A POLYPLOID SPECIES COMPLEX OF SPIROGYRA COMMUNIS (CHLOROPHYTA) OCCURRING IN NATURE 1

Investigations were conducted to determine whether ploidal changes found in laboratory cultures of Spirogyra also occur in nature. In an earlier study filament types identifiable as three different species (Spirogyra singu-laris Nordstedt, S. communis (Hassall)Kütz., S. fragilis Jao) arose from an original clonal culture through vegetative growth and sexual reproduction. These three “species” or filament groups differed in filament width, chloroplast number, zygospore size, and chromosome number. The differences in chromosome number represented a polyploid series of diploid (S. communis), triploid (S. fragilis), and tetraploid (S. singularis) forms in which width increased with ploidal level. The three width groups constituted a “species complex.” Five years after isolation of the original strain in this species complex, filaments corresponding to two of the width groups (S. singularis and S. communis) were found at the original collection site in the Santa Catalina Mountains in southern Arizona. The two field-collected groups were indistinguishable from the laboratory species complex in morphology and chromosome number. Homothallic conjugation within the two field width groups yielded progeny similar to those from homothallic conjugation of groups in the laboratory species complex. Filament widths of progeny were generally within the width limits of respective parental groups. The four possible intergroup crosses between the two laboratory and two field width groups yielded progeny similar to the wider parent (S. singularis) or the parent of intermediate width (S. fragilis). Progeny characteristics were determined by the width groups of parents, regardless of whether parents came from the laboratory or field. The similarities in morphology, chromosome numbers, and reproductive behavior of laboratory and field width groups imply that the laboratory species complex of S. communis has a natural counterpart in the field.     

芦苇细胞培养中的染色体稳定性及诱变效应

培养一年后的芦苇愈伤组织中,仍以80%的八倍体细胞占绝对优势。染色体数目变异范围在105—26之间。而 EMS 处理的愈伤组织与末经处理的愈伤组织相比较,明显地具有比较高的染色体数目变异和倍性变异。     

RELATIONSHIP BETWEEN PLOIDAL LEVEL AND CAM IN FIVE SPECIES OF TALINUM (PORTULACACEAE)

Plants (N = 102) from 23 populations of Talinum, representing five morphologically similar species, were examined in a test of the hypothesis that ploidal level may be correlated with levels of Crassulacean acid metabolism. When grouped by species and ploidal level, two groups of tetraploid plants, T. calcaricum and tetraploid individuals of T. calycinum, had significantly greater malic acid accumulations than any other group, including diploid individuals of T. calycinum. Another tetraploid, T. teretifolium, did not show greater malic acid fluctuations than the diploids, including two putative ancestors (T. mengesii and T. parviflorum). Similarly, malic acid fluctuations in tetraploid individuals of T. parviflorum were not different from diploid individuals of the same species. Nonetheless, when all plants were compared, nocturnal accumulations of malic acid in tetraploid plants were significantly greater than those of diploid plants.     

PATTERNS OF GENOTYPIC DIVERSITY IN CLONAL PLANT SPECIES

We compile and analyze data on the population genetic structure of broad-sense clonal plant populations where sexual recruitment is rare or absent. The data from 27 studies show a common theme: multiclonal populations of intermediate diversity and evenness tend to be the rule, most clones are restricted to one or a few populations, and widespread clones are exceptional. While a few studies have demonstrated that ecological differences among sympatric clones do occur, more experimental and theoretical studies are necessary to determine the role of selection and other evolutionary forces in maintaining clonal polymorphism.     

EVIDENCE FOR WIDESPREAD COURTSHIP DURING COPULATION IN 131 SPECIES OF INSECTS AND SPIDERS,AND IMPLICATIONS FOR CRYPTIC FEMALE CHOICE

Male courtship behavior is generally thought to function prior to copulation, as an inducement to the female to allow the male to copulate with her; this study indicates however, that male courtship during and following copulation (“copulatory courtship”) is common in insects and spiders (81% of 131 species in 102 genera and 49 families, mostly Coleoptera, Hemiptera, Diptera, and Araneioidea). Copulatory courtship is apparently evolutionarily labile, as expected if it is under sexual selection; intrageneric variation occurred in all 17 genera in which more than one species was observed. In 81% of 94 species with copulatory courtship, the male abandoned the female soon after copulation ended; thus, copulatory courtship appears not to function generally to induce acceptance of further copulatory attempts. The most likely explanation for copulatory courtship is that it represents attempts by males to influence cryptic female choice. This suggests that an aspect of sexual selection by female choice not considered by Darwin may be more important than previously appreciated and that the common practice in evolutionary studies of measuring male reproductive success by counting numbers of copulations may sometimes be misleading because of cryptic female choice during and after copulation.     

关于物种形成机制及物种定义的新观点

很早以前,分类学家开始根据生物表型特征上的差异来识别和区分物种,自达尔文以后,人们认识到不同的物种是由共同祖先进化而来的,在定义物种时引入了"谱系"的概念.达尔文着重强调物种不仅是可以变化的,而且这些变异最终可以使一个种内的成员彼此分离,形成新种(Darwin,1859).     

CHANGES IN THE DNA SYNTHESIS PATTERN OF PARAMECIUM WITH INCREASED CLONAL AGE AND INTERFISSION TIME

The clonal age in paramecia refers to the total number of vegetative divisions a clone has undergone since its origin at autogamy (self-fertilization). As clonal age increases, the interfission time usually increases. The DNA synthesis pattern of cells of different ages was compared by autoradiographic analysis of the DNA synthesis of synchronized cells at various time intervals during the cell cycle (from one division to the next). The study showed that the G₁ period (the lag in DNA synthesis post division) was constant, irrespective of interfission time or clonal age; but the duration of the DNA synthesis period increased with increased interfission time or clonal age. Therefore, we have shown for the first time that the G₁ period is fixed, and the S period is increased in a eukaryotic unicellular organism as a function of interfission time and clonal age.     

SEASONAL CHANGES IN FAVOURABILITY OF CATTLE DUNG IN CENTRAL QUEENSLAND FOR THREE SPECIES OF DUNG-BREEDING INSECTS

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The favourability of cattle dung from a native pasture near Rockhampton, Queensland, as a food source was tested monthly in the laboratory for 2 yr using 3 dung-breeding insects: the buffalo fly, Haematobia irritans exigua De Meijere; the bush fly, Musca vetustissima Walker; and a dung beetle, Euoniticellus intermedius (Reiche). Dung produced by cattle grazing on this pasture during the summer wet season yielded larger flies of both species and more broods from the dung beetle than dung from the same pasture in winter. When reared in summer dung, the buffalo fly almost attained its maximum recorded size but the bush fly and dung beetle reached ca two-thirds maximum recorded size and brood production respectively. Bush flies failed to breed in dung collected for 4 consecutive months in winter each year but survival of buffalo flies showed no seasonal trends.
The early response of the buffalo fly to improving dung quality in late winter/early spring gives it an advantage enabling its populations to increase earlier than those of its competitors, including the dung beetle, E. intermedius.     

IRON-MEDIATED CHANGES IN THE GROWTH OF LAKE ERIE PHYTOPLANKTON AND AXENIC ALGAL CULTURES1

The effect of iron enrichment on algal growth and photosynthesis was investigated using natural assemblages of Lake Erie phytoplankton and axenic cultures of Anabaena, Scenedesmus and Selenastrum. Cell yield and photosynthesis were frequently inhibited in the presence of unchelated iron over the range of 3.6 to 53.7 μM iron as FeCl₃. In lake water and in a defined medium with low nutrient concentrations, the degree of inhibition by iron could be reduced by chelating the iron with EDTA or by enriching the cultures with phosphorus. Chemical analyses revealed that the EDTA efectively reduced the ability of the ferric iron to remove soluble phosphorus from the media. EDTA was also observed to reduce rather than enhance iron uptake by axenic cultures of A. flos-aquae. These data support the hypothesis that additions of EDTA to low-nutrient media may serve to stimulate algal growth in the presence of iron by preventing the iron from altering extracellular concentrations of soluble ions essential for algal metabolism. In medium with high nutrient concentrations, the soluble phosphorus concentration was not appreciably altered by either EDTA-chelated or unchelated iron enrichment (0.9 to 53.7 μM). Instead, the observed enhancement of cell yield by EDTA-chelated iron in nutrient-rich media appeared to be due to the direct effect of iron on intracellular metabolic processes.     

GRAZER-INDUCED COENOBIAL FORMATION IN CLONAL CULTURES OF SCENENDESMUS OBLIQUUS (CHLOROCOCCALES, CHLOROPHYCEAE)

Five strains of the phenotypically plastic alga Scenedesmus obliquus (Turpin) Kützing were cultured in standard medium or in medium containing filtered water from a Daphnia culture to examine grazer-induced coenobia formation. Strains varied considerably in their response to Daphnia chemicals. A rapid formation of four- and eight-celled coenobia was observed in the presence of Daphnia water in three strains. One strain showed numerous irregular aggregates with more than eight cells per colony, and no colony formation occurred in a fifth strain. In standard medium, all cultures remained unicellular. Growth rates were affected by Daphnia water in four strains and were different among strains. The chl a concentration was significantly different among strains but was not influenced by Daphnia water. The specific absorption coefficient was reduced at larger colony sizes, suggesting a possible cost associated with colony formation. The phenomenon of grazer-induced coenobia formation seems widespread but not universal within the species S. obliquus.     

两种女贞光合作用季节特性研究

以徐州自然条件下生长的常绿女贞和落叶女贞为材料,在不同季节测定了它们的叶绿素含量、光合速率、呼吸速率、光合作用的最适温度。结果表明,两种女贞各测定的生理指标都有季节特性。在自然条件下,两种女贞的光合速率皆为夏季最高,冬季最低,与叶绿素含量变化相一致。在冬季常绿女贞的净光合速率接近于零,而落叶女贞的净光合速率为负值,但仍保持较高的呼吸强度。光合作用的最适温度测定结果表明,常绿女贞适应环境温度变化的能     

IDENTIFICATION OF LATICIFERS IN EMBRYOIDS DERIVED FROM CALLUS AND SUSPENSION CULTURES OF ASCLEPIAS SPECIES (ASCLEPIADACEAE)

Laticifers were identified in frozen sections of embryoids from callus and suspension cultures of Asclepias syriaca (common milkweed) by an indirect fluorescent antibody technique. Sections were treated with the IgG fraction of rabbit anti-latex antiserum, produced with field-collected A. syriaca latex as a source of antigens, and with fluorescein-conjugated IgG fraction goat anti-rabbit IgG. Laticifers were identified by their fluorescence in embryoids dissected from 3–4-month-old callus cultures and in embryoids from 2-month-old suspension cultures. Laticifers are not present in early globular embryoids of A. syriaca but embryoids similar in shape to late globular stage zygotic embryos possess branching laticifers typical of zygotic material. Sections on control slides, treated with whole serum or IgG fraction from whole serum, both from an uninjected rabbit, contained no fluorescent cells. No laticifers were detected with the fluorescent antibody assay in A. tuberosa embryoids.     

烟草愈伤组织分化和芽原基形成期间呼吸代谢途径的改变

接种在继代培养基上的柳叶烟草愈伤组织,未观察到组织分化和芽原基形成。在分化培养基上生长的愈伤组织,接种后第6天可见拟分生组织和管胞分化,9—12天有芽原基形成,15—18天可观察到苗端结构。根据碘乙酸、Na_3PO_4和丙二酸抑制试验,以及3-磷酸甘油醛脱氢酶与琥珀酸脱氢酶活性测定结果,初步表明烟草愈伤组织呼吸中存在有EMP、HMP和TCAC代谢途径.在发生输导组织和芽原基分化的愈伤组织中(接种后第6—12天),HMP途径的运行程度较高;而芽原基的继续生长(培养12天以后),则与EMP途径的增加有关;分化培养基上生长的愈伤组织,始终较继代培养愈伤组织具有较高的FCAC活性水平。     

CHANGES IN THE CAPACITY FOR CLONAL GROWTH AND DIFFERENTIATION IN VITRO OF THE VERTEBRAL CARTILAGE CELLS WITH EMBRYONIC DEVELOPMENT. 1. CULTURE IN THE STANDARD MEDIUM

When culturing the vertebral cartilage cells of the chick embryo, the youngest embryo from which the dissociated single cell of the cartilage gives rise to the differentiated cartilage colony (CMC) in the given conditions of the clonal cell culture is at st.26. At this stage, percentage of such cells to make CMC in vitro is less than 0.1% of the inoculated single cells. With development, percentage of such “stabilized” cells increases, finally reaching to 35% at st.40. In embryos from st.29 to st.36, many of the cultured single cells give rise to the regressing colonies (RGC) which show some proliferation at the early stage in vitro, but in due time cease to proliferate and regress.