers of Nymphaeaceae and implications for complex insect entrapment pollination mechanisms in early angiosperms.

Based on recent molecular systematics studies, the water lily lineage (Nymphaeales) provides an important key to understanding ancestral angiosperm morphology and is of considerable interest in the context of angiosperm origins. Therefore, the fossil record of Nymphaeales potentially provides evidence on both the timing and nature of diversification of one of the earliest clades of flowering plants. Recent fossil evidence of Turonian age (approximately 90 million years B.P.) includes fossil flowers with characters that, upon rigorous analysis, firmly place them within Nymphaeaceae. Unequivocally the oldest floral record of the Nymphaeales, these fossils are closely related to the modern Nymphaealean genera Victoria (the giant Amazon water lily) and Euryale. Although the fossils are much smaller than their modern relatives, the precise and dramatic correspondence between the fossil floral morphology and that of modern Victoria flowers suggests that beetle entrapment pollination was present in the earliest part of the Late Cretaceous.

Animals↗
PubMed2004

Pollen limitation causes an Allee effect in a wind-pollinated invasive grass (Spartina alterniflora).

It is usually assumed that pollen availability does not limit reproduction in wind-pollinated plants. Little evidence either supporting or contradicting this assumption exists, despite the importance of seed production to population persistence and growth. We investigated the role of pollen limitation in an invasive estuarine grass (Spartina alterniflora), with a manipulative pollen supplementation and exclusion experiment in areas of high population density and at the low-density leading edge of the invasion. We also quantified pollen deposition rates on stigmas and pollen traps along a windward to leeward gradient. We found pollen impoverishment at the low-density leading edge of a large invasion, causing an 8-fold reduction in seed set. We found 9-fold more pollen on stigmas of high-density plants than on those of low-density plants. Pollen deposition rates on stigmas and traps did not increase downwind of low-density plants but did increase downwind of high-density plants and dropped off precipitously across a gap that lacked pollen donors. The delay of appreciable numbers of seed caused by pollen limitation persists for decades until vegetative growth coalesces plants into continuous meadows, and this Allee effect has slowed the rate of spread of the invasion.

Ecosystem↗
PubMed2006

Genetic effects of chronic habitat fragmentation in a wind-pollinated tree.

Habitat fragmentation poses a serious threat to plants through genetic changes associated with increased isolation and reduced population size. However, the longevity of trees, combined with effective seed or pollen dispersal, can enhance their resistance to these effects. The European beech (Fagus sylvatica) dominates forest over large regions of Europe. We demonstrate that habitat fragmentation in this species has led to genetic bottlenecks and the disruption of the species' breeding system, leading to significantly elevated levels of inbreeding, population divergence, and reduced genetic diversity within populations. These results show that, in contrast with the findings of previous studies, forest fragmentation has a negative genetic impact, even in this widespread, wind-pollinated tree. The identification of significant effects of forest fragmentation in beech demonstrates that trees are not at reduced risk from environmental change. This should be accounted for in the management of remaining natural and seminatural forest throughout the world.

Ecology↗
PubMed1982

Simulated and empiric wind pollination patterns of conifer ovulate cones.

Wind tunnel analyses of conifer ovulate cones indicate that the total geometry of the cone enhances the probability of pollen entrapment. Aerodynamic characteristics of cone scale-bract complexes are such that suspended pollen is directed toward the micropyles of attached ovules. Within the taxa examined, there appears to be a preferential entrapment by ovulate cones of pollen of the same species. The data are interpreted as evidence for an aerodynamic reciprocity between wind-suspended pollen and the structure of ovulate cones which increases the frequency of pollination and the potential for fertilization.

Journal Article↗
PubMed1983

Hawkmoth pollination of Mirabilis longiflora (Nyctaginaceae).

A guild composed of very-long-tubed hawkmoth flowers (nectar tubes, 9 cm or more long), belonging to different genera and families, occurs in the American Southwest. Our knowledge of the hawkmoth associates of these flowers is fragmentary. Mirabilis longiflora, a member of the guild with a tube 10.0-10.5 cm long, was found to be visited and pollinated mainly by Manduca quinquemaculata with a proboscis 10.7-11.6 cm long in the Chiricahua Mountains of southeastern Arizona. This example fits in with four other previously reported cases. The long-tongued Man. quinquemaculata is now known to be associated with five species of very long-tongued hawkmoth flowers in the Southwest, and Man. rustica has been found on one of them.

Journal Article↗
PubMed2003

Juvenile nitrogen uptake capacities and root architecture of two open-pollinated families of Picea abies. Effects of nitrogen source and ectomycorrhizal symbiosis.

This study was carried out to find early physiological differences occurring in young seedlings between two contrasting Picea abies open-pollinated families (OPF), one with high- and one with low-growth performance in the field by, determining their N uptake capacities and their root architecture. We used three potential N-sources in forest soil solution, NO3-, NH4+ and amino acids, to establish N uptake rates by the plants, whether or not associated with a fungus isolated from the field and identified as Paxillus involutus. NO3- fluxes were determined locally at the root surface using NO3(-)-selective microelectrodes whereas NH4+ and amino acid (L-glutamate and L-aspartate) uptake rates were calculated from their depletion of the incubation solution by the whole root system. Root systems were digitised in order to determine the number and the length of different root types. In non-mycorrhizal plants, the results showed that the most distinguishing parameters between OPF were NO3- uptake rates measured in the white tip of the secondary roots and the root architecture, with higher values determined in high-growth than in low-growth field performance OPF. The presence of the mycorrhizal fungus decreased NO3- uptake rates in both OPF and had an opposite effect on root architecture by increasing it in low-growth and decreasing it in high-growth field performance OPF, respectively. In non-mycorrhizal plants, NH4+ and amino-acid uptake rates were not different between OPF. Mycorrhizal symbiosis did not change NH4+ uptake rates whereas it increased that of amino acids, specifically that of L-aspartate in the low-growth field performance OPF. Taken together these results suggest that the measurement of local fluxes in roots of young plants could be a good potential tool for the early evaluating of growth capacity of Picea abies OPF.

Amino Acids↗