Competition between ectomycorrhizal fungi colonizing Pinus densiflora

 Interactive competition of Pisolithus tinctorius (Pers.) Coker et Couch with an unidentified species Tanashi 01 and Suillus luteus (L.: Fr.) S. F. Gray was investigated using a rhizobox. Pinus densiflora Sieb. et Zucc. was used as the host plant and mycelia were distinguished by hyphal color. The speed of mycelial spread differed between the fungi;P. tinctorius and Tanashi 01 grew faster than S. luteus. A P. tinctorius mycorrhizal seedling and a Tanashi 01 mycorrhizal seedling were transplanted on opposite sides of the rhizobox. The mycelia and mycorrhizae of P. tinctorius were overgrown by Tanashi 01 hyphae and development of P. tinctorius was gradually inhibited. The areas occupied by mycelia and mycorrhiza of P. tinctorius decreased by 52% and 37%, respectively, 154 days after transplantation relative to that at 91 days. In the overlap area of P. tinctorius and Tanashi 01, the latter fungus infected new root tips emerging from P. tinctorius mycorrhiza, which lacked a mantle of P. tinctorius hyphae, and formed a composite mycorrhizal structure. P. tinctorius mycorrhizae were progressively replaced by Tanashi 01 mycorrhizae. Mycelial spread of P. tinctorius and S. luteus were naturally inhibited but there was no interaction in mycorrhizal formation. Accepted: 18 June 1999     

斯洛维尼亚池塘中大蟾蜍的交配模式

为了解大蟾蜍( Bufo bufo)的配对成功是否与身体大小有关,在蟾蜍产卵之前,我们在斯洛文尼亚捕捉和测量了2 224只成体样本。在这些捕获的个体中, 1 772只为雄性, 452只为雌性,其中355对处于抱对状态。雌性的体长(从吻端到泄殖腔的距离)一般比雄性稍长。无论雄性还是雌性,抱对者的体长均大于未抱对者。抱对的雄性和雌性的体长具有显著的正相关。我们所发现的大小匹配的交配模式,与从其它普通蟾蜍种群得到的结果一致[动物学报51 (3) : 513 -515 , 2005]。     

Impacts of climate and density on the duration of the tadpole stage of the common toad Bufo bufo

In an ongoing long-term study of a breeding population of common toads Bufo bufo at a pond in southern England, the dates of first spawning have been recorded since 1980, the dates of toadlet emergence since 1984, and the numbers of emergent toadlets estimated since 1988. The dates when spawn was first laid varied considerably between years from the earliest on 2 February 1993 (day 33) to the latest on 19 March 1996 (day 79). The duration of the tadpole stage was negatively correlated with the date of appearance of first spawn and was up to 30 days longer in early spawning years than in late ones. Despite this, toadlets still emerged from the natal pond up to 36 days earlier in early spawning years than in late ones. Significant positive correlations were found between the duration of the tadpole stage and both the proportion of days during the tadpole stage when the minimum ground temperature was at or below 0°C and the proportion of days when 10 mm or more rain fell. Tadpole mortality was positively correlated with the proportion of days during the tadpole stage when the minimum ground temperature was at or below 1.5°C. Evidence was also found to suggest that tadpole mortality was density-dependent, being proportionately higher when initial tadpole numbers were high than when they were low. Received: 7 May 1999 / Accepted: 19 July 1999     

Competition between the larvae of the introduced cane toad Bufo marinus (Anura: Bufonidae) and native anurans from the Darling Downs area of southern Queensland

Bufo marinus (L) has been present in the northern edge of the Darling River catchment for more than 25 years and the species currently occupies an area north of Chinchilla on the northern Darling Downs. This paper reports on preliminary findings of competition trials between larvae of B. marinus and native anurans in the Darling Downs area. Trials conducted in artificial ponds (1.4 × 1.2 × 0.2 m) indicated that Bufo reduced the growth of three native species (Limnodynastes tasmaniensis (Gunther), Limnodynastes terraereginae (Fry) and Notaden bennetti (Gunther)), and in some trials reduced the survival of two species (L. tasmaniensis and L. terraereginae). A fourth species (Limnodynastes ornatus (Grey)) showed higher growth rates with Bufo resulting from a non-significant reduction in survival in those treatments. One of two trials conducted in enclosures (1.0 × 0.5 × 0.4 m) placed in a permanent water body indicated that B. marinus had a negative effect on growth of L. tasmaniensis. A survey of 30 breeding sites in the area found that Bufo used only a small number of water bodies in one breeding season and showed little overlap of pool use with most native species. Therefore, although B. marinus may negatively affect growth and survival of native anurans under some circumstances, the potential impact of B. marinus may be minimal if there are always many breeding sites where native anurans can breed in the absence of B. marinus. A more extensive assessment of temporal and spatial overlap of water body use by B. marinus and native anurans is needed to understand the exact impact of B. marinus in this region.     

Coexistence and interference between a native perennial grass and non-native annual grasses in California

Little is known about the potential for coexistence between native and non-native plants after large-scale biological invasions. Using the example of native perennial bunchgrasses and non-native annual grasses in California grasslands, we sought to determine the effects of interference from non-native grasses on the different life stages of the native perennial bunchgrass Nassella pulchra. Further, we asked whether N. pulchra interferes with non-native annual grasses, and whether competition for water is an important component of these interspecific interactions in this water-limited system. In a series of field and greenhouse experiments employing neighbor removals and additions of water, we found that seedling recruitment of N. pulchra was strongly seed-limited. In both field and greenhouse, natural recruitment of N. pulchra seedlings from grassland soil was extremely low. In field plots where we added seeds, addition of water to field plots increased density of N. pulchra seedlings by 88% and increased total aboveground N. pulchra seedling biomass by almost 90%, suggesting that water was the primary limiting resource. In the greenhouse, simulated drought early in the growing season had a greater negative effect on the biomass of annual seedlings than on the seedlings of N. pulchra. In the field, presence of annuals reduced growth and seed production of all sizes of N. pulchra, and these effects did not decrease as N. pulchra individuals increased in size. These negative effects appeared to be due to competition for water, because N. pulchra plants showed less negative pre-dawn leaf water potentials when annual neighbors were removed. Also, simply adding water caused the same increases in aboveground biomass and seed production of N. pulchra plants as removing all annual neighbors. We found no evidence that established N. pulchra plants were able to suppress non-native annual grasses. Removing large N. pulchra individuals did not affect peak biomass per unit area of annuals. We conclude that effects of interference from non native annuals are important through all life stages of the native perennial N. pulchra. Our results suggest that persistence of native bunchgrasses may be enhanced by greater mortality of annual than perennial seedlings during drought, and possibly by reduced competition for water in wet years because of increased resource availability. Received: 12 November 1998 / Accepted: 4 August 1999     

Temporal stability in hybridization between Bufo microscaphus and Bufo woodhousii (Anura: Bufonidae): Behavior and morphology

I analyzed temporal variation in hybridization between the southwestern toad (Bufo microscaphus) and Woodhouse's toad (Bufo woodhousii) along the Virgin River in southwestern Utah and northwestern Arizona. Bufo woodhousii is largely restricted to the floodplain of the Virgin River from southern Nevada to the vicinity of St. George, Utah. By contrast, B. microscaphus is confined primarily to the tributaries of the Virgin River, only occupying the Virgin River proper exclusive of B. woodhousii along its upper reaches east of La Verkin Creek. As in all other zones of sympatry for these bufonids, behavior and morphology provide clear evidence of hybridization at a number of sites along the Virgin River. Analysis of morphology and behavior indicates that the distribution of these taxa and their hybrids is largely unchanged relative to that documented forty years ago by Blair (1955). Comparisons of morphological hybrid index scores reveal slight shifts in relative numbers of parental taxa at only one site. Hybridization between these anurans has been relatively stable geographically, and may be related to the nature of the riparian habitat available for breeding.     

New Karyological and Morphometric Data on Poorly Known Bufo surdus and Bufo luristanicus in Comparison with Data of Diploid Green Toads of the Bufo viridis Complex from South of Iran

Previous studies on the Bufo viridis complex, which is distributed broadly across Iran, are incomplete and restricted to a few regions or a few samples. In this paper a new detailed study on the B. viridis complex in southern of Iran （from West to East） is presented. The analysis of 18 morphometric characters with univariate and multivariate methods reveals significant differences between three members of the B. viridis complex namely B. variabilis, B. luristanicus, and B. surdus distributed in southern part of Iran. Our result help to resolve an old taxonomic problem about B. surdus subgroup （taxa closely related to B. surdus） confirming that B. luristanicus and B. surdus are distinct species. Moreover, for the first time we report and describe karyotype details of B. luristanicus and B. surdus which confirmed that they are diploid. Karyological studies demonstrate that all toads from three mentioned species have 2n = 22 chromosomes. These chromosomes are arranged into two groups. First group has six large chromosomes and the second group is composed of five small chromosomes. These chromosomes are metacentric or submetacentric. The number of submetacentric chromosomes is different in three mentioned species of B. viridis complex. Neither sexual heteromorphism, nor secondary constriction was observed in any pairs of chromosomes.     

Inductive interactions required for mesodermal differentiation in Bufo arenarum gastrulae

 Dorso-marginal epithelium, a distinct crescent-shaped region in the early gastrula of Bufo arenarum, appears after involution as a narrow dorso-median strip of archenteric endoderm close to the notochord. In explant cultures, this layer showed an extreme dorsalizing activity, promoting the formation of notochordal structures from ventro-mesodermal cells. In the presence of ectoderm, this inductive activity was expanded resulting in a wide range of dorso-lateral components such as notochord, muscle, nephric tubules, mesothelium and mesenchyme. The mesodermal origin of these derivatives was confirmed by the use of FDA (fluorescein-dextran-amine)-labelled explants. Extensive mesodermal development in cultures seems to require cell contacts between the inner aspect of the dorso-marginal epithelium and mesodermal cells. When such contacts were prevented, cultures would only differentiate erythrocytes as a result of a purely ectodermal stimulus. Bisection of the dorso-marginal epithelium in whole embryos resulted in the development of a duplicated set of axial structures, clearly showing the role of the epithelium as a dorsal organizer. Received: 30 July 1996 / Accepted: 20 February 1997     

辽宁产中华大蟾蜍和花背蟾蜍蝌蚪形态特征的比较和分析

对中华大蟾蜍 Bufo gargarizans和花背蟾蜍B. raddei 第36期蝌蚪外形和口部形态结构进行详细观察和描述,并进行了定量比较和分析.中华大蟾蜍蝌蚪体背观呈长卵圆形,全身黑褐色;尾呈桨形,背腹鳍透明无斑;唇齿式为2(2)/3 (即Ⅰ:1+1/Ⅲ).花背蟾蜍蝌蚪体背观呈卵圆形,体背面和侧面为灰黑色或深灰色,腹面灰色有金属光泽;尾呈纺锤形,背鳍近透明,其上有黑色细纹,腹鳍透明无色;唇齿式为2(2)/3(即Ⅰ:1+1/Ⅲ),个别为2(2)/3(1)(即Ⅰ:1+1/1+1:Ⅱ).两种蟾蜍蝌蚪在体色、体型、尾色、尾型、口盘形态结构以及繁殖等方面有着明显区别.对辽宁和华西产的中华蟾蜍蝌蚪的分析表明两地蝌蚪在形态特征方面基本相同,显示出蝌蚪在种内的稳定性.编制了两种蟾蜍蝌蚪的简明检索表,供野外调查和监测参考.     

Flow cytometric analysis of the chromosomes and stability of a wheat cell-culture line

A rapidly growing, long-term suspension culture derived from Triticum aestivum L. (wheat) was synchronized using hydroxyurea and colchicine, and a chromosome suspension with chromosomes was made. After staining with the DNA-specific fluorochromes Hoechst 33258 and Chromomycin univariate and bivariate flow-cytometry histograms showed 15 clearly resolved peaks corresponding to individual chromosome types or groups of chromosomes with similar DNA contents. The flow karyotype was closely similar to a histogram of DNA content measurements of Feulgen-stained chromosomes made by microdensitometry. We were able to show the stability of the flow karyotype of the cell line over a year, while a parallel subculture had a slightly different, stable, karyotype following different growth conditions. The data indicate that flow cytometric analysis of plant karyotypes enables accurate, statistically precise chromosome classification and karyotyping of cereals. There was little overlap between individual flow-histogram peaks, so the method is useful for flow sorting and the construction of chromosome specific-recombinant DNA libraries. Using bivariate analysis, the AT:GC ratio of all the chromosomes was remarkably similar, in striking contrast to mammalian flow karyotypes. We speculate about a fundamental difference in organization and homogenization of DNA sequences between chromosomes within mammalian and plant genomes. Received: 24 April 1996 / Accepted: 24 May 1996     

Effects of water-column mixing on bacteria,phytoplankton, and rotifers under different levels of herbivory in a shallow eutrophic lake

Water-column mixing is known to have a decisive impact on plankton communities. The underlying mechanisms depend on the size and depth of the water body, nutrient status and the plankton community structure, and they are well understood for shallow polymictic and deep stratified lakes. Two consecutive mixing events of similar intensity under different levels of herbivory were performed in enclosures in a shallow, but periodically stratified, eutrophic lake, in order to investigate the effects of water-column mixing on bacteria abundance, phytoplankton abundance and diversity, and rotifer abundance and fecundity. When herbivory by filter-feeding zooplankton was low, water-column mixing that provoked a substantial nutrient input into the euphotic zone led to a strong net increase of bacteria and phytoplankton biomass. Phytoplankton diversity was lower in the mixed enclosures than in the undisturbed ones because of the greater contribution of a few fast-growing species. After the second mixing event, at a high biomass of filter-feeding crustaceans, the increase of phytoplankton biomass was lower than after the first mixing, and diversity remained unchanged because enhanced growth of small fast-growing phytoplankton was prevented by zooplankton grazing. Bacterial abundance did not increase after the second mixing, when cladoceran biomass was high. Changes in rotifer fecundity indicated a transmission of the phytoplankton response to the next trophic level. Our results suggest that water-column mixing in shallow eutrophic lakes with periodic stratification has a strong effect on the plankton community via enhanced nutrient availability rather than resuspension or reduced light availability. This fuels the basis of the classic and microbial food chain via enhanced phytoplankton and bacterial growth, but the effects on biomass may be damped by high levels of herbivory. Received: 3 May 1999 / Accepted: 13 April 2000     

Chloride Currents in Skeletal Muscles of Bufo arenarum

Cl⁻ currents (I _Cl) were measured in short fibers (1–2 mm) from the lumbricalis muscle of toads (Bufo arenarum) with two microelectrodes (15°C). Initially the fibers were equilibrated in a high K⁺-containing solution: (mm) K₂SO₄ 68; Na₂SO₄ 20; KCl 60; CaSO₄ 8; MgSO₄ 1; HEPES 2.5. Constant pulses were applied when all the external K⁺ was replaced by Cs⁺: Cs₂SO₄ 68; Na₂SO₄ 20; CsCl 60; CaSO₄ 8; HEPES 2.5 (pH 7.5). Under these conditions about 80–90% of the current is carried by Cl⁻. The current-voltage relation is almost linear implying constant conductance and hence voltage-independent permeability. The voltage dependence of the net Cl⁻ current could be fitted by constant field equation with a P _Cl of 3.3 × 10⁻⁶ cm/sec. In a separate group of experiments a two-pulse technique was used to estimate the availability and the inactivation of the initial I _Cl during a test pulse. After returning the potential to the holding potential for various times, test pulses of the same amplitude and duration of the prepulses were applied. The initial current during the test pulse was 70% of the initial current during the prepulse and the recovery was complete in less than 300 msec with a linear relationship between the current during the test pulse and the amplitude of the preceding prepulse. When the test pulses were preceded by a positive prepulse, the initial current for any given test pulse was larger than with a negative prepulse. If we assumed that the initial current during the test pulse is a measure of the number of channels open at the end of the prepulse, these results suggest that hyperpolarizing pulses inactivate and depolarizing prepulses activate the I _Cl. Received: 31 March 1995/Revised: 27 October 1995     

Intraguild predators and the spatial distribution of a parasitoid

An experimental plot of the aphid Aphis fabae on various host plant species was colonized by natural populations of the aphidiine parasitoid Lysiphlebus fabarum and insect predators, especially coccinellids. Parasitism of A. fabae by L. fabarum was significantly depressed on plants bearing coccinellids. The number of parasitized aphids increased with aphid abundance on three plant species (Papaver dubium, Rumex obtusifolius, Vicia faba), but not on the plant species (Chenopodium album) which bore very high numbers of coccinellids. In complementary laboratory experiments, L. fabarum offered a choice between odours of plants infested with A. fabae and/or coccinellids selected the odour fields from coccinellid treatments at significantly lower frequency than the odour fields of other treatments. It is concluded that avoidance of coccinellids by L. fabarum contributes to the negative association between the abundance of coccinellids and parasitoids in the field. Received: 22 March 1999 / Accepted: 22 March 2000     

Characteristics of genetic variation in the progenies of protoplast-derived plants of rice, Oryza sativa cv Nipponbare

Genetic variation in protoplast-derived rice (Oryza sativa L.) plants was characterized using first and second generation selfed progenies. A total of 133 regenerated plants were obtained from ten protoplasts of the japonica rice cultivar Nipponbare. Sixty two regenerated plants which set enough seeds for the subsequent field tests at the next generation and were derived from five protoplasts were selected, and their selfed seeds were used as the first selfed-seed progeny generation). Fifteen plants were selected from each of the 15 lines, and their selfed seeds were used for tests at the generation. Thirty seven lines (60%) segregated plants with detrimental mutant characters of yellow-green phenotype, dwarf stature, dense and short panicle, or low seed fertility. According to the segregation patterns in the lines having mutated plants among those originated from the same protoplasts, the stages of mutation induction were estimated. Additionally, five quantitative traits were changed in almost all and lines. Varied quantitative traits of heading date, number of spikelets per panicle, and seed fertility, were in a heterozygous state. However, culm and panicle lengths showed high uniformity, whereas reduced culm and panicle lengths were caused by mutational changes in polygenes and/or multiple genes. Received: 20 March 1996 / Accepted: 21 June 1996     

Specifying the introgressed regions from H. argophyllus in cultivated sunflower (Helianthus annuus L.) to mark Phomopsis resistance genes

A method based upon targetting of intro-gressed markers in a Phomopsis-resistant line (R) of cultivated sunflower, issuing from a H. argophyllus cross was used to mark the Phomopsis resistance regions. Our study was based upon 203 families derived from a cross between an inbred line susceptible to Phomopsis (S1) and the introgressed resistant line (R). Families were checked for Phomopsis resistance level in a design with replicated plots and natural infection was re-inforced by pieces of contaminated stems. Thirty four primers were employed for RAPD analysis. Out of 102 polymorphic fragments between (S1) and H. argophyllus, seven were still present in (R) suggesting that they marked introgressions of H. argophyllus into (R). The plants were scored for the presence or absence of 19 fragments obtained from five primers, and the relationships between the presence/absence of fragments in plants and Phomopsis resistance/susceptiblity in the progenies was determined by using an analysis of variance. We found that at least two introgressed regions, as well as favourable factors from sunflower, contributed to the level of Phomopsis resistance in cultivated sunflower. Received: 28 June 1996 / Accepted: 5 July 1996     

Gliadin polymorphism in wild and cultivated einkorn wheats

To study the relationships between different species of the Einkorn group, 408 accessions of Triticum monococcum, T. boeoticum, T. boeoticum ssp. thauodar and T. urartu were analyzed electrophoretically for their protein composition at the Gli-1 and Gli-2 loci. In all the species the range of allelic variation at the loci examined is remarkable. The gliadin patterns of T. monococcum and T. boeoticum were very similar to one another but differed substantially from those of T. urartu. Several accessions of T. boeoticum and T. monococcum were shown to share the same alleles at the Gli-1 and Gli-2 loci, confirming the recent nomenclature that considers these wheats as different subspecies of the same species, T. monococcum. The gliadin composition of T. urartu resembled that of the A genome of polyploid wheats more than did T. boeoticum or T. monococcum, supporting the hypothesis that T. urartu, rather than T. boeoticum, is the donor of the A genome in cultivated wheats. Because of their high degree of polymorphism the gliadin markers may help in selecting breeding parents from diploid wheat germ plasm collections and can be used both to search for valuable genes linked to the gliadin-coding loci and to monitor the transfer of alien genes into cultivated polyploid wheats. Received: 8 July 1996 / Accepted: 12 July 1996     

Pattern duplications in larvae of the polyembryonic wasp Copidosoma floridanum

 Copidosoma floridanum is a polyembryonic wasp that undergoes total cleavage of the egg followed by proliferation of blastomeres to produce up to 2,000 embryos from a single egg. This unusual mode of development raises several questions about how axial polarity is established in individual embryonic primordia. By examining embryonic development of larvae with duplicated structures (conjoined larvae), we determined that conjoined larvae form by mislocalization of two embryonic primordia to a common chamber of the extraembryonic membrane that surrounds individual embryos. Analysis of an anterior marker, Distalless, in mislocalized early embryos indicated that anterior structures form independently of one another. This suggests each embryonic primordium has some intrinsic polarity. However, during germband extension embryos usually fuse in register with each other, resulting in conjoined larvae with heads facing each other. Analysis of the posterior segmental marker, Engrailed, in conjoined embryos suggested that fusion in register initiates during germband extension. Thus, even though embryonic primordia initially have a random axial orientation, conjoined larvae usually possess a common orientation due to reorientation during germband extension. These observations suggest that differential cellular affinities during segmentation play an important role in embryo fusion. Received: 13 June 1996 / Accepted: 15 August 1996     

Highly polymorphic microsatellites of rice consist of AT repeats, and a classification of closely related cultivars with these microsatellite loci

Microsatellites consisting of AT repeats are highly polymorphic in rice genomes and can be used to distinguish between even closely related japonica cultivars in Japan. Polymorphisms of 20 microsatellite loci were determined using 59 japonica cultivars, including both domestic and modern Japanese cultivars. Although the polymorphisms of these 20 microsatellite loci indicated that the Japanese cultivars were genetically quite similar, microsatellites consisting of AT repeats showed high gene diversity even among such closely related cultivars. Combinations of these hypervariable microsatellites can be employed to classify individual cultivars, since the microsatellites were stable within each cultivar. An identification system based on these highly polymorphic microsatellites could be used to maintain the purity of rice seeds by eliminating contamination. A parentage diagnosis using 17 polymorphic microsatellite loci clearly demonstrated that plants which carried desired chromosome regions had been selected in breeding programs. Thus, these hypervariable microsatellites consisting of AT repeats should promote the selection of plants which carry desired chromosomes from genetically similar parents. Backcrossing could also help to eliminate unnecessary chromosome regions with microsatellite polymorphisms at an early stage in breeding programs. Received: 8 July 1996 / Accepted: 12 July 1996     

Polymorphism, distribution, and segregation of AFLP markers in a doubled haploid rice population

We exploited the newly developed amplified fragment length polymorphism (AFLP) technique to study the polymorphism, distribution and inheritance of AFLP markers with a doubled haploid rice population derived from ‘IR64’/‘Azucena’. Using only 20 pairs of primer combinations, we detected 945 AFLP bands of which 208 were polymorphic. All 208 AFLP markers were mapped and distributed over all 12 chromosomes. When these were compared with RFLP markers already mapped in the population, we found the AFLP markers to be highly polymorphic in rice and to follow Mendelian segregation. As linkage map of rice can be generated rapidly with AFLP markers they will be very useful for marker-assisted backcrossing. Received: 11 April 1996 / Accepted: 14 June 1996     

Invertebrate grazer-periphyton interactions in a eutrophic marsh pond

SUMMARY. 1. The effects of two different invertebrate grazer guilds on the periphytic algal community were studied in a marsh pond in Manitoba, Canada over one entire open-water season.
2. Microcrustaceans (cladocerans, copepods, ostracods), which were numerically dominant in the unperturbed grazer community, effectively reduced the periphytic algal biomass to a persistent, depauperate residual assemblage throughout the season.
3. The perturbed grazer community, enclosed and treated with ro-tenone, was composed primarily of chironomids and oligochaetes. This community permitted a more diverse algal community to develop except when grazer numbers peaked.
4. When grazer numbers in the perturbed community were at a maximum, the algal assemblage appeared to be 'overgrazed'. Algal biomass was reduced below the minimum characteristic of the unperturbed community.
5. There was an inverse relationship between algal biomass and grazer numbers in both perturbed and unperturbed communities, but variation in degree of response was much greater in the perturbed system than in the unperturbed one.