bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of day length on germination of seeds Collected in Alaska
Authors: Densmore Roseann V.
Published: April 2006

Day length control can effectively limit seed germination to favorable seasons, but this phenomenon has been studied in relatively few wild plants. I tested species from interior Alaska for day length control of germination under controlled conditions, and I also monitored germination phenology in natural habitats. Unstratified and cold‐stratified seeds were germinated on short (13 h) and long (22 h) day length and in the dark at constant and alternating temperatures. On long day length, unstratified Ledum decumbens and Saxifraga tricuspidata seeds germinated from 5°C to 20°C, but on short day length few or no seeds germinated at 5°C and 10°C and germination was reduced at higher temperatures. Unstratified seeds of Diapensia lapponica and Chamaedaphne calyculata germinated only at 15°C and 20°C on long day length, and short day length completely inhibited germination. Cold stratification widened the temperature range for germination on both long and short day lengths, but germination was still lower on short than long day length. Germination phenology in natural habitats was consistent with germination in controlled conditions. In these species, short day length and low temperatures interact to inhibit germination in the fall. After overwintering, seeds germinate in the spring at low temperatures and on long day lengths. The inhibitory effect of short day length is not important in the spring because day length is already long at snowmelt.
Gene flow among small populations of a self‐incompatible plant: an interaction between demography and genetics
Authors: Goodell Karen , Elam Diane R. , Nason John D. , Ellstrand Norman C.
Published: April 2006

We assessed the effects of population size and genetic relatedness on rates of pollen gene flow into experimental populations of the insect‐pollinated, self‐incompatible plant Raphanus sativus. We created synthetic populations of sizes 2, 5, 10, and 20 with three genetic structures (full siblings, half siblings, and unrelated plants). Following pollination in a natural setting, we conducted a simple paternity exclusion analysis using the allozyme genotypes of progeny to measure apparent gene flow and Monte Carlo simulations to estimate total gene flow. Estimates of apparent pollen gene flow rates ranged from 0 to 100% and were similar in rank to estimates of total gene flow. There were significant effects of population size and relatedness on the rate of apparent gene flow, and there were significant population size by relatedness interactions. Populations of size 2 had higher gene flow rates than larger populations, gene flow being negatively associated with the level of cross‐compatibility (as measured by hand pollinations). Gene flow into populations of size 2 was also negatively associated with the distance to the nearest population of size 10 or 20. These results suggest that interactions among demography (population size), genetics (cross‐compatibility), and ecology (pollinator behavior) are important influences on pollen gene flow rates into small plant populations.
Is there a floral parasite mutualism in cycad pollination? the pollination biology of Encephalartos villosus (Zamiaceae)
Authors: Donaldson John S.
Published: April 2006

Observations and experiments were carried out over 5 yr to distinguish between wind and insect pollination in the cycad Encephalartos villosus Lemaire (Zamiaceae). They were also designed to determine whether a pollination mutualism exists between E. villosus and Antliarhinus zamiae (Thunberg) (Coleoptera: Brentidae), an obligate ovule parasite that routinely parasitizes a large proportion of the ovules. The percentage of fertilized ovules dropped slightly when wind was excluded from the megastrobilus. However, when insects were excluded by either net bags or insecticide there was a substantial decrease in the proportion of fertilized ovules. Five beetle species belonging to four families were found on the strobili at the time of pollination. Using data on the effectiveness of pollen transfer to the receptive ovule, as well as data on abundance and pollen loads, a pollinator importance value (PIV) was determined for each beetle species and a pollinator importance index (PII) was determined for each population. PII values showed that an undescribed weevil (Porthetes sp., Curculionidae) was consistently the most important pollinator. A. zamiae and an undescribed beetle species within the Xenoscelinae (Languriidae) played a minor role in pollination, and their contributions varied from year to year and between populations. Two additional beetle species, Metacucujus goodei Endrödy‐Younga (Boganiidae) and a second species of Xenoscelinae, had very low PII values and probably had little or no effect on pollination. Low PIV scores for A. zamiae were a result of its low numbers on the microstrobilus and the tendency of the beetles to remain on the outside of the megastrobilus. In the interaction between E. villosus and A. zamiae, the cycad does not appear to benefit significantly from a pollination service and I interpret this to mean that the relationship is antagonistic rather than mutualistic. There is, however, a possible mutualism between Porthetes sp. and E. villosus.
Phylogenetic analyses of “higher” Hamamelididae based on plastid sequence data
Authors: Manos Paul S. , Steele Kelly P.
Published: April 2006

Phylogenetic relationships were examined within the “higher” Hamamelididae using 21 species representing eight families and related outgroups. Chloroplast DNA sequences encoding the matK gene (~1 kilobase) provided 258 informative nucleotide sites. Phylogenetic analysis of this variation produced one most parsimonious tree supporting three monophyletic groups. In this tree, Nothofagus was basal to a well supported clade of remaining “higher” hamamelids, in which Fagaceae, including Fagus, were sister to a clade of core “higher” hamamelids that share wind‐pollination, bicarpellate flowers, granular pollen walls, and reduced pollen apertures. Within the core “higher” hamamelids three subclades were resolved, Myricaceae, (Casuarina‐(Ticodendron‐(Betulaceae))), and (Rhoiptelea‐Juglandaceae). Each subclade was well supported but relationships among them were not. The basal position of Nothofagus within the matK tree is consistent with the fossil record of “higher” hamamelids in which Nothofagus pollen appears earlier than microfossils with affinities to other modern “higher” hamamelids. This placement supports the exclusion of Nothofagus from Fagaceae and suggests two hypotheses for the origin of the cupule. The cupule may be ancestral within “higher” hamamelids and subsequently lost in core members of the clade or there may have been two independent origins. It is suggested that the three clades (1) Nothofagaceae, (2) Fagaceae, and (3) Juglandaceae, Rhoiptelea, Myricaceae, Casuarina, Ticodendron, and Betulaceae be considered at the ordinal level and that traditional orders, such as Fagales sensu Cronquist (Fagaceae, Nothofagaceae, and Betulaceae) be abandoned. Comparative analyses of matK sequences with previously published rbcL sequences demonstrate that for the taxa considered here matK sequences produced trees with greater phylogenetic resolution and a higher consistency index.
Evaluation of atpB nucleotide sequences for phylogenetic studies of ferns and other pteridophytes
Authors: Wolf Paul G.
Published: April 2006

Inferring basal relationships among vascular plants poses a major challenge to plant systematists. The divergence events that describe these relationships occurred long ago and considerable homoplasy has since accrued for both molecular and morphological characters. A potential solution is to examine phylogenetic analyses from multiple data sets. Here I present a new source of phylogenetic data for ferns and other pteridophytes. I sequenced the chloroplast gene atpB from 23 pteridophyte taxa and used maximum parsimony to infer relationships. A 588‐bp region of the gene appeared to contain a statistically significant amount of phylogenetic signal and the resulting trees were largely congruent with similar analyses of nucleotide sequences from rbcL. However, a combined analysis of atpB plus rbcL produced a better resolved tree than did either data set alone. In the shortest trees, leptosporangiate ferns formed a monophyletic group. Also, I detected a well‐supported clade of Psilotaceae (Psilotum and Tmesipteris) plus Ophioglossaceae (Ophioglossum and Botrychium). The demonstrated utility of atpB suggests that sequences from this gene should play a role in phylogenetic analyses that incorporate data from chloroplast genes, nuclear genes, morphology, and fossil data.
Population and genetic structure of the West African rain forest liana Ancistrocladus korupensis (Ancistrocladaceae)
Authors: Foster Paul F. , Sork Victoria L.
Published: April 2006

Ancistrocladus korupensis D. W. Thomas & Gereau (Ancistrocladaceae) is a recently described liana from Cameroon. Its leaves yield the alkaloid michellamine B, which shows in vitro activity against HIV. The only known population is limited to ~ 15 000 ha within Korup National Park and its immediate surroundings. This study: (1) describes ecological patterns (geographic range, population density, stage and size class distributions, host tree characteristics, and seed dispersal patterns) of A. korupensis; (2) quantifies patterns of genetic variation on species and subpopulation levels and fine‐scale genetic structure; (3) describes variation in michellamine B content; and (4) makes conservation recommendations based on ecological and genetic data. Ecological data from 457 individuals from seven sites indicate that the A. korupensis population is dominated by canopy‐climbing individuals. Population densities are low with values ranging from 2.5 to 12.9 individuals/ha. Reproduction data suggest limited seed dispersal, episodic fruiting, and no vegetative reproduction. Allozyme data indicate low genetic diversity with only 7.1% of the 14 loci polymorphic. Values for Hobs and He were 0.022 (± 0.000 SE) and 0.041 (± 0.000 SE), respectively. Wright's F statistics analysis suggests that A. korupensis is highly inbred (FIS = 0.455) with moderate levels of subpopulation differentiation (FST = 0.1153). Michellamine B content was best predicted by leaf type but also showed a significant relationship for stage class. The occurrence of rare, private alleles in most of the sites, low overall population size and density, and low availability of individuals for recruitment into the adult stage class are important considerations for the rational management of A. korupensis.
Morphological, geographical, and ecological differentiation in the Carex Willdenowii complex (Cyperaceae)
Authors: Naczi Robert F. C. , Reznicek Anton A. , Ford Bruce A.
Published: April 2006

Field studies as well as principal components analysis and analyses of variance of specimen measurements revealed morphologic variation within Carex willdenowii correlated with differences in geographical distribution and habitat characteristics. C. willdenowii is actually a complex of three species, C. basiantha Steudel, C. willdenowii Willdenow, and C. superata Naczi, Reznicek, & B.A. Ford, sp. nov. Carex basiantha is a calciphile of moist forests in the southern United States. It has relatively long culms and terminal spikes with long staminate portions. Carex willdenowii is a calcifuge of dry forests in the northeastern United States and immediately adjacent Canada. It has relatively long culms and terminal spikes with short staminate portions. Carex superata is a facultative calciphile of moist to dry forests of the southeastern United States. It has relatively short culms and terminal spikes with long staminate portions. Synonymies, typifications, descriptions, and citations of representative specimens are provided for each species, along with an identification key. The recognition of previously unsuspected diversity in a species from a region with a relatively well‐known flora suggests the systematics of other common, widespread, and morphologically divergent species should be investigated.
Gall‐inducing insects provide insights into plant systematic relationships
Authors: Abrahamson Warren G. , Melika George , Scrafford Robert , Csóka György
Published: April 2006

Field surveys of cynipid gall‐inducer occurrences on Quercus species were conducted in Florida, North Carolina, and Pennsylvania, USA. All cynipids demonstrated strong host species and organ fidelity. One result of this specialization is effective niche partitioning among cynipids. The host‐association patterns of these specialist herbivores should reflect similarities among oaks, thus we clustered oak species according to their cynipid distributions. Cynipids distinguished small differences among their hosts. A dendrogram of oak species based on cynipid distributions was largely congruent with botanical arrangements. Cynipid occurrences offer information helpful to resolving some aspects of oak systematics. Collaborative efforts between taxonomic botanists and entomologists will be useful in resolving a variety of plant and insect systematic problems.
Within‐Population Genetic Diversity of Taraxacum officinale (Asteraceae): Differential Genotype Response and Effect on Interspecific Competition
Authors: Vavrek Milan C.
Published: April 2006

Clonal offspring of five morphologically distinct individuals of Taraxacum officinale were planted in a greenhouse experiment with each of three competitors, Plantago major, Poa pratensis and Trifolium pratense. The competitors were chosen to represent a series of competitive environments experienced by a natural population of T. officinale through the year. Differences in size, morphology, and response to the competitive environments were found among clones and support classification of the five individuals as distinct genotypes. Both differential competitive responses (alteration in performance) and competitive effects (impediment by competitor performance) were exhibited among genotypes. The differential response by the T. officinale genotypes to the competitors indicates that the biotic environment may influence the genetic structure of a population. The biotic environment in this case is determined by the sequential appearance and dominance of competitors in a field rather than the spatial distribution of these competitors. Since competitors change in relative dominance across seasons, competition is likely to be a component of the genotype by season interaction that had been observed in the natural population. Thus, differential responses among genotypes to a temporally and spatially fluctuating biotic environment may contribute to the maintenance of within‐population genetic diversity.
Origins of domestication and polyploidy in oca (Oxalis tuberosa: Oxalidaceae): nrDNA ITS data
Authors: Emshwiller Eve , Doyle Jeff J.
Published: April 2006

As part of a study aimed at elucidating the origins of the octoploid tuber crop “oca,” Oxalis tuberosa, DNA sequences of the internal trancribed spacer of nuclear ribosomal DNA (nrDNA ITS) were determined for oca and several wild Oxalis species, mostly from Bolivia. Phylogenetic analysis of these data supports a group of these species as being close relatives of oca, in agreement with morphology and cytology, but at odds with traditional infrageneric taxonomy. Variation in ITS sequences within this group is quite low (0–7 substitutions in the entire ITS region), contrasting with the highly divergent (unalignable in some cases) sequences within the genus overall. Some groups of morphologically differentiated species were found to have identical sequences, notably a group that includes oca, wild populations of Oxalis that bear small tubers, and several other clearly distinct species. The presence of a second, minor sequence type in at least some oca accessions suggests a possible contribution from a second genome donor, also from within this same species group. ITS data lack sufficient variation to elucidate the origins of oca precisely, but have identified a pool of candidate species and so can be used as a tool to screen yet unsampled species for possible progenitors.
Dioecy and the evolution of pollination systems in Schiedea and Alsinidendron (Caryophyllaceae: Alsinoideae) in the Hawaiian Islands
Authors: Weller Stephen G. , Sakai Ann K. , Rankin Anne E. , Golonka Annette , Kutcher Brenda , Ashby Karen E.
Published: April 2006

The transition from biotic to wind pollination and the consequences of this transition for the evolution of dioecious breeding systems were investigated in Schiedea and Alsinidendron (Caryophyllaceae: Alsinoideae), genera endemic to the Hawaiian Islands. The potential for wind pollination was studied for five species of Schiedea using a wind tunnel. Morphological correlates of wind pollination for these species were then used to infer the presence or absence of wind pollination in the remaining Schiedea species. Hermaphroditic Alsinidendron and Schiedea species, which occur in mesic to wet forests, or less commonly in dry habitats, show little or no indication of wind pollination. These species had low pollen:ovule ratios, large relative pollen size, diffuse inflorescences, substantial nectar production in several cases, and appear to be biotically pollinated or autogamous. Sexually dimorphic species, which all occur in dry habitats, are wind pollinated, based on wind tunnel results or morphological adaptations indicating the potential for wind pollination. These adaptations include high pollen:ovule ratios, small pollen size, moderately to highly condensed inflorescences, and reduced nectaries and nectar production. Shifts to wind pollination and dimorphism are strongly correlated in Schiedea, suggesting the close functional relationship of the two phenomena.
Studies in Neotropical paleobotany. XI. Late Tertiary vegetation and environments of southeastern Guatemala: palynofloras from the Mio‐Pliocene Padre Miguel Group and the Pliocene Herreri´a Formation
Authors: Graham Alan
Published: April 2006

Plant microfossils are reported from the late Tertiary Padre Miguel Group and the Pliocene Herreri´a Formation of southeastern Guatemala. The most abundant palynomorphs are cf. Acrostichum (maximum 45%), Cyperaceae (29%), cf. Antrophyum (27%), monolete fern spores (16%), and Pinus (11%). Pollen grains of Picea, Juglans, Quercus, and Ulmus, primarily from the Padre Miguel flora, reveal the presence of a northern cool‐temperate element. The younger Herreri´a flora is more lowland and warm temperate. In the absence of evidence for substantially higher elevations, the differences between the Neogene and modern vegetation are attributed mostly to climate. MAT (mean annual temperature) is estimated 2°–3°C cooler than at present for the Padre Miguel flora, and ∼3.5°C warmer for the Herreri´a flora. There is little evidence for arid vegetation, and the tropical rain forest was absent or poorly represented. These data are consistent with those of other fossil floras in the region and with trends suggested by isotopic paleotemperature analysis and global sea‐level changes. The Guatemala assemblages further provide evidence that the current version of the tropical rain forest is recent in origin and has undergone considerable change in its range and composition throughout the late Cenozoic.
Primary classification and phylogeny of the polemoniaceae, with comments on molecular cladistics
Authors: Grant Verne
Published: April 2006

The system of classification of the Polemoniaceae currently in use was published by Grant in 1959. Much new evidence concerning relationships in the family has been obtained by numerous workers since 1959, and the old system is in need of revision. A revised system down to the genus level, based on conventional and unconventional characters, including molecular evidence, is presented here. Nineteen genera are grouped into eight tribes and two subfamilies. Three new tribes are described: Acanthogilieae, Loeselieae, and Leptodactyloneae. Several genera are transferred to new groups. The phylogeny of the family is discussed in the light of both the older and new evidence. The approach used in constructing both the 1959 and new systems is that of evolutionary systematics. Two recent (1996, 1997) family‐wide surveys of cpDNA and rDNA use cladistic methods of analysis to arrive at sets of major groups. Some of this molecular evidence has been adopted for the present revised system. However, much incongruence still exists between the new sets of clades, on the one hand, and the present revised system or the still‐viable parts of the 1959 system on the other hand. The incongruences call for an examination and comparison of the contrasting methods of evolutionary systematics and molecular cladistics. A fundamental flaw in the 1996 and 1997 treatments is the attempt to classify plants on the basis of single‐gene gene trees.
Allozyme diversity in the endangered pitcher plant Sarracenia rubra ssp. alabamensis (Sarraceniaceae) and its close relative S. RUBRA ssp. RUBRA
Authors: Jo Mary , Godt W. , Hamrick J. L.
Published: April 2006

Genetic variability in the federally endangered pitcher plant Sarracenia rubra ssp. alabamensis was assessed in eight Alabama populations using starch gel electrophoresis. Ten populations of the more widespread Sarracenia rubra ssp. rubra were sampled in the southeastern United States for comparison. Fifteen allozyme loci representing 13 enzyme systems were scored for each species. In contrast to S. oreophila and S. jonesii, two previously analyzed endangered pitcher plants, genetic diversity was high for both S. rubra subspecies. Within ssp. alabamensis the percentage polymorphic loci (Ps) was 80.0, the mean number of alleles per polymorphic locus was (APS) = 2.58, and expected heterozygosity (Hes) was 0.209. Genetic diversity was slightly lower for ssp. rubra (Ps = 73.3, APs = 2.91, and Hes = 0.177). The proportion of total genetic diversity found among populations was fairly low for both species (Gst = 0.09 for ssp. alabamensis and 0.14 for ssp. rubra). Little genetic divergence has occurred between the two subspecies as indicated by the lack of diagnostic alleles, the proportion of total genetic diversity between taxa (Gst = 0.09), and the genetic identity estimate (I = 0.90). The relatively high genetic diversity found for ssp. alabamensis indicates that the maintenance of its evolutionary potential is possible if population sizes are maintained or increased. Low levels of genetic diversity found within small Georgia ssp. rubra populations indicate that genetic erosion may increase extinction risks for these populations.
Variation of silica bodies in leaf epidermal long cells within and among seventeen species of Oryza (Poaceae)
Authors: Whang Sung Soo , Kim Kyungsik , Hess Wilford M.
Published: April 2006

Morphometric procedures were used with scanning electron microscopy backscattered images to study silica bodies in epidermal long cells of four different leaf veins of 17 of the 20 species of Oryza. The veins studied were midrib, large vein, small vein, and marginal vein. Image analysis was used to study morphological variations among the silica bodies. Statistical analyses were based on 11 variables. Even within a single leaf, silica bodies were not uniform. However, the degree of morphological variation normally showed a distribution of morpholgical types around one modal shape. The most significant differences observed were between silica bodies of the midrib and those of other veins. Bodies varied with respect to both size and shape. Computer‐assisted image analysis is an effective tool for categorizing basic data and for statistical analysis of variation among silica bodies. Morphological variation among silica bodies of a single leaf may be related to water‐conducting systems and their influence on silica availability and phytolith formation.
Development of protein bodies and accumulation of carbohydrates in a soybean (Leguminosae) shriveled seed mutant
Authors: Chen Zhijian , Ilarslan Hilal , Palmer Reid G. , Shoemaker Randy C.
Published: April 2006

The soybean seed mutant T311, when grown under specific environmental conditions, produces shriveled seed. This research investigated changes in development of protein bodies and accumulation of carbohydrates during seed development by comparing the mutant with P2180 seeds. The shriveled seeds contained larger protein bodies but fewer protein bodies per cell than round seeds. Protein bodies in T311 seeds included more dispersed crystals and less globoid regions than P2180 seeds. The elemental compositions of the crystals and of whole seeds in T311 were different from that in P2180 seeds. Starch breakdown was reduced with concomitant lower soluble sugar content in T311 seeds after the D11 stage (10.0–11.9 mm long seeds). The reduced starch breakdown and lowered soluble sugar content were consistent with lower α‐amylase activity and earlier and greater water loss in T311 seeds. Changes in development of protein bodies and accumulation of carbohydrates were associated with the development of the shriveled seeds.
Field tests of density‐ and frequency‐dependent selection in Erigeron annuus (Compositae)
Authors: Bennington Cynthia C. , Stratton Donald A.
Published: April 2006

Selection may maintain genetic diversity in natural populations if the physical or biotic environment is variable over space and/or time. Because density and genotype frequencies can be heterogeneous, and because genotypes may differ in competitive ability, both density‐ and frequency‐dependent selection have been considered to be potentially important evolutionary processes. To address the possibility that intraspecific interactions among plants are a source of fitness variation in Erigeron annuus, we conducted field experiments over 2 yr that were designed to examine the potential of population density, genotype frequency, and their interaction to act as selective agents. In both experiments, apomictic genotypes of Erigeron were paired. Seedlings were planted into plots that differed in density and the identity of minority and majority genotype. There was evidence for a differential effect of density among genotypes for only one year's experiment, suggesting that density‐dependent selection is either weak or temporally variable. Genotype frequency had no effect on fitness in either year, and thus there was no evidence for frequency‐dependent selection. In addition, the lack of a frequency × density interaction demonstrates that resource partitioning, one mechanism for frequency dependence, is not strong among Erigeron genotypes. If frequency‐dependent selection does occur in this species, it is either too weak to detect even in large field experiments, or occurs only in the presence of a selective agent (e.g., pathogens) that was lacking in our experiments.
Allozyme variation and genetic relationships among species in the Carex willdenowii complex (Cyperaceae)
Authors: Ford Bruce A. , McQueen D. A. Ross , Naczi Robert F. C. , Reznicek Anton A.
Published: April 2006

A taxonomic study by Naczi, Reznicek, and Ford (American Journal of Botany, 85, 434–447, 1998) has determined that three species (Carex willdenowii, C. basiantha, and C. superata) can be recognized within the C. willdenowii complex. To determine the amount of genetic divergence within and between these species, allozyme analyses were conducted on 14 populations distributed from Pennsylvania to eastern Texas. Seventeen loci were surveyed, 13 of which were polymorphic, with all populations being polymorphic at one or more loci. Interspecific genetic identities ranged from 0.560 (C. willdenowii and C. basiantha) to 0.807 (C. basiantha and C. superata). Alleles for the isozymes Aat‐1, Dia‐1, Idh‐2, Mdh‐2, Per‐1, Pgm‐1, and Pgm‐2 served to distinguish C. willdenowii from C. basiantha and C. superata. Carex basiantha and C. superata were recognized by alleles of Mdh‐2, Pgm‐1, and Tpi‐2. The genetic identities of populations within species were high and exceeded 0.957. A caespitose growth habit and perigynia in close proximity to the staminate flowers suggest adaptations for selfing and therefore low levels of heterozygosity. Paradoxically, the values for expected heterozygosities (Hexp) were always lower than those obtained by direct count (Hobs): F values were highly negative, indicating heterozygous excess. Disassortative mating and selection are discussed as possible mechanisms for maintaining heterozygous excess within populations.
Analysis of developmental preformation in the alpine herb Caltha leptosepala (Ranunculaceae)
Authors: Aydelotte Allison R. , Diggle Pamela K.
Published: April 2006

Developmental preformation is ubiquitous among alpine and arctic tundra plant species and may cause a delay in plant morphological responses to environmental variation. The duration of preformation and seasonal pattern of development were examined in Caltha leptosepala to identify characteristics of architecture and development that may influence the timing of plant responses to environmental cues, both within a single growing season and between years. All structures in C. leptosepala are preformed: leaves are initiated one or two growing seasons before they mature and flowers are initiated one growing season before maturation. Features of development and architecture in C. leptosepala, however, appear to differ from the determinate growth patterns of other exclusively preforming species, and may allow within‐season variability in the seasonal development and maturation of structures. Cohorts of leaves initiated are asynchronous with maturation cohorts, and each year the number of leaf primordia per plant at snowmelt exceeds the number to mature aboveground. Therefore, some flexibility in whether leaves complete a 2‐yr or 3‐yr developmental trajectory might occur. Plasticity in reproductive phenotype might also occur via the process of floral abortion. Despite developmental characteristics that might facilitate the expression of phenotypic plasticity, only slight variability was observed in the duration of preformation or in the seasonal pattern of initiation and emergence of structures. Growth patterns of C. leptosepala thus appear to be fundamentally constrained, and limitations to annual growth may assure that sufficient preformed primordia remain belowground at the end of each growing season for maturation of a full cohort during the subsequent season.
Genetic diversity and breeding system in a group of neotropical epiphytic ferns (Pleopeltis; Polypodiaceae)
Authors: Hooper Elisabeth A. , Haufler Christopher H.
Published: April 2006

Epiphytes are ecologically important components of tropical forests worldwide and yet they have been underrepresented in studies of reproductive biology. Given the presumed ephemeral nature of their substrates, and the importance of dispersal and colonization, epiphytes might be expected to undergo substantial inbreeding to ensure reproductive success, as in weedy terrestrial plants. While there is some evidence for inbreeding in epiphytic angiosperms, the only previous studies of fern epiphytes indicate that they are predominantly outcrossing. The present study reports on the genetic diversity and breeding system of six members of the Neotropical epiphytic fern genus Pleopeltis (Polypodiaceae). A survey of isozyme variability using starch gel electrophoresis revealed high population levels of polymorphism (P = 0.62), allelic diversity (A = 2.3), and individual heterozygosity (Ho = 0.181), but little differentiation among conspecific populations (I ≥ 0.98; Gst = 0.048), and high interpopulational gene flow rates (Nm > 1). In addition, there was no indication of homozygote excess within populations that might indicate a history of selfing in these ferns: populations generally conformed to Hardy‐Weinberg expected genotype frequencies, and both Wright's inbreeding coefficient (Fis) and Holsinger's intragametophytic selfing rates approached zero. Possible mechanisms limiting inbreeding in these ferns include antheridiogen activity and high levels of genetic load that would lead to inbreeding depression upon selfing.
Reproductive biology and population genetic structure ofKandelia candel(Rhizophoraceae), a viviparous mangrove species
Authors: Sun Mei , Wong K. C. , Lee Joe S.Y.
Published: April 2006

The pollination biology, mating system, and population genetic structure ofKandelia candelwere investigated. Field observations on its pollination and reproductive biology suggested that this species is pollinator dependent for fruit set, and bee activities can lead to substantial geitonogamous selfing. Quantitative analysis of the mating system parameters was performed using progeny arrays assayed for allozyme markers. Multilocus outcrossing rates (tm) were estimated to be 0.697 ± 0.091 and 0.797 ± 0.062 in two populations. In comparison to other plant species with mixed‐mating system, the level of allozyme variation was very low in the 13 populations sampled along the coastlines of Hong Kong. At the species level, the proportion of polymorphic loci was 20%, number of alleles per locus was 1.2, and heterozygosity was 0.0362. The total gene diversity was primarily distributed within populations (HS= 0.0339), and the coefficient of genetic differentiation among populations was low (GST= 0.064). This pattern of population genetic structure suggests that gene flow, primarily in the form of water‐dispersed seedlings in viviparous mangrove species, is not as limited as previously thought. However, microgeographic pattern in allele frequency at the marker loci could still be detected between the western and eastern coastal populations.
Population‐level responses to nutrient heterogeneity and density by Abutilon theophrasti (Malvaceae): an experimental neighborhood approach
Authors: Casper Brenda B. , Cahill James F.
Published: April 2006

An experimental approach was used to examine the effects of spatial nutrient heterogeneity and planting density on the sizes of plants within populations of Abutilon theophrasti. Planting locations were generated using random numbers and replicated among populations growing on two different scales of heterogeneity and homogeneous soils. The same quantity of nutrients (dehydrated cow manure) was added to each population, regardless of the spatial nutrient distribution. The higher density was achieved by adding additional planting locations to those present at the lower density. Plant biomass was compared among ten planting locations present in all populations. Plants in seven locations were smaller at the higher density, but the spatial distribution of nutrients affected plant size in only two locations. At the population level, the higher density reduced mean plant biomass and increased both total biomass and the coefficient of variation in biomass, a measure of size inequality. Only when populations on both scales of heterogeneity were together compared with those on homogeneous soils were population‐level measurements found to be significantly affected by soil treatment; heterogeneity resulted in decreased total biomass and an increase in the coefficient of variation, apparently due to an increase in the number of small plants in the population. These results, together with the finding that fine root biomass increased in nutrient‐enriched patches, suggest that on heterogeneous soils most plants were able to access nutrient patches.
Specialized phloem parenchyma cells in Norway spruce (Pinaceae) bark are an important site of defense reactions
Authors: Franceschi Vincent R. , Krekling Trygve , Berryman Alan A. , Christiansen Erik
Published: April 2006

The bark anatomy of Norway spruce clones that were resistant or susceptible to Ceratocystis polonica, a bark‐beetle‐vectored fungal pathogen, was compared. The major difference concerned the axial parenchyma cells, called polyphenolic parenchyma (PP cells) because of their vacuolar deposits. The phenolic nature of the deposits was indicated by autofluorescence under blue light, and immunocytochemical studies demonstrating PP cells are enriched in phenylalanine ammonia lyase (EC 4.3.1.5), a key enzyme in phenolic synthesis. Susceptible‐clone PP cells occurred as single rows filled with dense deposits. The resistant clone had 40% more PP cells, which occurred in rows two cells thick plus as individual cells scattered among the sieve cells and had lighter deposits. Trees inoculated with fungus were analyzed but a distinct fungal response could not be separated from the general wound response. In the resistant clone, phenolic bodies were reduced in size and density or disappeared completely 12 d after wounding, and PP cell size increased. The susceptible‐clone phenolics and cell size changed only slightly. These data show that PP cells are active in synthesis, storage, and modification of phenolics in response to wounding, providing an important site of constitutive and inducible defenses.
Effects of inbreeding on traits that influence dispersal and progeny density in Cakile edentula var. Lacustris (Brassicaceae)
Authors: Donohue Kathleen
Published: April 2006

Inbreeding may influence the intensity of sibling competition by altering the number of offspring produced or by changing plant morphology in ways that influence seed dispersion patterns. To test this possibility, effects of inbreeding on seed production and on traits that influence progeny density were measured using experimental pollinations of flowers of Cakile edentula var. lacustris. Different flowers on a plant were either hand pollinated with self pollen (with and without emasculation) or foreign pollen, or they were allowed to be pollinated naturally. Selfed flowers matured significantly fewer viable seeds than outcrossed flowers (10.3% less seed maturation with inbreeding depression of 19.2%), due in large part to a greater percentage of proximal seed abortions and lower germination success. Plants grown from selfed seeds tended to have lower seed production (37 fewer seeds on average, with inbreeding depression of 16.2%), caused in part by an increase in the percentage of fruits with proximal seed abortions, although this effect was not significant. Inbreeding depression in total fitness was 29.0%, which corresponds to a difference of 46 seeds per pollinated ovule. Selfing rate estimates were usually intermediate to high, indicating that inbreeding effects observed in this study would be present in naturally pollinated progeny. Although the influence of inbreeding directly on dispersal was negligible, the predicted reduction in sibling competition caused by reduced seed production resulted in an estimate of inbreeding depression of 17.5%, which is 11.5% lower than that measured under uniform conditions. Consequently, inbreeding depression estimated under natural dispersion patterns may be lower than that estimated under uniform conditions since seeds from self‐ and cross‐pollination may not experience the same competitive environment in the field. Inbreeding in the maternal generation, therefore, could influence progeny fitness not only by determining the genetic composition of progeny, but also by influencing the competitive environment in which progeny grow.
Interaction between ants and seeds of a nonmyrmecochorous neotropical tree, Cabralea canjerana (Meliaceae), in the Atlantic forest of southeast Brazil
Authors: Pizo Marco A. , Oliveira Paulo S.
Published: April 2006

On the forest floor of two Atlantic forest sites in southeast Brazil, we recorded 26 ant species (12 genera) interacting with the seeds of Cabralea canjerana (Meliaceae), a typical ornithochorous tree whose seeds are covered by a lipid‐rich aril. The ants treat the arillate seeds in three different ways: (1) the large ponerine ants Pachycondyla striata and Odontomachus chelifer individually remove the seeds to their nests, (2) many species (Pheidole spp.) recruit workers to remove the aril on the spot, or (3) Solenopsis spp. recruit nestmates and cover the seeds with soil before removing the aril on the spot. The ants remove the aril exceptionally rapidly, and removal greatly facilitates seed germination. Seed predation by insects below fruiting trees is severe, and field experiments using vertebrate exclosures showed that rodents also prey heavily upon seeds found near parent trees. Ponerine ants actively remove seeds from this predation‐prone zone. By removing bird‐manipulated and naturally fallen seeds, ants can play a key role in the fate of medium‐sized seeds like those of C. canjerana.
Genome size and karyotype evolution in the slipper orchids (Cypripedioideae: Orchidaceae)
Authors: Cox Antony V. , Abdelnour Gregory J. , Bennett Michael D. , Leitch Ilia J.
Published: April 2006

Nuclear DNA contents (4C) were estimated by Feulgen microdensitometry in 27 species of slipper orchids. These data and recent information concerning the molecular systematics of Cypripedioideae allow an interesting re‐evaluation of karyotype and genome size variation among slipper orchids in a phylogenetic context. DNA amounts differed 5.7‐fold, from 24.4 pg in Phragmipedium longifolium to 138.1 pg in Paphiopedilum wardii. The most derived clades of the conduplicate‐leaved slipper orchids have undergone a radical process of genome fragmentation that is most parsimoniously explained by Robertsonian changes involving centric fission. This process seems to have occurred independently of genome size variation. However, it may reflect environmental or selective pressures favoring higher numbers of linkage groups in the karyotype.
Growth and mitotic potential of multicelled fibers of cotton (Malvaceae)
Authors: Hof Jack Van't , Saha Sukumar
Published: April 2006

We tested the hypothesis that the growth of multicelled cotton fibers of Gossypium hirsutum, cultivar MD51 ne, occurs exclusively within the tip cell. Direct cellular measurements proved the hypothesis incorrect. The results show that all cells within a fiber grow and that the relative growth of the tip cell is reduced as the number of cells per fiber increases. Also, measurements of two‐ and three‐celled fibers show that the two daughter nuclei in two‐celled fibers differ. The ability to divide resides primarily, if not exclusively, with the basal cell. Thus, the fate of the tip‐cell nucleus is fixed while that of the base cell is not. This rule is unaltered by the presence of IAA (indoleacetic acid) and GA3 (gibberellic acid‐3) in the culture medium.
Seed bank influences on genetic diversity in the rare annual Clarkia springvillensis (Onagraceae)
Authors: McCue Kimberlie A. , Holtsford Timothy P.
Published: April 2006

The potential for seed banks to significantly affect the genetic structure of populations was recognized nearly two decades ago. However, there has been little empirical work that examines the problem. In this study, we explore the possibility that the seed bank of a rare annual, Clarkia springvillensis, could act as a buffer against the genetic consequences of small population size. We examined the adult and seed bank cohort in three natural populations. The seed bank was surveyed by collecting soil cores twice during the growing season: postgermination and post seed set. The genetic constitution of the adults and seed bank cohort was determined by examining eight polymorphic isozyme loci via starch gel electrophoresis. The total genetic diversity in the seed bank (Ht = 0.355) was significantly higher than in the adults (Ht = 0.260). Additionally, Fst estimates of genetic differentiation among populations showed significantly less differentiation among population seed banks (Fst = 0.008) than among adults (Fst = 0.045). These results are in agreement with the expectation that seed banks would act to maintain genetic diversity in populations as well as have the effect of slowing differentiation of populations.
The effect of the external medium on the gravitropic curvature of rice (Oryza sativa, Poaceae) roots
Authors: Staves Mark P. , Wayne Randy , Leopold A. Carl
Published: April 2006

The roots of rice seedlings, growing in artificial pond water, exhibit robust gravitropic curvature when placed perpendicular to the vector of gravity. To determine whether the statolith theory (in which intracellular sedimenting particles are responsible for gravity sensing) or the gravitational pressure theory (in which the entire protoplast acts as the gravity sensor) best accounts for gravity sensing in rice roots, we changed the physical properties of the external medium with impermeant solutes and examined the effect on gravitropism. As the density of the external medium is increased, the rate of gravitropic curvature decreases. The decrease in the rate of gravicurvature cannot be attributed to an inhibition of growth, since rice roots grown in 100 Osm/m3 (0.248 MPa) solutions of different densities all support the same root growth rate but inhibit gravicurvature increasingly with increasing density. By contrast, the sedimentation rate of amyloplasts in the columella cells is unaffected by the external density. These results are consistent with the gravitational pressure theory of gravity sensing, but cannot be explained by the statolith theory.
Carbon exchange between Polysiphonia lanosa (Rhodophyceae) and its brown algal host
Authors: Ciciotte Steve L. , Thomas Robert J.
Published: April 2006

Polysiphonia lanosa and its preferred Ascophyllum nodosum host exchange 14C‐labeled photoassimilates. Exchange was demonstrated by injecting 14C‐bicarbonate into air bladders on 15–30 cm cultured sections of field‐collected host blades. Each section bore rhizoidally attached Polysiphonia. In a separate set of experiments, Polysiphonia on similar host material was surface treated with 14C‐bicarbonate in sealed vessels. Movement of radioactive label was detected by autoradiographic and liquid scintillation techniques. On average, 10.5% of total label moved from host to hemiparasite following the first treatment, and 9.7% moved from hemiparasite to host following the second. Reciprocal exchange of tagged photoassimilates may play an important role in the specificity of the relationship between these two algal species.
Female fertility per flower and trade‐offs between size and number in Claytonia virginica (Portulacaceae)
Authors: Morgan Martin T.
Published: April 2006

A consistent and paradoxical feature in flowering plants is the production of many more flowers than appear required for female fertility through fruit and seed production. Many mechanistic hypotheses for this observation share key assumptions about (1) limited resources available for reproduction and (b) greater female fertility benefits from larger flowering‐time investment. Here I investigate these assumptions in two populations of Claytonia virginica. I also test predictions from theoretical analyses, comparing patterns of flowering allocation and fertility per flower in 18 populations of C. virginica. Results support the assumption that larger benefits accrue from greater flowering‐time investment. The between‐population pattern of flowering allocation and fertility per flower is also consistent with theoretical expectation, although not statistically significant. Not supported is the assumption that reproduction occurs under strong resource constraint. Possible reasons for this discrepancy are discussed.