bluuebunny/crossref_metadata_2025 huggingface dataset:
Herbarium studies on the distribution of anther‐smut fungus (Microbotryum violaceum) and Silene species (Caryophyllaceae) in the eastern United States
Authors: Antonovics Janis , Hood Michael E. , Thrall Peter H. , Abrams Joseph Y. , Duthie G. Michael
Published: February 2008

We used herbarium specimens of Silene virginica, S. caroliniana, S. rotundifolia, and S. latifolia to survey the incidence of anther‐smut disease (caused by Microbotryum violaceum sensu lato) in the eastern USA. We found no evidence of a collector bias against diseased specimens. Diseased specimens were frequently found in collections of S. virginica and S. caroliniana, but not in those of S. rotundifolia or S. latifolia. Disease incidence in S. virginica and S. caroliniana increased significantly over the past century and was higher in marginal populations. The absence of disease in specimens of S. rotundifolia is consistent with field observations, but its presence in natural populations of S. latifolia (especially in Virginia) suggests that the disease is recently introduced. Changes in the host distributions were also evident. The relative abundance of S. caroliniana declined over time (especially further north), while the relative abundance of S. virginica increased. Silene latifolia was absent or rare south of Pennsylvania before ca. 1920, indicating that S. latifolia and its anther smut are likely to be recent introductions in Virginia. Methods are also presented that quantify the completeness of coverage provided by herbarium specimens.
A comparative flower and fruit anatomical study ofQuercus acutissima, a biennial‐fruiting oak from theCerrisgroup (Fagaceae)
Authors: Borgardt Sandra J. , Nixon Kevin C.
Published: February 2008

A developmental series of flowers and fruits ofQuercus acutissima(subgenusQuercussectionCerris) was collected over a growing season and examined for an intersectional, comparative anatomical study. Pistillate flowers of the current growing season, each consisting of a pistil with three long, slightly recurved styles, six tepals, and an inconspicuous ovary subtended by a few cycles of cupule scales, emerged in early May, were pollinated by mid‐May, and then were quiescent for the remainder of the growing season. Flowers from the previous growing season resumed growth in mid‐May, each forming three locules delimited by septa in the ovary, with two bitegmic, epitropous ovules developing in each locule. Mature embryo sacs were present by mid‐July of the second growing season, although embryos were not observed until early August. Fruit maturation was complete by late September. Features that have not been described previously for the sectionCerrisinclude early‐lignifying endocarp trichomes, persistent septa, and leaf primordia buttresses on the embryo. A comparison of flower and fruit developmental features with sectionsQuercussensu stricto andLobataerevealed a mosaic of shared features among the three sections.
Evolution of genome size in the angiosperms
Authors: Soltis Douglas E. , Soltis Pamela S. , Bennett Michael D. , Leitch Ilia J.
Published: February 2008

Genome size varies extensively across the flowering plants, which has stimulated speculation regarding the ancestral genome size of these plants and trends in genome evolution. We investigated the evolution of C‐values across the angiosperms using a molecular phylogenetic framework and C‐values not previously available for crucial basal angiosperms, including Amborella, Illiciaceae, and Austrobaileya. Reconstructions of genome size across the angiosperms and extant gymnosperms indicate that the ancestral genome size for angiosperms is very small (1C ≤ 1.4 pg), in agreement with an earlier analysis of Leitch et al. (1998). Furthermore, a very small genome size (1C ≤ 1.4 pg) is ancestral not only for the angiosperms in general, but also for most major clades of flowering plants, including the monocots and the eudicots. The ancestral genome of core eudicots may also have been very small given that very low 1C‐values appear to be ancestral for major clades of core eudicots, such as Caryophyllales, Saxifragales, and asterids. Very large genomes occur in clades that occupy derived positions within the monocots and Santalales.
Distinct geographic structure as evidenced by chloroplast DNA haplotypes and ploidy level in Japanese Aucuba (Aucubaceae)
Authors: Ohi Tetsuo , Kajita Tadashi , Murata Jin
Published: February 2008

The geographic distribution of diploid and tetraploid cytotypes and cpDNA haplotypes throughout the entire range of Aucuba japonica was investigated. We measured relative genome size using flow cytometry and sequenced two cpDNA intergenic regions, atpB‐rbcL and psbA‐trnH (GUG). Two haplotypes include both diploids and tetraploids; four others are all tetraploids. Based on the combination of these haplotypes and cytotypes, eight “haplo‐cytotypes” can be defined, which show a distinct geographic structure. Two diploid haplo‐cytotypes are distributed in the southwestern part and six tetraploid ones in the northeastern part of the Japanese archipelago. Diploid and tetraploid haplo‐cytotypes with the same haplotype are, in one case, disjunctively distributed, and in another case, in contact. The phylogenetic relationships of haplo‐cytotypes indicate that the traditional circumscription of A. japonica is paraphyletic. One lineage consists of four tetraploid haplo‐cytotypes and another of diploid and tetraploid haplo‐cytotypes plus A. chinensis. Tetraploidization occurred independently at least three times, once at the base of the former lineage and twice in the latter. Taking the geographic, cytological, and phylogenetic evidence into account, the formation of the present geographic differentiation pattern of haplo‐cytotypes through postglacial expansion from glacial refugia is discussed.
Development of biochemical specialization and organelle partitioning in the single‐cell C4 system in leaves of Borszczowia aralocaspica (Chenopodiaceae)
Authors: Voznesenskaya Elena V. , Edwards Gerald E. , Kiirats Olavi , Artyusheva Elena G. , Franceschi Vincent R.
Published: February 2008

The terrestrial plant Borszczowia aralocaspica (Chenopodiaceae) has recently been shown to contain the entire C4 photosynthesis mechanism within individual, structurally and biochemically polarized chlorenchyma cells rather than in a dual cell system, as has been the paradigm for this type of carbon fixation (Nature 414: 543–546, 2001). Analysis of carbon isotope composition and 14CO2 fixation shows that photosynthesis and growth of B. aralocaspica occurs through carbon acquired by C4 photosynthesis. The development of this unique single‐cell C4 system in chlorenchyma cells was studied by analysis of young (0.2–0.3 cm length), intermediate (ca. 0.5–0.6 cm length), and mature leaves (ca. 3 cm length). The length of chlorenchyma cells approximately doubles from young to intermediate and again from intermediate to the mature leaf stage. In young chlorenchyma cells, there is a single type of chloroplast; the chloroplasts are evenly distributed throughout the cytosol, and all contain starch and rubisco. During leaf development, the activities of phosphoenolpyruvate carboxylase (PEPC; which is cytosolic), rubisco, and pyruvate,Pi dikinase (PPDK) increase on a chlorophyll basis. As leaves mature, chloroplasts differentiate into two distinct structural and biochemical types that are spatially separated into the proximal and distal parts of the cell (the proximal end being closest to the center of the leaf). The early stages of this polarization are observed in intermediate leaves, and the polarization is fully developed in mature leaves. The chloroplasts in the distal ends of the cell have reduced grana and little starch, while those at the proximal ends have well‐developed grana and abundant starch. In mature leaves, PPDK is expressed in chloroplasts at the distal end of the cells, while rubisco and adenosine diphosphate glucose (ADPG) pyrophosphorylase are selectively expressed in chloroplasts at the proximal end of the cell. Mitochondrial polarization also occurs during development as nicotinamide‐adenine dinucleotide phosphate‐malic enzyme (NAD‐ME) and the photorespiratory enzyme glycine decarboxylase are expressed in mature but not young leaves and are localized in mitochondria at the proximal end of the cells. The data show that single‐cell C4 develops from a single pool of identical organelles that develop differential biochemical functions and spatial partitioning in the cell during maturation.
Origin(s) of the diploid hybrid species Helianthus deserticola (Asteraceae)
Authors: Gross Briana L. , Schwarzbach Andrea E. , Rieseberg Loren H.
Published: February 2008

Homoploid hybrid speciation has traditionally been considered a rare event, dependent on the establishment of both a novel, balanced genotype and reproductive isolating barriers between the new species and its progenitors. However, more recent studies have shown that synthetic hybrids converge toward the chromosomal structure of natural hybrids after only a few generations, suggesting that this phenomenon may be more frequent than previously assumed. Here, the possibility that the diploid hybrid species Helianthus deserticola arose from more than one hybrid speciation event was investigated using patterns of variation from cpDNA, 18 nuclear microsatellite loci, and population interfertility. Helianthus deserticola contains cpDNA haplotypes characteristic of both parental species, is polyphyletic with one parental species based on nine microsatellite loci, and has a high degree of interfertility among populations. The data are consistent with either a single origin followed by introgression with the parental species or multiple origins. Analysis of microsatellite variation places the origin of H. deserticola between 170 000 and 63 000 years before present, making it unlikely that anthropogenic disturbances influenced its origin. Finally, the hybrid species generally has lower levels of genetic diversity but higher levels of differentiation among populations than either parental species.
Responses of common and successional heathland species to manipulated salt spray and water availability
Authors: Griffiths Megan E. , Orians Colin M.
Published: February 2008

Coastal sandplain heathlands are a rare plant community in the northeastern United States. Salt spray and water availability are likely important factors determining heathland distribution. Field surveys and manipulative experiments were performed to examine heathland species' responses to salt spray and water availability. We surveyed field distributions of four typical heathland species: Solidago puberula, Solidago rugosa, Gaylussacia baccata, and Myrica pensylvanica. The distributions of two native tree species, Pinus rigida and Quercus ilicifolia, were also surveyed because they succeed into coastal heathlands with low disturbance frequency. We then manipulated salt spray and water in the field and measured species' water status, necrosis, and growth responses to the treatments. Predawn xylem pressure potential and necrosis were strongly affected by high salt spray and low water availability. Shoot elongation was also limited in S. puberula and S. rugosa grown in high salt, low water treatments. Gaylussacia baccata and Q. ilicifolia were particularly sensitive to high salt spray and low water, suggesting that they might excluded be from areas with those conditions. The interaction between salt spray and water availability could affect the landscape scale and should be incorporated into conservation management plans.
Floral color change in Weigela middendorffiana (Caprifoliaceae): reduction of geitonogamous pollination by bumble bees
Authors: Ida Takashi Y. , Kudo Gaku
Published: February 2008

We examined the significance of retaining color‐changed flowers in pollination success of Weigela middendorffiana through a single visit of bumble bees. Inner parts of flowers changed color with age from yellow to red. In an investigation of the mating system, duration of each color phase, reproductive ability of each of the color‐phase flowers, and the effects of color‐changed flowers on bumble bee behavior (1) flowers of this species were self‐incompatible, (2) color‐changed flowers provided little reward to pollinators and little residual reproductive ability, (3) the timing of floral color change was delayed with the progress of flowering season within individual plants, while the duration of the red phase shortened with the progress of flowering season, and (4) red‐phase flowers did not attract bumble bees at a distance but did contribute to reducing the number of successive flower visits during a single stay within the plants. Red‐phase flowers seemed to indicate the low reward level of old flowers and functioned as a cue to discourage pollinators from staying longer on the same plant. Our results predict that the retention of color‐changed flowers without sexual function can enhance the pollination success of a whole plant through male function by reducing successive flower visits during a single stay of pollinators, i.e., geitonogamous pollination.
Heterozygote advantage in the American chestnut,Castanea dentata(Fagaceae)
Authors: Stilwell Kevin L. , Wilbur Henry M. , Werth Charles R. , Taylor Douglas R.
Published: February 2008

The American chestnut (Castanea dentata; Fagaceae) was a dominant canopy tree in the Appalachian Mountains of North America. Since the introduction of the chestnut blight fungus (Cryphonectria parasitica; Valsaceae) in America, the American chestnut has been reduced to a predominantly clonal, understory species. Our objective was to determine whether the ecological changes and absence of new recruits have influenced the population genetics of American chestnut. Leaf samples were collected from four populations in southwestern Virginia. Electrophoretic data from five polymorphic loci were used to determine the genetic diversity and population structure of the populations and subpopulations. Growth data and infection status were recorded for one of the populations to determine their relationship with heterozygosity.Fstatistics revealed a significant amount of differentiation among subpopulations and an excess of heterozygotes within subpopulations. Heterozygous individuals also had higher rates of vegetative growth. The superior performance and excess of heterozygotes suggests that selection favors heterozygous individuals. The prolonged absence of sexual reproduction inC. dentatahas allowed subtle fitness differences to accumulate to the extent that they have had significant effects on the genetics of chestnut populations.
Variation in pollinator effectiveness in swamp milkweed, Asclepias incarnata (Apocynaceae)
Authors: Ivey Christopher T. , Martinez Pocholo , Wyatt Robert
Published: February 2008

The contribution of a pollinator toward plant fitness (i.e., its “effectiveness”) can determine its importance for the plant's evolutionary ecology. We compared pollinators in a population of Asclepias incarnata (Apocynaceae) for several components of pollinator effectiveness over two flowering seasons to evaluate their importance to plant reproduction. Insects of the order Hymenoptera predominate in A. incarnata pollination, but there appears to be no specialization for pollination within this order. Pollinators varied significantly in nearly every component of effectiveness that we measured, including pollen load, removal and deposition of pollen, pollination efficiency (deposition/removal), flower‐handling time, and potential for geitonogamy (fractional pollen deposition). The visitation rate of pollinators also varied significantly between years and through time within years. Pollination success and percentage fruit‐set of unmanipulated plants in the population also varied significantly between years, and pollination success varied among sample times within years. Most components of effectiveness were weakly correlated, suggesting that the contributions of visitor species toward pollination varied among effectiveness components. Mean flower‐handling time, however, was strongly correlated with several components, including pollen removal and deposition, pollination efficiency, and fractional pollen deposition. These findings highlight the significance of pollination variability for plant reproduction and suggest that time‐dependent foraging behaviors may play an important role in determining pollinator effectiveness.
Prevalence and predictability of handling effects in field studies: results from field experiments and a meta‐analysis
Authors: Hik David S. , Brown Melissa , Dabros Anna , Weir Jackie , Cahill James F.
Published: February 2008

Various effects on plant growth associated with handling or touching plants are well documented from greenhouse and laboratory studies, but are generally unknown or ignored under field conditions. We examined the prevalence of the effects of handling, at levels typical of many ecological experiments, on aboveground biomass and damage by invertebrate herbivores for a total of 16 common species from three plant communities in western Canada. Significant effects of handling were observed in the alpine meadow and grassland, but not in the boreal forest. Handling reduced aboveground biomass and increased the mean intensity of invertebrate leaf damage for most species. A meta‐analysis of the relationship between plant traits and response to handling indicated that woody plants and species without strong chemical or conspicuous morphological defenses were most strongly affected. Overall, our results indicate that potentially confounding effects of routinely sampling plants in the field are widespread and merit further investigation.
Reassessment of phylogenetic relationships in Clarkia sect. Sympherica
Authors: Ford V. S. , Gottlieb L. D.
Published: February 2008

Clarkia (Onagraceae) is a genus of 42 annual species, mostly native to California, that has served as a model for many studies of plant evolutionary biology, particularly morphological, cytological, and genetic divergence; reproductive isolation; and speciation. Section Sympherica is the largest section with eight diploid and one allotetraploid species. Species in the section have provided important evidence about the evolution of reproductive isolation (C. lingulata derived from C. biloba) and large morphological change (C. dudleyana thought to be sister to the morphologically distinct C. heterandra, recently transferred into Clarkia from the monotypic Heterogaura). Clarkia epilobioides, another diploid species in the section, was previously shown to be one parent of the allotetraploid C. delicata, the other parent being C. unguiculata from sect. Phaeostoma. Lewis and Lewis (1955) interpreted the parentage of C. delicata and other evidence of intersectional hybridization to mean that the diploid sections of the genus, though highly diverse, were closely related and should be maintained in the single genus Clarkia. Here we assess phylogenetic relationships among the species of sect. Sympherica and related species by analyzing the nucleotide sequences of PgiC1 and PgiC2, a pair of paralogous genes that encode the cytosolic isozyme of phosphoglucose isomerase (EC 5.3.1.9). The major results were the following: (1) C. unguiculata and both genomes of C. delicata are within a well‐defined “Sympherica” clade; thus, C. delicata should not be considered an intersectional hybrid; (2) C. heterandra belongs in the clade and is closely related to C. unguiculata; and (3) on the evidence of PgiC1, C. dudleyana is not in the clade and is not closely related to C. heterandra.
Intraspecific cpDNA variations of diploid and tetraploid perennial buckwheat, Fagopyrum cymosum (Polygonaceae)
Authors: Yamane Kyoko , Yasui Yasuo , Ohnishi Ohmi
Published: February 2008

We investigated the phylogenetic and biogeographic relationships of natural populations of diploid and tetraploid Fagopyrum cymosum (Polygonaceae). Intraspecific variation of chloroplast DNA sequences was detected in three regions approximately 5 kb long in total: the 3′ end of rbcL, accD and associated intergenic spacer region, the trnC (GCA)‐rpoB spacer region, the trnK (UUU) intron, and the matK region. The accessions of F. cymosum were divided into two major groups, a Tibet‐Himalayan clade and a Yunnan‐Sichuan clade, with a high bootstrap probability. It was estimated that these two clades diverged about 0.7 million years ago. The geographical and climatic interruption by the Hengduanshan mountains might have caused the genetic divergence in F. cymosum. Autotetraploid populations of F. cymosum have arisen allopatrically from a diploid progenitor at least twice, once in the Tibet‐Himalayan area and once in the Yunnan‐Sichuan area. This conclusion reinforces a previous study based on allozyme variation. We also found that F. tataricum, a close relative of F. cymosum, was completely included within the Tibet‐Himalayan clade in the phylogenetic tree. This suggests that F. tataricum speciated from F. cymosum in the Tibet‐Himalayan area.
Sexes show contrasting patterns of leaf and crown carbon gain in a dioecious rainforest shrub
Authors: Nicotra Adrienne B. , Chazdon Robin L. , Montgomery Rebecca A.
Published: February 2008

The sexes of dioecious species may differ in a range of vegetative and reproductive traits as well as in physiological traits. In Siparuna grandiflora, a Neotropical dioecious shrub, we examined differences in leaf‐level photosynthesis of different classes of leaf age and, using simulation models, explored whether differences in leaf‐level carbon gain led to sex differences in whole‐plant daily carbon gain. Male plants had higher photosynthetic capacity at the leaf level. As leaves of both sexes aged their photosynthetic capacity and specific leaf area declined as expected. Simulations of daily carbon gain using the architecturally explicit model Y‐Plant and a non‐architectural model incorporating a wide range of realistic light environments revealed that the difference in leaf‐level photosynthetic capacity did not translate into greater crown‐level carbon gain for males. Rather, differences in patterns of allocation to leaf area allow females to achieve higher crown‐level carbon gain. The results demonstrate that sex differences at the leaf level do not necessarily predict patterns at the whole‐plant level.
Allometry and development in herbaceous plants: functional responses of meristem allocation to light and nutrient availability
Authors: Bonser Stephen P. , Aarssen Lonnie W.
Published: February 2008

We examined the relationship between meristem allocation and plant size for four annual plant species: Arabidopsis thaliana, Arenaria serphyllifolia, Brassica rapa, and Chaenorrhinum minus. Gradients of light and nutrient availability were used to obtain a range of plant sizes for each of these species. Relative allocation to reproductive, inactive, and growth meristems were used to measure reproductive effort, apical dominance, and branching intensity, respectively. We measured allocation to each of these three meristem fates at weekly intervals throughout development and at final developmental stage. At all developmental stages reproductive effort and branching intensity tended to increase with increasing plant size (i.e., due to increasing resource availability) and apical dominance tended to decrease with increasing plant size. We interpret these responses as a strategy for plants to maximize fitness across a range of environments. In addition, significant differences in meristem response among species may be important in defining the range of habitats in which a species can exist and may help explain patterns of species competition and coexistence in habitats with variable resource availability.
Long‐term patterns of shrub expansion in a C4‐dominated grassland: fire frequency and the dynamics of shrub cover and abundance
Authors: Heisler Jana L. , Briggs John M. , Knapp Alan K.
Published: February 2008

Worldwide, grassland ecosystems have experienced a major shift in growth‐form dominance as woody plant species have expanded and replaced native grasses. In the C4‐dominated grasslands of central North America, a reduction in fire frequency is the most cited cause of this shift in growth forms as fire both enhances grass productivity and constrains the establishment and expansion of native woody vegetation. Using an 18‐yr plant species composition data set, we quantified patterns of change in shrub cover, frequency, and species richness associated with three distinct fire regimes. During the study period (1983–2000), shrub cover increased most dramatically in sites in which the frequency of fire was once every 4 yr (intermediate frequency; 28.6%) followed by sites in which fire occurred only once during the 18‐yr period (low frequency; 23.7%). Annual fire effectively prevented the recruitment of new woody species, but even with this high fire frequency, shrub cover increased slightly (3.7%). Comparatively, shrub species richness increased by three and six, respectively, in the intermediate‐ and low‐frequency fire sites. These data indicate that within this grassland, periods without fire are necessary for recruitment of both new individuals and additional shrub species; however, once established, shrub cover will increase regardless of fire frequency and even annual fire will not reduce shrub abundance.
Systematics and evolution of tribe Sinningieae (Gesneriaceae): evidence from phylogenetic analyses of six plastid DNA regions and nuclear ncpGS
Authors: Perret Mathieu , Chautems Alain , Spichiger Rodolphe , Kite Geoffrey , Savolainen Vincent
Published: February 2008

For nearly all species in the three genera of tribe Sinningieae (Gesneriaceae), Sinningia, Paliavana, and Vanhouttea (mostly in southeastern Brazil) plus 10 outgroups, we have sequenced six non‐coding DNA regions (i.e., plastid intergenic spacers trnT‐trnL, trnL‐trnF, trnS‐trnG, atpB‐rbcL, and introns in the trnL and rpl16 genes) and four introns in nuclear plastid‐expressed glutamine synthetase gene (ncpGS). Separate and combined analyses of these data sets using maximum parsimony supported the monophyly of Sinningieae, but the genera Paliavana and Vanhouttea were found embedded within Sinningia; therefore a new infrageneric classification is here proposed. Mapping of pollination syndromes on the DNA‐based trees supported multiple origins of hummingbird and bee syndromes and derivation of moth and bat syndromes from hummingbird flowers. Perennial tubers were derived from perennial stems in non‐tuberous plants.
Major evolutionary events in the origin and diversification of the fern genus Polystichum (Dryopteridaceae)
Authors: Little Damon P. , Barrington David S.
Published: February 2008

Recent advances in molecular systematics of the ferns make it possible to address long‐standing questions about classification of the major fern genera, such as the worldwide genus Polystichum (Dryopteridaceae), comprising at least 200 species. In this study we examined rbcL sequences and morphological characters from 55 fern taxa: 34 were from Polystichum and 21 were from other genera in the Dryopteridaceae. We found that Phanerophlebia, possibly including Polystichopsis, is the sister group to Polystichum sensu lato (s.l.), including Cyrtomium. Polystichum as commonly recognized is paraphyletic. Our results lead us to suggest recognizing the clade of earliest diverging Polystichum species as a distinct genus (Cyrtomidictyum) and to continue to recognize Cyrtomium as a separate genus, leaving a monophyletic Polystichum sensu stricto (s.s.). We resolved a tropical American clade and an African clade within Polystichum s.s. However, the resemblance between the once‐pinnate, bulb‐bearing calciphilic species found in Asia and the West Indies appears to be the result of convergent evolution. Optimizing our morphological character transformations onto the combined phylogeny suggests that the common ancestor of Polystichum s.l. and Phanerophlebia had evolved the common features of the alliance, including ciliate petiole‐base scales, once‐pinnate fronds, ultimate segments with scarious tips, peltate indusia, and microscales.
Contrasting selection modes at the Adh1 locus in outcrossing Miscanthus sinensis vs. inbreeding Miscanthus condensatus (Poaceae)
Authors: Chiang Yu‐Chung , Schaal Barbara A. , Chou Chang‐Hung , Huang Shong , Chiang Tzen‐Yuh
Published: February 2008

We estimated DNA sequence variation of the Adh1 locus in the outcrossing Miscanthus sinensis (Poaceae) and its close selfing relative, M. condensatus. Tajima's test of selection is significantly negative for both overall exons and replacement sites in M. sinensis. Among its entire sample, nucleotide diversity of nonsynonymous sites is higher than that of synonymous sites. A McDonald and Kreitman test of neutrality indicates an excess of intraspecific replacement polymorphisms, suggesting possible directional selection toward advantageous mutants. However, frequent intragenic recombination suggests both purifying and positive selection is unlikely. Recent demographic expansions coupled with relaxation of purifying selection may have resulted in elevated genetic diversity at the Adh1 locus as well as the trnL‐trnF intergenic spacer of cpDNA in this outcrossing species. In contrast, low levels of genetic diversity were detected at both the Adh1 locus and the cpDNA spacer in M. condensatus, consistent with bottlenecks associated with selfing in all populations. While Tajima's D and Fu and Li's F statistics did not reveal deviation from neutrality at the Adh1 locus in M. condensatus, 12 replacements vs. 10 synonymous changes were detected. Based on pairwise comparisons of the dN/dS ratio, lineages of closely related populations of the species distributed along saline habitats appeared to be under directional selection.
Frequency‐dependent fitness of hybrids between oilseed rape (Brassica napus) and weedyB. rapa(Brassicaceae)
Authors: Hauser Thure P. , Damgaard Christian , Jørgensen Rikke B.
Published: February 2008

Fitness of interspecific hybrids is sometimes high relative to their parents, despite the conventional belief that they are mostly unfit. F1hybrids between oilseed rape (Brassica napus) and weedyB. rapacan be significantly more fit than their weedy parents under some conditions; however, under other conditions they are less fit. To understand the reasons, we measured the seed production ofB. napus,B. rapa, and different generations of hybrid plants at three different densities and in mixtures of different frequencies (including pure stands).Brassica napus,B. rapa, and backcross plants (F1♀ ×B. rapa) produced many more seeds per plant in pure plots than in mixtures and more seeds in plots when each was present at high frequency. The opposite was true for F1plants that produced many more seeds thanB. rapain mixtures, but fewer in pure stands. Both vegetative and reproductive interactions may be responsible for these effects. Our results show that the fitness ofbothparents and hybrids is strongly frequency‐dependent and that the likelihood of introgression of genes between the species thus may depend on the numbers and densities of parents and their various hybrid offspring in the population.
Female sterility in Ulmus minor (Ulmaceae): a hypothesis invoking the cost of sex in a clonal plant
Authors: López‐Almansa J. C. , Pannell J. R. , Gil L.
Published: February 2008

A high incidence of individuals with low seed set was found in two populations of the field elm Ulmus minor, a European tree that reproduces sexually and via vegetative propagation through root sprouting. One population was a seminatural stand, while the other was established by artificial propagation of genotypes sampled widely across Spain. The low seed set in both populations was due to both pre‐ and post‐zygotic factors, the importance of which vary between genotypes. These factors included gynoecial malformations that produced a non‐ovulated pistil, early gynoecial necrosis (i.e., necrosis before any opportunities for pollination), and seed abortion. Female sterility gave rise to two classes of individuals: trees that were largely female‐sterile but dispersed normal quantities of viable pollen, and trees that dispersed both normal pollen and substantial numbers of seeds. Reduced production of protein‐rich seeds may increase the resource availability for clonal propagation, helping to maintain female‐sterile individuals with hermaphrodites.
Stomatal frequency adjustment of four conifer species to historical changes in atmospheric CO2
Authors: Kouwenberg Lenny L. R. , McElwain Jennifer C. , Kürschner Wolfram M. , Wagner Friederike , Beerling David J. , Mayle Francis E. , Visscher Henk
Published: February 2008

The species‐specific inverse relation between atmospheric CO2 concentration and stomatal frequency for many woody angiosperm species is being used increasingly with fossil leaves to reconstruct past atmospheric CO2 levels. To extend our limited knowledge of the responsiveness of conifer needles to CO2 fluctuations, the stomatal frequency response of four native North American conifer species (Tsuga heterophylla, Picea glauca, Picea mariana, and Larix laricina) to a range of historical CO2 mixing ratios (290 to 370 ppmV) was analyzed. Because of the specific mode of leaf development and the subsequent stomatal patterning in conifer needles, the stomatal index of these species was not affected by CO2. In contrast, a new measure of stomatal frequency, based on the number of stomata per millimeter of needle length, decreased significantly with increasing CO2. For Tsuga heterophylla, the stomatal frequency response to CO2 changes in the last century is validated through assessment of the influence of other biological and environmental variables. Because of their sensitive response to CO2, combined with a high preservation capacity, fossil needles of Tsuga heterophylla, Picea glauca, P. mariana, and Larix laricina have great potential for detecting and quantifying past atmospheric CO2 fluctuations.
Phylogenetic evaluation of Xylothamia, Gundlachia, and related genera (Asteraceae, Astereae) based on ETS and ITS nrDNA sequence data
Authors: Urbatsch Lowell E. , Roberts Roland P. , Karaman Vesna
Published: February 2008

Previous molecular investigations of the phylogenetic relationship for Xylothamia employed exemplar taxa and indicated its affiliation is either with the Gutierrezia or the Ericameria alliances. The present 3′ ETS and ITS nrDNA gene phylogenies yielded the unexpected result that Xylothamia is polyphyletic. Species within its circumscription are placed into two well‐supported evolutionary lineages with other genera of Astereae. Of nine species of Xylothamia, four species plus Gundlachia constitute one clade. The other five species are placed in a sister clade with several other genera including Amphiachyris, Bigelowia, Euthamia, Gutierrezia, and others. Except for X. johnstonii and X. palmeri, these five species of Xylothamia have little affinity for one another or for other genera in the same clade. Morphological similarities in foliar features between certain species in both lineages are possibly from a convergence resulting in adaptation to arid habitats. Such similarities were also the basis, in part, for their taxonomic treatment within Xylothamia or their earlier affiliation with Ericameria, which has similar features. The uncharacteristic leaf form in Xylothamia purpursii has a pattern of adaptation considerably different from its allies. Whether the Xylothamia‐containing clades are related to Solidaginineae or represent an independently derived lineage remains equivocal because this outcome rested with the choice of data and optimality criteria.
Pollination systems of trees in Kakachi, a mid‐elevation wet evergreen forest in Western Ghats, India
Authors: Devy M. Soubadra , Davidar Priya
Published: February 2008

A long‐term survey (1990–2000) of pollination modes of 86 tree species was carried out at Kakachi, a mid‐elevation wet forest site in southern Western Ghats, India. Observations were made on 86 tree species. This comprises 80% of the total arborescent species present in the site. Approximately 75% of these species were specialized to a single pollinator group such as bee, beetle, or moth. Pollinators from diverse groups pollinate the remaining 25% of the tree species. Global comparison with other wet forest sites showed that diversity and specialized pollination modes observed in Kakachi bore closer resemblance to other lowland than montane forest sites described so far. However, the number of pollinators involved in pollination was comparable with montane sites. We examine the consequences that might have led to selection of the observed pollination modes in Kakachi. We discuss the conservation implications of these results.
Relationships among time, frequency, and duration of flowering in tropical rain forest trees
Authors: Bawa Kamaljit S. , Kang Hyesoon , Grayum Michael H.
Published: February 2008

Flowering patterns are defined by the timing, duration, and frequency of flowering. Plants, particularly in the tropics, vary enormously with respect to these main variables of flowering. We used data from 302 tree species in a wet tropical forest to test a series of predictions regarding timing, duration, and frequency of flowering and examined the effect of each variable on the other two. Because timing, duration, and frequency of flowering can be constrained by phylogeny, we analyzed the data before and after considering phylogenetic effects at the level of family. Flowering activity peaked in the first wet season from May to July, refuting our prediction of peak flowering during the dry season. Our prediction that most species should flower several times a year was supported when species flowering more or less continually throughout the year were included in this category. Our prediction that supra‐annually flowering species should be the least frequent was also supported with some qualifications. As we predicted, species flowering several times a year bloomed relatively briefly per flowering episode. Our prediction of shorter flowering duration for species flowering in the dry season and for those with a temporal separation between flowering and vegetative growth was also supported. Furthermore, supra‐annually flowering species flowered for a shorter duration than annually flowering species and had a higher probability of flowering in the dry season compared to episodically or annually flowering species. Phylogeny significantly constrained variation in flowering frequency, but not in flowering time or duration, among confamilial species.
Population genetic structure of wildPhaseolus lunatus(Fabaceae), with special reference to population sizes
Authors: Zoro Bi Irié , Maquet Alain , Baudoin Jean‐Pierre
Published: February 2008

To set up an in situ conservation strategy forPhaseolus lunatus, we analyzed the genetic structure of 29 populations in the Central Valley of Costa Rica. Using 22 enzyme loci, we quantified the proportion of polymorphic loci (Pp), the mean number of alleles per locus (A), and the mean effective number of alleles per locus (Ae), which equaled to 10.32%, 1.10, and 1.05, respectively. The total heterozygosity (HT), the intrapopulation genetic diversity (HS), and the interpopulation genetic diversity (DST) were 0.193, 0.082, and 0.111, respectively. The genotypic composition of the analyzed populations showed a deviation from the Hardy‐Weinberg proportions (FIT= 0.932). This disequilibrium was due to either genetic differentiation between populations (FST= 0.497) or nonrandom mating within populations (FIS= 0.866). From the level of genetic differentiation between populations and the private alleles frequencies estimates, gene flow was calculated:NmW= 0.398 andNmS= 0.023, respectively. The results suggested that wild Lima bean maintains most of its isozyme variation among populations. Significant positive correlation was observed between population size andPp,A, andHo(observed heterozygosity), whereas no correlation was observed with the average fixation index of population (F). The loss of genetic variability in populations was attributed to inbreeding and the bottleneck effects that characterized the target populations. In situ conservation and management procedures for wild Lima bean are discussed.
Environmental influences on the phenology and abundance of flowering by Androsace septentrionalis (Primulaceae)
Authors: Inouye David W. , Saavedra Francisca , Lee‐Yang Wendy
Published: February 2008

We studied the timing and abundance of flowering by Androsace septentrionalis L. (Primulaceae), an indeterminate winter annual or short‐lived perennial, in 2 × 2 m plots at the Rocky Mountain Biological Laboratory in Colorado, USA, from 1982 to 2000. Flowers were counted every other day for most or all of the growing season in seven plots in a rocky meadow habitat and nine plots in a wet meadow habitat. The phenology and abundance of flowering were both highly variable, with mean dates of first flowering ranging from 16 May to 12 July and maximum daily counts of flowers ranging from 1 to 1187. Snowmelt date was the primary determinant of timing of flowering. For rocky meadow plots, the previous year's summer precipitation and the current year's average minimum temperature in May had significant effects on maximum number of flowers produced, but no environmental variable we considered was significantly correlated with flower abundance in the wet meadow plots. Length of flowering in individual plots ranged from 2 to 85 d, and many plot‐years had both primary (about 1 mo) and secondary (about 10–12 d) flowering periods. The predicted increase in variability of precipitation accompanying climate change will affect negatively the long‐term abundance and persistence of this species at our study site.
Phylogenetics of the genus Scaevola (Goodeniaceae): implication for dispersal patterns across the Pacific Basin and colonization of the Hawaiian Islands
Authors: Howarth Dianella G. , Gustafsson Mats H. G. , Baum David A. , Motley Timothy J.
Published: February 2008

Scaevola, the only genus of Goodeniaceae that has extensively radiated outside of Australia, has dispersed throughout the Pacific Basin, with a few species reaching the tropical coastal areas of the Atlantic and Indian Oceans. Five Australian and most of the non‐Australian species are placed in Scaevola section Scaevola based on their fleshy fruits, indeterminate inflorescences, and more arborescent habits. Analyses of ITS sequence data demonstrate that Scaevola is a monophyletic group if S. collaris is excluded and Diaspasis filifolia is included. The genus is Australian in origin, but there have been at least six separate dispersal events from Australia. Four of these dispersals each resulted in single extra‐Australian species. The remaining two were followed by radiations that gave rise to large groups, each including one of the widespread strand species, S. taccada and S. plumieri. Remarkably, three of the six dispersals established species on the remote Hawaiian Archipelago, representing at present the largest number of colonizations by any flowering plant genus to these islands.
The pollination biology of two paniculate agaves (Agavaceae) from northwestern Mexico: contrasting roles of bats as pollinators
Authors: Molina‐Freaner Francisco , Eguiarte Luis E.
Published: February 2008

Paniculate agaves from tropical deserts depend on nectar‐feeding bats for their reproduction, while species from extratropical areas near the northern limit of Leptonycteris curasoae are pollinated by diurnal and nocturnal insects and birds. Agave angustifolia is a paniculate agave with a broad distribution in Mexico whose range coincides with the distribution of L. curasoae, while A. subsimplex has a narrow distribution in Sonora within the range of nectar‐feeding bats. We studied the pollination biology of A. angustifolia and A. subsimplex in northwestern Mexico to evaluate the relative importance of bat pollination in a region where L. curasoae is seasonal. Flower visitors included a wide variety of animals, with bats having greater visitation rates in A. angustifolia. A pollinator‐exclusion experiment revealed that bats were responsible for most of the control fruit set in A. angustifolia, whereas for A. subsimplex, diurnal and nocturnal visitors were equally effective. Overall, our data indicate that in central Sonora, A. angustifolia depends on nectar‐feeding bats for its sexual reproductive success, while A. subsimplex relies on both diurnal and nocturnal pollinators. Given the contrasting distribution ranges of paniculate agaves, our results seem to support the trend from specialization to generalization along the continuum of tropical to extratropical deserts.
The response of Ammophila breviligulata and Spartina patens (Poaceae) to grazing by feral horses on a dynamic mid‐Atlantic barrier island
Authors: Seliskar Denise M.
Published: February 2008

Ammophila breviligulata, American beachgrass, and Spartina patens, salt meadow hay, have been grazed by feral horses on the dunes of Assateague Island for hundreds of years; however, because of a significant increase in the horse population since the 1960s, overgrazing and dune erosion have become problems. Grazing was assessed on foredunes of four different morphologies along a 21‐km stretch of the Maryland portion of the island using 17 exclosure plot pairs. In addition to decreased cover and biomass of the two species, plant structure was significantly affected by grazing. Leaf length and width, stem diameter, and stem density of A. breviligulata and stem diameter of S. patens were reduced in the grazed plots. Especially sensitive to grazing were reproductive characteristics. Percentage of plants in flower, height of flowering stems, and inflorescence length were all significantly reduced by grazing (nongrazed individuals measured). Species composition was not affected by horse accessibility.
Are Mojave Desert annual species equal? Resource acquisition and allocation for the invasive grass Bromus madritensis subsp. rubens (Poaceae) and two native species
Authors: DeFalco Lesley A. , Bryla David R. , Smith‐Longozo Vickie , Nowak Robert S.
Published: February 2008

Abundance of invasive plants is often attributed to their ability ot outcompete native species. We compared resource acquisition and allocation of the invasive annual grass Bromus madritensis subsp. rubens with that of two native Mojave Desert annuals, Vulpia octoflora and Descurainia pinnata, in a glasshouse experiment. Each species was grown in monoculture at two densities and two levels of N availability to compare how these annuals capture resources and to understand their relative sensitivities to environmental change. During >4 mo of growth, Bromus used water more rapidly and had greater biomass and N content than the natives, partly because of its greater root‐surface area and its exploitation of deep soils. Bromus also had greater N uptake, net assimilation and transpiration rates, and canopy area than Vulpia. Resource use by Bromus was less sensitive to changes in N availability or density than were the natives. The two native species in this study produced numerous small seeds that tended to remain dormant, thus ensuring escape of offspring from unfavorable germination conditions; Bromus produced fewer but larger seeds that readily germinated. Collectively, these traits give Bromus the potential to rapidly establish in diverse habitats of the Mojave Desert, thereby gaining an advantage over coexisting native species.