bluuebunny/crossref_metadata_2025 huggingface dataset:
Effectiveness of bats as pollinators of Stenocereus stellatus (Cactaceae) in wild, managed in situ, and cultivated populations in La Mixteca Baja, central Mexico
Authors: Arias‐Cóyotl Ethel , Stoner Kathryn E. , Casas Alejandro
Published: February 2008

Stenocereus stellatus is an endemic, self‐incompatible, columnar cactus found in central Mexico where many of its wild populations have been fragmented. As an economically important species of fruit‐producing cactus, S. stellatus occurs in wild, managed in situ, and cultivated populations. The objectives of this study were to determine the effective pollinators of S. stellatus, to compare pollinator visits and reproductive parameters among the three types of populations, and to determine if nectar feeding‐bats are moving among populations. Effective pollinators were the nectarivorous bats Choeronycteris mexicana, Leptonycteris curasoae, and L. nivalis. Fewer total visits per flower per night and fewer visits by Choeronycteris were observed in cultivated populations, while the opposite pattern was observed for Leptonycteris. One aggressive interaction was filmed in which Choeronycteris was physically displaced by Leptonycteris, and Choeronycteris visits were significantly affected by Leptonycteris visits. Cultivated populations received more pollen grains and had more fruit set. Variation in pollinator visits between different populations and the consequent effects on reproductive success were likely a result of competition between bat species, and differences in foraging and in sensitivity of bat species to human populations. Three marked L. curasoae traveled 15 km from their roosting site to their foraging area, and one visited cultivated and managed populations, suggesting that this species may be particularly important in moving pollen among populations.
Role of accelerated style senescence in pathogen defense
Authors: Valdivia Elene R. , Cosgrove Daniel J. , Stephenson Andrew G.
Published: February 2008

Plants, like animals, suffer from a variety of diseases that are transmitted via their sexual organs. In many species, the flowers senesce rapidly after pollination or fertilization. In ongoing studies of the impacts of a transposon insertional mutation in the gene that encodes the most abundant isoform of a major group‐1 pollen allergen of maize, we found that pollen tubes with the mutant allele grow significantly slower in vivo than pollen with the wild‐type allele. Here, we report that under field conditions, maize silks (styles) pollinated with pollen bearing the slower‐growing mutant allele take significantly longer to senesce, and the resulting ears (infructescences) have dramatically higher incidence of “fungal ear rot” disease than silks pollinated with pollen bearing the wild‐type allele. Because ear rot fungi gain access to the developing ear by growing on and through the silks, we propose that accelerated senescence of silks after fertilization is a defense against pathogens such as those causing ear rot. In addition, we divided the silks on each ear into two halves and experimentally varied the type of pollen (wild type, mutant, unpollinated) that was placed onto each half of the silks. Senescence of unpollinated silks was accelerated when ovaries on the other half of the ear were fertilized.
Inbreeding effects on blossom volatiles in Cucurbita pepo subsp. texana (Cucurbitaceae)
Authors: Ferrari Matthew J. , Stephenson Andrew G. , Mescher Mark C. , De Moraes Consuelo M.
Published: February 2008

Self‐pollination by plants gives rise to inbreeding depression. There is increasing recognition that plant inbreeding can have significant implications for interactions between plants and other organisms, including insects and pathogens. Many of these interactions are mediated by plant‐derived volatiles, but the effects of inbreeding on volatile production have not previously been investigated. We examined variation in flower volatile production by the wild gourd Cucurbita pepo subsp. texana as a function of inbreeding, sex of the flower, and maternal line. We compared first‐generation selfed progeny to outcrossed progeny to assess variation in blossom volatiles due to mating system. Our data indicate that self‐pollination reduces total volatile production and changes the relative composition of individual compounds released by C. pepo subsp. texana blossoms. These findings have potentially important implications for interactions between C. pepo subsp. texana and its pollinators and herbivores—including diabroticite cucumber beetles, which vector the bacterial pathogen Erwinia tracheiphila—because previous studies have shown that a number of the individual compounds that vary with inbreeding level can influence insect behavior. We also found significant differences between the volatile profiles of male and female flowers and across maternal families.
Are differences in breeding mechanisms and fertility among populations contributing to rarity in Grevillea rhizomatosa (Proteaceae)?
Authors: Gross C. L. , Caddy H. A. R.
Published: February 2008

Plant breeding systems are seldom studied across the breadth of a species' range. For many systems, this precludes an informed assessment of the evolutionary biology of a species, particularly of the factors that shape fecundity. Grevillea rhizomatosa is a threatened species of shrub known only from a 7 × 8 km area and c. 2000 plants in northern New South Wales, Australia. The species reproduces asexually from rhizomatous suckers, and fruit are only produced in a few populations. Over two flowering seasons, we investigated the extent of sexual reproduction and the mechanisms of infertility in five populations that span the range of the species. Seed were produced in three of the five populations. The breeding system varied among populations from obligate outcrossing to facultative outcrossing to fully sterile. Fruit to flower ratios were below 0.13 in the fertile populations but within the range found in other species of Grevillea. Pollinator limitation was not linked to infertility. Stigmatic opening and receptivity were functional in all populations. Interpopulation crosses using fertile pollen failed to recover fertility in an infertile population. A breakdown in female and male fertility mechanisms was found including a fault in the mechanical release of pollen from anthers, <10% viable pollen, and a post‐pollen‐deposition event that prevents fertile pollen from effecting seed‐set. In the infertile populations pollen was not released from anthers, resulting in flowers projecting barren pollen‐presenters. Sexually reproducing populations are threatened by the incursion of asexual forms that may be favored by frequent disturbance from wild‐fires.
Traits of invasives reconsidered: phenotypic comparisons of introduced invasive and introduced noninvasive plant species within two closely related clades
Authors: Muth Norris Z , Pigliucci Massimo
Published: February 2008

In attempting to determine the traits associated with invasive plant species, ecologists have often used species native to the invaded range as “control species.” Because many native species themselves are aggressive colonizers, comparisons using this type of control do not necessarily yield information relevant to distinctions between invasive and noninvasive species. Here we implement an alternative study design that compares phenological, architectural, size, and fitness traits of several introduced invasive species to introduced noninvasive species within two genera of Asteraceae (CrepisandCentaurea). While there were many significant differences between the genera, there were few shared attributes among invasive or noninvasive congeners, even for traits as seemingly important as the number of inflorescences produced and the size of seed heads. Instead, the results suggest that differences in invasiveness between closely related species is better explained as the result of complex trait interactions and specific introduction histories.
Pinus baileyi(sectionPinus, Pinaceae) from the Paleogene of Idaho, USA
Authors: Erwin Diane M , Schorn Howard E
Published: February 2008

Pinus baileyifrom the Paleogene of Idaho was initially related to the bristlecone pineP. longaeva(subgen.Strobus, sect.Parrya, subsect.Balfourianae) from western North America. Unlike the centromucronate condition inP. longaeva,P. baileyicones have raised umbos that are excentromucronate, i.e., the mucro positioned in the upper umbo field above the keel. Cone size and scale morphology shows thatP. baileyimore closely resembles excentromucronate pines of subsects.HalepensesandPinussensuGernandt et al. (2005,Taxon54: 29–42), but is most similar toP. resinosa, P. kesiya, andP. massonianaof subsect.Pinus. Morphologically,P. baileyiresembles the fossil speciesP. princetonensisandP. arnoldiifrom the Eocene Princeton Chert, British Columbia, Canada.Pinus baileyiextends the western North American range of ovulate cones resembling subsect.Pinusfrom the middle Eocene of British Columbia, Canada and Washington, USA to the Oligocene of Idaho, USA.Pinus baileyi,and possiblyP. princetonensisandP. arnoldii, indicates the presence of early populations of subsect.Pinus‐type pines in the western cordillera of North America, raising the possibility thatP. resinosaandP. tropicalismay have evolved from this group.
High interpopulation genetic differentiation and unidirectional linear migration patterns in Myricaria laxiflora (Tamaricaceae), an endemic riparian plant in the Three Gorges Valley of the Yangtze River
Authors: Liu Yifei , Wang Yong , Huang Hongwen
Published: February 2008

Myricaria laxiflora is restricted to the riverbanks of the Yangtze River valley and will be completely lost owing to the construction of the Three Gorges Dam. Genetic diversity and structure of nine natural and one ex situ populations were investigated using amplified fragment length polymorphisms (AFLPs). A moderate level of gene diversity was found in natural populations, while the ex situ population had the highest. The F statistics calculated by different approaches consistently revealed a high genetic differentiation among natural populations, contributing >45% of the total gene diversity. The Bayesian‐based analysis differentiated nine independent populations in accordance with the sites sampled. Estimates of gene flow by FST and coalescent‐based simulation analysis indicated a restricted recurrent gene exchange among populations (Nm = 0.290–0.401), whereas genetic distance‐based clustering and coalescent‐based assignment analyses revealed significant genetic isolation among populations. The migration pattern in M. laxiflora is best explained by a classical metapopulation model, but with a unique unidirectional direction underlined by hydrochoric force that drove dispersal of seeds and propagules from upstream toward downstream populations. Previous efforts in preserving genomic integrity in ex situ conservation were evaluated, and the results provide valuable information to formulate conservation guidelines for successfully reintroducing M. laxiflora to the wild.
Female compensation through the quantity and quality of progeny in a gynodioecious plant, Geranium maculatum (Geraniaceae)
Authors: Chang Shu‐Mei
Published: February 2008

One of the major evolutionary trends in flowering plants is the evolution of unisexual flowers (male or female) from perfect flowers. This transition has occurred repeatedly in many taxa and has generated a wonderful array of variation in sexual expression among species. Theoretical studies have proposed a number of mechanisms to explain how this level of variation could be maintained in natural systems. One possible mechanism is the female compensation hypothesis, which predicts that female mutants require an increase in their seed fitness in order to invade a hermaphroditic system. Using Geranium maculatum, I tested this hypothesis and showed that female mothers produced more and larger seeds than hermaphroditic mothers even though they were indistinguishable in their vegetative traits and the flower production. Seeds from females were also more likely to germinate and produced seedlings with larger above‐ and belowground biomass. These seedlings were more likely to flower than those from hermaphrodites in at least one of the two populations studied. Combined, these results indicated that females in G. maculatum did compensate for their loss of male function by producing more and better seeds than hermaphrodites. This provides a mechanism for the maintenance of female plants in this species.
A quantitative synthesis of pollen supplementation experiments highlights the contribution of resource reallocation to estimates of pollen limitation
Authors: Knight Tiffany M , Steets Janette A , Ashman Tia‐Lynn
Published: February 2008

Our understanding of pollen limitation depends on a realistic view of its magnitude. Previous reviews of pollen supplementation experiments concluded that a majority of plant species suffers from pollen limitation and that its magnitude is high. Here, we perform a meta‐analysis and find evidence that publication bias, experimental design, and the response variable chosen all influence the magnitude of pollen limitation. Fail‐safe numbers indicate that publication bias exists for some measures of pollen limitation; significant results are more likely to be published and therefore available for review. Moreover, experiments conducted on only a fraction of a plant's flowers and reproductive episodes report ~8‐fold higher effect sizes than those on all flowers produced over the entire lifetime, likely because resource reallocation among flowers and across years contributes to estimates of pollen limitation. Studies measuring percentage fruit set report higher values of pollen limitation than those measuring other response variables, such as seeds per fruit, perhaps because many plant species will not produce fruits unless adequate pollen receipt occurs to fertilize most ovules. We offer suggestions for reducing the bias introduced by methodology in pollen supplementation experiments and discuss our results in the context of optimality theory.
Phylogenetic analysis of the grape family (Vitaceae) based on three chloroplast markers
Authors: Soejima Akiko , Wen Jun
Published: February 2008

Seventy‐nine species representing 12 genera of Vitaceae were sequenced for the trnL‐F spacer, 37 of which were subsequently sequenced for the atpB‐rbcL spacer and the rps16 intron. Phylogenetic analysis of the combined data provided a fairly robust phylogeny for Vitaceae. Cayratia, Tetrastigma, and Cyphostemma form a clade. Cyphostemma and Tetrastigma are each monophyletic, and Cayratia may be paraphyletic. Ampelopsis is paraphyletic with the African Rhoicissus and the South American Cissus striata nested within it. The pinnately leaved Ampelopsis form a subclade, and the simple and palmately leaved Ameplopsis constitutes another with both subclades containing Asian and American species. Species of Cissus from Asia and Central America are monophyletic, but the South American C. striata does not group with other Cissus species. The Asian endemic Nothocissus and Pterisanthes form a clade with Asian Ampelocissus, and A. javalensis from Central America is sister to this clade. Vitis is monophyletic and forms a larger clade with Ampelocissus, Pterisanthes, and Nothocissus. The eastern Asian and North American disjunct Parthenocissus forms a clade with Yua austro‐orientalis, a species of a small newly recognized genus from China to eastern Himalaya. Vitaceae show complex multiple intercontinental relationships within the northern hemisphere and between northern and southern hemispheres.
Allometric theory and the mechanical stability of large trees: proof and conjecture
Authors: Niklas Karl J. , Spatz Hanns‐Christof
Published: February 2008

Recent allometric theory has postulated that standing leaf mass will scale as the 3/4 power of stem mass and as the 3/4 power of root mass such that stem mass scales isometrically with respect to root mass across very large vascular plant species with self‐supporting stems. We show that the isometric scaling of stem mass with respect to root mass (i.e., MS ∝ MR) can be derived directly from mechanical theory, specifically from the requirement that wind‐induced bending moments acting at the base of stems must be balanced by a counter‐resisting moment provided by the root system to prevent uprooting. This derivation provides indirect verification of the allometric theory. It also draws attention to the fact that leaf, stem, and root biomass partitioning patterns must accommodate the simultaneous performance of manifold functional obligations.
Post‐dispersal embryo development, germination phenology, and seed dormancy in Cardiocrinum cordatum var. glehnii (Liliaceae s. str.), a perennial herb of the broadleaved deciduous forest in Japan
Authors: Kondo Tetsuya , Sato Chihiro , Baskin Jerry M. , Baskin Carol C.
Published: February 2008

In an investigation of seed germination in Cardiocrinum cordatum var. glehnii, embryos in fresh seeds in October were underdeveloped and did not grow until September of the following year. Then, they grew rapidly and had fully elongated by early November. In the second spring after dispersal, radicles emerged under snow in late March and after snowmelt in April. Cotyledons emerged soon after radicles. In several laboratory experiments, embryos grew at 15°/5°C (light 12 h/ dark 12 h) following 25°/15°C. Radicles emerged from seeds with fully elongated embryos at 5°–15°C after cold stratification at 0°–5°C. Cotyledons emerged in 2 wk from seeds with a radicle at 15°/5°C to 30°/20°C. Although seeds require c. 18–19 mo after dispersal to germinate in nature, under controlled conditions, they required only 9 mo with a sequence of 25°/15°C → 15°/5°C → 0°–5°C → 15°/5°C. This is practical knowledge for propagation of plants from seeds. GA3 treatment partially substituted for the high temperature requirement. Based on dormancy‐breaking requirements, the seeds have deep simple morphophysiological dormancy (MPD). A literature review of seed dormancy in taxa of Liliaceae s. str. showed that phylogenetic position in this case is not a good predictor of level of MPD.
Relaxed pollinator‐mediated selection weakens floral integration in self‐compatible taxa ofLeavenworthia(Brassicaceae)
Authors: Anderson Ingrid A. , Busch Jeremiah W.
Published: February 2008

Natural selection should favor the integration of floral traits that enhance pollen export and import in plant populations that rely upon pollinators. If this is true, then phenotypic correlations between floral traits should weaken in self‐fertilizing groups that do not require pollinator visitation to produce seed. We tested this hypothesis inLeavenworthia, a plant genus in which there have been multiple independent losses of the sporophytic self‐incompatibility system found throughout the Brassicaceae. In particular, we conducted phylogenetically independent contrasts of floral trait correlations between two pairs of self‐incompatible (SI) and self‐compatible (SC) sister taxa. In support of the hypothesis that pollinator‐mediated selection integrates floral traits, we found that both SCLeavenworthiataxa have weaker overall floral correlations in comparison to sister taxa that rely upon pollinators. The two independently derived SCLeavenworthiaflowers have significantly weaker stamen–petal or pistil–petal correlations, respectively, whereas the stamen–pistil correlation remains constant. These patterns suggest that relaxation of pollinator‐mediated selection weakens the integration of traits associated with pollen export and import. The retention of high stamen–pistil correlations in the SC taxa ofLeavenworthiafurther implies that the integration of these traits is either constrained or maintained by selection favoring the successful transfer of pollen within flowers to secure self‐pollination.
Effects of an exotic plant and habitat disturbance on pollinator visitation and reproduction in a boreal forest herb
Authors: Totland Ørjan , Nielsen Anders , Bjerknes Anne‐Line , Ohlson Mikael
Published: February 2008

The invasion of exotic species into natural habitats is considered to be a major threat to biodiversity, and many studies have examined how exotic plants directly affect native plant species through competitive interactions for abiotic resources. However, although exotics can have potentially great ecological and evolutionary consequences, very few researchers have studied the effect of exotics on the interactions between plants and their mutualistic partners, such as pollinators, and none have reported on such impacts in logged and undisturbed boreal forest ecosystems. Here we show how experimental introductions of an exotic plant species (Phacelia tanacetifolia Bentham) affect pollinator visitation and female reproductive success of a native plant (Melampyrum pratense L.) in recently disturbed (i.e., logged) and in undisturbed boreal forest habitats. The presence of Phacelia significantly increased the number of bumble bees entering plots in both habitat types. However, the exotic species had a strong negative impact on the visitation rate to the native species in both habitat types. Despite this negative impact on pollinator visitation, the exotic had no effect on female reproductive success of the native species in any habitat. Our results show that seed production may be more robust than pollinator visitation to exotic invasion, irrespective of habitat disturbance history.
Reproductive biology of three fern species may contribute to differential colonization success in post‐agricultural forests
Authors: Flinn Kathryn M.
Published: February 2008

Because selfing enables a single individual to reproduce in a new location, the ability to self‐fertilize should enhance plants' capacity for colonization. This study examined whether selfing ability correlated with successful migration in three fern species, Dryopteris carthusiana, Dryopteris intermedia, and Polystichum acrostichoides, which vary in their ability to colonize forests on abandoned agricultural lands in central New York, USA. Polystichum acrostichoides is much more frequent in forests that were never cleared for agriculture, D. carthusiana is more frequent in forests that developed on former fields, and D. intermedia is equally frequent in the two forest types. To test the hypothesis that better‐colonizing species and post‐agricultural forest populations have greater selfing ability, I assessed the sporophyte production of gametophytes grown in isolation and in pairs of varying relatedness. Dryopteris carthusiana had the highest reproductive success and selfing ability and P. acrostichoides the lowest. These results support the hypothesis that selfing may facilitate colonization in these species. They also exemplify the general pattern that polyploid fern species have higher rates of self‐fertilization than related diploids, as the allotetraploid D. carthusiana had greater selfing ability than both diploid species.
Reproductive biology of the dioecious Canary Islands endemic Withania aristata (Solanaceae)
Authors: Anderson Gregory J. , Bernardello Gabriel , Opel Matthew R. , Santos‐Guerra Arnoldo , Anderson Mona
Published: February 2008

We confirmed functional dioecy of Withania aristata via field and greenhouse studies. Male flowers are significantly larger. Female flowers bear stamens with no pollen; males bear 220 000 grains. Stigmata of male flowers senesce in buds. Anatomical observations confirm more ovules in females and an ovarian nectary in both sexes. We detected nectar in female flowers in the greenhouse but found no nectar in males. Thus, males offer pollen and females nectar. Females bear large numbers of fruits and, infrequently, male plants bear few significantly smaller fruits with few seeds. Outcrosses of females (self crosses impossible without pollen) yielded fruits in young buds, older buds, and open flowers. Self crosses of male flowers succeeded only with very young buds. Although functionally dioecious, this species manifests self‐compatibility; however, no fruits are produced autonomously. Bee species (Lassioglossum, Amegilla, Apis) visit flowers and mature buds. Bud visits in which bees force petal tips apart, coupled with self‐compatibility, may explain infrequent fruit on males. Thus, dioecy in W. aristata seems to have evolved from self‐compatible ancestors, that leaky dioecy may have been favored during colonization, and, that despite autogamy and a low floral visition rate, this endemic enjoys a high rate of reproductive success.
Multiple pollinator visits to Mimulus ringens (Phrymaceae) flowers increase mate number and seed set within fruits
Authors: Karron Jeffrey D. , Mitchell Randall J. , Bell John M.
Published: February 2008

The timing and effectiveness of pollinator visitation to flowers is an important factor influencing mating patterns and reproductive success. Multiple pollinator probes to a flower may increase both the quantity and genetic diversity of progeny, especially if single probes deposit insufficient pollen for maximal seed set or if the interval between probes is brief. When pollen carryover is limited, sequential pollen loads may also differ markedly in sire representation. We hypothesized that these conditions help explain high levels of multiple paternity in Mimulus ringens fruits. We documented all bee visits to individual flowers, quantified resulting seed set, and determined paternity for 20 seeds per fruit. Most (76%) flowers received multiple probes, and the interval between probes was usually <30 min. Flowers probed multiple times produced 44% more seeds than flowers probed once. All fruits were multiply sired. Flowers receiving a single probe averaged 3.12 outcross sires per fruit, indicating that single probes deposit pollen from several donors. Multiple paternity was even greater after three or more probes (4.92 outcross sires), demonstrating that sequential visits bring pollen from donors not represented in the initial probe.
The taxonomic value of fruit wing types in the order Apiales
Authors: Liu Mei (Rebecca) , Plunkett Gregory M. , Lowry Porter P. , Wyk Van Ben‐Erik , Tilney Patricia M.
Published: February 2008

This study shows that structural data, when carefully examined, can provide valuable characters for delimiting monophyletic groups and can complement DNA with observable features to recognize and circumscribe taxa. In the angiosperm order Apiales, traditional classification has relied heavily (often exclusively) on fruit characters. Recent molecular systematic studies, however, provided a radically different picture of relationships, calling into question the utility of fruit characters. We have studied fruit anatomy from 18 genera (Annesorhiza, Asteriscium, Astrotricha, Choritaenia, Dasispermum, Elaeoselinum, Heptaptera, Hermas, Heteromorpha, Laretia, Molopospermum, Myodocarpus, Pachypleurum, Peucedanum, Polemanniopsis, Polylophium, Rouya, and Tordylium) that represent all major taxonomic groups of Apiales characterized by winged fruits and the full range of wing types. Fruit anatomy closely corresponded with the phylogenetic position of these genera, as suggested by molecular studies. Fruit features of taxonomic importance include developmental origin of the wings, carpel shape, presence of vittae, woodiness of the endocarp, position of crystals, and type of carpophores. Despite the long history of recognizing umbellifers as a “natural group,” few studies have been able to provide structural characters to help circumscribe the clades identified by molecular data. The interpretations presented are an important step toward erecting a stable system of classification for this difficult family.
Impact of mate availability, population size, and spatial aggregation of morphs on sexual reproduction in a distylous, aquatic plant
Authors: Brys Rein , Jacquemyn Hans , Hermy Martin
Published: February 2008

In distylous, self‐incompatible plants, clonal propagation, unbalanced floral morph frequencies, and reduced population size can interfere with the functioning of distyly by compromising legitimate intermorph pollinations, resulting in reduced reproductive output. Here, we examined the mating system and the impact of mate availability, population size, and spatial aggregation of morphs on reproductive output in the distylous, clonal, aquatic plant Hottonia palustris. Controlled pollinations under greenhouse conditions detected no spontaneous selfing without the action of a pollen vector (autonomous autogamy) and demonstrated very low fruit and seed development after self‐pollination. Intermorph (legitimate) crossings resulted in high reproductive output in both floral morphs (long‐ and short‐styled individuals), whereas intramorph (illegitimate) crossings decreased fruit and seed development by more than 50%, indicating that the species has partial intramorph‐incompatibility. In natural populations, small population size and increasing deviation of floral morph frequencies negatively affected reproductive outcome. Individuals of the majority morph type developed significantly fewer fruit and seeds than individuals of the minority morph type. This rapid decline in fecundity was symmetrical, indicating that regardless of which morph was in the majority, the same patterns of negative frequency‐dependent mating occurred. Increasing spatial isolation between compatible morphs significantly reduced fruit and seed set in both morphs similarly. This study provides clear indications of frequency‐ and context‐dependent mating in natural populations of a distylous plant species.
Old fronds serve as a vernal carbon source in the wintergreen fern Dryopteris intermedia (Aspleniaceae)
Authors: Tessier Jack T. , Bornn Matthew P.
Published: February 2008

Maintaining green leaves beyond the growing season has been hypothesized to benefit plants by supplying either a nutrient or a carbon source. Understanding such ecophysiological aspects of plants will help us to appreciate how a species functions in its environment and predict how it might be affected by future changes in that environment. The wintergreen fern species Dryopteris intermedia does not retranslocate nitrogen and phosphorus from old fronds in spring, but photosynthesis does take place in the old fronds during this season. To determine if carbon fixed in the old fronds is translocated to other parts of the plant, we labeled old fronds with 13C via photosynthetic uptake and examined old fronds, new fronds, fine roots, and rhizomes for 13C content 1 day and 1 month after labeling the old fronds. Vernally fixed carbon was translocated to the new fronds but not significantly to the below ground tissues. Old fronds in this species, therefore, serve as a carbon source for vernal growth of new fronds. This is the first study in which a fern was labeled with 13C to track vernally fixed carbon from old fronds to the rest of the plant in a wintergreen species. Future research should examine the precise timing of this carbon movement and examine other species for a similar or contrasting strategy.
On the origin of the sweet‐smelling Parma violet cultivars (Violaceae): wide intraspecific hybridization, sterility, and sexual reproduction
Authors: Malécot Valéry , Marcussen Thomas , Munzinger Jérôme , Yockteng Roxana , Henry Max
Published: February 2008

Parma violets are reputed for their double, fragrant flowers and have been cultivated for centuries in Europe. However, due to a rather atypical morphology their taxonomic affinity has not been clarified. Authors have proposed an origin from three possible species, Viola alba, V. odorata, or V. suavis, or a hybrid origin. Using both ITS sequence variation and allozyme variation in 14 putative loci, we showed that the Parma violet cultivars have their origin within Viola alba and that they are best included in the Mediterranean subsp. dehnhardtii. There is no trace of interspecific hybridization. However, the cultivars appear to have a single origin in a wide hybrid within V. alba, involving parental plants from the eastern and western Mediterranean region; historical literature sources seem to indicate Turkey and Italy, respectively. The Parma violet cultivars possess high levels of allozyme heterozygosity and to some extent also within‐individual ITS sequence variation. Losses of heterozygosity and within‐individual ITS sequence variation in some of the cultivars indicate subsequent rare events of sexual reproduction, presumably through cleistogamous seed set. We unambiguously identify the closest wild relative of this group of cultivars, allowing growers to develop new selection procedures, and show a peculiar molecular process associated with human selection.
How to determine sapling buckling risk with only a few measurements
Authors: Jaouen Gaëlle , Alméras Tancrède , Coutand Catherine , Fournier Meriem
Published: February 2008

Tree buckling risk (actual height/critical buckling height) is an important biomechanical trait of plant growth strategies, and one that contributes to species coexistence. To estimate the diversity of this trait among wide samples, a method that minimizes damage to the plants is necessary. On the basis of the rarely used, complete version of Greenhill's model (1881,Proceedings of the Cambridge Philosophical Society4(2): 65–73), we precisely measured all the necessary parameters on a sample of 236 saplings of 16 species. Then, using sensitivity (variance) analysis, regressions between successive models for risk factors and species ranks and the use of these models on samples of self‐ and nonself‐supporting saplings, we tested different degrees of simplification up to the most simple and widely used formula that assumes that the tree is a cylindrical homogeneous pole. The size factor had the greatest effect on buckling risk, followed by the form factor and the modulus of elasticity of the wood. Therefore, estimates of buckling risk must consider not only the wood properties but especially the form factor. Finally, we proposed a simple but accurate method of assessing tree buckling risk that is applicable to a wide range of samples and that requires mostly nondestructive measurements.
Density and seed set in a self‐compatible forb, Penstemon digitalis (Plantaginaceae), with multiple pollinators
Authors: Zorn‐Arnold Barbara , Howe Henry F.
Published: February 2008

Seed production may be limited because flowers do not get enough suitable pollen or because plants lack the resources to make seeds. We used replicated plantings to test factors that influence effects of bumblebee behavior on pollen limitation, as measured by the difference in seed set between hand‐ and naturally pollinated flowers, of Penstemon digitalis in patches of four to 41 flowering individuals. Seed set per flower was 376% higher in the largest as compared with the smallest Penstemon patches. This positive density dependence reflects activity of long‐tongued bees, which (1) have higher effective density as patch size increases, (2) visit greater proportions of plants as patch size increases, and (3) visit smaller proportions of flowers per visited plant as patch size increases. Our results suggest that economics of flight and maneuverability of large, long‐tongued bumblebees lead them to transfer more pollen between than within Penstemon plants in large patches. Density of smaller, short‐tongued bumblebees was not positively associated with Penstemon seed set, but these bees may be important pollinators at low plant densities. Our experimental system indicates a clear positive relationship between activity of effective pollinators and seed set in a species capable of pollinating itself.
Effects of self‐pollination and outcrossing with cultivated plants in small natural populations of American ginseng, Panax quinquefolius (Araliaceae)
Authors: Mooney Emily H. , McGraw James B.
Published: February 2008

For rare plants, self‐pollination and inbreeding can increase in small populations, while unusual levels of outcrossing can occur through restoration efforts. To study both inbreeding and outcrossing, we performed experimental pollinations using Panax quinquefolius (American ginseng), a wild‐harvested plant with a mixed mating system. For inbreeding, plants were either cross‐pollinated within the population or self‐pollinated, which resulted in a higher proportion of seeds from self‐pollinated flowers. For outcrossing, wild plants were either cross‐pollinated within the population or with cultivated plants from West Virginia or Wisconsin. Offspring of all crosses were followed for 4 yr. Two‐yr‐old seedlings from self‐pollination had 45% smaller leaf areas and 33% smaller heights relative to those from cross‐pollination. Leaf area is a positive predictor of longer‐term survival in wild populations. Our results suggest inbreeding depression, which is unexpected in this self‐fertile species. Seedlings from crosses with cultivated plants had 127% greater leaf area and 165% greater root biomass relative to outcrosses within the population. The accelerated growth suggests genetic differences between wild and cultivated populations, but outbreeding depression may not appear until later generations. Assessment of the ultimate fitness consequences of introducing cultivated genotypes requires monitoring over longer time periods.
Sporophytic inbreeding depression in mosses occurs in a species with separate sexes but not in a species with combined sexes
Authors: Taylor Philip J. , Eppley Sarah M. , Jesson Linley K.
Published: February 2008

Inbreeding depression is a critical factor countering the evolution of inbreeding and thus potentially shaping the evolution of plant sexual systems. Current theory predicts that inbreeding depression could have important evolutionary consequences, even in haploid‐dominant organisms. To date, no data have been reported on inbreeding depression in moss species. Here, we present data on the magnitude of inbreeding depression in sporophytic traits of moss species with contrasting breeding systems. In Ceratodon purpureus (Ditrichaceae), a moss species with separate sexes, self‐fertilizations between sibling gametophytes (intergametophytic selfing) significantly reduced fitness in two of four traits quantified, with seta length and capsule length having inbreeding coefficients significantly different from zero, resulting in a cumulative inbreeding depression that was also significantly greater than zero (δ = 0.619 ± 0.076). In hermaphroditic Funaria hygrometrica (Funariaceae), there was no evidence of inbreeding depression in seta length, spore number, capsule mass, or capsule length resulting from sporophytes generated by self‐fertilization within an individual (intragametophytic selfing), and cumulative inbreeding depression was also not different from zero (δ = 0.038 ± 0.022). These results provide evidence that, despite haploid dominance, inbreeding depression can be expressed at the diploid stage in mosses and may have implications for the evolution and maintenance of combined versus separate sexes in mosses.
Molecular phylogenetics of tribe Poranthereae (Phyllanthaceae; Euphorbiaceae sensu lato)
Authors: Vorontsova Maria S. , Hoffmann Petra , Maurin Olivier , Chase Mark W.
Published: February 2008

Novel insights into the evolutionary history of a taxonomically complex tropical plant group were gained in this study using DNA sequence data. A molecular phylogenetic analysis of the newly circumscribed and expanded tribe Poranthereae (Phyllanthaceae) is presented. Sampling included 97 accessions for 63 of c. 120 species. Largely congruent results have been obtained from nuclear ribosomal ITS and plastid matK sequences. These analyses support the recognition of Andrachne and Leptopus as distinct genera. The deceptively similar Andrachne section Phyllanthopsis, Andrachne ovalis, and Leptopus decaisnei are separate lineages to be segregated. Zimmermannia and Zimmermanniopsis are embedded in Meineckia; Oreoporanthera is embedded in Poranthera; and Archileptopus is embedded in Leptopus. Andrachne section Pseudophyllanthus is polyphyletic, the two Madagascan endemics emerging as a sister clade to Meineckia. The noncontiguous distributions of Andrachne sensu lato and Leptopus sensu lato were found to be the result of separate evolutionary histories of morphologically similar clades, whereas Andrachne sensu stricto and Meineckia remain geographically disjunct. Actephila and Leptopus are sisters with a sympatric distribution in humid Asia. Presence of petals appears to be plesiomorphic for the tribe. Petals are reduced in Actephila and Oreoporanthera and lost in the Meineckia clade.
Potomacanthus lobatus gen. et sp. nov., a new flower of probable Lauraceae from the Early Cretaceous (Early to Middle Albian) of eastern North America
Authors: von Balthazar Maria , Pedersen Kaj Raunsgaard , Crane Peter R. , Stampanoni Marco , Friis Else Marie
Published: February 2008

A charcoalified fossil flower, Potomacanthus lobatus gen. et sp. nov., is described from the Early Cretaceous (Early to Middle Albian) Puddledock locality, Virginia, USA. Internal floral structure was studied using nondestructive synchrotron‐radiation x‐ray tomographic microscopy (SRXTM). The flower is bisexual and trimerous. The perianth consists of two whorls of tepals. The androecium has two whorls of fertile stamens. Anthers open by two distally hinged valves. The gynoecium consists of a single carpel that is plicate in the style and ascidiate in the ovary and contains a single pendant ovule. The fossil flower shares many similarities with flowers of extant Lauraceae and is unlike flowers of other families of Laurales. However, the fossil flower also differs in detail from all extant or fossil Lauraceae, particularly in configuration of the androecium. The new taxon, together with previously described but more fragmentary material from the Puddledock locality, provides the earliest fossil record of plants more closely related to Lauraceae than to any other extant family. It reveals several derived morphological characters that are potential synapomorphies among extant representatives of the family Lauraceae and contributes to the growing evidence for an early diversification of Laurales before the end of the Early Cretaceous.
Analysis of substage associations in prophase I of meiosis in floral buds of wild‐type Arabidopsis thaliana (Brassicaceae)
Authors: Stronghill Patti E. , Hasenkampf Clare A.
Published: February 2008

We developed an improved cytological protocol for producing high quality, light microscope images of plant meiotic chromosomes. Because the technique works on species with small genomes and thick microsporocyte cell walls, it should be useful for studying the wild relatives of Arabidopsis and other eudicots with small genomes. Combining this improved fixation protocol with our new analysis of associated substages in floral buds, we can unambiguously assign individual meiotic cells to particular substages of prophase I in Arabidopsis thaliana, even for difficult distinctions such as that between late zygotene or early diplotene. In this report we provide the first estimate of the individual duration of the zygotene and pachytene substages (4.8 h and 10.0 h, respectively) in A. thaliana. We also have examined the diffuse substage of prophase I and report that during this post‐pachytene substage, nuclei retain the association of homologous nucleolus organizer regions and homologous centromeres, despite the generally diffuse chromatin and generally unpaired chromosome regions. Additionally, we have observed that centromeric regions of the chromosomes of diffuse‐stage nuclei are highly condensed, more so than those of any other substage of prophase I.
Sex chromosomes in flowering plants
Authors: Ming Ray , Wang Jianping , Moore Paul H. , Paterson Andrew H.
Published: February 2008

Sex chromosomes in dioecious and polygamous plants evolved as a mechanism for ensuring outcrossing to increase genetic variation in the offspring. Sex specificity has evolved in 75% of plant families by male sterile or female sterile mutations, but well‐defined heteromorphic sex chromosomes are known in only four plant families. A pivotal event in sex chromosome evolution, suppression of recombination at the sex determination locus and its neighboring regions, might be lacking in most dioecious species. However, once recombination is suppressed around the sex determination region, an incipient Y chromosome starts to differentiate by accumulating deleterious mutations, transposable element insertions, chromosomal rearrangements, and selection for male‐specific alleles. Some plant species have recently evolved homomorphic sex chromosomes near the inception of this evolutionary process, while a few other species have sufficiently diverged heteromorphic sex chromosomes. Comparative analysis of carefully selected plant species together with some fish species promises new insights into the origins of sex chromosomes and the selective forces driving their evolution.
Visitation, effectiveness, and efficiency of 15 genera of visitors to wild radish,Raphanus raphanistrum(Brassicaceae)
Authors: Sahli Heather F. , Conner Jeffrey K.
Published: February 2008

Plant–pollinator interactions are one of the most important and variable mutualisms in nature. Multiple pollinators often visit plants and can vary in visitation rates, pollen removal and deposition, and spatial and temporal distribution, altering plant reproduction and patterns of pollinator‐mediated selection. Although some visitors may not be effective pollinators, pollinator effectiveness is rarely estimated directly as seed set resulting from a single visit by each taxon visiting generalist plants. For two years, effectiveness of visitors to wild radish,Raphanus raphanistrum, was quantified by counting seeds set and pollen grains removed as a result of a single visit. We calculated a pollinator's importance to plant reproduction as the product of visitation rate and single‐visit seed set, and regressed pollinator body size on pollen‐removal and on seed set effectiveness. Although pollinators differed in effectiveness and visitation rates, pollinator importance was primarily determined by visitation rates. In contrast to similar 2‐yr studies, pollinator assemblage composition varied little, suggesting pollinator‐mediated selection can be consistent across years for this generalist. Larger pollinators were more effective than smaller at effecting seed set, but body size was a poor predictor of pollen removal ability. Instead, pollen‐removal effectiveness may be more influenced by foraging behavior than size.
Duodichogamy and androdioecy in the Chinese Phyllanthaceae Bridelia tomentosa
Authors: Luo Shixiao , Zhang Dianxiang , Renner Susanne S.
Published: February 2008

Flowering plants commonly separate male and female function in time, but rarely are the two stages synchronized within and among individuals. One such temporal mating system is duodichogamy in which each plant produces two batches of male flowers that are temporally separated by a batch of female flowers, with within‐individual synchrony and among‐individual asynchrony to ensure mating partners. Duodichogamy is known only from a few species in four genera in unrelated families. We report on duodichogamy in the Chinese tree species Bridelia tomentosa (Phyllanthaceae), a common colonizer of disturbed habitats. In three populations monitored over 2 yr, most trees flowered in the order male → female → male, and resting periods between flowering bouts precluded selfing almost completely. Individuals flowered for several weeks, with the onset of flowering slightly asynchronous among trees. Pollination was by flies, and experimental pollen supplementation of a subset of a tree's flowers did not increase fruit set, suggesting high levels of insect visitation and possible resource limitation. Nineteen percent of the 166 trees monitored skipped the first male phase, and another 13% skipped the female phase, remaining male in both years (and also a third year). The regular presence of pure males, if genetically fixed, would make B. tomentosa androdioecious in addition to duodichogamous. Comparison of duodichogamous taxa known so far shows that all have few ovules, fitting with the hypothesis that duodichogamy may result from male competition for access to a small supply of ovules.