bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple resonance damping or how do trees escape dangerously large oscillations?
Authors: Spatz Hanns‐Christof , Brüchert Franka , Pfisterer Jochen
Published: February 2008

To further understand the mechanics of trees under dynamic loads, we recorded damped oscillations of a Douglas fir (Pseudotsuga menziesii) tree and of its stem without branches. Eigenfrequencies of the branches were calculated and compared to the oscillation frequency of the intact tree. The term eigenfrequency is used here to characterize the calculated resonance frequency of a branch fixed at the proximal end to a solid support. All large branches had nearly the same frequency as the tree. This property is a prerequisite for the distribution of mechanical energy between stem and branches and leads to an enhanced efficiency of damping. We propose that trees constitute systems of coupled oscillators tuned to allow optimal energy dissipation.
Cryptic species and host specificity in the ectomycorrhizal genus Strobilomyces (Strobilomycetaceae)
Authors: Sato Hirotoshi , Yumoto Takakazu , Murakami Noriaki
Published: February 2008

Taxonomical classification of higher fungi remains an important challenge and can benefit from the application of molecular analysis. We propose that the ectomycorrhizal (EM) fungal taxa might include a number of cryptic species because there are few morphological characteristics useful for distinguishing among these fungi. Previously, host specificity in most EM fungi was thought to be low, but we suspect that confusion of cryptic species has led to an underestimate of fungal host specificity. We analyzed both nuclear and mitochondrial DNA sequences from Strobilomyces fungi and obtained evidence that what were previously described as four species can be grouped into 14 distinct lineages, suggesting that these lineages might be distinct biological species. Moreover, we identified host plants for Strobilomyces via nucleotide sequencing of both fungal and plant DNA from EM samples. Most lineages of Strobilomyces tested in this study were associated only with Fagaceae trees, even though Strobilomyces species were previously thought to be generalists with regard to hosts. Thus, we present an approach useful for identifying cryptic species and detecting the true host range of a set of EM fungi in natural conditions.
The impact of pollination syndrome and habitat on gene flow: a comparative study of two Streptocarpus (Gesneriaceae) species
Authors: Hughes Mark , Möller Michael , Edwards Trevor J. , Bellstedt Dirk U. , de Villiers Margaret
Published: February 2008

Gene flow through pollen and seed dispersal is important in terms of population differentiation and eventually speciation. Seed and pollen flow are affected in turn by habitats and pollen vectors. We examined the effect of different pollinators and habitats on gene flow by comparing two species of Streptocarpus, using microsatellite and chloroplast RFLP markers. Populations of the forest‐dwelling S. primulifolius were highly differentiated according to nuclear microsatellite data and had mutually exclusive chloroplast haplotypes. This result is congruent with infrequent seed dispersal and limited between‐population foraging by the long‐tongued fly pollinator Stenobasipteron wiedemanni. In contrast, populations of S. dunnii growing in exposed crags had lower levels of population differentiation according to both nuclear and chloroplast data, congruent with a hypothesis of more effective between population seed dispersal and greater pollen‐mediated gene flow due to the sunbird pollinator Nectarinia famosa. The population genetic behavior of these species is reflected in their taxonomy and phylogenetic position; S. primulifolius belongs to a taxonomically complex clade in which recent speciation is evident, while the clade containing S. dunnii is characterized by taxonomically well‐defined species on longer phylogenetic branches. Our study shows that pollinator movements and seed dispersal patterns are a major determinant of the evolutionary trajectories of these species.
Effects of floral display size and biparental inbreeding on outcrossing rates in Delphinium barbeyi (Ranunculaceae)
Authors: Williams Charles F.
Published: February 2008

Floral display size represents a tradeoff between the benefits of increased pollinator visitation and the quantity of pollen received vs. the costs of increased self‐pollination and reduced pollination quality. Plants with large floral displays often are more attractive to pollinators, but pollinators visit more flowers per plant. Intraplant foraging movements should increase self‐pollination through geitonogamy, lowering outcrossing rates in large plants. Local genetic structure should also increase inbreeding and decrease outcrossing estimates, if pollinators move between neighboring, related plants. These predictions were tested in a population of larkspurs (Delphinium barbeyi) in Colorado. Allozymes were used to estimate outcrossing rates of plants varying in display size. Floral displays varied widely (2–1400 flowers; 1–26 inflorescences per plant), and outcrossing rate decreased significantly with increasing display size. Large, multistalked plants self over twice as frequently as single‐stalked plants (46 vs. 21%). Local population structure is significant, and biparental inbreeding depresses outcrossing in plants surrounded by genetically similar neighbors. Protandry, coupled with stereotypical bottom‐up pollinator foraging, reduces self‐fertilization by autogamy or geitonogamy within inflorescences. Selfing is predominantly (>60%) by geitonogamy between inflorescences in large plants. Geitonogamy may be a significant cost to plants with large floral displays if inbreeding depression and/or pollen and ovule discounting results. If so, floral display size, particularly inflorescence number, may be under contrasting selection for pollination quantity vs. quality.
Correlated evolution of fruit size and sexual expression in andromonoeciousSolanumsectionsAcanthophoraandLasiocarpa(Solanaceae)
Authors: Miller Jill S. , Diggle Pamela K.
Published: February 2008

Andromonoecy is hypothesized to evolve as a mechanism enabling plants to independently allocate resources to female and male function. If staminate flower production is a mechanism to regulate allocation to female function (i.e., fruit production), then large‐fruited species should be more strongly andromonoecious than smaller‐fruited taxa because more resources are required to mature large fruit. We combined phylogenetically independent contrast analyses with extensive phenotypic characterization under common greenhouse conditions to examine the predicted relationship between fruit mass and the strength of andromonoecy among 13 species inSolanumsectionsAcanthophoraandLasiocarpa. The strength of andromonoecy, defined as the proportion of staminate flowers produced within inflorescences, was significantly and positively associated with fruit mass in both naïve and phylogenetically independent analyses. Our results are consistent with the hypothesis that andromonoecy functions as a mechanism to regulate allocation to female function and suggest that the strength of andromonoecy is also associated with resource limitation. In general, we find that strong andromonoecy appears to arise via reductions in hermaphroditic flower number. However, increases in staminate flowers have also contributed to transitions to strong andromonoecy in certain species. Finally, our analyses identified a suite of correlated characters (flower size, ovary width, fruit mass) that are associated with changes in the sexual expression of andromonoecy.
Sexually dimorphic inflorescence traits in a wind‐pollinated species: heritabilities and genetic correlations in Schiedea adamantis (Caryophyllaceae)
Authors: Weller Stephen G. , Sakai Ann K. , Culley Theresa M. , Campbell Diane R. , Ngo Paul , Dunbar‐Wallis Amy K.
Published: February 2008

Sexual dimorphism may be especially pronounced in wind‐pollinated species because they lack the constraints of biotically pollinated species that must present their pollen and stigmas in similar positions to ensure pollen transfer. Lacking these constraints, the sexes of wind‐pollinated species may diverge in response to the different demands of pollen dispersal and receipt, depending on the magnitude of genetic correlations preventing divergence between sexes. Patterns of sexual dimorphism and genetic variation were investigated for inflorescence traits in Schiedea adamantis (Caryophyllaceae), a species well adapted to wind‐pollination, and compared to S. salicaria, a species with fewer adaptations to wind pollination. For S. adamantis, dimorphism was pronounced for inflorescence condensation and its components, including lateral flower number and pedicel length. Within sexes, genetic correlations between traits may constrain the relative shape of the inflorescence. Correlations detected across sexes may retard the evolution of sexual dimorphism in inflorescence structure, including features favoring enhanced dispersal and receipt of pollen. Despite genetic correlations across sexes, common principal components analysis showed that genetic variance–covariance matrices (G matrices) differed significantly between the sexes, in part because of greater genetic variation for flower number in hermaphrodites than in females. G matrices also differed between closely related S. adamantis and S. salicaria, indicating the potential for divergent evolution of inflorescence structure despite general similarities in morphology and pollination biology.
Molecular phylogeny of Macaranga, Mallotus, and related genera (Euphorbiaceae s.s.): insights from plastid and nuclear DNA sequence data
Authors: Kulju Kristo K. M. , Sierra Soraya E. C. , Draisma Stefano G. A. , Samuel Rosabelle , van Welzen Peter C.
Published: February 2008

Macaranga and Mallotus (Euphorbiaceae s.s.) are two closely related, large paleo(sub)tropical genera. To investigate the phylogenetic relationships between and within them and to determine the position of related genera belonging to the subtribe Rottlerinae, we sequenced one plastid (trnL‐F) and three nuclear (ITS, ncpGS, phyC) markers for species representative of these genera. The analyses demonstrated the monophyly of Macaranga and the paraphyly of Mallotus and revealed three highly supported main clades. The genera Cordemoya and Deuteromallotus and the Mallotus sections Hancea and Oliganthae form a basal Cordemoya s.l. clade. The two other clades, the Macaranga clade and the Mallotus s.s. clade (the latter with Coccoceras, Neotrewia, Octospermum, and Trewia), are sister groups. In the Macaranga clade, two basal lineages (comprising mostly sect. Pseudorottlera) and a crown group with three geographically homogenous main clades were identified. The phylogeny of the Mallotus s.s. clade is less clear because of internal conflict in all four data sets. Many of the sections and informal infrageneric groups of Macaranga and Mallotus do not appear to be monophyletic. In both the Macaranga and Mallotus s.s. clades, the African and/or Madagascan taxa are nested in Asian clades, suggesting migrations or dispersals from Asia to Africa and Madagascar.
Glomeromycotean associations in liverworts: a molecular, cellular, and taxonomic analysis
Authors: Ligrone Roberto , Carafa Anna , Lumini Erica , Bianciotto Valeria , Bonfante Paola , Duckett Jeffrey G.
Published: February 2008

Liverworts form endophytic associations with fungi that mirror mycorrhizal associations in tracheophytes. Here we report a worldwide survey of liverwort associations with glomeromycotean fungi (GAs), together with a comparative molecular and cellular analysis in representative species. Liverwort GAs are circumscribed by a basal assemblage embracing the Haplomitriopsida, the Marchantiopsida (except a few mostly derived clades), and part of the Metzgeriidae. Fungal endophytes from Haplomitrium, Conocephalum, Fossombronia, and Pellia were related to Glomus Group A, while the endophyte from Monoclea was related to Acaulospora. An isolate of G. mosseae colonized axenic thalli of Conocephalum, producing an association similar to that in the wild. Fungal colonization in marchantialean liverworts suppressed cell wall autofluorescence and elicited the deposition of a new wall layer that specifically bound the monoclonal antibody CCRC‐M1 against fucosylated side groups associated with xyloglucan and rhamnogalacturonan I. The interfacial material covering the intracellular fungus contained the same epitopes present in host cell walls. The taxonomic distribution and cytology of liverwort GAs suggest an ancient origin and multiple more recent losses, but the occurence in widely separated liverwort taxa of fungi related to glomeromycotean lineages that form arbuscular mycorrhizas in tracheophytes, notably the Glomus Group A, is better explained by host shifting from tracheophytes to liverworts.
Estimation of gene flow into fragmented populations ofBursera simaruba(Burseraceae) in the dry‐forest life zone of Puerto Rico
Authors: Dunphy Brian K. , Hamrick James L.
Published: February 2008

We examined the impact of habitat fragmentation on gene flow in populations of the neotropical treeBursera simaruba. In particular, we compared the effectiveness of three common techniques to estimate gene flow in the context of a highly disturbed system. Paternity analysis on emerging seedlings from eight small (N= 3 to 9) stands of trees showed that between 45% and 100% of seedlings were sired from outside their stand, indicating pollen moved readily over the isolation distances examined. Based on six populations of 21–24 trees each, estimates of allozyme genetic diversity (Ps= 73.3%;He= 0.244) were higher than those reported for species with similar life history traits. Indirect,FST‐based gene flow estimates for these six populations yielded an estimate of 3.57 migrants per generation, although possible violations of model assumptions limit the reliability of the estimate. A twogener analysis showed pollen moved either 320 m or 361 m and that there were only 2.46 effective pollen donors per maternal tree. Despite the potential for long‐distance pollen movement, seed abortion was high, especially in stands with fewer than four trees. Population size, rather than isolation distance, appears to limit reproduction in the populations examined.
Hybridization and morphogenetic variation in the invasive alien Fallopia (Polygonaceae) complex in Belgium
Authors: Tiébré Marie‐S. , Bizoux Jean‐P. , Hardy Olivier J. , Bailey John P. , Mahy Grégory
Published: February 2008

The invasive alien knotweeds, Fallopia spp. (Polygonaceae), are some of the most troublesome invasive species in Europe and North America. Invasive success in Fallopia may be enhanced by multiple hybridization events. We examined the pattern of hybridization and its evolutionary consequences in Belgium with a concerted analysis of ploidy levels (chromosome counts and flow cytometry), morphological variation, and genetic variation (RAPDs). At least four taxa with different ploidy levels were part of the pattern of invasion in Belgium. Hybrid F. ×bohemica with various chromosome numbers restored the genotypic diversity that was lacking in the parental species. Hybrid genotypes were mainly assigned to a specific genetic pool and not to a mixture between the genetic pools of the putative parental species as would be expected for hybrids. Parental species and hexaploid hybrids differed significantly for a set of well‐defined morphological characters, enabling future researchers to distinguish these taxa. On the basis of our results, the importance of hybridization has probably been underestimated in large parts of the adventive range of alien Fallopia species, pointing to the need for concerted molecular and morphological analyses in the study of the evolutionary consequences of hybridization.
Evolution of shoot apical meristem structures in vascular plants with respect to plasmodesmatal network
Authors: Imaichi Ryoko , Hiratsuka Rie
Published: February 2008

Vascular plants have evolved shoot apical meristems (SAMs), whose structures differ among plant groups. To clarify the evolutionary course of the different structural types of SAMs, we compared plasmodesmatal networks in the SAMs for 17 families and 24 species of angiosperms, gymnosperms, and pteridophytes, using transmission electron microscopy (TEM). The plasmodesmata (PD) in almost all cell walls in median longitudinal sections of SAMs were counted, and the PD density per unit area was calculated for each cell wall. Angiosperm and gymnosperm SAMs have low densities, with no difference between stratified (tunica‐corpus) and unstratified structures. SAMs of ferns, including Psilotum and Equisetum, have average densities that are more than three times higher than those of seed plants. Interestingly, microphyllous lycopods have both the fern and seed‐plant types of PD networks; Selaginellaceae SAMs with single apical cells have high PD densities, while SAMs of Lycopodiaceae and Isoetaceae with plural initial cells have low PD densities, equivalent to those of seed plants. In summary, PD networks are strongly correlated to SAM organizations—SAMs with single and plural initial cells have the fern and seed‐plant types of PD, respectively. The two SAM organizations may have evolved separately in lycophytes and euphyllophytes and may be associated with gain or loss of the ability to form secondary PD.
Bizonoplast, a unique chloroplast in the epidermal cells of microphylls in the shade plant Selaginella erythropus (Selaginellaceae)
Authors: Sheue Chiou‐Rong , Sarafis Vassilios , Kiew Ruth , Liu Ho‐Yih , Salino Alexandre , Kuo‐Huang Ling‐Long , Yang Yuen‐Po , Tsai Chi‐Chu , Lin Chun‐Hung , Yong Jean W. H. , Ku Maurice S. B.
Published: February 2008

Study of the unique leaf anatomy and chloroplast structure in shade‐adapted plants will aid our understanding of how plants use light efficiently in low light environments. Unusual chloroplasts in terms of size and thylakoid membrane stacking have been described previously in several deep‐shade plants. In this study, a single giant cup‐shaped chloroplast, termed a bizonoplast, was found in the abaxial epidermal cells of the dorsal microphylls and the adaxial epidermal cells of the ventral microphylls in the deep‐shade spike moss Selaginella erythropus. Bizonoplasts are dimorphic in ultrastructure: the upper zone is occupied by numerous layers of 2–4 stacked thylakoid membranes while the lower zone contains both unstacked stromal thylakoids and thylakoid lamellae stacked in normal grana structure oriented in different directions. In contrast, other cell types in the microphylls contain chloroplasts with typical structure. This unique chloroplast has not been reported from any other species. The enlargement of epidermal cells into funnel‐shaped, photosynthetic cells coupled with specific localization of a large bizonoplast in the lower part of the cells and differential modification in ultrastructure within the chloroplast may allow the plant to better adapt to low light. Further experiments are required to determine whether this shade‐adapted organism derives any evolutionary or ecophysiological fitness from these unique chloroplasts.
Comparative height–crown allometry and mechanical design in 22 tree species of Kuala Belalong rainforest, Brunei, Borneo
Authors: Osunkoya Olusegun O. , Omar‐Ali Kharunnisa , Amit Norratna , Dayan Juita , Daud Dayanawati S. , Sheng Tan K.
Published: February 2008

In rainforests, trunk size, strength, crown position, and geometry of a tree affect light interception and the likelihood of mechanical failure. Allometric relationships of tree diameter, wood density, and crown architecture vs. height are described for a diverse range of rainforest trees in Brunei, northern Borneo. The understory species follow a geometric model in their diameter–height relationship (slope, β = 1.08), while the stress–elasticity models prevail (β = 1.27–1.61) for the midcanopy and canopy/emergent species. These relationships changed with ontogeny, especially for the understory species. Within species, the tree stability safety factor (SSF) and relative crown width decreased exponentially with increasing tree height. These trends failed to emerge in across‐species comparisons and were reversed at a common (low) height. Across species, the relative crown depth decreased with maximum potential height and was indistinguishable at a common (low) height. Crown architectural traits influence SSF more than structural property of wood density. These findings emphasize the importance of applying a common reference size in comparative studies and suggest that forest trees (especially the understory group) may adapt to low light by having deeper rather than wider crowns due to an efficient distribution and geometry of their foliage.
Genomic relationships between the cultivated peanut (Arachis hypogaea, Leguminosae) and its close relatives revealed by double GISH
Authors: Seijo Guillermo , Lavia Graciela I. , Fernández Aveliano , Krapovickas Antonio , Ducasse Daniel A. , Bertioli David J. , Moscone Eduardo A.
Published: February 2008

Arachis hypogaeais a natural, well‐established allotetraploid (AABB) with 2n= 40. However, researchers disagree on the diploid genome donor species and on whether peanut originated by a single or multiple events of polyploidization. Here we provide evidence on the genetic origin of peanut and on the involved wild relatives using double GISH (genomic in situ hybridization). Seven wild diploid species (2n= 20), harboring either the A or B genome, were tested. Of all genomic DNA probe combinations assayed,A. duranensis(A genome) andA. ipaensis(B genome) appeared to be the best candidates for the genome donors because they yielded the most intense and uniform hybridization pattern when tested against the corresponding chromosome subsets ofA. hypogaea. A similar GISH pattern was observed for all varieties of the cultigen and also forA. monticola. These results suggest that all presently known subspecies and varieties ofA. hypogaeahave arisen from a unique allotetraploid plant population, or alternatively, from different allotetraploid populations that originated from the same two diploid species. Furthermore, the bulk of the data demonstrated a close genomic relationship between both tetraploids and strongly supports the hypothesis thatA. monticolais the immediate wild antecessor ofA. hypogaea.
Phylogenetic systematics and character evolution in the angiosperm family Haloragaceae
Authors: Moody Michael L. , Les Donald H.
Published: February 2008

The poorly known Haloragaceae R. Br. (Saxifragales) are highly diverse in habit (small trees to submerged aquatics) and labile in floral merosity (2–4), both uncommon among the core eudicots. This family has a cosmopolitan distribution, but taxonomic diversity is concentrated in Australia. An explicit phylogenetic approach has not previously been utilized to examine relationships or character evolution in this family. We used molecular evidence from nrDNA ITS and cpDNAtrnKandmatKregions under both Bayesian and parsimony analyses to address phylogenetic relationships. Combined molecular analyses defined a monophyletic Haloragaceae with the woody genera (Haloragodendron,Glischrocaryon) sister to the rest. Relationships among many genera were well resolved, with genera as currently delimited generally well supported, although there were notable exceptions; a new genus (Trihaloragis) is recognized, and the aquatic genusMeionectesis again distinct fromHaloragis. Three new species combinations are also recognized. There are multiple (two or three) origins of the submerged aquatic habit in the family and potentially an intermediate reversal to the terrestrial habit, neither previously demonstrated in a core eudicot family using an explicit phylogenetic hypothesis. Ancestral character analyses suggest two origins of trimerous flowers and multiple reductions to dimerous flowers throughout Haloragaceae.
Inferring phylogeny at low taxonomic levels: utility of rapidly evolving cpDNA and nuclear ITS loci
Authors: Mort Mark E. , Archibald Jenny K. , Randle Christopher P. , Levsen Nicholas D. , O'Leary T. Ryan , Topalov Katarina , Wiegand Catherine M. , Crawford Daniel J.
Published: February 2008

Plant molecular systematic studies of closely related taxa have relied heavily on sequence data from nuclear ITS and cpDNA. Positive attributes of using ITS sequence data include the rapid rate of evolution compared to most plastid loci and availability of universal primers for amplification and sequencing. On the other hand, ITS sequence data may not adequately track organismal phylogeny if concerted evolution and high rDNA array copy number do not permit identification of orthologous copies. Shaw et al. (American Journal of Botany 92: 142–166) recently identified nine plastid regions that appear to provide more potentially informative characters than many other plastid loci. In the present study, sequences of these loci and ITS were obtained for six taxonomic groups in which phylogenetic relationships have been difficult to establish using other data. The relative utility of these regions was compared by assessing the number of parsimony informative characters, character congruence, resolution of inferred trees, clade support, and accuracy. No single locus emerged as the best in all lineages for any of these measures of utility. Results further indicated that in preliminary studies, sampling strategy should include at least four exemplar taxa. The importance of sampling data from independent distributions is also discussed.
Environmental effects on pollen–pistil compatibility between Phlox cuspidata and P. drummondii (Polemoniaceae): implications for hybridization dynamics
Authors: Ruane Lauren G. , Donohue Kathleen
Published: February 2008

Postpollination mechanisms of reproductive isolation can critically influence the amount of gene flow between hybridizing species. While much evidence exists for genetically based pollen–pistil incompatibility, we show that environmental variation also influences the postpollination performance of heterospecific pollen in the annual Phlox hybrid system. Thus, the environmental segregation of species can influence hybridization dynamics. We found that P. cuspidata was restricted to soils of low Ca concentrations in the field and performed better under experimentally low Ca; P. drummondii was able to inhabit high‐Ca soils and sometimes performed better in this environment. To determine whether soil Ca influenced pollen–pistil compatibility in a manner that alters pollen siring success, single‐donor pollinations were performed in a completely factorial crossing design between species, maternal Ca environments, and paternal Ca environments. Maternal and paternal environments interacted in their effects on pollen–pistil compatibility for both inter‐ and intraspecific crosses, such that pollen performance was highest when mothers and fathers were grown in different soil Ca environments. These results suggest that when Phlox species predictably inhabit different environments, environmental heterogeneity can impede the processes of speciation and local adaptation by enhancing the performance of pollen dispersed across species and environments.
Adaptive radiation of shrubby tarweeds (Deinandra) in the California Islands parallels diversification of the Hawaiian silversword alliance (Compositae–Madiinae)
Authors: Baldwin Bruce G.
Published: February 2008

Phylogenetic analyses of nuclear rDNA transcribed spacers and cytogenetic studies of interspecific hybrids reported here upholdCarlquist's hypothesis (1965,Island Biology) that shrubby tarweeds (Deinandra) of Guadalupe Island, Mexico, are products of in situ radiation in the California Islands, where evidence of plant diversification has been equivocal. Based on the rDNA findings, the Guadalupe Island endemics (D. frutescens,D. greeneanasubsp.greeneana, andD. palmeri) constitute a clade that arose since the late Pliocene, well after the origin of Guadalupe Island and diversification of annual, mainland Californian lineages ofDeinandra. High interfertility and normal meiosis in F1hybrids between the three endemics contrast with reduced interfertility (to complete intersterility) and meiotic irregularities in F1hybrids between other, mostly mainland species ofDeinandra. Cloned rDNA sequences provided no convincing evidence of introgression among the Guadalupe Island deinandras; morphological, phenological, and/or habitat differences among those taxa indicate ecological barriers to gene flow and a probable role for ecological divergence in diversification. Biosystematic and molecular phylogenetic data for shrubby tarweeds of Guadalupe Island and another secondarily woody, oceanic‐island tarweed lineage, the Hawaiian silversword alliance, reveal strikingly similar evolutionary histories. Both groups violate Baker's Rule by stemming from self‐incompatible ancestors in western North America, and each has undergone within‐island diversification without evolution of strong sterility barriers among lineages. Evolutionary parallels between these Hawaiian and California Island lineages of Madiinae, first suggested by Carlquist, may reflect characteristics of tarweeds that facilitate insular colonization and adaptive radiation.
How robust is nonrandom mating in wild radish: do small pollen loads coupled with more competing pollen donors lead to random mating?
Authors: Shaner Marieken G. M. , Marshall Diane L.
Published: February 2008

In previous studies of the weedy annual Raphanus sativus we have demonstrated that mating is nonrandom in greenhouse plants, suggesting that sexual selection is possible. To investigate how these greenhouse results might translate to conditions more similar to the field, we manipulated both pollen load size and the number of competing pollen donors on stigmas. While the smallest pollen loads (22 grains per stigma) were small enough to reduce fruit and seed set, seed siring success was unaffected by pollen load size. When the number of competing donors in a mixed pollination was increased to four, the proportion of seeds sired by the pollen donors was the furthest from expectation, suggesting that nonrandom mating increases as the number of donors per pollination increases. There was no significant interaction between pollen load size and number of competitors per pollination. Overall, mating remained nonrandom across all treatments. Thus differential seed paternity is likely to occur in the field as well as in the greenhouse.
Evolution of Lecythidaceae with an emphasis on the circumscription of neotropical genera: information from combined ndhF and trnL‐F sequence data
Authors: Mori Scott A. , Tsou Chi‐Hua , Wu Chi‐Chih , Cronholm Bodil , Anderberg Arne A.
Published: February 2008

The Lecythidaceae comprise a pantropical family best known for the edible seeds of the Brazil nut (Bertholletia excelsa) and the cannon‐ball tree (Couroupita guianensis), which is planted as a botanical curiosity in subtropical and tropical gardens. In addition, species of the family are often among the most common in neotropical forests, especially in the Amazon Basin. The Brazil nut family is diverse and abundant in the Amazon and is considered to be an indicator of undisturbed or scarcely disturbed lowland forests; thus, what is learned about its evolution, ecology, and biogeography may suggest similar patterns for other Amazonian tree families. We used combined data sets derived from the ndhF and trnL‐F genes to elucidate relationships of genera in both the Old and New Worlds that have been associated with Lecythidaceae. Our molecular tree agrees with the recognition of Napoleonaeaceae and Scytopetalaceae. Within the Lecythidaceae, there is molecular support for recognizing three subfamilies: Foetidioideae, Planchonioideae, and Lecythidoideae. We then focused on genera of the Lecythidoideae and found support for recognizing Allantoma (when the actinomorphic‐flowered species of Cariniana are included in it), Grias, Gustavia, Corythophora, Couratari, and Couroupita, but conclude that Cariniana, Lecythis, and Eschweilera are not monoyphyletic. Because the position of the monotypic Bertholletia excelsa in relation to the other zygomorphic‐flowered genera is not resolved, we are not able to comment on its generic relationships.
Phylogenetic relationships and ecological speciation in the mistletoeTristerix(Loranthaceae): the influence of pollinators, dispersers, and hosts
Authors: Amico Guillermo C. , Vidal‐Russell Romina , Nickrent Daniel L.
Published: February 2008

Phylogenies can provide valuable information on biotic and abiotic factors associated with speciation. We examined species relationships inTristerix(Loranthaceae), a genus of 11 species with an Andean distribution from Colombia to Chile. A previous classification dividedTristerixinto subgeneraTristerix(two species) andMetastachys(nine species). We tested this classification by generating a molecular phylogeny of the genus using nuclear ribosomal DNA ITS and chloroplastatpB‐rbcLintergenic spacer andtrnL‐Fregions. All partitions generally gave congruent trees, thus a combined analysis was conducted.Tristerixwas composed of a northern clade (six species) and a southern clade (four species).Tristerix verticillatusandT. penduliflorus(Metastachys) were strongly supported as members of the (southern) subgenusTristerixclade. Speciation appears to be correlated with the emergence of matorral and cloud forest biomes and is driven by interactions with pollinators and seed dispersers.Tristerix aphyllusis sister toT. corymbosusof the matorral, not to neighboring temperate forest populations, thus rendering the latter species paraphyletic. This ecological speciation event may have occurred in sympatry.Tristerixprovides excellent examples of how, during the orography of the Andes, many dynamic and interacting ecological factors have influenced their speciation.
Delimitation of major lineages withinCuscutasubgenusGrammica(Convolvulaceae) using plastid and nuclear DNA sequences
Authors: Stefanović Saša , Kuzmina Maria , Costea Mihai
Published: February 2008

SubgenusGrammica, the largest and most diverse group in the parasitic genusCuscuta, includes 130 species distributed primarily throughout the New World, with Mexico as its center of diversity. To circumscribe the subgenus and assess the relationships among its major lineages, we conducted the first phylogenetic study ofGrammicausing plastidtrnL‐Fand nrITS sequences from a wide taxonomic sampling covering its morphological, physiological, and geographical diversity. With the exception of one species belonging elsewhere, the subgenus was found to be monophyletic. The results further indicate the presence of 15 well‐supported major clades withinGrammica. Some of those lineages correspond partially to earlier taxonomic treatments, but the majority of groups are identified in this study for the first time. The backbone relationships among major clades, however, remain weakly supported or unresolved in some cases. The phylogenetic results indicate that the fruit dehiscence character is homoplastic, thus compromising its value as a major taxonomic and evolutionary feature. While several striking cases of long‐distance dispersal are inferred, vicariance emerges as the most dominant biogeographical pattern forCuscuta. Species placed within one of the clades with a predominantly South American distribution are hypothesized to have substantially altered plastid genomes.
Gravitropism in the starch excess mutant of Arabidopsis thaliana
Authors: Vitha Stanislav , Yang Ming , Sack Fred D. , Kiss John Z.
Published: February 2008

Amyloplasts are hypothesized to play a key role in the cellular mechanisms of gravity perception in plants. While previous studies have examined the effects of starch deficiency on gravitropic sensitivity, in this paper, we report on gravitropism in plants with a greater amount of starch relative to the normal wild type. Thus, we have studied the sex1 (starch excess) mutant of Arabidopsis thaliana, which accumulates extra starch because it is defective in a protein involved in the regulation of starch mobilization. Compared to the wild type (WT), sex1 seedlings contained excess starch in cotyledons, hypocotyls, the root–hypocotyl transition zone, the body of the root, root hairs, and in peripheral rootcap cells. Sedimented amyloplasts were found in both the WT and in sex1 in the rootcap columella and in the endodermis of stems, hypocotyls, and petioles. In roots, the starch content and amyloplast sedimentation in central columella cells and the gravitropic sensitivity were comparable in sex1 and the WT. However, in hypocotyls, the sex1 mutant was much more sensitive to gravity during light‐grown conditions compared to the WT. This difference was correlated to a major difference in size of plastids in gravity‐perceiving endodermal cells between the two genotypes (i.e., sex1 amyloplasts were twice as big). These results are consistent with the hypothesis that only very large changes in starch content relative to the WT affect gravitropic sensitivity, thus indicating that wild‐type sensing is not saturated.
Gametophyte ecology and demography of epiphytic and terrestrial tropical ferns
Authors: Watkins James E. , Mack Michelle K. , Mulkey Stephen S.
Published: February 2008

Factors that influence the distribution of ferns are poorly understood and likely reflect the ecology of both the sporophyte and the gametophyte generation. Little study has been done on the ecology of the gametophyte generation, especially in regard to tropical species. The goal of this study was to examine demography and the influence of light and disturbance on the distribution of the gametophytes of several tropical epiphytic, hemiepiphytic, and terrestrial fern species. Through a series of observational and experimental studies, we found that increased terrestrial gametophyte density and richness were related to both increased light and disturbance. By contrast, increased light had no influence, and increased disturbance negatively affected epiphytic density. Over a 25‐mo demographic study, epiphytic and hemiepiphytic species had significantly greater longevities and lower recruitment rates than terrestrial species. Such unique strategies may have evolved in response to different disturbance regimens between the two habitats. Terrestrial species encounter and are adapted to more frequent disturbance and have invested in rapid gametophyte growth and recruitment. Epiphytic species may be more influenced by bryophyte competition, and in habitats of relatively low disturbance, they have invested in greater size and longevities. In such systems, gametophytes are able to survive for years waiting for favorable recruitment conditions.
Structure and development of the upper haustorium in the parasitic flowering plant Cuscuta japonica (Convolvulaceae)
Authors: Lee Kyu Bae
Published: February 2008

The anatomical and ultrastructural development of the haustorium of the Cuscuta japonica, a holoparasitic angiosperm, growing on the host plant Impatiens balsamina was studied. After the shoot tips of light‐grown parasite seedlings contacted the host, the upper haustorium (external to the host organ) developed through three main successive stages of the haustorial initials, the meristem, and the endophyte primoridium (EP) within the middle layer of the cortex of the parasite stem. The haustorial initial cells were characterized by abundant starch‐bearing amyloplasts and mitochondria with an expanded intermembrane space. The meristem cells had numerous large chloroplasts with well‐developed thylakoids, reflecting the capability for photosynthesis. Commonly, all three stages of haustorial cells contained conspicuous, large nuclei with enlarged nucleoli and dense cytoplasm including many other organelles, indicating a very active metabolism. In the final stage of upper haustorium development, the meristem cells differentiated into the EP, a host‐penetrating tissue. The primordium had smaller file cells at the proximal end and elongate digitate cells at the distal end. The file cells divided actively, while the digitate cells contained abundant chloroplasts, dictyosomes, rough endoplasmic reticulum, and other organelles, suggesting that the EP was cytohistologically well organized for penetration into the host tissue.
An evaluation of mechanisms preventing growth and survival of two native species in invasive Bohemian knotweed (Fallopia ×bohemica, Polygonaceae)
Authors: Siemens Tania J. , Blossey Bernd
Published: February 2008

Restoring native diversity to habitats dominated by invasive plants requires improved understanding of mechanisms that allow introduced plants to retain dominance. We used a factorial transplant experiment to assess whether light limitation, nutrient limitation, or allelopathic interference by Fallopia ×bohemica reduces growth or survival of Eupatorium perfoliatum or Acer saccharinum. Increased light improved A. saccharinum performance but had no effect on E. perfoliatum growth. Increased light had no effect on A. saccharinum survival but improved E. perfoliatum survival. Activated carbon addition had short‐term benefits allowing E. perfoliatum plants to grow for 4 wk and increased A. saccharinum leaf width but not biomass. Nutrient addition had no beneficial effect on transplants. These results in combination with the outcome of a cutting experiment suggest that F. ×bohemica achieves competitive superiority primarily by limiting access to light. Species‐specific effects and significant interaction effects particularly of light and activated carbon suggest additional mechanisms. Allelopathic interference or interaction with microbial soil organisms may contribute to the lack of native species in populations of F. ×bohemica. Restoration efforts should combine selective F. ×bohemica control with soil amendments (such as activated carbon) to assess their potential to facilitate return of native species to invaded habitats.
Secondary phloem anatomy of Cycadeoidea (Bennettitales)
Authors: Ryberg Patricia E. , Taylor Edith L. , Taylor Thomas N.
Published: February 2008

Secondary phloem anatomy of several species of Cycadeoidea is described from trunks in the Wieland Collection, Peabody Museum of Natural History. The trunks were collected from the Lakota Formation, Lower Cretaceous, Black Hills of South Dakota. Secondary phloem is extensively developed and consists of alternating, tangential bands of fibers and sieve elements, with rare phloem parenchyma. Uniseriate rays, 2–22 cells high, occur between every one to three files of the axial system. Fibers are long, more than 1200 μm, approximately 26.6–34.2 μm in diameter, and have slit‐like apertures on the lateral walls. Sieve elements range from 16–25 μm in diameter and are up to 500 μm long. Elliptical sieve areas appear on both end and radial walls and measure 10 μm across; minute spots, which may represent sieve pores, are present within the sieve areas. Secondary phloem of North American Cycadeoidea is similar in organization (alternating tangential bands) and cell types (sieve cells, fibers, axial parenchyma) to that known in other extant and fossil cycadophytes and some seed ferns. The unusual pattern of cell types and thickness of secondary phloem is discussed in the context of plant habit, phloem efficiency, and potential phylogenetic importance.
Assessing genetic stability of a range of terrestrial microalgae after cryopreservation using amplified fragment length polymorphism (AFLP)
Authors: Müller Julia , Day John G. , Harding Keith , Hepperle Dominik , Lorenz Maike , Friedl Thomas
Published: February 2008

Cryopreservation is the long‐term, indefinite storage of living biological resources at ultralow temperatures. It is almost universally assumed that cryogenic storage supports genetic and phenotypic stability of organisms. However, certain components of the cryopreservation process, particularly some cryoprotective additives (CPAs) and free radical mediated cryoinjury, may potentially cause genetic alterations. Genetic integrity in cryopreserved microalgae was assessed using a very sensitive molecular fingerprinting technique, AFLP, on 28 terrestrial microalgal strains. In about half of all investigated strains the AFLP fingerprints revealed, with high levels of reproducibility, clearly detectable genomic differences after cryopreservation employing a widely used standard two‐step cooling protocol. Differences ranged from a single fragment position to multiple fragment changes and were compared to differences found between wild‐type and UV‐light‐ or radioisotope‐induced mutants of Parachlorella kessleri. The basis of the changes are discussed in terms of their reversibility, as may be the case if they are attributed to DNA methylation and/or whether they are true mutations that may potentially manifest in the phenotype. The possibility that cryopreservation selects for genotypically different subpopulations of microalgae is also considered.
Is Cycas revoluta (Cycadaceae) wind‐ or insect‐pollinated?
Authors: Kono Masumi , Tobe Hiroshi
Published: February 2008

Among the Cycadales (Cycadaceae and Zamiaceae), the Zamiaceae are known to be insect‐pollinated. In contrast, the Cycadaceae are still considered wind‐pollinated, although some doubt has been cast on several species, including Cycas revoluta. Using a large population of C. revoluta on Yonaguni Island (Okinawa, Japan), we performed exclusion experiments, documented insects from male and female cones, and analyzed the morphology of the apical part of the ovule to determine the pollination method of this species. Insect exclusion resulted in a notable reduction in seed set, except in a few individuals growing near male cones. The amount of airborne pollen was abundant within a 2‐m radius of male cones but decreased markedly beyond this distance. Pollen grains of C. revoluta were found on the body of Carpophilus chalybeus (Nitidulidae, Coleoptera), one of a few species of insects collected from both male cones and female cones far from males. We conclude that C. revoluta relies on both wind (anemophily) and insect pollination (entomophily), although such anemophily is restricted to female trees growing within a 2‐m radius of male trees. The nitidulids are not host specific to this cycad and primarily feed on plant tissue but serve as pollinators during pollen release. Cycas revoluta appears to be in an initial mode of animal pollination, as opposed to the host‐specific insect pollination observed in most Zamiaceae.
Molecular phylogeny, biogeography, and systematics of Dicerandra (Lamiaceae), a genus endemic to the southeastern United States
Authors: Oliveira Luiz O. , Huck Robin B. , Gitzendanner Matthew A. , Judd Walter S. , Soltis Douglas E. , Soltis Pamela S.
Published: February 2008

Dicerandra, an endemic mint of the southeastern United States, comprises nine species, all of which are threatened or endangered and restricted to sandhill vegetation and a mosaic of scrub habitats. Molecular phylogenetic analyses of Dicerandra based on data from the nuclear and plastid genomes for all 13 taxa of the genus, identified two strongly supported clades, corresponding to the four annual and to the five perennial species of Dicerandra. However, the nuclear and plastid trees were incongruent in their placement of two perennial taxa, D. cornutissima and D. immaculata var. savannarum, perhaps due to ancient hybridization or to lineage sorting. Based on these analyses, the widespread D. linearifolia is not monophyletic, with populations of D. linearifolia var. linearifolia falling into either western or eastern clades. The western clade, comprising populations of D. linearifolia var. linearifolia and var. robustior, occurs in an area drained by rivers flowing toward the Gulf of Mexico, whereas the eastern clade, comprising populations of D. linearifolia var. linearifolia, D. densiflora, D. odoratissima, and D. radfordiana (i.e., all the annual species), occupies a region drained by rivers flowing to the Atlantic Ocean. Although this pattern of genetic differentiation between populations from these two river drainages has been documented in several animal species, it has not previously been reported for plants. A revised subgeneric classification is presented to reflect the annual and perennial clades.