滇鼠刺花的形态发生（鼠刺科）

在扫描电镜下 ,观察了滇鼠刺 (IteayunnanensisFranch .)花的形态发生。花 3朵一束 ,排成总状花序。花器官为轮状结构 ,向心发生 ;花萼以 2 /5螺旋式相继发生 ,5个花瓣原基几乎同步地在花萼内侧与其互生的位置发生。雄蕊单轮对萼。当雄蕊发生后 ,花顶中心的分生组织开始凹陷 ,成为浅锅状 ;在其周围出现一个环状的分生组织 ,随之 ,2心皮原基产生 ,进而发育为马蹄形。初期的心皮相互分离 ,随着进一步发育 ,心皮内卷 ,彼此靠近、紧贴 ,逐渐于腹面合生 ,形成 2室的中轴胎座 ;花柱的腹维管束通过薄壁组织连通 ;花期柱头融合 ,因此该种为合生心皮。对鼠刺属 (Itea)及相关类群花发育性状和花结构进行了比较 ,支持把鼠刺属提升为鼠刺科 (Iteaceae)的观点。     

滇鼠刺花的形态发生(鼠刺科)

在扫描电镜下,观察了滇鼠刺(Itea yunnanensis Franch.)花的形态发生.花3朵一束,排成总状花序.花器官为轮状结构,向心发生;花萼以2/5螺旋式相继发生,5个花瓣原基几乎同步地在花萼内侧与其互生的位置发生.雄蕊单轮对萼.当雄蕊发生后,花顶中心的分生组织开始凹陷,成为浅锅状;在其周围出现一个环状的分生组织,随之,2心皮原基产生,进而发育为马蹄形.初期的心皮相互分离,随着进一步发育,心皮内卷,彼此靠近、紧贴,逐渐于腹面合生,形成2室的中轴胎座;花柱的腹维管束通过薄壁组织连通;花期柱头融合,因此该种为合生心皮.对鼠刺属(Itea)及相关类群花发育性状和花结构进行了比较,支持把鼠刺属提升为鼠刺科(Iteaceae)的观点.     

Disturbance-dependent spatial distribution of sexes in a gynodioecious understory shrub

Several ecological conditions and processes occurring naturally in plant populations may lead to spatial aggregation of sexes within populations of sexually polymorphic species. In addition, ecological disturbances such as forest management or fire could also affect the spatial distribution of sexes within populations. Spatial aggregation of sexes can have important consequences for the fitness of the individuals in sex-biased patches through increased pollen limitation and/or variation in the male fitness of hermaphrodites. Therefore, spatial aggregation of sexes could be relevant for the maintenance of the sexual polymorphism in plant species. Here, we used point pattern analysis to study the spatial distribution of female and hermaphrodite individuals within a single population of the gynodioecious understory shrub Daphne laureola, inhabiting a young pine reforestation and the adjacent natural undisturbed area. In the undisturbed area, we found that hermaphrodites were distributed randomly whereas females were spatially aggregated at short distances. Such aggregation could result from narrower ecological amplitude, cyto-nuclear determination of sex and limited dispersal and/or increased cloning in females. In the reforested area, females were slightly more abundant and the two sexes were randomly distributed among all plants. Recolonization processes after certain forest disturbances could thus favour the establishment of females and alter the spatial distribution of sexes in this understory species.     

A Review of the Fossil Record of the Genus Itea (Iteaceae, Saxifragales) with Comments on its Historical Biogeography

Itea is a genus of about 20 species of trees and shrubs that are today native to southeastern North America, eastern Asia, and eastern Africa. In this paper, I review the fossil record of Itea, which is based on four types of fossils: diporate, psilate pollen attributed to Itea or the dispersed pollen genus Iteapollis; carpofossils representing fruits and seeds attributed to Itea europaea; flowers preserved in amber and assigned to Adenanthemum iteoides; and leaf impressions attributed to Itea. The distributions of these fossils indicate that Itea was present in western North America from the early Eocene to Miocene, in eastern North America beginning no later than the early Miocene, and in western Eurasia from the late Eocene to Pliocene. Only one datapoint is known from eastern Asia; it is early Miocene in age. Based on the fossil record, it can be inferred that Itea crossed between continents over both the Bering Land Bridge and North American Land Bridge, and that it reached Africa from Europe via Anatolia. Thus, it is predicted that the sole extant North American species, I. virginica, may be most closely related to the sole extant African species, I. rhamnoides. The potential application of Itea fossils to calibrating phylogenetic trees generated from molecular sequence data is also discussed.     

Flowering phenology, display size, and fruit set in an understory dioecious shrub, Aucuba japonica (Cornaceae)

I investigated the effects of display size and flowering phenology on fruit set in Aucuba japonica, an understory dioecious shrub pollinated by opportunistic insects. Natural variations in display size, flowering phenology, and fruit set were monitored in 1997. A hand-pollination experiment was also conducted to check whether pollen limitation was a factor in fruit set in the field. Increases in floral display size did not affect fruit set; the proportion of flowers that set fruit was almost constant irrespective of the total number of flowers per inflorescence, the total number of inflorescences per plant, and the total number of flowers per plant. The hand-pollination experiment showed that fruit set was not pollen limited despite the low mating probability that resulted from the combination of dioecism and the species' dependence on opportunistic pollinators. This was due, in part, to the fact that female flowers did not have a predetermined period of receptivity, but instead remained receptive until they received pollen. In contrast, flowering phenology did affect fruit set. Fruit set was most abundant when male and female flowering was most abundant. This suggests there was some degree of pollen limitation during the part of the flowering season when male flowers were scarce.     

Matter-economical roles of evergreen leaves inAucuba japonica,an understory shrub in the warm-temperate region of Japan

Seasonal dynamics in nitrogen and phosphorus content were examined for each component organ ofAucuba japonica, an evergreen understory shrub in the warmtemperate region of Japan. Evergreen foliage was the largest pool for each nutrient; nitrogen and phosphorus were accumulated and stored in autumn and then redistributed in the spring. For individual leaves, such seasonal accumulations and redistributions were repeated through two or three years and then at leaf fall, an additional amount was withdrawn. Rapid growth of new shoots and flowers during spring was supported by the massive redistribution of the nutrients from the old foliage. The redistribution accounted for 85% and 65% of the total nitrogen and phosphorus input to the new shoots, respectively. Such a high ratio of redistribution resulted in a conservative nutrient economy, and must be positively related to the photosynthetic production in the ligh-limited environment.     

Matter-economical roles of the evergreen foliage ofAucuba japonica,an understory shrub in the warm-temperate region of Japan

Leaf demography and productivity ofAucuba japonica, an understory shrub in the warm-temperate region, were examined and dry matter economy was analyzed to evaluate the roles of the evergreen foliage. Turnover of leaves occurred during a short period in spring. The mean leaf life span was about 2.6 years. Annual NAR (net assimilation rate) of each sample shoot was calculated from the biomass and the total dead mass estimated from scars of leaves and floral parts. The average NAR was 1.34±0.22 g·g⁻¹·yr⁻¹. The ratio of dry matter produced by leaves during their whole life span to the initial investment was 3.45±0.37. The annual NAR calculated for individual plants was negatively related to the life span of their leaves. The seasonal change in SLW (specific leaf weight) showed that the reserve material in leaves was accumulated from autumn to early spring and was consumed for the growth of new organs in the following season. The dry matter withdrawn in spring from the overwintering foliage amounted to 40% of dry mass of the new organs developed.     

Cadmium-dependent oxygen limitation affects temperature tolerance in eastern oysters (Crassostrea virginica Gmelin)

Marine ectotherms, including oysters are exposed to variable environmental conditions in coastal shallow waters and estuaries. In the light of global climate change, additional stressors like pollution might pose higher risk to populations. On the basis of the concept of oxygen- and capacity-limited thermal tolerance in aquatic ectotherms (40), we show that a persistent pollutant, cadmium, can have detrimental effects on oysters (Crassostrea virginica). During acute warming from 20 to 28 degrees C (4 degrees C/48 h) standard metabolic rate (SMR) rose in control and cadmium-exposed (50 microg Cd2+/l) animals, with a consistently higher SMR in Cd-exposed oysters. Additionally, Cd-exposed oysters showed a stronger temperature-dependent decrease in hemolymph oxygen partial pressures. This observation indicates that the effect of temperature on aerobic metabolism was exacerbated due to the additional Cd stress. The oxygen delivery systems could not provide enough oxygen to cover Cd-induced elevated metabolic demands at high temperatures. Interestingly, cardiac performance (measured as the heart rate and hemolymph supply to tissues) rose to a similar extent in control and Cd-exposed oysters with warming indicating that cardiac output was unable to compensate for elevated energy demand in Cd-exposed oysters. Together with the literature data on metal-induced reduction of ventilatory capacity, these findings suggest that synergistic effects of elevated temperatures and cadmium exposure led to oxygen limitation by impaired performance in oxygen supply through ventilation and circulation. Overall, cadmium exposure resulted in progressive hypoxemia in oysters at high temperatures, suggesting that the thermal tolerance window is narrowed in marine ectotherms inhabiting polluted areas compared with pristine environments.     

Effects of flooding on photosynthesis and root respiration in saltcedar (Tamarix ramosissima), an invasive riparian shrub

The introduced shrub Tamarix ramosissima invades riparian zones, but loses competitiveness under flooding. Metabolic effects of flooding could be important for T. ramosissima, but have not been previously investigated. Photosynthesis rates, stomatal conductance, internal (intercellular) CO₂, transpiration, and root alcohol dehydrogenase (ADH) activity were compared in T. ramosissima across soil types and under drained and flooded conditions in a greenhouse. Photosynthesis at 1500 μmol quanta m⁻² s⁻¹ (A₁₅₀₀) in flooded plants ranged from 2.3 to 6.2 μmol CO₂ m⁻² s⁻¹ during the first week, but A₁₅₀₀ increased to 6.4–12.7 μmol CO₂ m⁻² s⁻¹ by the third week of flooding. Stomatal conductance (g_s) at 1500 μmol quanta m⁻² s⁻¹ also decreased initially during flooding, where g_s was 0.018 to 0.099 mol H₂O m⁻² s⁻¹ during the first week, but g_s increased to 0.113–0.248 mol H₂O m⁻² s⁻¹ by the third week of flooding. However, photosynthesis in flooded plants was reduced by non-stomatal limitations, and subsequent increases indicate metabolic acclimation to flooding. Root ADH activities were higher in flooded plants compared to drained plants, indicating oxygen stress. Lower photosynthesis and greater oxygen stress could account for the susceptibility of T. ramosissima at the onset of flooding. Soil type had no effect on photosynthesis or on root ADH activity. In the field, stomatal conductance, leaf water potential, transpiration, and leaf δ¹³C were compared between T. ramosissima and other flooded species. T. ramosissima had lower stomatal conductance and water potential compared to Populus deltoides and Phragmites australis. Differences in physiological responses for T. ramosissima could become important for ecological concerns.     

Fire tolerance of a resprouting <Emphasis Type="Italic">Artemisia</Emphasis> (Asteraceae) shrub

In North America, most Artemisia (Asteraceae) shrub species lack the ability to resprout after disturbances that remove aboveground biomass. We studied the response of one of the few resprouting Artemisia shrubs, Artemisia filifolia (sand sagebrush), to the effects of prescribed fires. We collected data on A. filifolia density and structural characteristics (height, canopy area, and canopy volume) in an A. filifolia shrubland in the southern Great Plains of North America. Our study sites included areas that had not been treated with prescribed fire, areas that had been treated with only one prescribed fire within the previous 5 years, and areas that had been treated with two prescribed fires within the previous 10 years. Our data were collected at time periods ranging from ½ to 5 years after the prescribed fires. Density of A. filifolia was not affected by one or two fires. Structural characteristics, although initially altered by prescribed fire, recovered to levels characteristic of unburned areas in 3–4 years after those fires. In contrast to most non-sprouting North American Artemisia shrub species, our research suggested that the resprouting A. filifolia is highly tolerant to the effects of fire.     

Molecular phylogeography of Carapichea ipecacuanha,an amphitropical shrub that occurs in the understory of both semideciduous and evergreen forests

The medicinal shrub Carapichea ipecacuanha (ipecac) is an amphitropic species with three disjunct areas of distribution. In the Brazilian Atlantic and Amazonian ranges, the species was associated mostly with the understory of seasonal semideciduous forests, whereas in the Central American–Colombian range, the species occurred in the understory of moist evergreen forests. We examined the phylogeographic structure of ipecac using chloroplast trnT‐trnL and nuclear internal transcribed spacer (ITS) sequences from 120 and 46 specimens, respectively. To complement existing data on root alkaloid profiles, we used high‐performance liquid chromatography to assess the levels of emetine and cephaeline in 33 specimens from the two Brazilian ranges. The three ranges shared neither nuclear nor chloroplast haplotypes. The phylogeographic structures showed an uneven distribution of genetic diversity, sharp breaks and high levels of genetic differentiation among ranges. Our results suggest that the extant populations are descendents of at least four distinct ancestral lineages. The Atlantic ipecacs showed higher levels of genetic diversity than ipecacs from the other two ranges; it is likely that they derive from two ancestral lineages, with long‐term persistence in that region. The Amazonian ipecacs were monomorphic with respect to the ITS and cpDNA sequences, which supports the view that there was a recent expansion from a single parental source after a strong genetic bottleneck. The existence of a fourth distinct lineage is apparent from the high levels of genetic and chemical differentiation that we identified in the Central American–Columbian ipecacs.     

Photochemical efficiency of adult and young leaves of the neotropical understory shrub Psychotria limonensis (Rubiaceae) in response to changes in the light environment

We explored the short-term adjustment in photochemical efficiency (Fv/Fm) in adult and young leaves of the understory neotropical shrub Psychotria limonensis Krause (Rubiaceae) in response to rapid changes in the light environment. Leaves were collected from 20 individual plants growing under sun and shade conditions on Gigante Peninsula, Barro Colorado Natural Monument (Republic of Panama), during the wet season of 1996. Leaves were distributed in four sequences of light treatments (AB leaves were expanded under sun and were transferred to shade, BA leaves experienced the opposite transfer, and the controls AA and BB leaves that were expanded and maintained under sun or shade conditions). Adult and young leaves did not differ in overall photochemical efficiency. Instead, differences were found among light environments, for which leaves transferred from shade to sun showed the lowest Fv/Fm ratios. There was no relationship between photochemical efficiency and leaf temperature. In P. limonensis, understory plants are susceptible of photoinhibition independently of the leaf ontogenetic stage. The approach utilized in this experiment allowed the rapid exploration of this capacity, and could be applied to poorly studied understory species.     

Bacteriophage Clearance in the Oyster (Crassostrea virginica)

Since relatively few quantitative immunological studies had been conducted with invertebrates, this study was designed to learn more about the immune potential of the oyster, a molluscan representative. Experiments measured the primary and secondary clearance rates of T2 coliphage in the oyster. The fate of phage injected intracardially or intramuscularly was traced by measuring serum and tissue fluid plaque-forming unit levels at various times postinjection. Phage-neutralizing activity was also measured. Although circulating T2-neutralizing antibody was not induced in the oyster, secondary injections of T2 were cleared more rapidly than primary injections. The difference in clearance rates between primary and secondary groups was not as pronounced in the oyster as in the lemon shark, an animal capable of producing high levels of serum antibody to T2.     

Density‐dependent mortality in adults,but not juveniles,of stream‐resident brown trout (Salmo trutta)

1. This study investigates when and where density dependence operates on the mortality rates of stream‐resident brown trout Salmo trutta. To this aim, I explored populations in habitats of different quality containing high, low or intermediate densities over broad scales of space and time. The study is based on census data of 170 cohorts quantified from recruitment to the total disappearance at 12 sites in four contrasting tributaries of the Rio Esva drainage (north‐western Spain), over the years 1986–2007. 2. Log₁₀‐transformed survivor density over time highlighted a consistent pattern for the 170 cohorts characterised by the occurrence of only two life stages. An early stage starts at recruitment, lasts about half the lifetime and shows no or negligible mortality. A threshold time at 425–620 days after emergence preceded a second stage of continuous and constant mortality until the final disappearance of the cohorts. Consequently, in all scenarios, mortality only occurred in the adult component and no effect of season, year, age‐class and/or reproductive stage was detected. 3. Substantial spatial and temporal variations typified both recruitment (range R = 0.01–1.62 ind m^?2) and adults’ mortality rates (range Z = 0.03–0.38 day^?1). Nested anova s revealed strong effects of site and year on both recruitment and mortality with sites interspersed along the stream gradients where recruitment and mortality were typically high relative to other sites located either nearby in the same stream or distant in another stream, where both recruitment and mortality rates were typically low or intermediate. 4. Adult mortality rates plotted against recruitment for the 170 cohorts pooled revealed a continuous, positive power relationship that explained 45.3% of variation in mortality rates over the whole range of recruitment values. Similarly, highly significant power relationships were elucidated for site‐specific mortality rates averaged across years and for annual‐specific mortality rates averaged across sites against the corresponding mean recruitment averaged across years and sites, respectively. These relationships support the hypothesis that the operation of density dependence is scale independent and context independent but operates in a continuous manner across all scenarios examined. 5. A chronic effect of density dependence on adult losses induces temporally persistent populations maintained by a low number of spawners. Apparently, the operation of density dependence adjusts the number of spawners to the availability of rearing and spawning habitat. This dynamic process may also help to explain the small effective population size (Ne) recently documented by genetic studies of stream‐living brown trout and other salmonids.     

Phylogeography and disjunct distribution in Lychnophora ericoides (Asteraceae), an endangered cerrado shrub species

Background and Aims

Lychnophora ericoides (Asteraceae) presents disjunct geographical distribution in cerrado rupestre in the south-east and central Brazil. The phylogeography of the species was investigated to understand the origin of the disjunct geographical distribution.

Methods

Populations in the south and centre of Serra do Espinhaço, south-east Brazil and on ten other localities in Federal District and Goiás in central Brazil were sampled. Analyses were based on the polymorphisms at chloroplast (trnL intron and psbA-trnH intergenic spacer) and nuclear (ITS nrDNA) genomes. From 12 populations, 192 individuals were sequenced. Network analysis, AMOVA and the Mantel test were performed to understand the relationships among haplotypes and population genetic structure. To understand better the origin of disjunct distribution, demographic parameters and time to most recent common ancestor (T_MRCA) were estimated using coalescent analyses.

Key Results

A remarkable differentiation between populations from the south-east and central Brazil was found and no haplotype was shared between these two regions. No significant effect of isolation by distance was detected. Coalescent analyses showed that some populations are shrinking and others are expanding and that gene flow between populations from the south-east and central Brazil was probably negligible.

Conclusions

The results strongly support that the disjunct distribution of L. ericoides may represent a climatic relict and that long-distance gene flow is unlikely. With an estimated time to most recent common ancestor (T_MRCA) dated from approx. 790 655 ± 36 551 years bp (chloroplast) and approx. 623 555 ± 55 769 years bp (ITS), it was hypothesized that the disjunct distribution may be a consequence of an expansion of the geographical distribution favoured by the drier and colder conditions that prevailed in much of Brazil during the Kansan glaciation, followed by the retraction of the distribution due to the extinction of populations in some areas as climate became warmer and moister.Key words: Disjunct geographical distribution, climatic relict, vicariance, coalescent analysis, phylogeography, endemism, Asteraceae, Lychnophora ericoides, Cerrado, cerrado rupestre, ITS, cpDNA     

Flexible pollination system in an unpalatable shrub Daphne miyabeana (Thymelaeaceae)

The stability of plant reproductive success is dependent on the reproductive system of the plant and the surrounding pollinator assemblages. Here we documented the pollination ecology of a shrub, Daphne miyabeana (Thymelaeaceae), that is unpalatable to deer in two different habitats (open and closed canopy) at a site with severe deer browsing. We found that 31.22 ± 3.07% (mean ± SE) and 9.01 ± 1.71% of the total number of D. miyabeana flowers become fruits in open and closed habitats, respectively. Although spontaneous selfing was possible, the fruit set of that was much lower than the fruit set of an artificial outcrossing treatment. In the closed habitat, the fruit set of the natural pollination was lower than that of artificial outcrossing, whereas in the open habitat the fruit set of those two were similar. In the open habitat, small bees were the major flower visitors, whereas in the closed habitat, ants were the major flower visitors, which did not contribute to pollination. Our findings suggest that D. miyabeana is pollinated by occasional visits of small bees, but it is also self‐compatible and spontaneous selfing is possible. Although its pollination is shaped by abiotic environmental factors, D. miyabeana can reproduce in different habitat conditions. These flexible reproductive systems may be an advantage in coping with the recent environmental change in forest habitats.     

Stable nitrogen and carbon isotope discrimination between juveniles and adults in an income-breeding small mammal (Peromyscus maniculatus)

We investigated the stable nitrogen- and carbon-isotope compositions of blood, liver, muscle and hair of income breeding deer mice (Peromyscus maniculatus) to determine the extent to which stable isotope compositions of mothers and offspring differed. We found small differences between the δ¹⁵N and δ¹³C values of dependent offspring and adult tissues (by a magnitude of −0.8‰ to 1.1‰ for ¹⁵N and 0.3–0.9‰ for ¹³C), and limited ¹⁵N discrimination between juvenile tissues and milk, which explains the small mother-offspring trophic effects in isotopic composition. Discrimination of ¹⁵N between offspring and adults was greater than expected but smaller than known for capital breeding mammals, suggesting that different biochemical pathways for milk production and processing may affect the discrimination of ¹⁵N in these systems.     

Dispersal of an introduced shrub (Crataegus monogyna) by the Brush-tailed Possum (Trichosurus vulpecula)

The Brush-tailed possum Trichosurus vulpecula eats the fleshy fruits of the introduced shrub Crataegus monogyna and defaecates intact seeds at least 0–50 m away. Viability of seeds recovered from faeces was >73%. comparable to the viability of fresh seeds (87.6%). Seed dispersal by possums has been largely neglected and may have important implications for invasion by woody weeds in Australasia.     

Simultaneous,independent, and additive effects of shrub facilitation and understory competition on the survival of a native forb (Penstemon palmeri)

There is increasing recognition that both competition and facilitation are important drivers of plant community dynamics in arid and semi-arid environments. Decades of research have provided a litany of examples of the potential for shrubs as nurse plants for establishment of desirable species, especially in water-limited environments. However, interactions with the existing understory community may alter the outcome of interactions between shrubs and understory plants. A manipulative experiment was conducted to disentangle interactions between a native forb species (Penstemon palmeri A. Gray), a native shrub (Artemisia tridentata Nutt.), and a diverse understory of exotic and native forbs and grasses in a semi-arid shrubland of Northern Utah, USA. Seedlings of P. palmeri were transplanted in a factorial design: (1) beneath shrub canopies or into their interspaces and (2) with understory interactions retained or removed. Transplant survival was tracked for roughly 1 year. Shrubs appeared to facilitate P. palmeri survival while interactions with the existing understory community were equivalently negative, leading to overall neutral interactions. Further, positive shrub interactions and negative understory interactions appeared to operate independently and simultaneously. While the debate over the importance of facilitation and competition in driving plant community dynamics continues, our observations strongly suggest that both have considerable effects on plant establishment in A. tridentata communities. Furthermore, our results inform the conservation and restoration of P. palmeri populations, and suggest the utility of nurse shrubs and/or understory thinning as strategies for increasing the diversity of desirable species in the arid and semi-arid western United States shrublands.