Deoxyribonuclease II activity in Sarcocystis fusiformis and S. gigantea cysts

In the cysts of S. fusiformis and S. gigantea parasites from the esophagus of buffaloes and sheep the increase in the deoxyribonuclease II activity during aging of cysts of both species has been established. It has been found that in all age groups of S. fusiformis cysts the activity of this enzyme is greater than in the corresponding age groups of S. gigantea.     

The dynamics of plant invasions: a case study of three exotic goldenrod species (Solidago L.) in Europe

The patterns of spread of the three exotic species Solidago altissima L., S. gigantea Ait. and S. graminifolia (L.) Salisb. after their introduction to Europe were investigated, based on herbarium specimens and literature records. The spread was analysed by mapping the localities for each decade since 1850. Cumulative numbers of localities as well as numbers of occupied grid squares showed a continuous increase since 1850 for all three species. The slopes, however, were significantly different among the species. Solidago gigantea had the highest colonization rate, followed by S. altissima , and finally S. graminifolia . The latter showed only a slight increase in abundance over time. The increase in diameter of the range in central Europe was logistic for S. altissima and S. gigantea with a rapid increase between 1850 and 1880. The spread of the species in area and time over Europe showed no clear front; new localities at large distances were simultaneously colonized. A large part of the actual range of S. altissima and S. gigantea was already achieved about 1950. It is assumed that the spread of the species followed the hierarchical diffusion model with several independent foci from which the species began to spread. The data suggest that S. altissima and S. gigantea will successfully spread further, leading to an increase in abundance and area, while S. graminifolia seems to spread slowly.     

西藏高原濒危植物西藏巨柏光合作用日进程

研究采用目前先进的光合作用测定系统L i-Cor-6400测定濒危物种西藏巨柏的光合作用,自然环境条件下的西藏巨柏光合日进程表现为单峰型曲线,在12:00时左右达到最高峰,其光合作用不存在“午休现象”。在12:00时,西藏巨柏的气孔限制值和水分饱和亏缺分别达到最大值,此时的水分利用效率较高,在9:00时,西藏巨柏获得一天中最大的表观量子效率,水分利用效率达到最大值。其蒸腾速率在13:00时最大,这个时间并不与光合速率最大值同步,这说明在西藏特殊的气候环境条件下,影响光合速率的因素很多。在光合速率的日进程中,高光合速率值(大于4.00μm o lCO2/(m2.s))持续时间在5h左右,这使得西藏巨柏的光合作用产物得以有效积累,也为西藏巨柏在半干旱环境中的生长创造了有利条件。     

Phylogenetic relationships and natural hybridization among the North American woody bamboos (Poaceae: Bambusoideae: Arundinaria)

In spite of the ecological and economic importance of temperate bamboos, relatively little is known about their population biology or evolutionary history. Recently, hybridization has emerged as a potential source of diversity in this group, as well as an underlying cause of taxonomic problems. As part of a broader phylogenetic study of the temperate bamboos, we report the results of an analysis of the North American Arundinaria gigantea species complex, including estimates of genetic variation and molecular evidence of natural hybridization among A. gigantea, A. tecta, and A. appalachiana. The study involved a comparative analysis of amplified fragment length polymorphisms (AFLPs) and chloroplast DNA sequences representing diversity within and among all three species plus individuals with intermediate or unusual morphological characteristics (putative hybrids). Molecular results support the recognition of three species previously defined on the basis of morphology, anatomy, and ecology, with most of the molecular variance accounted for by among-species variation. Molecular evidence also demonstrates that A. tecta and A. appalachiana are sister species, forming a clade that is significantly divergent from A. gigantea. The role of hybridization in the phylogenetic history of Arundinaria is discussed along with implications for the evolution and taxonomy of the temperate woody bamboos.     

Fertility of Vriesea gigantea Gaud. (Bromeliaceae) in southern Brazil

Plant fertility is a central subject of many questions in plant evolutionary and conservation biology. Pollen availability, abiotic resources, and flowering pattern can limit fruit and seed production. Open pollination and pollen supplementation studies are used to estimate any pollen limitation in natural populations. To study the impact of these factors on the reproductive success of Vriesea gigantea, an epiphytic bromeliad in the Atlantic Rainforest in Brazil, its fertility in four natural populations in Itapu? State Park was assessed by considering plant and inflorescence size, flower production, fruit and seed set, flower and fruit set pattern, and seed viability and germination rate. Supplemental pollination in adult plants was used to determine whether fruit production in V. gigantea is limited by reception of pollen. The results showed that V. gigantea has a high production of flowers, fruits, and seeds. Seeds are highly viable in all populations, presenting an average germination rate of 94% (SE ± 3.5). Plants of V. gigantea from Itapu? State Park are highly fertile. The high proportion of fruit and seed set after manual hand pollination indicates that the species is self-compatible. Pollination treatments showed evidence of pollinator limitation in the Itapu? State Park population.     

Ecological divergence among five co-occurring species of old-field goldenrods

Approximately 130 species of goldenrods are native to North America and many occur sympatrically. Such cooccurrence among closely related species raises the question of whether differences among the species in smallscale distribution and growth forms facilitate their co-occurrence. We investigated five goldenrods that frequently co-occur within their native ranges in Pennsylvania USA old fields. We measured goldenrod abundances, soil textures, nutrients, pH, and moisture within 30 old fields, and determined biomass allocation and flower and seed traits for each goldenrod species at a common site. Ordination revealed that Solidago altissima and S. gigantea were associated with fields having circum-neutral soils, whereas Euthamia graminifolia and S. rugosa achieved their highest abundances on acidic soils. Soil clay content and moisture may be associated with a further separation of species as the abundance of S. altissima tended to be higher on well-drained soils while S. gigantea had a tendency to attain its highest abundances on moist soils that had relatively stable moisture levels over time. Euthamia was more likely to be abundant on clay-rich soils while S. rugosa was often associated with soils containing little clay. Solidago juncea tended to associate with droughty soils that underwent marked soil-moisture changes over time. The latter goldenrod had the greatest absolute and relative root mass, the least absolute and relative leaf mass, highest seed-reproductive allocation, and heaviest achenes. In contrast, S. gigantea and Euthamia, which were often associated with more mesic and stable soil moisture conditions, allocated the least to roots and relatively high amounts of mass to leaves. Solidago gigantea, S. altissima, and Euthamia are invasive species across Europe. The species with the highest colonization rate across Europe, S. gigantea, allocated the most to reproduction in our study, while S. altissima, with the second highest colonization rate, was highly clonal producing the most rhizome mass. Life-history trait variation among goldenrods appears to be linked to differences in small-scale distributions and rates of colonization.     

The influence of oviposition phenology on survival in host races of Eurosta solidaginis

Phenological differences between host plants can contribute to allochronic isolation of host races of phytophagous insects. Host races of the gallmaking fly, Eurosta solidaginis, that live on different species of goldenrod (Solidago altissima and S. gigantea) exhibit different emergence phenologies. These differences could result from adaptation to corresponding phenological differences between the hosts in periods of optimal suitability for gall formation and survival to adulthood. In order to test this, some flies of each host race were allowed to emerge naturally while the emergence times of others were manipulated to correspond to the emergence and oviposition periods of the other host race. Percent gall formation and survival to adulthood were examined for three oviposition periods: the peak time of emergence and oviposition of the earlier-emerging host race (that from S. gigantea), that of the later-emerging host race (that from S. altissima), and a week after the peak emergence of the host race from S. altissima. Flies of both host races were allowed to ovipuncture plants of the appropriate species during each of these periods. Plant relative growth rates were measured during each of these periods. The experiment was repeated twice over a two-year period. Relative growth rates of both host species were highest during the earliest oviposition period (the period during which the host race from S. gigantea normally emerges). Percent gall formation was significantly correlated with plant relative growth rate, but the coefficient of determination was low. In both years of the study, percent gall formation of both host races was highest during the earliest oviposition period (the period during which the host race from S. gigantea normally oviposits). Likewise, percent survival to adulthood in both host races was highest during the earliest oviposition period. There was no significant effect of oviposition period on the percent of larval death due to parasitism by Eurytoma gigantea or predation by Mordellistena unicolor. These results suggest that the host race from S. altissima does not emerge at the time that its host is optimally suited for gall formation or survival to adulthood. Therefore, differences in emergence phenologies do not appear to be due to corresponding phenological differences between the host species in suitability for gall formation or survival to adulthood.     

Dinocrocuta gigantea头骨的发现

本文记述了甘肃和政县晚中新世地层中发现的一个完整的巨鬣狗头骨;讨论了它的分类地位,修正了 Schlosser 1903年建种时的一些鉴定错误.巨鬣狗是鬣狗科中一个十分特化的成员,应代表一个独立的属.根据命名规则,我们采用 N. schmidt-Kittler 1976年所创的 Dinocrocuta. 因此,这个种应订正为 Dinocrocuta gigantea (schlosser, 1903).     

Does a giant tortoise taxon substitute enhance seed germination of exotic fleshy-fruited plants?

Aims The use of exotic species as taxon substitutes to restore lost ecological interactions is currently hotly debated. Aldabrachelys gigantea giant tortoises have recently been introduced to three islands in the Mascarene archipelago (Ile aux Aigrettes, Round Island and Rodrigues) to resurrect herbivory and seed dispersal functions once performed by extinct giant tortoises. However, potential unintended impacts by frugivore substitutes on native ecosystems, e.g. whether they will facilitate the germination of exotic plant species, are largely unknown. We investigated whether A. gigantea introduced to Rodrigues in 2006 could enhance the germination percentage of four widespread fleshy-fruited exotic species on the island. Using germination trials to forecast unintended impacts that could arise from the introduction of a frugivorous taxon substitute enables conservation managers to limit potential adverse negative interactions before they occur.Methods In germination trials that ran over 4 months, we investigated the effects of ingestion (gut passage and deposition in faeces) by sub-adult and adult A. gigantea on the germination percentage of four exotic fleshy-fruited plant species introduced to Rodrigues. We fed fruits of these plant species to sub-adult and adult A. gigantea to test how variation in age and size of the frugivore would affect seed germination. Feeding of distinctly coloured plastic pellets together with the fruits allowed us to test for individual tortoise effects on seed germination.Important findings Ingestion by A. gigantea increased the percentage of seeds germinating of Mimusops coriacea and Lantana camara, but not percentage of germination of Veitchia merrillii or Wikstroemia indica. Seeds were more likely to germinate following ingestion by sub-adult rather than adult tortoises, which may be a consequence of the shorter gut passage time observed for sub-adults. Our results demonstrate that introduced frugivorous taxon substitutes could facilitate germination of exotic and invasive plants and highlight the need for conservation managers to weigh the risk of taxon substitutes potentially facilitating the germination and recruitment of exotic fleshy-fruited plants against the benefit of restoring lost seed dispersal functions of threatened indigenous plants. Our findings also highlight the importance of considering age and size variation in frugivores, in particular in long-lived taxa such as giant tortoises, when studying ingestion effects on the germination performance of plants.     

广东阳春百涌自然保护区桫椤科植物资源调查

广东阳春百涌自然保护区属云开山脉,区内桫椤科植物资源丰富,但具体种类及其资源量并无准确资料,为此我们开展了相关野外调查和统计。调查表明,保护区内共有4种桫椤科植物,即桫椤Alsophila spinulosa、大叶黑桫椤Gymnosphaera gigantea、小黑桫椤G. metteniana和黑桫椤G. podophylla。依据保护区内桫椤科植物主要沿林道分布的特点,提出了按林道长度估算资源量的方法,据估算,保护区内有桫椤约900株,大叶黑桫椤约1.5万株,小黑桫椤约320株,黑桫椤约4500株。阳春百涌保护区是华南地区大叶黑桫椤的主要保存地。     

Genetics, experience, and host-plant preference in Eurosta solidaginis: implications for host shifts and speciation

Host-associated mating is crucial in maintaining the partial reproductive isolation between the host races of Eurosta solidaginis (Diptera: Tephritidae), a fly that forms galls on Solidago altissima and S. gigantea. (We refer to flies reared from S. gigantea as gigantea flies and those reared from S. altissima as altissima flies.) We measured the host preference of males and females of both host races, F1 hybrids between the host races, F2, and backcrosses to both host races. Male and female altissima flies and female gigantea flies had high host fidelity, whereas male gigantea flies had low host fidelity. This result suggests that there may be gene flow between the host races due to nonassortative mating that occurs when male gigantea mate with altissima females on S. altissima. This indicates assortative-mating mechanisms in addition to host-associated mating are required to produce the partial reproductive isolation between the host races that has been observed. Nongenetic factors had no influence on host preference. Larval conditioning did not influence host preference: reciprocal F1 hybrids reared in S. altissima and S. gigantea both preferred S. gigantea. Adult experience had no impact on host preference: females preferred their natal host plant regardless of which host they encountered first as an adult. The hypothesis that maternal effects influence preferences was rejected because male and female flies did not show a consistent preference for the host plant of their mother. We also found no evidence that preference was a sex-linked trait because F1 and backcrosses to the host races with different combinations of X chromosomes from the two host races preferred S. gigantea. Our results indicate that host preference is not determined by a large number of genes because preference of hybrids did not correspond to the proportion of the genome derived from each host race. The strength of the ovipuncture preference for S. gigantea by gigantea females, the females of both reciprocal F1 hybrids, the backcross to gigantea, and F2s indicates that preference is inherited nonadditively at a limited number of loci. The F1 female hybrids, however, had a weaker host preference for S. gigantea than the pure gigantea host race, indicating that there may be incomplete dominance or modifier loci. Males had different host preference patterns than females, with individual male gigantea and male F1 hybrids usually exhibiting preference exclusively for S. gigantea or S. altissima. One hypothesis explaining the difference in host preference between males and females is that the same gene influences both female and male host preference, but it is a sex-influenced gene. Thus, males carrying the gene for S. gigantea preference have an intermediate host preference, whereas females have a strong host preference to S. gigantea. In summary, we found that the host preference that produces host-associated mating is inherited nonadditively at a relatively small number of loci on autosomal genes. This mode of inheritance meets the assumptions of models of sympatric speciation, indicating that the host races could have evolved in sympatry.     

Mitochondrial differentiation, introgression and phylogeny of species in the Tegenaria atrica group (Araneae: Agelenidae)

The relationships between the three members of the Tegenaria atrica group ( T. atrica , T. saeva and T. gigantea ) were examined with DNA sequence data from mitochondrial CO1, 16S rRNA, tRNA^leu(CUN) and ND1 genes. Members of this group of large house spiders have overlapping distributions in western Europe and hybridize with each other to a variable degree. The close relatedness of all three species was supported by all analyses. T. saeva and T. gigantea are more closely affiliated than either is to T. atrica . Haplotypes clearly assignable to T. gigantea were also present in many specimens of T. saeva , suggesting asymmetrical introgression of mtDNA from T. gigantea into T. saeva . Molecular clock calibrations (CO1) suggest that deeper divisions within the genus Tegenaria may be in excess of 10 million years old, and that the evolutionary history of the T. atrica group has been moulded by Quaternary glacial–interglacial cycles.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 79–89.     

扇贝核糖体ITS1和5S rDNA序列的遗传变异及亲缘关系分析

为探讨引进种岩扇贝(Crassadoma gigantea)及虾夷扇贝(Patinopecten yessoensis)、栉孔扇贝(Chlamys farreri)和海湾扇贝(Argopecten irradians)的遗传变异及其之间的亲缘关系, 研究对4种扇贝的核糖体ITS1序列及5S rDNA序列进行了测定, 获得了4种扇贝的ITS1和5S rDNA全序列以及18S rDNA的部分序列, 并进行了序列特征、遗传多样性、遗传距离及系统发育等相关分析。结果显示, 基于ITS1序列的单倍型数、核苷酸变异位点、单倍型多样性指数、核苷酸多样性指数及平均核苷酸差异数分别在2—6、1—12、0.425—0.800、0.00081—0.00486和0.366—2.442; 基于5S 序列的相应参数分别在2—5、1—14、0.533—0.841、0.00108—0.01058和0.533—5.726。4种扇贝均表现出较低的多样性水平(π<0.01)。此外, 4种扇贝基于2种方法计算的种间遗传距离分别在0.040—0.121和0.042—0.413, 均表现为岩扇贝与虾夷扇贝的遗传距离最近, 而岩扇贝与海湾扇贝遗传距离最远。并且系统进化树分析显示岩扇贝与虾夷扇贝独自聚为一支, 说明引进物种岩扇贝与虾夷扇贝的亲缘关系较近。研究结果将为岩扇贝的种质资源保护以及今后的遗传育种研究工作提供参考信息。     

The pre-symbiotic growth of arbuscular mycorrhizal fungi is induced by a branching factor partially purified from plant root exudates

Arbuscular mycorrhizal (AM) symbiosis is an association between obligate biotrophic fungi and more than 80% of land plants. During the pre-symbiotic phase, the host plant releases critical metabolites necessary to trigger fungal growth and root colonization. We describe the isolation of a semipurified fraction from exudates of carrot hairy roots, highly active on germinating spores of Gigaspora gigantea, G. rosea, and G. margarita. This fraction, isolated on the basis of its activity on hyphal branching, contains a root factor (one or several molecules) that stimulates, directly or indirectly, G. gigantea nuclear division. We demonstrate the presence of this active factor in root exudates of all mycotrophic plant species tested (eight species) but not in those of nonhost plant species (four species). We negatively tested the hypothesis that it was a flavonoid or a compound synthesized via the flavonoid pathway. We propose that this root factor, yet to be chemically characterized, is a key plant signal for the development of AM fungi.     

西藏半干旱区3种柏树对干旱胁迫的生理响应特征

以巨柏、大果圆柏和香柏3年生盆栽苗为材料,采用自然干燥法控水,在4个土壤含水量梯度(T1、T2、T3、T4)下测定了3种柏树光合-光响应曲线、光合作用参数和保护酶的活性,以探讨它们对干旱胁迫的生理响应特征。结果显示:(1)3种柏树光合-光响应曲线随干旱胁迫加剧的变化趋势基本相同,当光量子通量密度(PFD)<200μmol.m-2.s-1,净光合速率随PFD的增强基本呈直线增长;当PFD达到1 200μmol.m-2.s-1左右时,净光合速率达到最大。(2)随着干旱胁迫的加剧,3种柏树的光饱和点下降而光补偿点升高,表观量子效率降低;水分利用效率在巨柏和大果圆柏中呈持续下降趋势,而香柏为先上升后下降,但水分利用效率平均值以香柏最大。(3)随着干旱胁迫的加剧,3种柏树SOD活性先升高后降低;巨柏和大果圆柏POD活性呈持续上升趋势,而香柏为先升高后降低;巨柏和大果圆柏的CAT活性先升高后降低,而香柏呈持续上升趋势;3种柏树的MDA含量均呈现逐渐升高趋势,但香柏的脂质过氧化程度远低于巨柏和大果圆柏。研究表明,香柏比巨柏和大果圆柏具有更强的抗旱适应性。     

Amino acids and their metabolites in Sarcocystis fusiformis and S. gigantea cysts

It has been established that cysts S. fusiformis and S. gigantea of parasites isolated from the esophagi of infected buffaloes and sheep have the identical set of free amino acids and their metabolites. These species differ from each other in 7 components of 34 studied that points to their metabolic closeness and to specific differences of sarcocysts from different hosts.     

Experimental heterochrony in hydractiniid hydroids: Why mechanisms matter

As with most clonal organisms, hydractiniid hydroids display a range of morphological variation from sheet-like to runner-like forms. Life history differences correlate with these morphological traits, exhibiting patterns commonly found in studies of heterochrony. Experimental studies of two hydractiniid species show that both morphological and life history heterochronies correlate with patterns of gastrovascular circulation. Similar experimental perturbations of energy metabolism, however, have opposite heterochronic effects on the two species. Treatment with 2,4-dinitrophenol, an uncoupler of oxidative phosphorylation, produced diminished peripheral circulation and sheet-like peramorphic morphologies in the runner-like species, Podocoryne carnea. In contrast, similar manipulations of the sheet-like species, Hydractinia symbiolongicarpus, produced variable peripheral circulation and more runner-like, juvenilized morphologies. These results diverge at the level of morphological and life history pattern, but are consistent when viewed in terms of the physiology of the gastrovascular system. Interpretations of patterns of heterochrony must focus on the physiological and developmental mechanisms which mediate the expression of heterochronic traits.     

Phenotypic variation of the introduced perennial Solidago gigantea in Europe

The exotic perennial Solidago gigantea belongs to the most widespread and abundant plant invaders in Europe, found throughout the range from northern Italy to southern Scandinavia. Morphological variation of this species in Europe was assessed by scoring plants from 22 populations along a north-south transect for quantitative and qualitative characters. All size related and floral characters varied significantly among populations. Size related characters exhibited large coefficients of variation and high intraclass correlations. Floral characters varied considerably less and showed rather narrow unimodal distributions. Pubescence of leaf main vein varied from glabrous to weakly pubescent. Leaf surfaces beneath as well as secondary veins were uniformly glabrous among the shoots. The first three principal components accounted for 56.5% of the variation and formed no separated clusters among the shoots sampled. Chromosome counts revealed only tetraploid cytotypes (2n=36). The low variation in taxonomic key characters and chromosome numbers suggest that the tetraploid cytotype of S.gigantea has became naturalized in Europe, probably the result of only few introductions of this species to Europe.     

Occurrence and impact of the root-rot biocontrol agent Phlebiopsis gigantea on soil fungal communities in Picea abies forests of northern Europe

The aim of this study was to assess belowground occurrence, persistence and possible impact of the biocontrol agent Phlebiopsis gigantea (Fr.) Jülich on soil fungi. Sampling of soil and roots of Picea abies (L.) H. Karst. was carried out at 12 P. gigantea-treated and five nontreated control sites representing 1- to 60-month-old clear-cuts and thinned forest sites in Finland and Latvia. The 454-sequencing of ITS rRNA from fine roots, humus and mineral soil resulted in 8626 high-quality fungal sequences. Phlebiopsis gigantea represented 1.3% of all fungal sequences and was found in 14 treated and nontreated sites and in all three substrates. In different substrates, the relative abundance of P. gigantea at stump treatment sites either did not differ significantly or was significantly lower than in nontreated controls. No significant correlation was found between the time elapsed since the tree harvesting and/or application of the biocontrol and abundance of P. gigantea in different substrates. In conclusion, the results demonstrate that P. gigantea occasionally occurs belowground in forest ecosystems but that stump treatment with the biocontrol agent has little or no impact on occurrence and persistence of P. gigantea belowground, and consequently no significant impact on soil fungi.     

Divergent phenologies may facilitate the coexistence of arbuscular mycorrhizal fungi in a North Carolina grassland

Interest in the diversity of arbuscular mycorrhizal (AM) fungal communities has been stimulated by recent data that demonstrate that fungal communities influence the competitive hierarchies, productivity, diversity, and successional patterns of plant communities. Although natural communities of AM fungi are diverse, we have a poor understanding of the mechanisms that promote and maintain that diversity. Plants may coexist by inhabiting disparate temporal niches; plants of many grasslands are either warm or cool season specialists. We hypothesized that AM fungi might be similarly seasonal. To test our hypothesis, we tracked the sporulation of individual AM fungal species growing within a North Carolina grassland. Data were collected in 1996 and 1997; in 1997, sampling focused on two common species. We found that AM fungi, especially Acaulospora colossica and Gigaspora gigantea, maintained different and contrasting seasonalities. Acaulospora colossica sporulated more frequently in the warm season, but Gi. gigantea sporulated more frequently in the cool season. Moreover, AM fungal species were spatially aggregated at a fine scale. Contrasting seasonal and spatial niches may facilitate the maintenance of a diverse community of AM fungi. Furthermore, these data may illuminate our understanding of the AM fungal influence on plant communities: various fungal species may preferentially associate with different plant species and thereby promote diversity in the plant community.