bluuebunny/crossref_metadata_2025 huggingface dataset:
Phylogenetic relationships of North American Antirrhinum (Veronicaceae)
Authors: Oyama Ryan K. , Baum David A.
Published: February 2008

Species of the genus Antirrhinum (Veronicaceae) provide excellent opportunities for research on plant evolution given their extensive morphological and ecological diversity. These opportunities are enhanced by genetic and developmental data from the model organism Antirrhinum majus. The genus Antirrhinum includes 15 New World species in section Saerorhinum and 21 Old World species in sections Antirrhinum and Orontium. Phylogenetic analyses of sequences of the internal transcribed spacer region (ITS) of nuclear ribosomal DNA were conducted for 19 Antirrhinum species, including all species from the New World, and 13 related genera in the tribe Antirrhineae. These analyses confirm the monophyly of Antirrhinum given the inclusion of the small genus Mohavea and exclusion of A. cyathiferum. The New World species, all of which are tetraploid, form a clade that is weakly supported as sister to the Old World sect. Orontium. The Old World species in sect. Antirrhinum form a well‐supported clade that is sister to the remainder of the genus. In addition, both molecular and morphological data are used in the most comprehensive effort to date focused on recovering the phylogenetic relationships among the extremely diverse species in section Saerorhinum.
A multivariate analysis ofHyospathe(Palmae)
Authors: Henderson Andrew J.
Published: February 2008

Previous systematic treatments of the neotropical palm genusHyospathehave recognized from two to 18 species. An explicit, quantitative, repeatable sequence of operations for delimiting and testing groups of specimens and applying species concepts is carried out. Multivariate statistical analysis of morphological data is used to delimit and test groups of specimens. Cluster analysis is used to distinguish between characters and traits. Analysis of qualitative and quantitative characters reveals six groups of specimens, and the Phylogenetic Species Concept is applied to these groups. Two species,H. peruvianaHenderson andH. frontinensisHenderson, are described as new. One of the specimen groups is large and widespread, and six geographically separate subgroups can be recognized within it. These subgroups can be distinguished by one or more significantly different quantitative characters. A Phylogenetic Subspecies Concept is applied to these subgroups. Three subspecies,H. eleganssubsp.costaricensisHenderson,H. eleganssubsp.sanblasensisHenderson, andH. eleganssubsp.tacarcunensisHenderson are described as new, and two new combinations are made:H. eleganssubsp.sodiroi(Dammer ex Burret) Henderson andH. eleganssubsp.concinna(H. E. Moore) Henderson. One subspecies occurring in the Amazon region is complex morphologically and is not resolved by the methods used here.
Molecular genetic evidence for interspecific hybridization among endemic Hispaniolan Bursera (Burseraceae)
Authors: Weeks Andrea , Simpson Beryl B.
Published: February 2008

Historically, genetic introgression among species as well as hybrid origins for species of the diploid tree genus Bursera (Burseraceae) have been proposed based on the supposition that individuals morphologically intermediate between sympatric “parent” species must be derived from hybridization. This study reports the first molecular genetic evidence for both unidirectional and reciprocal interspecific hybridization within Bursera. Phylogenies of hybrids and other species in B. subgenus Bursera are reconstructed based on nuclear and chloroplast sequence data. Compelling evidence supports the hybrid origin of three endemic Hispaniolan species: B. brunea (B. nashii × B. simaruba), B. gracilipes (B. spinescens × B. simaruba), and B. ovata (B. simaruba × B. spinescens). Cloning studies of nuclear markers from B. ovata suggests that this species is an introgressed or later backcross generation hybrid and thus reproduces sexually.
Environmental and genetic effects on flowering differences between northern and southern populations of Arabidopsis lyrata (Brassicaceae)
Authors: Riihimäki Mona , Savolainen Outi
Published: February 2008

Arabidopsis lyrata (Brassicaceae) is a close outcrossing relative of A. thaliana. We examine flowering time variation of northern and southern A. lyrata populations in controlled environmental conditions, in a common garden experiment with A. thaliana, and in the field. Southern populations of A. lyrata flowered earlier than northern ones in all environmental conditions. Individuals from southern populations were more likely to flower in short days (14 h light) than northern ones, and all populations had a higher probability of flowering and flowered more rapidly in long days (20 h). The interaction of population and day length significantly affected flowering probability, and flowering time in one of two comparisons. The common garden experiment demonstrated differences between populations in the response to seed cold treatment, but growth chamber experiments showed no vernalization effect after 4 wk of rosette cold treatment. In a field population in Norway, a high proportion of the plants flowered in each year of the study. The plants progressed to flowering more rapidly in the field and common garden than in the growth chamber. The genetic basis of these flowering time differences here can be further studied using A. thaliana genetic tools.
Reproductive ecology of distylous Palicourea Padifolia (Rubiaceae) in a tropical montane cloud forest. I. Hummingbirds' effectiveness as pollen vectors
Authors: Ornelas Juan Francisco , Jiménez Leonor , González Clementina , Hernández Angélica
Published: February 2008

The adaptiveness of distyly has been typically investigated in terms of its female function, specifically pollen receipt. However, pollen loads on stigmas can only provide moderate support for Darwin's hypothesis of the promotion of legitimate crosses. To determine the effectiveness of hummingbirds as pollen vectors between floral morphs and the consequences in terms of male (pollen transfer) and female function (pollen receipt) in Palicourea padifolia (Rubiaceae), floral visitors, their foraging modes, and temporal patterns of floral visitation were observed and documented. Differences in pollen and stigma morphology, pollen flow, rates of pollen deposition, and/or stigmatic pollen loads were then evaluated for their contribution toward differences in reproductive output between floral morphs. A pollination experiment with stuffed hummingbirds that varied in bill size was done to evaluate the contribution of bill variation toward differences between floral morphs in pollen receipt and pollen transfer and female reproductive output. Anthers of long‐styled flowers contained significantly more and smaller pollen grains than those of short‐styled flowers, independently of corolla and anther lengths. The shape and orientation of the stigma lobes differed between morphs and were significantly longer among short‐styled flowers. Hummingbird visitation rates did not differ significantly between floral morphs, and foraging movements from focal plants towards neighboring plants were independent of floral morph. Stigmatic pollen loads under field conditions and those after controlled hummingbird visitation, along with rates of pollen accumulation through the day indicated that stigmas of short‐styled flowers receive proportionately more legitimate (intermorph) pollen grains than did those of long‐styled flowers. However, the species of hummingbird was marginally significant in explaining variation in pollen deposition on stigmas. Lastly, intermorph pollinations of P. padifolia resulted in significant differences in fruit production between floral morphs, independent of pollination treatment and pollinator species; short‐styled flowers proportionately developed almost twice the number of fruits developed by long‐styled flowers.
A molecular phylogenetic study of Graptopetalum (Crassulaceae) based on ETS, ITS, RPL16, and TRNL‐F nucleotide sequences
Authors: Acevedo‐Rosas Raúl , Cameron Kenneth , Sosa Victoria , Pell Susan
Published: February 2008

Nuclear ETS and ITS, as well as plastid rpl16 and trnL‐F DNA sequences were used to determine relationships among species of Graptopetalum (Crassulaceae) and closely related genera. Graptopetalum is member of a group of taxa restricted to North America, one of the centers of diversity of Crassulaceae; however, their phylogenetic relationships are not yet understood. Nineteen species of Graptopetalum and 24 species from nine other genera of Crassulaceae were sampled for use in three separate parsimony analyses: ITS alone, ETS alone, and a combined nuclear + plastid DNA analysis using all four gene regions. The ETS data set had the highest number of parsimony‐informative sites, about 30% more than in ITS, but the most fully resolved tree resulted when the four DNA regions were combined. Only four subclades of the tree received moderate to strong bootstrap support, one of which includes all species of Graptopetalum having a single whorl of stamens. However, Graptopetalum is not monophyletic. Instead, Tacitus bellus and select species of Cremnophila, Sedum, and Echeveria are interspersed among species of Graptopetalum and show evidence of grouping according to geographical range of distribution more so than habit or floral morphology.
Duabanga‐like leaves from the Middle Eocene Princeton chert and comparative leaf histology of Lythraceae sensu lato
Authors: Little Stefan A. , Stockey Ruth A. , Keating Richard C.
Published: February 2008

A permineralized lythraceous leaf type found in close association with fruits, stems, and roots of Decodon allenbyensis Cevallos‐Ferriz et Stockey in the Middle Eocene Princeton chert of British Columbia, Canada, is described. Midribs have a prominent C‐shaped midvein surrounded by sclerenchyma, with an adaxial epidermis of rectangular to rounded cells lacking enlarged mucilage cells. Leaves are dorsiventral, 180–270 μm thick at the lamina, with a double palisade layer. Abaxial epidermal cells have prominent papillae, and these epidermal cells can be infected by fungi, forming dark sterile stromata. Fossil leaves are similar to those of Myrtales and are compared to those of Lythraceae sensu lato. Although these leaves are thought to belong to the previously described Decodon allenbyensis found in the same chert layer, they lack the diagnostic features of extant Decodon leaves. Instead they share most anatomical similarities with Duabanga grandiflora Roxburgh ex DC Walpers (Lythraceae, subfamily Duabangoideae) including vascular tissues, palisade and spongy mesophyll, bundle fibers, and abaxial epidermal papillae. Duabanga grandiflora differs from the fossil in having mucilaginous cells and a consistently V‐shaped abaxial midrib. Although anatomically similar to Duabanga, the fossil leaves are considered those of D. allenbyensis, based on association and the depositional environment prior to preservation. Recent phylogenetic analyses place Duabanga and Decodon in separate clades within Lythraceae, but relationships between these clades are not well supported, indicating that fossil leaves should provide useful anatomical characters for elucidating relationships within Lythraceae.
Incidence, size and spatial structure of clones in second‐growth stands of coast redwood, Sequoia sempervirens (Cupressaceae)
Authors: Douhovnikoff Vladimir , Cheng Adelaide M. , Dodd Richard S.
Published: February 2008

The ecology and evolutionary potential of coast redwood (Sequoia sempervirens) is significantly influenced by the important role clonal spread plays in its reproduction and site persistence. In nine second‐growth stands, amplified fragment length polymorphisms (AFLPs) were used to identify redwood clonal architecture. Clones (multistem genets) dominated sites by representing an average of 70% of stems measured, ranging in size from two to 20 stems. As a result, a relatively small number of genets can monopolize a disproportionate amount of site resources, are more likely to persist over time, and have greater on‐site genetic representation. Clones were not limited to fairy‐ring structures, but consisted of a wide range of shapes including concentric rings, ring chains, disjunct, and linear structures. Between‐ramet distances of up to 40 m were measured, indicating that clonal reproduction is not limited to basal stump resprouting. Clonal structure in second‐growth stands was similar to earlier reports from old growth, emphasizing the importance of site persistence and long‐term, gradual site development. Smaller ramet numbers per genet in old growth is probably due to local within‐genet self thinning. Management and conservation of redwoods will benefit from a better understanding of the dynamics and structure of clonal spread in these forests.
Genetic variation of introduced Hawaiian and native Costa Rican populations of an invasive tropical shrub, Clidemia hirta (Melastomataceae)
Authors: DeWalt Saara J. , Hamrick J. L.
Published: February 2008

Clidemia hirta is one of the most common woody invasive plants in mesic to wet forests in Hawaii, where it was introduced around 1940. The species is relatively uncommon by comparison in its native range of Central and South America and some Caribbean Islands. We examined genetic variation in allozymes of 20 C. hirta populations on four Hawaiian Islands to determine the introduction history. For comparison, we measured genetic variation in 20 native populations across Costa Rica. Mean levels of genetic variation in Hawaiian and Costa Rican populations were low compared to other woody or introduced plants (11.5–12.5% polymorphic loci, 2.05–2.50 alleles per polymorphic locus, and 0.045–0.063 expected heterozygosity). Most genetic diversity was held within rather than among populations in both areas (GST = 0.120 and 0.271 in Hawaii and Costa Rica, respectively). Hawaiian populations had a high degree of genetic similarity, and no genetic differentiation was found among the four Hawaiian Islands sampled. These patterns of genetic variation in Hawaii suggest that no intraspecific hybridization of genotypes from different parts of the native range has occurred and that introductions to the different islands came from the same or similar source populations. The low levels of genetic diversity in parts of both the native and introduced ranges suggest that genetic variation is unrelated to invasiveness in C. hirta.
Cushion size, surface roughness, and the control of water balance and carbon flux in the cushion mossLeucobryum glaucum(Leucobryaceae)
Authors: Rice Steven K. , Schneider Nicole
Published: February 2008

We explored the size dependence of water balance and carbon flux in the cushion mossLeucobryum glaucum(Leucobryaceae). Conductance to water vapor (ga) was modeled empirically using 4–24 cm diameter cushions (N= 14) evaluated across wind speeds from 0.7 to 4.3 m/s in a wind tunnel. Model parameters included wind speed (u), kinematic viscosity (v), cushion diameter (Ld), and surface roughness (Lr). The modelga= −9.62(u/v)1.21·Ld−0.35·Lr‐in−1.85(whereLr‐inrepresents a dimensionless form ofLr;R2= 0.88) indicates negative relationships betweengaand bothLdandLr. These predictions were evaluated during a 5‐d field experiment where water loss and net carbon exchange (estimated by ΔF/Fm′) were monitored. In the field (N= 18, 4–34 cm diameter cushions),Lr, but notLd, controlled rates of evaporation due to additional turbulence that reduced size dependence of cushions along the forest floor. However, the duration of positive net carbon gain varied from 1.4 to 4.4 d and was significantly longer in larger diameter cushions. Thus, under field conditions, size‐dependent changes in surface‐area‐to‐volume relationships influence the duration of net carbon gain more than differences in water flux and lead to a strong size dependence of water balance and carbon flux.
Phylogeny of Amorpheae (Fabaceae: Papilionoideae)
Authors: McMahon Michelle , Hufford Larry
Published: February 2008

The legume tribe Amorpheae comprises eight genera and 240 species with variable floral form. In this study, we inferred a phylogeny for Amorpheae using DNA sequence data from the plastid trnK intron, including matK, and the nuclear ribosomal ITS1, 5.8S, and ITS2. Our data resulted in a well‐resolved phylogeny in which the tribe is divided into the daleoids (Dalea, Marina, and Psorothamnus), characterized by generally papilionaceous corollas, and the amorphoids (Amorpha, Apoplanesia, Errazurizia, Eysenhardtia, and Parryella), characterized by non‐papilionaceous flowers. We found evidence for the paraphyly of Psorothamnus and for the monophyly of Dalea once D. filiciformis is transferred to monophyletic Marina. Errazurizia rotundata is more closely related to Amorpha than to the other errazurizias, and Eysenhardtia is supported to be monophyletic. The monotypic Parryella and Apoplanesia are placed within the amorphoids. Among Papilionoideae, trnK/matK sequence data provide strong evidence for the monophyly of Amorpheae and place Amorpheae as sister to the recently discovered dalbergioid clade.
Structural integration at the shoot apical meristem: models, measurements, and experiments
Authors: Kwiatkowska Dorota
Published: February 2008

The shoot apical meristem (SAM) produces stem and initiates leaves. Its structure is maintained despite a continuous flow of cells basipetally from the distal portion of the meristem. The apoplasm and symplasm are the obvious means of cell integration, and their role in chemical cell‐to‐cell signaling is known. However, the cell wall apoplasm is most likely also involved in a mechanical integration mode, in which mechanical stress and strains (elastic and plastic strain, i.e., growth) are putative signaling factors. Shoot apex cells grow symplastically and their growth is in general anisotropic. Therefore tensor of growth rates that depends on the displacements caused by growth is the most suitable physical entity to describe growth. The tensor approach introduces the concept of principal directions of growth, i.e., the directions in which growth rates attain extremal values. Because of the symplastic mode of growth, the cell wall pattern within the shoot apical meristem informs us about the sequence and planes of cell divisions and about the deformation of existing walls. In consequence, within the meristem, periclines and anticlines can be recognized, both representing the principal directions of growth.
The consequences of clone size for paternal and maternal success in domestic apple (Malus × domestica)
Authors: Routley Matthew B. , Kron Paul , Husband Brian C.
Published: February 2008

Clonal growth in plants can increase pollen and ovule production per genet. However, paternal and maternal reproductive success may not increase because within‐clone pollination (geitonogamy) can reduce pollen export to adjacent clones (pollen discounting) and pollen import to the central ramets (pollen limitation). The relationship between clone size and mating success was investigated using clones of Malus × domestica at four orchards (blocks of 1–5 rows of trees). For each block, maternal function was measured as fruit and seed set in all rows and paternal function as siring rate estimated from isozyme profiles in the first row of the adjacent block. Expected relations between reproductive success and clone size were generated from simulations and data on pollen dispersal in this species. Siring rate per clone averaged 70% and did not increase significantly with block size, consistent with simulations of pollen dispersal under pollen discounting. Simulations also indicated that the ratio of compatible to incompatible pollen received by a tree should decline with increased block size and from the periphery to the center of blocks. However, female function was not significantly reduced among block sizes or within blocks. The results suggest that paternal function may be more sensitive to the effects of clonality than female function.
Hybridization and gene flow between a day‐ and night‐flowering species ofZaluzianskya(Scrophulariaceae s.s., tribeManuleeae)
Authors: Archibald Jenny K. , Wolfe Andrea D. , Johnson Steven D.
Published: February 2008

Despite apparent ethological isolation based on specialized pollination systems, hybridization between day‐floweringZaluzianskya microsiphonand night‐floweringZ. natalensishas been proposed due to intermediate individuals found in sympatric populations of these species. The extent of this putative hybridization was investigated using inter‐simple sequence repeat (ISSR) markers and principal components analysis (PCA) of morphological traits. The species are genetically similar, but show some intra‐ and interspecific variation in band frequencies. Neighbor‐joining analyses of the ISSR data demonstrated that although the species largely formed distinct groups, several individuals from the sympatric populations of each species and the “hybrids” clustered together rather than with members of their own species. These results are consistent with hybridization, although they could also indicate historical similarity. Nine loci were present only in individuals ofZ. microsiphon, the “hybrids,” and sometimes the sympatric individuals ofZ. natalensis. In contrast, only one locus showed the reverse pattern. This suggests unidirectional gene flow fromZ. microsiphontoZ. natalensis, which is also supported by population‐level examinations of four loci. Ordination revealed separate phenotype clusters for each species, with hybrid individuals located in between but often closer to theZ. natalensiscluster. One hypothesis is that hybrids are backcrossing withZ. natalensis, leading to introgression ofZ. microsiphongenetic material.
Testing the adaptive nature of radiation: growth form and life history divergence in the African grass genusEhrharta(Poaceae: Ehrhartoideae)
Authors: Verboom G. Anthony , Linder H. Peter , Stock William D.
Published: February 2008

In most documented examples of adaptive radiation, the processes underlying divergence in form and function are poorly explored and remain speculative. Here, data from a comparative seedling growth experiment are used to explore growth form divergence inEhrharta, a group of grasses that radiated in seasonally arid environments of the Cape region of South Africa. Seedlings of eightEhrhartaspecies of variable growth form were grown in liquid culture under conditions of high resource availabilty for 56 d, during which time changes in dry mass, allocation, and leaf parameters were measured. The results of this experiment reveal the existence of distinct seedling growth patterns that are associated with differences in adult plant form and seasonal drought survival strategy. Specifically, species that utilize a reseeding strategy have higher seedling growth rates and flower earlier than species that persist by vegetative means. A correlation between species'growth rates and their native substrates suggests that edaphic heterogeneity has been central in directing the evolution of alternative persistence strategies and growth forms. Parsimony reconstruction identifies slow growth and an association with nutrient‐deficient sandstone‐derived soils as ancestral inEhrharta, with fast growth evolving after a transition to richer shale‐ and granite‐derived soils. The emergence of annual species in two fast‐growth lineages suggests that the latter is a key step in the evolution of an ephemeral strategy. An association between plant function and habitat identifies the radiation ofEhrhartaas adaptive.
Dactylorhiza (Orchidaceae) in European Russia: combined molecular and morphological analysis
Authors: Shipunov Alexey B. , Fay Michael F. , Pillon Yohan , Bateman Richard M. , Chase Mark W.
Published: February 2008

Four plastid and two nuclear (internal transcribed spacer [ITS] ribosomal DNA) markers were used in this study of the Dactylorhiza maculata and D. incarnata complexes (Orchidaceae: Orchidinae) to determine diversity and taxonomic distribution of haplotypes, hybridization frequencies, and maternal parentage of hybrids in 125 samples from 78 populations from European Russia and the Caucasus. A morphometric study of all populations revealed significant correspondence between morphological and plastid DNA data. Most D. maculata sensu stricto (s.s.) specimens from Russia have D. fuchsii haplotypes; this could be evidence for introgression or widespread hybridization between these species in northern Russia. Heterogeneity within populations is much higher for ITS data and is strongly correlated with latitude. Both plastid and nuclear data are significantly correlated with distribution along a south–north axis. Several haplotypes and ITS alleles uncommon in western Europe are more widely distributed in Russia, whereas some frequent haplotypes from western Europe are absent.
Coarse‐ versus fine‐grained water stress in Arabidopsis thaliana (Brassicaceae)
Authors: Engelmann Kathleen E. , Schlichting Carl D.
Published: February 2008

The effects of coarse vs. fine‐grained variation in water regime on 13 accessions of Arabidopsis thaliana were compared and it was found that the scale of environmental variation can lead to differences in which traits are affected and in the magnitude and direction of effect. Coarse‐grained (between individual) variation was studied by comparing plants that received high or low amounts of water on a daily basis. Fine‐grained (within individual) variation was distributed across the coarse‐grained treatments; plants in the fine‐grained treatment received the same amount of water per week as the corresponding high and low coarse‐grained treatments; however, in the fine‐grained treatments, plants received their entire weekly water allotment over 2 days. The number of leaves produced, days to bolting, length of bolt, number of basal and lateral branches, and survival to 30 days after bolting were measured and analyzed by ANOVA. Plants grown in high water generally produced more leaves, taller main axes, more branches and had increased survival, relative to those in low water. Bolting date showed a significant genotype specific effect of water level. Plants grown under fine‐grained variation in watering had taller main axes relative to constant water. There were significant interactions between both types of variation for bolting date, main axis height, and survival. Principal components for all traits were loaded such that the components themselves were also independently affected by genotype, water level, variability of water level (grain), and level‐by‐grain interactions in ways that were largely predicted by their component traits. Overall, the effects of fine‐grained variation were subtler than those of coarse‐grained variation: fewer traits responded, and the magnitude of the responses was smaller. Nevertheless, the responses to fine‐grained variation are distinct from those of coarse‐gained variation, differing with respect to which traits respond and in the direction of response, and must therefore be treated as independent sources of environmental variation.
Volatile composition, emission pattern, and localization of floral scent emission in Mirabilis jalapa (Nyctaginaceae)
Authors: Effmert Uta , Große Jana , Röse Ursula S. R. , Ehrig Fred , Kägi Ralf , Piechulla Birgit
Published: February 2008

We elucidated scent components, daily emission patterns, and the localization of floral scent release of Mirabilis jalapa. Volatiles emitted by the whole plant as well as by detached flowers were investigated using dynamic headspace analysis and gas chromatography/ mass spectrometry. Among several constituents including (Z)‐3‐hexenyl acetate, β‐myrcene, (Z)‐ocimene, and benzyl benzoate, the monoterpene (E)‐β‐ocimene was the major fragrance component. Fragrance release occurred in a time‐dependent manner. The emission of volatiles, including (E)‐β‐ocimene, showed an evening‐specific maximum (1700–2000 pm). The emission of (Z)‐3‐hexenyl acetate reached its maximum 3 h later. Histological (neutral red staining) and morphological studies (electron and light microscopy) of the flower surface and tissues of M. jalapa revealed differences in surface structures and tissue characteristics. The flower could be divided into four main sections, including the tube, the transition zone between tube and limb, a star‐shaped center of the limb, and petaloid lobes of the limb. These petaloid lobes are the site of (E)‐β‐ocimene release. Stomata and trichomes found on the abaxial flower surface were not directly involved in fragrance release. Clear indications of osmophores involved in scent release could not be found. Thus, the results indicate that floral volatiles probably are released by diffuse emission in M. jalapa.
Correlated evolution of leaf shape and trichomes in Begonia dregei (Begoniaceae)
Authors: McLellan Tracy
Published: February 2008

Structural features of leaves, including size, shape, and surfaces, vary greatly throughout the plant kingdom. In both functional and phylogenetic analyses of leaves, the various morphological aspects are often considered independently of each other, although it is likely that many combinations of features do not occur at random due to either functional constraint or genetic correlation. The distribution of variation in leaf morphology in the highly variable Begonia dregei species complex was examined in natural populations and in F2 offspring from a cross between plants from two populations. Leaf shape was quantified using several morphometric measures, and trichomes on leaves were counted and measured. Correlations between leaf shape and the numbers and size of trichomes were examined. There were significant correlations between the shapes of leaves and the presence, number, and size of trichomes among populations and in hybrid plants. Deeply incised leaves had larger numbers of longer trichomes at the sinuses. Higher numbers of trichomes on upper leaf surfaces occurred together with trichomes at the petiole and on the abaxial surface. The potential for independent evolution of leaf shape and trichomes in this group is limited. Hypotheses to explain the correlated development of leaf shape and trichomes are discussed.
Chemistry and geographic variation of floral scent in Yucca filamentosa (Agavaceae)
Authors: Svensson Glenn P. , Hickman Michael O. , Bartram Stefan , Boland Wilhelm , Pellmyr Olle , Raguso Robert A.
Published: February 2008

We identified volatiles from the floral headspace of Yucca filamentosa using gas chromatography and mass spectrometry and analyzed floral scent composition and variation among populations pollinated by different yucca moth species. Twenty‐one scent compounds were repeatedly identified and most could be categorized into two major classes: (1) homoterpenes derived from the sesquiterpene alcohol nerolidol and (2) long chain aliphatic hydrocarbons. Two biosynthetic pathways are thus responsible for the majority of floral volatiles in Y. filamentosa. The homoterpene E‐4,8‐dimethylnona‐1,3,7‐triene, which is released systemically by higher plants upon herbivory, was the most abundant compound. Two di‐oxygenated compounds not previously reported as floral compounds also were detected. No differentiation in floral scent was observed between populations pollinated by different yucca moths, nor was there any correlation between chemical distance and geographic distance among populations. The total release rate of volatiles differed significantly among populations, but not between populations with different pollinators. The combination of unique compounds and low variation in the fragrance blend may reflect highly selective attraction of obligate pollinators to flowers. The observed lack of differentiation in floral scent can putatively explain high moth‐mediated gene flow among sites, but it does not explain conservation of odor composition across populations with different pollinators.
Paleoactaea gen. nov. (Ranunculaceae) fruits from the Paleogene of North Dakota and the London Clay
Authors: Pigg Kathleen B. , DeVore Melanie L.
Published: February 2008

Paleoactea nagelii Pigg & DeVore gen. et sp. nov. is described for a small, ovoid ranunculaceous fossil fruit from the Late Paleocene Almont and Beicegel Creek floras of North Dakota, USA. Fruits are 5–7 mm wide, 4.5–6 mm high, 10–13 mm long, and bilaterally symmetrical, containing 10–17 seeds attached on the upper margin in 2–3 rows. A distinctive honeycomb pattern is formed where adjacent seeds with prominent palisade outer cell layers abut. Seeds are flattened, ovoid, and triangular. To the inside of the palisade cells, the seed coat has a region of isodiametric cells that become more tangentially elongate toward the center. The embryo cavity is replaced by an opaline cast. This fruit bears a striking resemblance to extant Actaea, the baneberry (Ranunculaceae), an herbaceous spring wildflower of North Temperate regions. A second species, Paleoactaea bowerbanki (Reid & Chandler) Pigg & DeVore nov. comb., is recognized from the Early Eocene London Clay flora, based on a single fruit. This fruit shares most of the organization and structure of P. nagelii but is larger and has a thicker pericarp. This study documents a rare Paleocene occurrence of a member of the buttercup family, a family that is today primarily herbaceous, and demonstrates a North Atlantic connection for an Actaea‐like genus in the Paleogene.
Genetic variation and structure in the expanding moss Pogonatum dentatum (Polytrichaceae) in its area of origin and in a recently colonized area
Authors: Hassel Kristian , Såstad Sigurd M. , Gunnarsson Urban , Söderström Lars
Published: February 2008

Genetic variation in the expanding moss species Pogonatum dentatum was studied using intersimple sequence repeat (ISSR) markers. The genetic consequences of range expansion were studied by comparing source populations in a mountain area with populations from a recently colonized lowland area in Sweden. Indices of genetic variation show slightly lower number of alleles per locus in the lowlands and a similar gene diversity in both areas. Three of four lowland populations had evidence of a recently passed bottleneck. Considerably higher haplotype diversity was found in the recently colonized lowlands compared to source populations in the mountains. Patterns of allelic diversity suggest that P. dentatum experiences loss of genetic variation through founder effects and genetic drift when expanding its distribution range. Higher haplotypic diversity, less linkage disequilibrium, and fewer compatible loci indicate that sexual recombination is relatively more important in the lowlands compared to the mountains. A likely explanation is higher success of establishment from spores in the lowlands, while clonal propagation predominates in the mountains. Less genetic differentiation among lowland populations indicates more gene flow in the lowland area, involving more spores and/or fragments moving among populations.
Sexes show differential tolerance to spittlebug damage and consequences of damage for multi‐species interactions
Authors: Cole Denise H. , Ashman Tia‐Lynn
Published: February 2008

Antagonists can play a role in sexual system evolution if tolerance or resistance is sex‐dependent. Our understanding of this role will be enhanced by consideration of the effects of antagonists on other plant–animal interactions. This study determined whether the sex morphs of a gynodioecious Fragaria virginiana differ in their susceptibility and response to damage by spittlebugs and whether damage altered pollinator attraction traits or interactions with other antagonists. Tolerance, but not resistance, to spittlebugs differed between the sexes. Generally, spittlebugs were more damaging to hermaphrodites than females, a finding in accord with the hypothesis that the pollen‐bearing morph is less tolerant of source‐damage than the pollen‐sterile morph when damage is incurred during flowering. In both sex morphs, spittlebugs reduced inflorescence height, increased petal size, but did not affect the number of open flowers per day, suggesting that the net effect of damage may be to increase pollinator attraction. Spittlebug infestation modified interactions with other antagonists in a sex‐dependent manner: spittlebugs reduced attack by bud‐clipping weevils in hermaphrodites but increased infection by leaf fungi in females. The complex interactions between plant sex, antagonists, and pollinator attraction documented here emphasize the importance of considering sex‐differential multi‐species interactions in plant sexual evolution.
Problems in measuring among‐family variation in inbreeding depression
Authors: Fox Charles W.
Published: February 2008

Understanding the sources of variation in inbreeding depression within populations is important for understanding the evolution of selfing rates. At the population level, inbreeding depression is due to decreased heterozygosity caused by inbreeding, which decreases overdominance and increases the frequency of expression of recessive deleterious alleles. However, within individual families inbreeding has two distinct consequences: it reduces heterozygosity and it restricts the alleles present in offspring to those present in the parent. Outcrossing both increases heterozygosity and brings new alleles into a family (compared to the alleles present if the plant is self‐pollinated). Both consequences of inbreeding affect offspring fitness, but the most common experimental design used to measure among‐family variation in inbreeding depression cannot distinguish them. The result is that variance in inbreeding depression among families is confounded by genetic variation in the traits being measured. Also, correlations (among families) between measures of inbreeding depression or between inbreeding depression and mean trait values are confounded by genetic variation in the traits being measured. I conclude that more complex crossing designs that allow estimation of breeding values for individual families are required to accurately detect and measure among‐family variation in inbreeding depression.
DNA content and expression of genes related to cell cycling in developing Gossypium hirsutum (Malvaceae) fibers
Authors: Taliercio Earl , Hendrix Bill , Stewart James McD.
Published: February 2008

The cell cycle in cotton (Gossypium hirsutum) fibers is poorly understood. The objective of this study was to evaluate the cell cycle status and DNA content in developing cotton fibers. The DNA content and cell cycle distribution in fiber and hypocotyl cells were determined by flow cytometry. Expression levels of minichrosomal maintenance protein (mcm), cyclin B, and a retinoblastoma‐like protein (rb) genes were determined with real‐time PCR in fibers and dividing and nondividing tissues. No endoreduplication occurred, nor did genome size or percentage of G1‐phase nuclei differ between hypocotyls and fibers. Approximately 13 and 17% of fiber nuclei were in the S phase in 14 days after anthesis (d) fibers and 25 d fibers, respectively. The mcm and cyclin B were expressed at higher levels in fibers than in mature leaves, but expression levels in fibers were less than 15% of meristematic tissues. Rb was expressed in fibers at levels less than 50% of mature leaves or meristematic tissues. Based on an apparent increase in S‐phase cells as fibers mature and the low level of expression of genes associated with cell cycle progression, we conclude that S‐phase arrest occurs in developing cotton fiber.
Vegetation patterns 25 years after the eruption of Mount St. Helens, Washington, USA
Authors: del Moral Roger , Lacher Iara L.
Published: February 2008

In 2004, we surveyed the vegetation on Mount St. Helens to document changes since 1992. We asked how communities differentiate and if they develop predictable relationships with local environments. We sought evidence from links between species and environment and changes in community structure in 271 250‐m2 plots. The habitats of the seven community types (CTs) overlapped broadly. Ordination methods demonstrated weak correlations among species distributions and location, elevation, and surface variables. Comparisons to 1992 by habitat demonstrated a large increase in plant cover and substantial development of vegetation structure. Pioneer species declined while mosses increased proportionately leading to more pronounced dominance hierarchies in most habitats. In Lupinus colonies, dominance declined, and diversity increased due to the increased abundance of formerly rare species. On once barren sites, dominance increased, but diversity changed slightly, which suggested the incipient development of competitive hierarchies. Weak correlations between vegetation and the environment suggested that initially stochastic establishment patterns had not yet been erased by deterministic factors. A vegetation mosaic that is loosely controlled by environmental factors may produce different successional trajectories that lead to alternative stable communities in similar habitats. This result has implications for restoration planning.
Embolized conduits of rice (Oryza sativa, Poaceae) refill despite negative xylem pressure
Authors: Stiller Volker , Sperry John S. , Lafitte Renee
Published: February 2008

Embolism reversal in rice plants was studied by testing the plant's ability to refill embolized conduits while xylem pressures were substantially negative. Intact, potted plants were water‐stressed to a xylem pressure of −1.88 ± 0.1 MPa and a 66.3 ± 3.8% loss of xylem conductivity (PLC) by cavitation. Stressed plants were carefully rewatered, allowing xylem pressure to rise, but not above the theoretical threshold of c. −0.15 MPa for embolism collapse. Despite xylem pressures being more negative than this threshold, the PLC fell significantly (28.5 ± 5.6%), indicating the refilling of vessels. Above c. −1.0 MPa, almost all plants regained their maximum hydraulic conductivity. Dye uptake experiments showed the same pattern of embolism refilling despite negative pressure. Refilling was prevented in plants that were light‐starved for 5 d, suggesting the unknown mechanism is dependent on metabolic energy. Results are among the first showing that herbaceous plants can reverse embolism without bulk xylem pressures rising near or above atmospheric.
Genic diversity, genetic structure, and mating system of Brewer spruce (Pinaceae), a relict of the Arcto‐Tertiary forest
Authors: Ledig F. Thomas , Hodgskiss Paul D. , Johnson David R.
Published: February 2008

Brewer spruce (Picea breweriana), a relict of the widespread Arcto‐Tertiary forests, is now restricted to a highly fragmented range in the Klamath Region of California and Oregon. Expected heterozygosity for 26 isozyme loci, averaged over 10 populations, was 0.121. More notable than the relatively high level of diversity when compared to other woody endemics was the strong decrease in expected heterozygosity with latitude. Differentiation (FST) was 0.152, higher than values for many north temperate conifers with larger distributions. The number of migrants per generation (Nm) was 1.34 or 2.70, depending on the method of estimation. Inbreeding appeared low;FISwas only 0.003, in agreement with multilocus population outcrossing rates (tm), which were generally well above 0.90. No difference intmwas found between isolated vs. clustered trees. However, the number of seeds per cone was greatest in the densest populations;tmis a measure of effective outcrossing after mortality in the embryonic stage, whereas a reduced number of seeds per cone indicates self pollination. Selfing increased after logging; outcrossing rate before logging was 0.961 and after logging, 0.756. Despite Brewer spruce's narrow, fragmented distribution, the outlook for its conservation was good, with the exception of possible negative effects of logging.
The role of pollination level on the reproduction of females and hermaphrodites in the gynodioecious plant Gypsophila repens (Caryophyllaceae)
Authors: López‐Villavicencio Manuela , Genton Benjamin J. , Porcher E. , Shykoff Jacqui A.
Published: February 2008

In gynodioecious plant species, females are expected to have more resources available for maturing seeds because pistillate flowers are smaller, do not produce pollen, and are thus less costly that perfect flowers. The potential female advantage arising from more abundant resources is, however, likely to vary depending on whether seed production is limited by resource or pollen availability. Here we experimentally investigated the influence of pollen and resource limitation on female advantage in a gynodioecious species using two levels of pollination. Total seed production of females was always greater than that of hermaphrodites: females produced more flowers and more fruits that contained similar numbers of seeds of similar mass. Under low pollination, female and hermaphrodite plants allocated resources to increased flower production rather than to increased seed size or quality. We did not detect any influence of pollen or resource limitation on female advantage, which remained similar under low (* abundant resources) and full pollination. Outcrossed fruits performed better than selfed fruits when the same plant received both selfed and outcrossed pollen on different flowers. These differences were not greater under high pollination, possibly because resources available for each fruit did not differ between our pollen intensity treatments.
Pollination ecology of Stenocereus queretaroensis (Cactaceae), a chiropterophilous columnar cactus, in a tropical dry forest of Mexico
Authors: Ibarra‐Cerdeña Carlos N. , Iñiguez‐Dávalos Luis I. , Sánchez‐Cordero Víctor
Published: February 2008

Flowers of columnar cacti are animal‐pollinated, often displaying a chiropterophylic syndrome. This study examined if the columnar cactus Stenocereus queretaroensis, a tropical species endemic to western Mexico, is bat‐pollinated, by studying its pollination biology and the foraging behavior of potential pollinators. Flowers were produced in winter through spring, peaking in April. Anthesis was nocturnal, and stigma and anther turgidity began around 2200 hours. Production of nectar secretion and highest sugar concentration and energy supply were nocturnal, peaking between 2200 and 2400 hours. Manual auto‐pollination and exclusion experiments showed that self‐pollination yielded no fruits, while nocturnal pollinators resulted in high fruit set and seed set compared to diurnal pollination treatments. The nectar‐feeding bat Leptonycteris curasoae (Phyllostomidae) was the main nocturnal pollinator with the highest effective pollination. Peak bat visitation coincided with peaks in nectar production. The high abundance of L. curasoae throughout the 4‐yr study, suggests that it is a seasonally reliable pollinator for this columnar cactus. While pollination syndromes have been increasingly called into question in recent years, this study suggests that at least for this system, there is a fairly close fit between pollinator and pollination syndrome.
Explosive seed dispersal in two perennial Mediterranean Euphorbia species (Euphorbiaceae)
Authors: Narbona Eduardo , Arista Montserrat , Ortiz Pedro L.
Published: February 2008

The distance of explosive dispersal, its pattern in time, and the relative importance of autochory have been studied in two diplochorous species: Euphorbia boetica and E. nicaeensis. The seeds of E. boetica released by explosive dispersal reached a median distance of 156 cm and a maximum of almost 8 m, while the distances reached by the seeds of E. nicaeensis were lower: a median of 132 cm and a maximum of 5 m. The differences in explosive dispersal distance between species seem to depend on both seed mass and caruncle retention. The seeds of both species present a caruncle, but in E. boetica this is tiny, and in most cases is shed during the explosion of the capsules. The distances reached by the seeds of these species, dispersed just by capsule explosion, were similar to or greater than the distances to which ants disperse seeds in the Mediterranean sclerophyllous vegetation. Diplochorous plants may maximize either the distance of primary dispersal or that of secondary dispersal. Given that the seeds of E. boetica, that lose their caruncles, are not gathered by myrmecochorous ants, the results suggest that E. boetica maximizes its primary dispersal distance, whereas E. nicaeensis favors its secondary dispersal.