bluuebunny/crossref_metadata_2025 huggingface dataset:
Origin and evolution of North American polyploid Silene (Caryophyllaceae)
Authors: Popp Magnus , Oxelman Bengt
Published: February 2008

Nuclear DNA sequences from introns of the low‐copy nuclear gene family encoding the second largest subunit of RNA polymerases and the ribosomal internal transcribed spacer (ITS) regions, combined with the psbE‐petL spacer and the rps16 intron from the chloroplast genome were used to infer origins and phylogenetic relationships of North American polyploid Silene species and their closest relatives. Although the vast majority of North American Silene species are polyploid, which contrasts to the diploid condition dominating in other parts of the world, the phylogenetic analyses rejected a single origin of the North American polyploids. One lineage consists of tetraploid Silene menziesii and its diploid allies. A second lineage, Physolychnis s.l., consists of Arctic, European, Asian, and South American taxa in addition to the majority of the North American polyploids. The hexaploid S. hookeri is derived from an allopolyploidization between these two lineages. The tetraploid S. nivea does not belong to any of these lineages, but is closely related to the European diploid S. baccifera. The poor resolution within Physolychnis s.l. may be attributed to rapid radiation, recombination among homoeologues, homoplasy, or any combination of these factors. No extant diploid donors could be identified in Physolychnis s.l.
Cascadiacarpa spinosa gen. et sp. nov. (Fagaceae): castaneoid fruits from the Eocene of Vancouver Island, Canada
Authors: Mindell Randal A. , Stockey Ruth A. , Beard Graham
Published: February 2008

Documenting the paleodiversity of well‐studied angiosperm families serves to broaden their circumscription while also providing a time‐specific reference point to mark the first occurrence of characters and appearance of lineages. More than 80 anatomically preserved specimens of spiny, cupulate fruits in various developmental stages have been studied from the Eocene Appian Way locality of Vancouver Island, British Columbia, Canada. Details of internal anatomy and external morphology are known for the cupules, fruits, and pedicels. Cupule spines branch and are often borne in clusters. Cupules lack clear sutures and are adnate to a single nut that is enclosed entirely with the exception of the apical stylar protrusion of the pistil. A central hollow cylinder of vascular tissue can be seen extending up the peduncle to the base of the fruit and along the inner wall of the cupule. The fruit has a sclerotic outer pericarp that grades into a parenchymatous mesocarp and a sclerotic endocarp lining the locules. Early in development, the two locules are divided by a thin septum to which the ovules are attached. Only one seed develops to maturity as evidenced by an embryo occupying the locule alongside an abortive apical ovule. Three‐dimensional reconstructions of these fruits have allowed for comparisons to both extinct and extant fagaceous taxa. The Appian Way fruits are most similar to extant Castanopsis species (Fagaceae) but differ in having only two locules. Cascadiacarpa spinosa gen. et sp. nov. Mindell, Stockey et Beard is the first occurence of a bipartite gynoecium and earliest known occurrence of hypogeous fruits in Fagaceae. The appearance of Casacadiacarpa in the Eocene of British Columbia supports a Paleogene radiation of the family. The numerous derived characters of these fruits show that evalvate, spiny, single‐fruited cupules of Fagaceae were present in the Paleogene of North America.
Development of the enigmatic peristome of Timmia megapolitana (Timmiaceae; Bryophyta)
Authors: Budke Jessica M. , Jones Cynthia S. , Goffinet Bernard
Published: February 2008

The Timmiaceae (Bryophyta) have been traditionally classified within the Bryales based on peristome architecture. Phylogenetic analyses of nucleotide sequences have revealed relationships that are incongruent with this hypothesis and have implicated an origin for this lineage early in the radiation of arthrodontous mosses (Bryopsida). This unexpected phylogenetic placement raises important questions about the evolutionary significance of the Timmia peristome, which differs from all other mosses by 64 isomorphic filaments topping the endostomial membrane. A developmental study of the peristome in Timmia megapolitana was undertaken to examine alignments of anticlinal cell walls in the inner peristomial layer (IPL) with those of the primary peristomial layer (PPL), a character that has been used to define major arthrodontous lineages. Criteria were established for assessing longitudinally homologous regions that contribute to the peristome‐forming region. Young sporophytes were examined using histological techniques, and the alignment of the cell wall divisions was quantified. Critical divisions in the IPL of T. megapolitana were determined to be symmetrical, similar to patterns in the Funariales. This research provides novel developmental observations for a putative ancestral lineage of arthrodontous mosses, reevaluates criteria used to compare developmental studies of different lineages and discusses the phylogenetic implications of these observations.
Mechanisms of prezygotic reproductive isolation between two sympatric species,Gelsemium rankiniiandG. sempervirens(Gelsemiaceae), in the southeastern United States
Authors: Pascarella John B.
Published: February 2008

Natural hybridization plays a critical role in speciation, the maintenance of reproductive isolation, and genetic introgression. While many plant species have hybrid swarms in areas of sympatry, the lack of hybrids among closely related sympatrically distributed species suggests that strong pre‐ and/or postzygotic barriers exist to hybridization.Gelsemium sempervirensandG. rankinii(Gelsemiaceae) are sympatrically distributed southeastern sister taxa that have strong postzygotic barriers to hybrid formation and high levels of genetic differentiation. In this study, two sympatric populations in Lowndes County, Georgia were surveyed from 1999–2005 to assess the role of temporal and pollinator isolation as potential prezygotic barriers. The populations had mostly non‐overlapping flowering periods in 2003–2005, with significant differences in time of peak flowering and length of flowering. Both species shared a similar community of flower visitors, with the apid beeHabropoda laboriosathe dominant visitor to both species. A choice experiment found thatH. laboriosavisited both species but preferredG. sempervirens. The primary prezygotic barrier is temporal isolation preventing hybridization in spite of the shared pollinators. This study suggests that reliance on a shared pollinator during speciation may limit opportunity for divergent selection on flowering time.
Pit membranes in tracheary elements of Rosaceae and related families: new records of tori and pseudotori
Authors: Jansen Steven , Sano Yuzou , Choat Brendan , Rabaey David , Lens Frederic , Dute Roland R.
Published: February 2008

The micromorphology of pits in tracheary elements was examined in 35 species representing 29 genera of Rosaceae and related families to evaluate the assumption that angiosperm pits are largely invariant. In most Rosaceae, pit membranes between fibers and tracheids frequently appear to have amorphous thickenings with an irregular distribution. Although these structures are torus‐like under the light microscope, observations by electron microscopy illustrate that they represent “pseudotori” or plasmodesmata‐associated thickenings. These thickenings frequently extend from the periphery of the pit membrane and form a cap‐like, hollow structure. Pseudotori are occasionally found in few Elaeagnaceae and Rhamnaceae and appear to be related to species with fiber‐tracheids and/or tracheids. True tori are strongly associated with round to oval pit apertures and are consistently present in narrow tracheary elements of Cercocarpus (Rosaceae), Planera (Ulmaceae), and ring‐porous species of Ulmus and Zelkova (Ulmaceae). Vestured pits with homogenous pit membranes are reported for Hemiptelea (Ulmaceae). The homoplastic nature of pit membrane characteristics may be related to functional adaptations in terms of safety and efficiency of water transport or may reflect different developmental processes of xylem elements. These observations illustrate that there is more variation in angiosperm pits than previously thought.
High seedling relative growth rate and specific leaf area are traits of invasive species: phylogenetically independent contrasts of woody angiosperms
Authors: Grotkopp Eva , Rejmánek Marcel
Published: February 2008

Understanding causal factors of exotic species invasions is important not only for prevention and prioritizing control efforts, but also for providing valuable insights into the underlying biology of contrasting life‐history strategies. In seedling growth analyses, invasive woody species were compared with less‐invasive woody species commonly cultivated in California using phylogenetically corrected procedures (12 phylogenetically independent contrasts). Invasive species were hypothesized to have higher seedling relative growth rates (RGRs) and specific leaf areas (SLAs) than did related less‐invasive species. In phylogenetically independent contrasts conducted among taxa within families, high seedling RGRs and SLAs have significant positive associations with woody plant invasiveness. For contrasts containing species invasive in mediterranean regions, invasive species had significantly larger root biomass allocation than did less‐invasive species. Optimization of fast seedling growth (high RGR) associated with opportunistic resource acquisition (high SLA) and increased root allocation to survive summer drought may be critical for the success of plant invaders in regions with mediterranean climates.
Dynamics of freeze–thaw embolism in Smilax rotundifolia (Smilacaceae)
Authors: Cobb Alexander R. , Choat Brendan , Holbrook N. Michele
Published: February 2008

Freeze–thaw cycles pose a major physiological challenge for all temperate perennial plants, but monocotyledonous vines face a still greater risk because their few large vessels are especially susceptible to embolism and are not replaced by secondary growth. The genus Smilax is particularly remarkable because it is widespread in the tropics but includes species that survive the hard frosts of New England winters. Smilax rotundifolia was monitored for a year for evidence of stem xylem freeze–thaw cavitation and refilling. Embolism of metaxylem was complete by late November and was completely reversed by late April, when root pressures rose as high as 100 kPa. Protoxylem remained full of sap throughout the year in cryogenic scanning electron micrographs. Three methods were used to quantify embolism: percent loss conductivity (PLC), gravimetric air fraction (GAF: mass of water in stem xylem relative to capacity), and cryogenic scanning electron microscopy (cryo‐SEM). The three methods corroborated one another well and gave quantitatively similar results. Osmolality of xylem sap extracted from exuding stems was 64 mol/kg (±7.0, N = 8), consistent with the root pressures observed. Strong root pressure can account for Smilax's survival in temperate regions with severe frosts, where few monocots with persistent aboveground organs are found.
Male‐biased nectar production in a protandrous herb matches predictions of sexual selection theory in plants
Authors: Carlson Jane E.
Published: February 2008

Nectar production may disproportionately benefit male relative to female pollination success. In such cases, sexual selection is often suggested as the cause of asymmetric benefits, yet sexual selection in plants—particularly plants with hermaphroditic flowers—is infrequently tested empirically. Here, I used a protandrous herb with male‐biased nectar production (Chrysothemis friedrichsthaliana, Gesneriaceae) to test predictions from sexual selection theory. During three flowering seasons, I measured nectar production, pollinator visits, and male and female fecundity following different numbers of cross‐pollination events. In accordance with sexual selection predictions, (1) nectar production was greater during the male phase by at least 65%; (2) visits by the main pollinator (hummingbird Phaethornis striigularis) were limiting for part of the season, indicating that plants had to compete for pollinator visits; (3) pollinators spent 53% more time per visit and made 86% more visits to male‐ vs. female‐phase flowers, suggesting that nectar increased male more than female pollination success; and (4) female fecundity was maximized by one visit, whereas male fecundity continued to increase with additional visits. Autonomous self‐pollination further reduced visit requirements for maximum female seed set. These findings match specific sexual selection predictions: they link an observable male bias in a secondary sexual trait (nectar) to positive responses of mating participants (pollinators), resulting in more mating opportunities for mate‐limited males, relative to apparently resource‐limited females. This field‐testing of theoretical predictions provides unique evidence that sexual selection helps maintain nectar production patterns in this and, quite likely, other hermaphroditic plant species.
Ancient paralogy in the cpDNA trnL‐F region in Annonaceae: implications for plant molecular systematics
Authors: Pirie Michael D. , Vargas Maria Paula Balcázar , Botermans Marleen , Bakker Freek T. , Chatrou Lars W.
Published: February 2008

The plastid trnL‐F region has proved useful in molecular phylogenetic studies addressing diverse evolutionary questions from biogeographic history to character evolution in a broad range of plant groups. An important assumption for phylogenetic reconstruction is that data used in combined analyses contain the same phylogenetic signal. The trnL‐F region is often used in combined analyses of multiple chloroplast markers. These markers are assumed to contain congruent phylogenetic signal due to lack of recombination. Here we show that trnL‐F sequences display a phylogenetic signal conflicting with that of other chloroplast markers in Annonaceae, and we demonstrate that this conflict results from ancient paralogy. TrnL‐F copy 2 diverged from trnL‐F copy 1 (as used in family‐wide phylogenetic analyses) in a direct ancestor of the Annonaceae. Although this divergence dates back 88 million years or more, the exons of both copies appear to be intact. In this case, assuming that (putative) chloroplast markers contain the same phylogenetic signal results in an incorrect topology and an incorrect estimate of ages. Our study demonstrates that researchers should be cautious when interpreting gene phylogenies, irrespective of the genome from which they are presumed to have been sampled.
Mannitol‐enhanced, fluid‐phase endocytosis in storage parenchyma cells of celery (Apium graveolens; Apiaceae) petioles
Authors: Etxeberria Ed , Gonzalez Pedro , Pozueta‐Romero Javier
Published: February 2008

We recently demonstrated the occurrence of a sucrose‐enhanced, fluid‐phase endocytic (FPE) mechanism of nutrient uptake in heterotrophic cells. In the present work, the possible enhancement/induction of FPE by photoassimilates other than sucrose was investigated by measuring the incorporation of the fluorescent endocytosis marker d‐TR (dextran‐Texas red, 3000 mw) into celery (Apium graveolens) petiole storage parenchyma (CSP), a tissue that transports and accumulates mannitol. Mannitol uptake in these cells is biphasic, with a hyperbolic phase at concentrations below 20 mM and a linear phase above 20 mM external solute concentration. In the absence of mannitol, or in its presence at concentrations within the hyperbolic phase, CSP cells accumulated low levels of d‐TR. Conversely, d‐TR accumulation by CSP cells was greatly enhanced in the presence of mannitol at concentrations within the linear phase. At high external mannitol concentration, d‐TR accumulation was prevented by the endocytic inhibitors LY294002 and latrunculin B. In addition, d‐TR uptake was temperature dependent under high mannitol concentration. Microscopic observations revealed that d‐TR accumulated in the vacuole. These data support the occurrence of an FPE mechanism in CSP cells that participates in trapping and transport of photoassimilates to the vacuole. The FPE mechanism is enhanced by high mannitol concentrations.
Characterization of Rubisco activase from thermally contrasting genotypes of Acer rubrum (Aceraceae)
Authors: Weston David J. , Bauerle William L. , Swire‐Clark Ginger A. , Moore Brandon d. , Baird Wm. Vance
Published: February 2008

The lability of Rubisco activase function is thought to have a major role in the decline of leaf photosynthesis under moderate heat (<35°C). To investigate this further, we characterized Rubisco activase and explored its role in the previously demonstrated thermal acclimation and inhibition of two genotypes of Acer rubrum originally collected from Florida (FL) and Minnesota (MN). When plants were grown at 33/25°C (day/night) for 21 d, the FL genotype compared to the MN genotype maintained about a two‐fold increase in leaf photosynthetic rates at 33–42°C and had a 22% increase in the maximal rate of Rubisco carboxylation (Vcmax) at 33°C under nonphotorespiratory conditions. Both genotypes had two leaf Rca transcripts, likely from equivalent alternative splicing events. The RCA1 and RCA2 proteins increased modestly in FL plants under warmer temperature, while only RCA2 protein increased in MN plants. Rubisco large subunit (RbsL) protein abundance was relatively unaffected in either genotype by temperature. These results support the idea that Rubisco activase, particularly the ratio of Rubisco activase to Rubisco, may play a role in the photosynthetic heat acclimation in A. rubrum and may have adaptive significance. This mechanism alone is not likely to entirely explain the thermotolerance in the FL genotype, and future research on adaptive mechanisms to high temperatures should consider activase function in a multipathway framework.
The evolution of distyly from tristyly in populations of Oxalis alpina (Oxalidaceae) in the Sky Islands of the Sonoran Desert
Authors: Weller Stephen G. , Domínguez César A. , Molina‐Freaner Francisco E. , Fornoni Juan , LeBuhn Gretchen
Published: February 2008

The evolution of distyly from tristyly was investigated in populations of Oxalis alpina at high elevations throughout the Sky Islands of the Sonoran Desert. Incompatibility systems in tristylous populations, where self‐incompatible short‐, mid‐, and long‐styled morphs occur in populations, vary from those typical of tristylous species in which each morph is equally capable of fertilizing ovules of the other two morphs, to breeding systems in which incompatibility relationships are asymmetric. In these populations, selection against the allele controlling expression of the mid‐styled morph is likely. The degree of modification of incompatibility in the short‐ and long‐styled morphs in 10 populations was strongly associated with fewer mid‐styled morphs, supporting models predicting the effect of these modifications of incompatibility on frequency of the mid‐styled morph. Self‐compatibility of the mid‐styled morph may be important for maintaining the frequency of this morph, depending on the level of self‐pollination, self‐fertilization, and the extent of inbreeding depression. Modifications of incompatibility in tristylous populations and the distribution of distylous populations of O. alpina in the Sky Island region have similar geographic components, indicating the potential importance of historical factors in the evolution of distyly from tristyly.
Do antheridiogens act via gametophyte size? A study of Woodwardia radicans (Blechnaceae)
Authors: Quintanilla Luis G. , de Soto Lucía , Jiménez Ares , Méndez Marcos
Published: February 2008

For many plants, sex is not fixed by genotype but determined by environmental conditions during development. In homosporous pteridophytes, sex is environmentally determined by the presence or absence of antheridiogens, maleness‐inducing pheromones. It has been proposed that antheridiogens primarily reduce growth rate, with small gametophyte size responsible for maleness. To test this hypothesis, the effects of antheridiogen and intergametophytic competition on gender expression and gametophyte size were studied in a culture experiment with Woodwardia radicans. We found that (1) antheridiogen inhibited growth of gametophytes; and (2) slow growth favored maleness, whereas fast growth favored femaleness, irrespective of the presence or absence of antheridiogen. Both conclusions are consistent with the hypothesis that, in W. radicans, antheridiogen effect is mediated by size. They also agree with the “size‐advantage” hypothesis in which energetic limitations associated with relatively small individual size impose a less severe limitation for male reproductive success than for female reproductive success. The results are also discussed with regard to a genetic sex‐determining pathway that has recently been identified.
Do epidermal lens cells facilitate the absorptance of diffuse light?
Authors: Brodersen Craig R. , Vogelmann Thomas C.
Published: February 2008

Many understory plants rely on diffuse light for photosynthesis because direct light is usually scattered by upper canopy layers before it strikes the forest floor. There is a considerable gap in the literature concerning the interaction of direct and diffuse light with leaves. Some understory plants have well‐developed lens‐shaped epidermal cells, which have long been thought to increase the absorption of diffuse light. To assess the role of epidermal cell shape in capturing direct vs. diffuse light, we measured leaf reflectance and transmittance with an integrating sphere system using leaves with flat (Begonia erythrophylla, Citrus reticulata, and Ficus benjamina) and lens‐shaped epidermal cells (B. bowerae, Colocasia esculenta, and Impatiens velvetea). In all species examined, more light was absorbed when leaves were irradiated with direct as opposed to diffuse light. When leaves were irradiated with diffuse light, more light was transmitted and more was reflected in both leaf types, resulting in absorptance values 2–3% lower than in leaves irradiated with direct light. These data suggest that lens‐shaped epidermal cells do not aid the capture of diffuse light. Palisade and mesophyll cell anatomy and leaf thickness appear to have more influence in the capture and absorption of light than does epidermal cell shape.
Hydrochory as a determinant of genetic distribution of seeds within Hibiscus moscheutos (Malvaceae) populations
Authors: Shimamura Ryouji , Kachi Naoki , Kudoh Hiroshi , Whigham Dennis F.
Published: February 2008

Seed dispersal is a major determinant of the spatial genetic structure of plant populations. In this study, we evaluated the role of distinct hydrologic regimes in determining the spatial genetic structure of the seed bank of the wetland plant Hibiscus moscheutos. We analyzed seeds in surface soil samples collected in the autumn and the following spring by determining their allozyme genotypes and estimated the pattern in seed movements during flooding. We selected study sites in nontidal and tidal wetlands with different flooding regimes. One nontidal site had no flooding, while the second nontidal site was inundated for most of the year. One tidal wetland site flooded with almost every tide, and a second tidal site was inundated at moderate frequency. Genetic makeup of the seed bank at the nonflooded site changed little between seasons. Secondary seed dispersal altered absolute allele frequencies at the other three sites, with the greatest change occurring at the two tidally influenced sites. This study demonstrates that secondary hydrochory influences the genetic composition of the seed bank and that hydrologic conditions play an important role in determining the local patterns in seed movements.
Gender‐specific inbreeding depression in a gynodioecious plant, Geranium maculatum (Geraniaceae)
Authors: Chang Shu‐Mei
Published: February 2008

In gynodioecious species, females coexist with hermaphrodites in natural populations even though hermaphrodites attract more pollinators, are capable of reproducing through pollen, and can self‐fertilize. This study tests the hypothesis that inbreeding depression helps to maintain females in natural populations. It also examines whether gender lineages that differ in selfing rates might experience different levels of inbreeding depression. Female and hermaphroditic lineages of the gynodioecious species Geranium maculatum were used in self, sib‐cross and outcross experiments to examine inbreeding depression levels and to determine whether these levels differ between hermaphroditic and female lineages. Six fitness correlates were measured in the greenhouse and compared among pollination types and between genders. Severe inbreeding depression was found for both individual fitness traits and cumulative fitness in early life history stages. Inbreeding depression levels were slightly higher in hermaphroditic than in female lineages, but this difference was not statistically significant. Because females are unable to self‐pollinate and are less likely to experience inbreeding than hermaphrodites under natural conditions, these results suggest that severe inbreeding depression could confer a selective advantage for females that could help to maintain females in natural populations.
Patterns of polyploid evolution in Greek marsh orchids (Dactylorhiza; Orchidaceae) as revealed by allozymes, AFLPs, and plastid DNA data
Authors: Hedrén Mikael , Nordström Sofie , Hovmalm Helena A. Persson , Pedersen Henrik Ærenlund , Hansson Sven
Published: February 2008

Polyploidy is common in higher plants, and speciation in polyploid complexes is usually the result of reticulate evolution. We examined variation in nuclear AFLP fingerprints, nuclear isozymes, and hypervariable plastid DNA loci to describe speciation patterns and species relationships in the Dactylorhiza incarnata/maculata polyploid complex (marsh orchids; Orchidaceae) in Greece. Several endemic taxa with restricted distribution have been described from this area, and to propose meaningful conservation priorities, detailed relationships need to be known. We identified four independently derived allopolyploid lineages, which is a pattern poorly correlated with prevailing taxonomy. Three lineages were composed of populations restricted to small areas and may be of recent origins from extant parental lineages. One lineage with wide distribution in northern Greece was characterized by several unique plastid haplotypes that were phylogenetically related and evidently older. The D. incarnata/maculata polyploid complex in Greece has high levels of genetic diversity at the polyploid level. This diversity has accumulated over a long time and may include genetic variants originating from now extinct parental populations. Our data also indicate that the Balkans may have constituted an important refuge from which northern European Dactylorhiza were recruited after the Weichselian ice age.
Inflorescence diversification in the “finger millet clade” (Chloridoideae, Poaceae): a comparison of molecular phylogeny and developmental morphology
Authors: Liu Qing , Peterson Paul M. , Columbus J. Travis , Zhao Nanxian , Hao Gang , Zhang Dianxiang
Published: February 2008

Within the Poaceae, inflorescence diversification and its bearing on phylogeny and evolution are exceedingly complex. We used phylogenetic information of the “finger millet clade,” a group of grasses with digitate inflorescences, to study the inflorescence diversification. This clade appears monophyletic in the morphological and molecular phylogenetic analyses. Three well‐supported clades are shown in our cpDNA‐derived phylogeny, with clades I and III consisting of species of Chloris and Microchloa, respectively, and clade II including species of Cynodon, Dactyloctenium, and Eleusine. Variation appears at different times throughout development. Changes involving primordium number and arrangement occur very early, changes involving duration of primordium activity occur much later. Characters derived from the comparison of developmental sequences were optimized onto the most parsimonious tree. The developmental characters were congruent with the molecular phylogeny. Two developmental characters may not be homologous in the Chloris subclade and the Cynodon subclade.
Relationships of cucumbers and melons unraveled: molecular phylogenetics ofCucumisand related genera (Benincaseae, Cucurbitaceae)
Authors: Ghebretinsae Amanuel G. , Thulin Mats , Barber Janet C.
Published: February 2008

Cucumis(Cucurbitaceae) comprises 33 species of annuals and perennials with a major native center of diversity in tropical and southern Africa. The genus includes some economically important and widely grown vegetables such as cucumbers and melons. Monophyly of the genus has been disputed in previous studies, but with only limited sampling. Relationships withinCucumisare thus poorly understood; moreover, the validity of the closely related genera has not been thoroughly tested. The present study was undertaken to test the monophyly ofCucumisand several closely related genera, to test sectional circumscriptions withinCucumis, and to understand the biogeographical history of the genus. We sequenced the nuclear ITS and plastidtrnS‐trnGregions for 40 ingroup and three outgroup taxa, representing all recognized subgenera and sections. Parsimony, maximum likelihood, and Bayesian analyses foundCucumella,Oreosyce,Mukia,Myrmecosicyos, andDicaelospermumnested withinCucumis. The clades recovered within theCucumiscomplex in some instances represent the first phylogenetically derived hypothesis of relationships, whereas others correspond to previous subgeneric and sectional classifications. At least four introductions from Africa to Asia, as well as one reintroduction to Africa, are suggested within theCucumiscomplex.Cucumis sativus(cucumber) is strongly supported as sister to the eastern AsianC. hystrix, whereasC. melo(melon) is strongly supported as sister toC. sagittatusin southern Africa.
Foraging behavior affects pollen removal and deposition in Impatiens capensis (Balsaminaceae)
Authors: Young Helen J. , Dunning Dan W. , von Hasseln Kyle W.
Published: February 2008

Flowers of most plant species are visited by a variety of animals. Some of these visitors are effective pollinators while others remove resources without transferring pollen. Studies comparing the effectiveness of different visitors as pollinators often compare taxa without considering variation in behavior within a taxon. Wilson and Thomson (Ecology 72: 1503–1507, 1991) documented the effects of honey bees and bumble bees on the pollination dynamics of Impatiens capensis. They found that pollen‐collecting honey bees removed large numbers of pollen grains from anthers but deposited little of it on stigmas; bumble bees, which sought nectar, removed less pollen but deposited more of it on stigmas. It is unclear whether the low pollen transfer efficiencies of honey bees are explained by their morphology or by their pollen‐collecting behavior. We repeated the work of Wilson and Thomson at a site where honey bees were foraging for nectar, not pollen. We measured the quantity of pollen remaining in anthers, the number of pollen grains deposited on stigmas, and seed production after single visits by honey bees and bumble bees. The differences between the taxa disappeared when they were foraging in a similar manner. Our results clearly demonstrate the importance of foraging behavior on the pollination effectiveness of floral visitors.
Differentiation and growth traits associated with acrotony in the apple tree (Malus ×domestica, Rosaceae)
Authors: Lauri Pierre‐Eric
Published: February 2008

Branching is a key factor in the evolutionary diversification of plants and is a main criterion for plant architecture analysis. Among descriptive features, acrotony is defined as increased vigor of the vegetative proleptic branches (from dormant buds), from the proximal to the distal part of the parent growth unit. I hypothesized that acrotony could be extended to other, usually poorly described, architectural traits. The study was conducted on two architecturally contrasting apple (Malus ×domestica) cultivars, ‘Pitchounette’ and ‘Chantecler.’ The proportion and size of various offspring entities were assessed according to their position along the shoot for 2 years after parent shoot growth. Acrotony was characterized by two inverse phenomena: an acropetal decrease in the proportion of latent buds and of laterals that aborted, and an acropetal increase in the proportion of reproductive laterals among growing laterals. Distally located reproductive laterals had more spur leaves and flowers and higher fruit set and flowered earlier than reproductive laterals lower on the parent annual shoot. The results suggest that the length‐based criterion used for acrotony should be integrated into a general conceptual framework in which the organogenetic potential of the axillary meristem increases from the proximal to the distal part of the annual shoot, leading to greater branching density, larger offspring, and a greater propensity for flower bud formation over consecutive years.
Giant cuticular pores in Eidothea zoexylocarya (Proteaceae) leaves
Authors: Carpenter Raymond J. , Jordan Gregory J. , Leigh Andrea , Brodribb Timothy J.
Published: February 2008

Ubiquitous, large diameter pores have not previously been adequately demonstrated to occur in leaf cuticles. Here we show conclusively that such structures occur in Eidothea zoexylocarya, a rainforest tree species of Proteaceae restricted to the Australian Wet Tropics. The pores are abundant, large‐diameter apertures (∼1 μm), that extend perpendicularly most of the way through the cuticle from the inside. They occur on both sides of the leaf, but are absent from the cuticle associated with stomatal complexes on the abaxial side. No such pores were found in any other species, including the only other species of Eidothea, E. hardeniana from New South Wales, and other species that have previously been purported to possess cuticular pores. To determine whether these pores made the cuticles more leaky to water vapor, we measured astomatous cuticular conductances to water vapor for E. zoexylocarya and seven other Proteaceae species of the Wet Tropics. Cuticular conductance for E. zoexylocarya was relatively low, indicating that the prominent pores do not increase conductance. The function of the pores is currently obscure, but the presence of both pores and an adaxial hypodermis in E. zoexylocarya but not E. hardeniana suggests evolution in response to greater environmental stresses in the tropics.
Multiclavula ichthyiformis (Fungi: Basidiomycota: Cantharellales: Clavulinaceae), a remarkable new basidiolichen from Costa Rica
Authors: Nelsen Matthew P. , Lücking Robert , Umaña Loengrin , Trest Marie T. , Will‐Wolf Susan , Chaves José Luis , Gargas Andrea
Published: February 2008

The new basidiolichen Multiclavula ichthyiformis Nelsen, Lücking, Umaña, Trest & Will‐Wolf is described from Costa Rica. The new species differs from other species of Multiclavula in having a basidiocarp with tomentose stipe and flattened lamina with nonamphigenous hymenium. Molecular sequence data (ITS) confirmed its placement within Multiclavula in the Clavulinaceae (Cantharellales, Agaricomycetes). The new lichen was discovered in a Central American paramo remnant, illustrating the importance of biotic inventories of fungi and lichens to increase our knowledge of the diversity of these groups in endangered tropical ecosystems. The new species was found as part of the TICOLICHEN project in Costa Rica.
Timing of self‐compatibility, flower longevity, and potential for male outcross success in Leptosiphon jepsonii (Polemoniaceae)
Authors: Weber Jennifer J. , Goodwillie Carol
Published: February 2008

When fertilization triggers flower senescence, early autonomous selfing may cause flowers to senesce before pollen has dispersed, discounting unused pollen. Selfing‐induced flower senescence was examined in Leptosiphon jepsonii, a species that varies in the timing of self‐compatibility. In field and greenhouse experiments, fertilization had a large effect on flower senescence; most outcrossed flowers senesced after 1 d whereas emasculated flowers lasted 2–5 d. In a comparison of inbred lines from three populations, longevity of autonomously selfed flowers of early self‐compatible individuals was significantly less than that of late self‐compatible individuals. In field experiments, autonomously selfed flowers were shorter‐lived in a predominantly early‐selfing population than in a predominantly late‐selfing population. Pollen was available and viable beyond the first day of anthesis, suggesting that reductions in flower longevity caused by autonomous selfing could incur a cost to male outcross fitness. We argue that this effect is likely to be most pronounced under intermediate rates of pollinator visitation. Observed pollinator visitation rates ranged from 0.035–0.775 visits per flower per day, indicating a potential for selfing‐induced flower senescence to incur pollen discounting in Leptosiphon jepsonii.
Chromosome numbers, nuclear DNA content, and polyploidy in Consolea (Cactaceae), an endemic cactus of the Caribbean Islands
Authors: Negrón‐Ortiz Vivian
Published: February 2008

Polyploidy, an important mechanism of plant evolution, was investigated in Consolea, an endemic Caribbean opuntioid genus represented by nine subdioecious species with very narrow distributions, including species classified as rare or threatened. Standard chromosome counting and flow cytometric analyses were used to determine chromosome numbers and ploidy of each taxon. Compared to the base number (x = 11), the mitotic and meiotic counts indicated that there are seven hexaploid (2n = 66) and two octoploid species (2n = 88); no diploids were found. Histograms of intact nuclei confirmed that all species are polyploid, with C‐DNA values ranging from 4.88–9.50 pg. The variation of DNA content was significantly higher for the octoploids than for the hexaploids. Male and female sexual morphs had similar DNA content, suggesting that there are no sex chromosomes. Cytomixis between cells and microsporocytes with no chromatin were observed. This provides a mechanism whereby gametes with variable chromosome numbers are produced, influencing reproduction and promoting speciation. In conclusion, C‐DNA content and chromosome number separated Consolea species into two groups, which may correspond to two phylogenetic lineages or indicate that polyploidization occurred independently, with comparable effects on C‐DNA content.
Complex distribution patterns of di‐, tetra‐, and hexaploid cytotypes in the European high mountain plant Senecio carniolicus (Asteraceae)
Authors: Suda Jan , Weiss‐Schneeweiss Hanna , Tribsch Andreas , Schneeweiss Gerald M. , Trávníček Pavel , Schönswetter Peter
Published: February 2008

DNA ploidy levels were estimated using DAPI‐flow cytometry of silica‐dried specimens of the European mountain plant Senecio carniolicus (Asteraceae), covering its entire distribution area in the Eastern Alps (77 populations, 380 individuals) and the Carpathians (five populations, 22 individuals). A complex pattern of ploidy level variation (2x, 4x, 5x, 6x, and 7x cytotypes) was found in this species, which has been considered uniformly hexaploid. Hexaploids predominated in the Eastern Alps and was the only cytotype found in the Carpathians, while odd ploidy levels (5x, 7x) constituted a small fraction of the samples (<1.3%). Tetraploids occurred in two disjunct areas, which correspond with putative Pleistocene refugia for silicicolous alpine plants. Diploids occurred in large portions of the Alps but were absent from areas most extensively glaciated in the past. Intrapopulational cytotype mixture was detected in 22 populations—the majority involving diploids and hexaploids—with intermediate ploidy levels mostly lacking, suggesting limited gene flow and the evolution of reproductive isolation. Significant and reproducible intracytotype variation in nuclear DNA content was observed. Higher genome size in western diploids might be due to ancient introgression with the closely related S. incanus or to different evolutionary pathways in the geographically separated diploids.
Expression of matK: functional and evolutionary implications
Authors: Barthet Michelle M. , Hilu Khidir W.
Published: February 2008

Strong phylogenetic signal from matK has rendered it an invaluable gene in plant systematic and evolutionary studies at various evolutionary depths. Further, matK is proposed as the only chloroplast‐encoded group II intron maturase, thus implicating MATK in chloroplast posttranscriptional processing. For a protein‐coding gene, matK has an unusual evolutionary mode and tempo, including relatively high substitution rates at both the nucleotide and amino acids levels. These evolutionary features have raised questions about matK function. In the current study, we examined matK RNA and protein from representative land plant species to provide insight into functional aspects of this unusual gene. We report the first evidence of a transcript for matK separate from the trnK precursor and demonstrate that a full‐length MATK protein exists in five angiosperm species. We also show that matK RNA and protein levels are regulated by light and developmental stage, suggesting functional roles for this putative maturase. Specifically, matK expression increased after etiolation and decreased at 4 weeks after germination. This work provides evidence for the expression of the only putative chloroplast‐encoded group II intron maturase and insight into regulation mechanisms relating to plant development and, indirectly, to photosynthesis.
Genetic consequences of pre‐Columbian cultivation for Agave murpheyi and A. delamateri (Agavaceae)
Authors: Parker Kathleen C. , Hamrick J. L. , Hodgson Wendy C. , Trapnell Dorset W. , Parker Albert J. , Kuzoff Robert K.
Published: February 2008

Pre‐Columbian farmers cultivated several species of agave in central Arizona from ca. A.D. 600–1350. Because of the longevity and primarily asexual reproduction of these species, relict agave clones remain in the landscape and provide insights into pre‐Columbian agricultural practices. We analyzed variation in allozyme allele frequencies to infer genetic effects of prehistoric cultivation on Agave murpheyi and A. delamateri, specifically to estimate genetic diversity and structure, to determine whether cultivated populations descended from a single clone, and to examine regional‐scale genetic variation. Agave murpheyi maintained more genetic diversity at the species and population levels than A. delamateri, and A. murpheyi populations typically included more multilocus genotypes. Relict plants from prehistoric fields reflect a more complex history than descent from a single clone; A. murpheyi populations may have included more diversity initially because bulbils (produced routinely in A. murpheyi but not A. delamateri) and possibly seed would have facilitated transport of genetically diverse planting stock. Genetic variation in both cultigens was lower than in most contemporary commercial crops but similar to that observed in modern traditional agricultural systems.
Variation in vegetative and flowering phenology in a forest herb caused by environmental heterogeneity
Authors: Dahlgren Johan P. , von Zeipel Hugo , Ehrlén Johan
Published: February 2008

Timing of seasonal plant development can affect biotic interactions and plant fitness. Phenology is governed largely by temperature and may therefore be affected by global climate warming, making this an important area of research. Several factors in addition to temperature may cause differences in phenology. We studied the influence of local environment, plant size, and reproductive effort on shoot emergence and flowering time of 290 individuals of Actaea spicata (Ranunculaceae), distributed among 25 plots in four populations. We used multiple regression and structural equation models (SEM) to study causal relationships. Among plots, soil temperature and canopy cover explained 63% of the variation in shoot emergence. Soil temperature, slope, and canopy cover together explained 83% of the variation in flowering time. Within plots, small plants on steep south‐facing slopes with high soil potassium concentrations emerged earlier in the year. Plants emerging earlier flowered earlier, but no environmental factors affected flowering time directly. We found no effects of reproductive effort. Our results support the view that flowering time of temperate forest herbs is constrained by several environmental factors acting indirectly through effects on shoot emergence time.
Molecular insights into the evolution of crop plants
Authors: Burger Jutta C. , Chapman Mark A. , Burke John M.
Published: February 2008

The domestication and improvement of crop plants have long fascinated evolutionary biologists, geneticists, and anthropologists. In recent years, the development of increasingly powerful molecular and statistical tools has reinvigorated this now fast‐paced field of research. In this paper, we provide an overview of how such tools have been applied to the study of crop evolution. We also highlight lessons that have been learned in light of a few long‐standing and interrelated hypotheses concerning the origins of crop plants and the nature of the genetic changes underlying their evolution. We conclude by discussing compelling evolutionary genomic approaches that make possible the efficient and unbiased identification of genes controlling crop‐related traits and provide further insight into the actual timing of selection on particular genomic regions.
The relative fitness of parental and hybrid Kunzea (Myrtaceae): The interaction of reproductive traits and ecological selection
Authors: Tierney David A. , Wardle Glenda M.
Published: February 2008

Up to 22% of plant species are the result of breeding among species—hybridization—directly conflicting with the prediction that hybrids, compared to parental species, are intermediate in character and of low fitness and little consequence. Few studies, however, have compared the fitness of hybrids and parental species under field conditions. This study evaluates components of fitness in the field for naturally occurring hybrids of the shrub Kunzea, relative to the parental speciesKunzea rupestris. Hybrid plants did not differ from the parental species in the level of effective pollination. Thus, we found no support for Grant's model (Evolution: International Journal of Organic Evolution3: 82–97) of reduced fitness of hybrids via reduced pollination level (the intermediate hypothesis). Hybrids displayed variable fitness across the measured fitness components. Seed set levels for hybrids were structured among populations, suggesting genetic structuring for this fitness component at this scale. The response of hybrids to fire (a major selective force in the study system) was partly consistent with a resource trade‐off model. Hybrids were large robust plants but most did not resprout after fire. Hence, the fitness of hybrids was complex. We developed a model for relative fitness to estimate fitness for species and hybrids with complex life histories.