bluuebunny/crossref_metadata_2025 huggingface dataset:
Sclerophylly in two contrasting tropical environments: low nutrients vs. low rainfall
Authors: Read Jennifer , Sanson Gordon D. , de Garine‐Wichatitsky Michel , Jaffré Tanguy
Published: February 2008

The defining characteristics of sclerophylly are mechanical (e.g., hardness, toughness, stiffness), but little is known about how they vary in contrasting environments and contribute to the adaptiveness of sclerophylly. Here we investigate how the degree and nature of sclerophylly in terms of leaf mechanics differ between vegetation of two contrasting stressful environments, maquis on nutrient‐deficient, moist sites and dry forest on moderate‐nutrient, drier sites. We measured toughness, strength, and stiffness at the level of the whole leaf (“structural”) and per unit thickness (“material”). Leaves of maquis plants were on average structurally stiffer, stronger, and tougher than those in dry forest. There was little difference in material properties between habitats, and leaf thickness was the main contributor to differences in structural mechanical properties between habitats. Flexural stiffness varied most among species and habitats, correlating strongly with leaf mass per area and thickness. We suggest that having thicker leaves allows efficient packaging of biomass to reduce branching costs in sunny but stressful environments, with subsequent impacts on structural mechanical properties. Sclerophylly is probably a complex phenomenon, however, with its mechanical constitution arising from both evolved mechanical properties that confer protection or resistance to stress and nonadaptive mechanical consequences of adaptation to stressful environments.
GIS‐based characterization of the geographic distributions of wild and cultivated populations of the Mesoamerican fruit tree Spondias purpurea (Anacardiaceae)
Authors: Miller Allison J. , Knouft Jason H.
Published: February 2008

Humans are having a profound impact on the geographic distributions of plant populations. In crop species, domestication has been accompanied by the geographic expansion of cultivated populations relative to their wild ancestors. We used a geographical information system (GIS)‐based approach to investigate differences in the environmental factors characterizing the geographic distributions of cultivated and wild populations of the Mesoamerican fruit tree Spondias purpurea. Locality data for 86 cultivated and 28 wild S. purpurea populations were used in conjunction with environmental data layers and Maxent, a maximum entropy application for predicting species distributions. Interpredictivity analyses and principal components analysis revealed that the predicted distribution of wild S. purpurea is nested within the cultivated distribution and that the ecological niche (defined by environmental characteristics) of cultivated S. purpurea has expanded relative to that of wild populations. Significant differences between wild and cultivated populations were detected for five environmental variables, corresponding to the expansion of S. purpurea during the domestication process from its native habitat in the Mesoamerican tropical dry forests into less seasonal habitats. These data suggest that humans have altered the range of habitats occupied by cultivated S. purpurea populations relative to their wild progenitors.
Generic delimitation and relationships in Ebenaceae sensu lato: evidence from six plastid DNA regions
Authors: Duangjai Sutee , Wallnöfer Bruno , Samuel Rosabelle , Munzinger Jérôme , Chase Mark W.
Published: February 2008

Phylogenetic relationships of the pantropical family Ebenaceae s.l. were investigated using plastid DNA sequence data from six regions:atpB,matK,ndhF,trnKintron,trnLintron, andtrnL‐trnFspacer. Sampling included representatives of all currently recognized genera of Ebenaceae,Diospyros,Euclea, andLissocarpa, and nearly all taxa that were previously recognized at the generic level, e.g.,Cargillia,Gunisanthus,Maba,Macreightia,Royena, andTetraclis. Our results strongly support monophyly of Ebenaceae s.l. and demonstrate that the previous infrafamilar classifications of the family do not circumscribe monophyletic groups. A new infrafamilial classification based on a phylogenetic approach is proposed here and consists of two subfamilies, Lissocarpoideae and Ebenoideae, and four genera,Lissocarpa,Euclea,Royena, andDiospyros. Relationships and potential synapomorphic characters are discussed and summarized. This study supports a western Gondwanan origin of family and indicates that both vicariant and long‐distance dispersal events played an important role in attaining current distributions.
A synchronous increase in hydraulic conductive capacity and mechanical support in conifers with relatively uniform xylem structure
Authors: Jagels Richard , Visscher George E
Published: February 2008

The dual function provided by longitudinal tracheids in conifers has led to a generally held trade‐off concept that increasing wall thickness and/or volume of latewood tracheids improves mechanical support, while increasing cell diameter and/or volume of earlywood tracheids enhances conductive potential. Yet, some conifers have either uniform cell structure across the growth ring or, at most, a small amount of latewood. How do these trees accomplish the needs for increasing support and conduction with height growth? We examined Metasequoia glyptostroboides, a species that we previously demonstrated improves its mechanical properties with increasing age without a change in specific gravity or secondary wall microfibril angle. In this paper, we showed that lignin and extractive contents are not contributing factors, and through composite structure analysis, we eliminated a role for tracheid length. Using micromorphometric analysis, we demonstrated that as cell diameter increases, total primary wall decreases, secondary wall increases, and strength and conductive capacity increase with no change in specific gravity. Meta‐analysis using other species of Cupressaceae, Podocarpaceae, and Araucariaceae provided strong corroborative evidence for this design strategy.
Evolution of biogeographic disjunction between eastern Asia and eastern North America inPhryma(Phrymaceae)
Authors: Nie Ze‐Long , Sun Hang , Beardsley Paul M. , Olmstead Richard G. , Wen Jun
Published: February 2008

This study examines molecular and morphological differentiation inPhrymaL., which has only one species with a well‐known classic intercontinental disjunct distribution between eastern Asia (EA) and eastern North America (ENA). Phylogenetic analysis of nuclear ribosomal ITS and chloroplastrps16andtrnL‐Fsequences revealed two highly distinct clades corresponding to EA and ENA. The divergence time between the intercontinental populations was estimated to be 3.68 ± 2.25 to 5.23 ± 1.37 million years ago (mya) based on combined chloroplast data using Bayesian and penalized likelihood methods. Phylogeographic and dispersal‐vicariance (DIVA) analysis suggest a North American origin ofPhrymaand its migration into EA via the Bering land bridge. Multivariate analysis based on 23 quantitative morphological characters detected no geographic groups at the intercontinental level. The intercontinental populations ofPhrymathus show distinct molecular divergence with little morphological differentiation. The discordance of the molecular and morphological patterns may be explained by morphological stasis due to ecological similarity in both continents. The divergence ofPhrymafrom its close relatives in the Phrymaceae was estimated to be at least 32.32 ± 4.46 to 49.35 ± 3.18 mya.
Stem diversity, cauline domatia, and the evolution of ant–plant associations inPipersect.Macrostachys(Piperaceae)
Authors: Tepe Eric J. , Vincent Michael A. , Watson Linda E.
Published: February 2008

Plants possess a variety of structures that harbor ant nests, and the morphology of these domatia determines the nature of ant–plant mutualisms in a given plant species. In this study, we report on the differences in anatomy between myrmecophytes ofPiper, which are regularly excavated by an obligate ant mutualist (Pheidole bicornis) and nonmyrmecophytes ofPiper, which consistently have solid stems. Stems of excavated plant species lacked outward evidence of modification; however, striking anatomical differences were apparent between hollow‐stemmed species before excavation and the remainder of the solid‐stemmed species studied. Prior to excavation by ants, stems of myrmecophytes were characterized by strongly heterogeneous piths in which a large, central area had relatively large cells lacking intracellular crystals with a periphery of smaller cells containing numerous crystals. The domatium excavated by the ants was restricted to the large‐celled region. This is the first report of the absence of crystals in ant‐excavated portions of stems of myrmecophytes. Cauline domatia became lined with 3–8 cell layers of suberized wound tissue, which may have an impact on nutrient absorption byPipermyrmecophytes.
Agroecosystem management for rare species ofPaysonia(Brassicaceae): integrating their seed ecology and life cycle with cropping regimens in a changing climate
Authors: Fitch Elizabeth A. , Walck Jeffrey L. , Hidayati Siti N.
Published: February 2008

Dormancy break and germination of seeds are governed by climatic cues, and predicted changes in climate may impact the ecology and conservation of species.Paysonia perforataandP. stonensisare rare brassicaceous winter annuals occurring primarily in fields on floodplains, where corn or soybeans are recommended for habitat maintenance. We tested the effects of precipitation, based on two predictions of changes in climate, on seed germination in these two species and placed the results into a management framework. Seeds of both species, collected during peak dispersal in late April/early May, were given various periods of light (or darkness) followed by darkness (or light) at summer temperatures before placement in darkness during late summer/early autumn in both laboratory and field. The light requirement was met earliest at 10 wk (mid‐July) on alternating wet/dry substrate (simulating current climatic conditions). However, seeds ofP. perforataandP. stonensiswere photostimulated earliest at 2 wk (mid‐May) and 6 wk (mid‐June), respectively, on a continuously moist substrate (simulating predicted future conditions). The soil seed bank could be depleted if plowing coincides with photostimulation of seeds. Fields should be prepared after dispersal but before seeds are photostimulated and harvesting completed before seed germination in early September. Because seeds are highly photostimulated in late summer, disturbance from harvesting must be low to prevent burial. Cultivation of soybean, particularly for forage, is better matched to the seed biology and life cycle ofPaysoniathan that of corn under current and predicted climates.
Paternal, maternal, and biparental inheritance of the chloroplast genome in Passiflora (Passifloraceae): implications for phylogenetic studies
Authors: Hansen A. Katie , Escobar Linda K. , Gilbert Lawrence E. , Jansen Robert K.
Published: February 2008

Patterns of inheritance of the chloroplast genome in Passiflora were analyzed by examining the progeny from both interspecific and intraspecific crosses. Artificial crosses of field‐collected material were performed in greenhouses at The University of Texas at Austin. DNA from fresh leaf material was analyzed by Southern blot techniques to identify the donor of the chloroplast genome. Initially, single progeny were analyzed for 11 crosses; two intraspecific crosses demonstrated maternal inheritance, whereas the nine interspecific crosses had paternal inheritance. Subsequently, the donor of the chloroplast genome was determined for multiple progeny in seven crosses. Passiflora oerstedii × P. retipetala showed strict paternal inheritance in all of 17 progeny. A series of five crosses and backcrosses between P. oerstedii and P. menispermifolia demonstrated strictly paternal inheritance. Finally, when 15 progeny were analyzed for the P. costaricensis × P. costaricensis cross, 12 of the 15 showed maternal inheritance, whereas the remaining three were biparental. Interestingly, all interspecific crosses had primarily paternal inheritance, whereas all intraspecific crosses had primarily maternal inheritance. The implications of heteroplasmy on phylogenetic analyses of chloroplast DNA are discussed.
Early ontogenetic patterns in chemical defense in Plantago (Plantaginaceae): genetic variation and trade‐offs
Authors: Barton Kasey E.
Published: February 2008

Predictions based on the plant age and growth–differentiation balance hypotheses of defense were tested in two congeneric species, Plantago lanceolata and P. major, by quantifying iridoid glycosides, defensive chemicals, in seeds and leaves during the first 6 wk of growth. Concentrations decreased from the seed to 2‐wk‐old seedling stage in P. lanceolata, but increased during this period in P. major. In both species, levels were similar for 2‐ and 4‐wk‐old plants, then significantly increased from 4 to 6 wk. Genetic variation in the ontogeny of iridoid glycoside production was significant in both species at the maternal family level and at the population level. To examine whether allocation costs could explain the low production of iridoid glycosides in seedlings, relationships between growth and defense (iridoid glycosides) were characterized. Growth and defense had a positive or null relationship in all age groups, indicating that there was no trade‐off in these plants at any age. This study provides some support for the growth–differentiation balance hypothesis, but offers no support for the plant age hypothesis. Measuring how herbivory affects plant fitness at different ontogenetic stages may shed light on these patterns in Plantago and on the evolution of the ontogeny of defense.
Determinants of biased sex ratios and inter‐sex costs of reproduction in dioecious tropical forest trees
Authors: Queenborough Simon A. , Burslem David F. R. P. , Garwood Nancy C. , Valencia Renato
Published: February 2008

Estimates of the sex ratio and cost of reproduction in plant populations have implications for resource use by animals, reserve design, and mechanisms of species coexistence, but may be biased unless all potentially reproductive individuals are censused over several flowering seasons. To investigate mechanisms maintaining dioecy in tropical forest trees, we recorded the flowering activity, sexual expression, and reproductive effort of all 2209 potentially reproductive individuals within 16 species of Myristicaceae over 4 years on a large forest plot in Amazonian Ecuador. Female trees invested >10 times more biomass than males in total reproduction. Flowering sex ratios were male‐biased in four species in ≥1 year, and cumulative 4‐year sex ratios were male‐biased in two species and for the whole family, but different mechanisms were responsible for this in different species. Annual growth rates were equivalent for both sexes, implying that females can compensate for their greater reproductive investment. There was no strict spatial segregation of the sexes, but females were more often associated with specific habitats than males. We conclude that male‐biased sex ratios are not manifested uniformly even after exhaustive sampling and that the mechanisms balancing the higher cost of female reproduction are extremely variable.
Crassulacean acid metabolism in the ZZ plant, Zamioculcas zamiifolia (Araceae)
Authors: Holtum Joseph A. M. , Winter Klaus , Weeks Mark A. , Sexton Timothy R.
Published: February 2008

Zamioculcas zamiifolia (Araceae), a terrestrial East African aroid, with two defining attributes of crassulacean acid metabolism (CAM) (net CO2 uptake in the dark and diel fluctuations of titratable acidity) is the only CAM plant described within the Araceae, a mainly tropical taxon that contains the second largest number of epiphytes of any vascular plant family. Within the Alismatales, the order to which the Araceae belong, Z. zamiifolia is the only documented nonaquatic CAM species. Zamioculcas zamiifolia has weak CAM that is upregulated in response to water stress. In well‐watered plants, day–night fluctuations in titratable acidity were 2.5 μmol H+·(g fresh mass)−1, and net CO2 uptake in the dark contributed less than 1% to daily carbon gain. Following 10 d of water stress, net CO2 uptake in the light fell 94% and net CO2 uptake in the dark increased 7.5‐fold, such that its contribution increased to 19% of daily carbon gain. Following rewatering, dark CO2 uptake returned to within 5% of prestressed levels. We postulate that CAM assists survival of Z. zamiifolia by reducing water loss and maintaining carbon gain during seasonal droughts characteristic of its natural habitat.
Infection by powdery mildew Erysiphe cruciferarum (Erysiphaceae) strongly affects growth and fitness of Alliaria petiolata (Brassicaceae)
Authors: Enright Stephanie M. , Cipollini Don
Published: February 2008

Garlic mustard (Alliaria petiolata) is an invasive biennial that negatively impacts plant and animal communities throughout North America and lacks significant herbivory in its invasive range. Throughout Ohio, many garlic mustard populations support the powdery mildew fungus Erysiphe cruciferarum, although disease incidence varies among populations and environments. Effects of infection on plant growth, as well as both plant and fungal responses to drought and light conditions, were examined on greenhouse‐grown, first‐year garlic mustard plants. Also, the effects of the fungus on plant growth and fitness were studied in a naturally growing population of second‐year plants in the field. Powdery mildew significantly reduced growth of first‐year plants in the greenhouse, eventually causing complete mortality. Simulated drought slowed both plant growth and disease development, independent of light conditions. In the field, plants with little incidence of disease after their first year grew taller during their second year, producing significantly more siliques and twice as many seeds as heavily diseased plants did. Seed germination rates did not differ between plants with different levels of disease severity. Consistent reductions in survival, growth, and fitness caused by fungal infection may reduce populations of garlic mustard. These effects may be more evident in moist sites that favor fungal development.
Swietenia (Meliaceae) flower in Late Oligocene–Early Miocene amber from Simojovel de Allende, Chiapas, Mexico
Authors: Castañeda‐Posadas Carlos , Cevallos‐Ferriz Sergio R. S.
Published: February 2008

The amber of Simojovel de Allende, Chiapas, Mexico, of Late Oligocene–Early Miocene age, has yielded a new flower representing the Meliaceae. The flower of Swietenia miocenica Castañeda‐Posadas & Cevallos‐Ferriz sp. nov. is characterized by small size; free calyx composed of five glabrous lobes, ciliolated along the margin lobes; corolla composed of five free, contortedly inserted petals with ciliolated margins; cylindrical staminal tube ending in 10 acuminate or toothed accessories and 10 sessile anthers; and a discoid stigma divided in five lobular stigmatic glands. The morphology of S. miocenica is well represented among Meliaceae. Although the new species shares many characters with Swietenia microphylla, small differences in the length and width of petals and the length of staminal tube support its recognition as a new species. The presence of this genus demonstrates the establishment of tropical communities in southern Mexico by the early Miocene and highlights the influence of the northern hemisphere flora on the extant neotropical flora of the area.
Molecular phylogenetics of Maxillaria and related genera (Orchidaceae: Cymbidieae) based on combined molecular data sets
Authors: Whitten W. Mark , Blanco Mario A. , Williams Norris H. , Koehler Samantha , Carnevali Germán , Singer Rodrigo B. , Endara Lorena , Neubig Kurt M.
Published: February 2008

The orchid genus Maxillaria is one of the largest and most common of neotropical orchid genera, but its current generic boundaries and relationships have long been regarded as artificial. Phylogenetic relationships within subtribe Maxillariinae sensu Dressler (1993) with emphasis on Maxillaria s.l. were inferred using parsimony analyses of individual and combined DNA sequence data. We analyzed a combined matrix of nrITS DNA, the plastid matK gene and flanking trnK intron, and the plastid atpB‐rbcL intergenic spacer for 619 individuals representing ca. 354 species. The plastid rpoC1 gene (ca. 2600 bp) was sequenced for 84 selected species and combined in a more limited analysis with the other data sets to provide greater resolution. In a well‐resolved, supported consensus, most clades were present in more than one individual analysis. All the currently recognized minor genera of “core” Maxillariinae (Anthosiphon, Chrysocycnis, Cryptocentrum, Cyrtidiorchis, Mormolyca, Pityphyllum, and Trigonidium) are embedded within a polyphyletic Maxillaria s.l. Our results support the recognition of a more restricted Maxillaria, of some previously published segregate genera (Brasiliorchis, Camaridium, Christensonella, Heterotaxis, Ornithidium, Sauvetrea), and of several novel clades at the generic level. These revised monophyletic generic concepts should minimize further nomenclatural changes, encourage monographic studies, and facilitate more focused analyses of character evolution within Maxillariinae.
Predicting the effects of nectar robbing on plant reproduction: implications of pollen limitation and plant mating system
Authors: Burkle Laura A. , Irwin Rebecca E. , Newman Daniel A.
Published: February 2008

The outcome of species interactions is often difficult to predict, depending on the organisms involved and the ecological context. Nectar robbers remove nectar from flowers, often without providing pollination service, and their effects on plant reproduction vary in strength and direction. In two case studies and a meta‐analysis, we tested the importance of pollen limitation and plant mating system in predicting the impacts of nectar robbing on female plant reproduction. We predicted that nectar robbing would have the strongest effects on species requiring pollinators to set seed and pollen limited for seed production. Our predictions were partially supported. In the first study, natural nectar robbing was associated with lower seed production inDelphinium nuttallianum, a self‐compatible but non‐autogamously selfing, pollen‐limited perennial, and experimental nectar robbing reduced seed set relative to unrobbed plants. The second study involvedLinaria vulgaris, a self‐incompatible perennial that is generally not pollen limited. Natural levels of nectar robbing generally had little effect on estimates of female reproduction inL. vulgaris, while experimental nectar robbing reduced seed set per fruit but not percentage of fruit set. A meta‐analysis revealed that nectar robbing had strong negative effects on pollen‐limited and self‐incompatible plants, as predicted. Our results suggest that pollination biology and plant mating system must be considered to understand and predict the ecological outcome of both mutualistic and antagonistic plant–animal interactions.
The taxonomic distribution of C4 photosynthesis in Amaranthaceae sensu stricto
Authors: Sage Rowan F. , Sage Tammy L. , Pearcy Robert W. , Borsch Thomas
Published: February 2008

C4 photosynthesis evolved multiple times in the Amaranthaceae s.s., but the C4 evolutionary lineages are unclear because the photosynthetic pathway is unknown for most species of the family. To clarify the distribution of C4 photosynthesis in the Amaranthaceae, we determined carbon isotope ratios of 607 species and mapped these onto a phylogeny determined from matK/trnK sequences. Approximately 28% of the Amaranthaceae species use the C4 pathway. C4 species occur in 10 genera—Aerva, Amaranthus, Blutaparon, Alternanthera, Froelichia, Lithophila, Guilleminea, Gomphrena, Gossypianthus, and Tidestromia. Aerva, Alternanthera, and Gomphrena contain both C3 and C4 species. In Aerva, 25% of the sampled species are C4. In Alternanthera, 19.5% are C4, while 89% of the Gomphrena species are C4. Integration of isotope and matK/trnK data indicated C4 photosynthesis evolved five times in the Amaranthaceae, specifically in Aerva, Alternanthera, Amaranthus, Tidestromia, and a lineage containing Froelichia, Blutaparon, Guilleminea, Gomphrena pro parte, and Lithophila. Aerva and Gomphrena are both polyphyletic with C3 and C4 species belonging to distinct clades. Alternanthera appears to be monophyletic with C4 photosynthesis originating in a terminal sublineage of procumbent herbs. Alpine C4 species were also identified in Alternanthera, Amaranthus, and Gomphrena, including one species (Gomphrena meyeniana) from 4600 m a.s.l.
Uniform genetic diversity, low differentiation, and neutral evolution characterize contemporary refuge populations of Taiwan fir (Abies kawakamii, Pinaceae)
Authors: Shih Fu‐Lung , Hwang Shih‐Ying , Cheng Yu‐Pin , Lee Pei‐Fen , Lin Tsan‐Piao
Published: February 2008

Based on fossil pollen, the distribution range of Taiwan fir [Abies kawakamii (Hay.) Ito] (Pinaceae) is smaller than it was 50 000 years ago. To characterize the present refuge populations of A. kawakamii, which survive only in subalpine forests in Taiwan, we surveyed nuclear genes and chloroplast intergenic spacers to assess the genetic diversity of Taiwan fir. Populations maintain high genetic diversity and contain similar numbers of haplotypes for the GapC (cytosolic glyceraldehyde 3‐phosphate dehydrogenase) fragment. Haplotypes for GapC are generally widespread, and population‐specific haplotypes accounted for 2.5% of the total. Differentiation among populations is very low (GST = 0.01). Only three haplotypes were detected for the cpDNA marker, and every population had one or two haplotypes. In a neutrality test, the variation in nucleotides did not deviate from that expected with neutral evolution for either marker. A retreat route to higher elevations was not evident from either the GapC or cpDNA markers. Hsuehshan was the site of the most divergent population in Taiwan. We concluded that uniform genetic diversity, low differentiation, low numbers of population‐specific haplotypes, and neutral evolution characterize contemporary refuge populations of Taiwan fir.
A comparative analysis of the Lactuca and Helianthus (Asteraceae) plastid genomes: identification of divergent regions and categorization of shared repeats
Authors: Timme Ruth E. , Kuehl Jennifer V. , Boore Jeffrey L. , Jansen Robert K.
Published: February 2008

We have sequenced two complete chloroplast genomes in the Asteraceae, Helianthus annuus (sunflower), and Lactuca sativa (lettuce), which belong to the distantly related subfamilies, Asteroideae and Cichorioideae, respectively. The Helianthus chloroplast genome is 151 104 bp and the Lactuca genome is 152 772 bp long, which is within the usual size range for chloroplast genomes in flowering plants. When compared to tobacco, both genomes have two inversions: a large 22.8‐kb inversion and a smaller 3.3‐kb inversion nested within it. Pairwise sequence divergence across all genes, introns, and spacers in Helianthus and Lactuca has resulted in the discovery of new, fast‐evolving DNA sequences for use in species‐level phylogenetics, such as the trnY‐rpoB, trnL‐rpl32, and ndhC‐trnV spacers. Analysis and categorization of shared repeats resulted in seven classes useful for future repeat studies: double tandem repeats, three or more tandem repeats, direct repeats dispersed in the genome, repeats found in reverse complement orientation, hairpin loops, runs of A's or T's in excess of 12 bp, and gene or tRNA similarity. Results from BLAST searches of our genomic sequence against expressed sequence tag (EST) databases for both genomes produced eight likely RNA edited sites (C → U changes). These detailed analyses in Asteraceae contribute to a broader understanding of plastid evolution across flowering plants.
Leaf damage and gender but not flower damage affect female fitness in Nemophila menziesii (Hydrophyllaceae)
Authors: McCall Andrew C.
Published: February 2008

Researchers can answer questions about the evolution or maintenance of separate sexes using dioecious plant systems. Because females in these species typically put more resources into reproductive effort than male plants, researchers have hypothesized that females may be less tolerant of the stresses found in marginal habitats. Herbivory can act as a biotic stressor that reduces resources in plants much like a marginal habitat can. Females may be limited by resources, and may thus be less tolerant to herbivory than males. Here, I explore the relationships between florivory, leaf herbivory, and gender in a gynodioecious, annual plant, Nemophila menziesii (Hydrophyllaceae, senso lato). I performed a crossed design experiment examining the main effects and interactions of plant gender, artificial leaf damage, and artificial flower damage on components of female plant fitness. Leaf damage decreased fruit set and females made significantly more fruit than hermaphrodites. However, contrary to theory, I found little evidence for a gender by damage interaction for either type of artificial herbivory. Based on these results, I propose more work exploring the effects of both source and sink damage in dioecious species to help elucidate where and when different sexual morphs are favored by natural selection.
Aerenchyma development and elevated alcohol dehydrogenase activity as alternative responses to hypoxic soils in the Piriqueta caroliniana complex
Authors: Benz Bryan R. , Rhode Jennifer M. , Cruzan Mitchell B.
Published: February 2008

The ability of plants to make morphological or physiological adjustments in response to environmental cues allows them to survive and reproduce under a wide range of conditions. One stress that plants are often exposed to is soil oxygen depletion due to flooding. Plants can respond to hypoxic soils by producing oxygen‐conducting aerenchymous tissue or through induction of enzymes in the ethanolic fermentation pathway. Here we use greenhouse experiments to examine flood responses in plants of the Piriqueta caroliniana (Turneraceae) complex, which occupy a range of moisture regimes. Morphotypes and hybrids in this complex exhibited contrasting responses to hypoxic conditions. Genotypes from flooded habitats developed aerenchyma and did not substantially elevate levels of alcohol dehydrogenase (ADH) activity, an enzyme associated with anaerobic respiration. Plants from drier sites, on the other hand, did not develop aerenchyma but had much higher levels of ADH activity. Plants with aerenchymous tissue had substantially higher rates of growth under sustained flooding. Results are consistent with the hypothesis that aerenchyma development is an effective strategy in habitats subject to persistent flooding, while elevating activity of enzymes for ethanolic fermentation is effective only under ephemeral flooding. The range of phenotypic responses observed illustrates contrasting adaptive strategies that can lead to habitat isolation and evolutionary divergence.
Chaetomium elatum(Kunze: Chaetomiaceae) as a root‐colonizing fungus in avocado: is it a mutualist, cheater, commensalistic associate, or pathogen?
Authors: Violi Helen A. , Menge John A. , Beaver Robert J.
Published: February 2008

Plants support numerous root colonists that may share morphological characteristics with mycorrhizal fungi but may play different roles in the rhizosphere. To determine the function of one such root‐colonizing fungus,Chaetomium elatum, the infectivity and composition of inoculum containingC. elatumwere varied independently of and in association with the known mutualistGlomus intraradicesunder two light intensities. Maximum plant benefit occurred with mixtures of bothG. intraradicesandC. elatumand under high light intensity. Under low light intensity and in monoculture,C. elatumfunctioned as a weak pathogen that was able to kill host plants. Here, maximum plant mortality was associated with the highest levels ofC. elatuminfectivity. WhenG. intraradiceswas present, no negative impact ofC. elatumwas detected. Intraspecific interactions were important in predicting sporulation rates for both fungi, whereas no interspecific fungal interactions were detected. In the presence ofG. intraradices,C. elatumappears to function as a “commensalistic associate,” neither impacting plant growth nor sporulation byG. intraradices. Overall,C. elatumappears to be multifunctional, serving as both a rhizoplane and rhizophere fungus, opportunistically colonizing plant roots and only becoming pathogenic when resources are severely limited and intraspecific competition is high. This multifunctional strategy may be shared with other fungi that form similar structures in roots.
Wood vessel diameter is related to elevation and genotype in the Hawaiian tree Metrosideros polymorpha (Myrtaceae)
Authors: Fisher Jack B. , Goldstein Guillermo , Jones Tim J. , Cordell Susan
Published: February 2008

We tested the hypothesis that trees growing at high elevations with occasional freezing temperatures have smaller diameter xylem vessels than trees of the same species growing at lower and warmer elevations. The young branch wood of the wide‐ranging Hawaiian tree species Metrosideros polymorpha (Myrtaceae) was examined in three natural field populations (high, middle, and low elevations: 2469, 1280, and 107 m a.s.l., respectively) and contrasted with seedlings from these populations that were grown in a common garden at middle elevation (1190 m). Previous studies showed that these populations have some genetic differences and have distinctive leaf structure and ecophysiological traits. Vessel diameter was significantly smaller in the high elevation field and common garden plants than in middle elevation plants. However, high elevation vessels were wider in common garden plants compared to field plants, indicating that vessel diameter is determined both by genotype (parental populations) and environment (growing conditions different from those of parents). Reduced vessel diameter has implications for resistance to cavitation induced by freezing and/or drought in plants growing near tree line in Hawaii.
Variation in ovule and seed size and associated size–number trade‐offs in angiosperms
Authors: Greenway Carly A. , Harder Lawrence D.
Published: February 2008

Unlike pollen and seed size, the extent and causes of variation in ovule size remain unexplored. Based on 45 angiosperm species, we assessed whether intra‐ and interspecific variation in ovule size is consistent with cost minimization during ovule production or allows maternal plants to dominate conflict with their seeds concerning resource investment. Despite considerable intraspecific variation in ovule volume (mean CV = 0.356), ovule production by few species was subject to a size–number trade‐off. Among the sampled species, ovule volume varied two orders of magnitude, whereas seed volume varied four orders of magnitude. Ovule volume varied positively among species with flower mass and negatively with ovule number. Tenuinucellate ovules were generally larger that crassinucellate ovules, and species with apical placentation (which mostly have uniovulate ovaries) had smaller ovules than those with other placentation types. Seed volume varied positively among species with fruit mass and seed development time, but negatively with seed number. Seeds grew a median 93‐fold larger than the ovules from which they originated. Our results provide equivocal evidence that selection minimizes ovule size to allow efficient resource allocation after fertilization, but stronger evidence that ovule size affords maternal plants an advantage in parent–offspring conflict.
Patterns of variation of a common fern (Athyrium filix‐femina; Woodsiaceae): population structure along and between altitudinal gradients
Authors: Schneller Jakob , Liebst Burgi
Published: February 2008

Genetic variability of Athyrium filix‐femina populations was evaluated with regard to phenotypic, allozyme, and RAPD variation in 20 Swiss populations along five altitudinal gradients at four different elevations in the northern Swiss Alps. Additionally, allozyme and phenotypic variations in one Italian and two Spanish populations were compared with the variation in the Swiss populations. We hypothesized that there will be statistically significant genetic differences among populations of different altitudes and sites. The results showed no substantial correlation between genetic variation and phenotypic variation among Swiss populations. These results imply that outbreeding and effective gene exchange (long‐distance spore dispersal) are the keys to population structure in this fern species, and as a consequence, phenotypic plasticity is assumed to be favored. This contrasts with results found in similar studies of herbaceous flowering plants where genetic adaptation to gradients like altitude is common. However, when data from the more distant Italian and Spanish populations of A. filix‐femina were included, significant variation was detected.
Carica papaya (Caricaceae): a case study into the effects of domestication on plant vegetative growth and reproduction
Authors: Niklas Karl J. , Marler Thomas E.
Published: February 2008

Few studies have quantitatively evaluated the gender specific effects of cultivation on plant growth and reproduction. The availability of cultivated and wild populations of different genders of Carica papaya L. (Caricaceae) on Guam provided an opportunity to study these effects quantitatively. We compared the gender specific allometry of height vs. basal stem diameter (H vs. D), stem slenderness ratio (H/D), and the height at first flowering (Hfl) of carpellate and staminate plants growing under natural conditions (N = 150 each) with those of carpellate and hermaphroditic plants (N = 250 each) from two cultivars (Sunrise and Tainung 2). These comparisons indicated that (1) wild carpellate and staminate plants are significantly taller than either gender of the two cultivars with equivalent D; (2) the scaling exponent governing the H vs. D relationship of both genders of wild plants is significantly higher than that of either cultivated gender; (3) cultivar type does not affect the H vs. D exponent, but gender expression does; (4) gender expression (but not cultivar‐type) also affects Hfl (cultivation substantially reduces carpellate plant Hfl); and (5) the onset of sexual maturity is associated with a dramatic reversal in H/D ontogeny. Cultivation therefore has “condensed” patterns of vegetative growth in a gender specific manner, whereas gender expression alters both vegetative and reproductive growth significantly more so than does cultivar‐type.
Leaf traits and leaf life spans of two xeric‐adapted palmettos
Authors: Abrahamson Warren G.
Published: February 2008

Plants of nutrient‐poor, arid environments often have leaf traits that include small size, sclerophylly, long life span, low nutrient concentration, and low photosynthetic rate. Hence, the success of two large‐leaved palmettos in peninsular Florida's seasonally xeric, nutrient‐impoverished uplands seems anomalous, given that their leaves are orders of magnitude larger than the leaves of sympatric species.An examination of a 16‐yr data set of leaf traits and leaf life spans across four vegetative associations differing in available light showed thatSerenoa repensandSabal etoniahad low rates of leaf production coupled with long leaf life spans reaching 3.5 yr in heavily shaded plants. The adaptation of these palmettos to xeric, nutrient‐poor habitats has generated dwarf statures, diminished leaf sizes and numbers, increased leaf life spans, and reduced rates of leaf production relative to other palms and congeners of more mesic sites. Leaf and petiole size, plant leaf canopy area, and leaf life span increased in both palmettos with decreasing available light, helping to compensate for reduced photosynthetic rates under shaded conditions and for the high leaf construction costs of the large, thick palmetto leaves. Large leaf size in these palmettos, likely due to phylogenetic conservatism, is compensated by other leaf traits (e.g., heavily cutinized epidermises, thick laminas) that increase survival in seasonally xeric, nutrient‐impoverished environments.
Floral sex allocation at individual and branch levels in Betula platyphylla var. japonica (Betulaceae), a tall, wind‐pollinated monoecious tree species
Authors: Kazuhiko Masaka
Published: February 2008

Floral sex allocation at the individual and first‐order branch levels and the relation between these levels were examined in Betula platyphylla var. japonica, a wind‐pollinated monoecious tree. Floral sex allocation at the individual level varied with resource availability in a pattern similar to that predicted by the Masaka and Takada model (Journal of Theoretical Biology 240: 114–125). Thus, individual trees with few reproductive resources produced only female or male inflorescences, whereas individuals with many resources rarely had a high male ratio (i.e., number of male inflorescences/total number of inflorescences). Furthermore, the number of male inflorescences tended to reach an upper limit, whereas the number of female inflorescences increased monotonically with increasing reproductive investment. The patterns of floral sex allocation at the first‐order branch level were analogous to those at the individual level. Thus, each first‐order branch of B. platyphylla var. japonica behaves like an individual, and the floral sex allocation of a given branch does not necessarily represent the individual tree. The effect of the individual‐level floral sex ratio on branch‐level floral sex allocation indicates that branch behavior is controlled by the individual.
Boreotropical migration explains hybridization between geographically distant lineages in the pantropical clade Sideroxyleae (Sapotaceae)
Authors: Smedmark Jenny E. E. , Anderberg Arne A.
Published: February 2008

To determine whether the fragmented pantropical distribution of present day Sideroxyleae primarily is the result of long‐distance dispersals or represents the remnants of a once continuous distribution in the northern hemisphere, the boreotropical flora, we used phylogenetic analyses of chloroplast and nuclear ribosomal DNA data, Bayesian molecular dating, and Bayesian estimation of ancestral areas. Incongruence between the two data sets was examined with a nuclear low copy gene phylogeny to discover any occurrences of reticulate evolution. The Pacific cladeNesolumawas shown to have two distinct copies of the nuclear low copy geneAAT, one from an African and one from an American ancestral lineage, indicating that it is of allopolyploid origin. We conclude that Sideroxyleae, including the ancestral lineages ofNesoluma, were part of the boreotropical flora and entered the New World via the north Atlantic land bridge. We also suggest that the distribution of extant species resulted from the cooling climate at the end of the Eocene.Sideroxylon oxyacanthumis shown not to belong in the group, but in Chrysophylloideae. A classification reflecting phylogenetic relationships, as well as new combinations for the species inNesolumaunderSideroxylon, is presented.
A generic 3D finite element model of tree anchorage integrating soil mechanics and real root system architecture
Authors: Dupuy Lionel X. , Fourcaud Thierry , Lac Patrick , Stokes Alexia
Published: February 2008

Understanding the mechanism of tree anchorage in a forest is a priority because of the increase in wind storms in recent years and their projected recurrence as a consequence of global warming. To characterize anchorage mechanisms during tree uprooting, we developed a generic finite element model where real three‐dimensional (3D) root system architectures were represented in a 3D soil. The model was used to simulate tree overturning during wind loading, and results compared with real data from two poplar species (Populus trichocarpa and P. deltoides). These trees were winched sideways until failure, and uprooting force and root architecture measured. The uprooting force was higher for P. deltoides than P. trichocarpa, probably due to its higher root volume and thicker lateral roots. Results from the model showed that soil type influences failure modes. In frictional soils, e.g., sandy soils, plastic failure of the soil occurred mainly on the windward side of the tree. In cohesive soils, e.g., clay soils, a more symmetrical slip surface was formed. Root systems were more resistant to uprooting in cohesive soil than in frictional soil. Applications of this generic model include virtual uprooting experiments, where each component of anchorage can be tested individually.
Molecular phylogeny suggests a single origin of insect symbiosis in the Pucciniomycetes with support for some relationships within the genus Septobasidium
Authors: Henk Daniel A. , Vilgalys Rytas
Published: February 2008

In the Pucciniomycetes, a class of fungi that includes the plant pathogenic rust fungi, insect parasitism is restricted to a single family, the Septobasidiaceae. The Septobasidiaceae form a variety of symbioses with scale insects and have remained largely unstudied since the 1930s. Transitions between plant and animal parasitism and between mutualism and parasitism cannot be fully addressed in the Basidiomycota without a clear phylogenetic hypothesis for the Septobasidiales. Here, molecular phylogenetic methods were applied to understand the origin of scale insect parasitism, test the monophyly of the order Septobasidiales, and evaluate the infrageneric concepts in the largest genus of scale insect parasites, Septobasidium. DNA sequence data from rRNA genes were used to infer higher‐level relationships within the Pucciniomycetes, and data from translation elongation factor 1‐alpha (tef1) were added for phylogenetic inference within the Septobasidiaceae. Data from tef1revealed different intron arrangements within Septobasidium, but the molecule did not provide much additional phylogenetically informative data. Likelihood‐model‐based phylogenetic analyses of 44 Pucciniomycotina taxa provided moderate support for a single origin of insect parasitism. Within the Septobasidiaceae, there was little or no support for a monophyletic Septobasidium, and well‐resolved subclades of Septobasidiumspecies contradict previous morphological delimitations of groups within the genus.
Effects of elevated CO2 on the tolerance of photosynthesis to acute heat stress in C3, C4, and CAM species
Authors: Dan Wang  , Heckathorn Scott A. , Barua Deepak , Joshi Puneet , Hamilton E. William , LaCroix Jacob J.
Published: February 2008

Determining the effect of elevated CO2 on the tolerance of photosynthesis to acute heat stress (AHS) is necessary for predicting plant responses to global warming because photosynthesis is heat sensitive and AHS and atmospheric CO2 will increase in the future. Few studies have examined this effect, and past results were variable, which may be related to methodological variation among studies. In this study, we grew 11 species that included cool and warm season and C3, C4, and CAM species at current or elevated (370 or 700 ppm) CO2 and at species‐specific optimal growth temperatures and at 30°C (if optimal ≠ 30°C). We then assessed thermotolerance of net photosynthesis (Pn), stomatal conductance (gst), leaf internal [CO2], and photosystem II (PSII) and post‐PSII electron transport during AHS. Thermotolerance of Pn in elevated (vs. ambient) CO2 increased in C3, but decreased in C4 (especially) and CAM (high growth temperature only), species. In contrast, elevated CO2 decreased electron transport in 10 of 11 species. High CO2 decreased gst in five of nine species, but stomatal limitations to Pn increased during AHS in only two cool‐season C3 species. Thus, benefits of elevated CO2 to photosynthesis at normal temperatures may be partly offset by negative effects during AHS, especially for C4 species, so effects of elevated CO2 on acute heat tolerance may contribute to future changes in plant productivity, distribution, and diversity.