Buried seed population in the herbaceous lomas on Loma Ancon in the coastal desert of central Peru

Herbaceous lomas in the Peruvian coastal desert, of South America establish in spring, and its habitat is limited to the southern or southwestern slopes along the coast that are affected by thick fog. The time of appearance, the duration and the thickness of the fog vary greatly from year to year, so the lomas can grow only in habitats with enough water to, sustain seed germination and plant growth. This paper studies the species composition and density of the buried seed population, of the herbaceous lomas of Loma Ancon in order to clarify the mechanisms of the lomas' establishment. The mean number of species with viable seeds was about, 12 spp. m⁻² and that of dead seeds was about 22 spp. m⁻². The dominant species wereSolanum tuberiferum, S. pinnatifidum andNolana humifusa, both in viable and dead seeds. Viable seed density was about 5000–8000 seeds m⁻², which is comparable with the seed densities of other herbaceous communities. Dead seed density was about 15000–27000 seeds m⁻², or nearly three times the viable seed density, because the rate of decomposition was slow in the extremely dry conditions. The net increase of viable seeds by seed production was estimated at about 5000 seeds m⁻² in 1980, and the increase in the number of dead seeds was 2200 seeds m⁻².     

Estimates of gene flow, genetic substructure and population heterogeneity in bracken (Pteridium aquilinum)

Bracken [ Pteridium aquilinum (L.) Kuhn] is a cosmopolitan species and is a noxious weed in many areas. Because of its abundance, particularly in Britain, bracken affords an ideal system for investigating various aspects of population genetics and evolution. High mobility of dispersal units (spores) suggests that rates of gene flow among distant populations should be high. Gene flow is a major evolutionary force that influences the genetic structure of populations. To examine the effects of gene flow on population heterogeneity and population substructuring in bracken, starch gel electrophoresis of enzymes was used to provide the necessary genetic database. Allele frequency data at 21 loci were obtained for seven British populations, one Majorcan and one from the eastern United States. A model was employed to estimate the amount of gene flow ( Nm ) at several levels. Gene flow among British populations was extremely high ( Nm = 36.51), one of the highest estimates reported for plants. Among eight European populations gene flow was lower (but still considered high) at Nm = 2.47. Trans-Atlantic gene flow was low ( Nm = 0.0926).
F -statistics were used to assess population heterogeneity and substructuring. The data indicate that, compared with other species, there is very little genetic differentiation among British populations of bracken. Indeed, it appears that the whole island is behaving as a single randommating population. This result is consistent with high levels of gene flow. Only one population (on the Isle of Arran) showed statistically significant genetic substructuring. Habitat heterogeneity on the island and age structure are hypothesized as possible causes of this result.
The data reported here support previous studies demonstrating that bracken is genetically polymorphic and is an outcrossing species.     

Isozyme analysis of progeny derived from (Allium fistulosum ×Allium cepa) ×Allium cepa

Summary Relatively large quantities of seed were obtained from the interspecific backcross (A. fistulosum xA. cepa) ×A. cepa allowing, for the first time, an extensive study of the heritable traits exhibited by backcross progeny. Two backcross populations, BC1034 and BC1040, distinguished by differentA. fistulosum parents, were characterized for the isozyme markersIdh-1, Adh-1, andPgi-1. Statistical methods are described to calculate cell probabilities for a mixed population of F₂ and BC₁ progeny, using an estimate of the fraction of F₂ progeny in the population derived from the isozyme data. Cell probability distributions were calculated for a mixed population with independent pairs of loci and a mixed population with nonindependent pairs of loci. The isozyme lociIdh-1 andPgi-1 appear to be linked, with a map distance estimated at 33 centimorgans (cM) in BC1034 and 42 cM in BC1040. The probability distribution model for linked loci did not account for all of the distorted segregation ratios inIdh-1 ×Adh-1 orPgi-1 ×Adh-1. The cytological literature does not support linkage betweenIdh-1 ×Adh-1 orPgi-1 ×Adh-1. The distorted segregation ratios for these pairs of loci are likely the result of genetic incompatibilities between the two species.Journal Article No. 1578, Agricultural Experiment Station, New Mexico State University, Las Cruces, NM, USA     

Microbial growth on carbon monoxide

The utilization of carbon monoxide as energy and/or carbon source by different physiological groups of bacteria is described and compared. Utilitarian CO oxidation which is coupled to the generation of energy for growth is achieved by aerobic and anaerobic eu- and archaebacteria. They belong to the physiological groups of aerobic carboxidotrophic, facultatively anaerobic phototrophic, and anaerobic acetogenic, methanogenic or sulfate-reducing bacteria. The key enzyme in CO oxidation is CO dehydrogenase which is a molybdo iron-sulfur flavoprotein in aerobic CO-oxidizing bacteria and a nickel-containing iron-sulfur protein in anaerobic ones. In carboxidotrophic and phototrophic bacteria, the CO-born CO₂ is fixed by ribulose bisphosphate carboxylase in the reductive pentose phosphate cycle. In acetogenic, methanogenic, and probably in sulfate-reducing bacteria, CODH/acetyl-CoA synthase directly incorporates CO into acetyl-CoA.In plasmid-harbouring carboxidotrophic bacteria, CO dehydrogenase as well as enzymes involved in CO₂ fixation or hydrogen utilization are plasmid-encoded. Structural genes encoding CO dehydrogenase were cloned from carboxidotrophic, acetogenic and methanogenic bacteria. Although they are clustered in each case, they are genetically distinct.Soil is a most important biological sink for CO in nature. While the physiological microbial groups capable of CO oxidation are well known, the type and nature of the microorganisms actually representing this sink are still enigmatic. We also tried to summarize the little information available on the nutritional and physicochemical requirements determining the sink strength. Because CO is highly toxic to respiring organisms even in low concentrations, the function of microbial activities in the global CO cycle is critical.     

Beta beta homodimers exist in native rabbit skeletal muscle tropomyosin and increase after denaturation-renaturation.

Native tropomyosin from rabbit skeletal muscle (RSTm) consists mainly of alpha alpha and alpha beta coiled coils (alpha/beta approximately 3-4/1). In some extant studies, no beta beta molecules have been found. In this study, RSTm from several different preparations was disulfide cross-linked, both preparation and cross-linking being done under nondenaturing conditions. The cross-linked product was assayed for the presence of beta beta molecules cross-linked at both C36 and C190 (beta = beta). In such cross-linked RSTm, 3-8% beta = beta is detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis, C4 reversed-phase high-performance liquid chromatography, and a free-solution capillary electrophoresis experiment. This percentage becomes approximately 4-10% beta beta when corrected for incomplete double cross-linking and is independent of protein concentration (0.1-10.0 mg/mL), indicating that the observed beta beta species are not artifacts due to intermolecular cross-linking. Upon denaturation and subsequent renaturation either by heating to 55 degrees C or by incubating at 45 degrees C followed by quenching to room temperature, or by guanidine hydrochloride exposure followed by phased renaturation by dialysis, the fraction of beta beta increases, indicating that the reassociation favors homodimer formation somewhat over random association. This result differs from the random association observed when the sulfhydryl on one of the chains is carboxyamidomethylated (Holtzer, M.E., Breiner, T., & Holtzer, A., 1984, Biopolymers 23, 1811-1833), and from the overwhelming heterodimer preferences reported for tropomyosins from other organisms (Lehrer, S.S., Qian, Y., & Hvidt, S., 1989, Science 246, 926-928; Lehrer, S.S. & Qian, Y., 1990, J. Biol. Chem. 265, 1134-1138).     

我国植物种群生态研究的成就与展望

种群生态学以种群作为研究对象,无论在理论上还是在方法上都是生态学中发展最快,最为活跃的一个领域,也是生态学研究中的一个极其重要的层次,因为它是物种存在和进化的基本单位,是生物群落和生态系统的基本组成。一、植物种群生态学研究的历史Graunt于1662年进行了人类种群的生命     

银额果蝇的B染色体研究:1.昆明群体的Bs数目和频率

本研究发现银额果蝇昆明群体有丝分裂中期核型中存在B染色体,出现频率为69.1%。目前,在已研究过的来自各个地区的银额果蝇中,昆明群体的B染色体频率最高。B染色体数目为1-6条。该群体内单雌系间的B染色体数目不同,个体间和细胞间的B染色体数目也不同。在核型中,B染色体最小,形态稳定,点状,C-带和G-带呈阳性。     

Genetic variation in relation to demography of peripheral pool frog populations (Rana lessonae)

Summary Genetic variation in an isolated northern metapopulation of the pool frog (Rana lessonae) in Sweden was compared to that of Central European populations using enzyme electrophoresis and literature data. Of the 31 loci scored, two (EST-2 andIDH-2) were polymorphic while no variation occurred in seven of the eight loci which are polymorphic in Central European populations.The heterozygosity level of the Swedish pool frogs is very low compared to that of other anuran populations, but their mean proportion of fertilized eggs within egg masses (97.5%) was not lower than in more heterozygous species, and their body size-specific fecundity did not differ from that of Polish conspecifics. The low genetic variability of the Swedish pool frogs is discussed in relation to features of the local populations such as size (N), calculated effective size (N _e ) reproductive success and probable history. It is concluded that long-term strong fluctuations in population size caused by reporductive failure in cold years have contributed more to the low genetic variability than could a single founder event due to a recent introduction by man.     

Expansion of the canine A blood group system

A detailed study of the canine A blood group system was undertaken, resulting in the expansion of this system into a three-factor, four-allelic one with the recognition of an additional subtype, a3. The serological and extensive family data supported the proposed genetic theory of four alleles with dominance with the order being Aa1, Aa2, Aa3 and A-. Gene frequencies of the alleles were determined in various breeds of dogs with frequencies in the general Brisbane population being 0.244 (Aa1), 0.042 (Aa2), 0.045 (Aa3) and 0.669 (A-).     

Characteristics of dispersal in sexually mature dragonflies

Abstract.

• 1 The population dynamics of a natural population of Sympetrum danae (Sulzer) were studied, by means of a mark—release—recapture method, to find indications of dispersal by mature adults. Additional information on orientation and the influence of phenotype (including age), density and weather was obtained by observations under natural conditions and in a large outdoor field cage.
• 2 80% of all mature adults caught around the natural pond were estimated to be immigrants. Considerable immigration was confirmed by the abdomen length of unmarked matures which did not accord with that expected from the locally emerged population. Total numbers captured and the minimum number known to be alive fell sharply at the time when most individuals were mature. At the same time, new matures continued to enter and disappear from the study area at an increasing rate.
• 3 Dispersive behaviour (escape flights) in the field enclosure was primarily age dependent in both sexes: it occurred from an age of 25–30 days onwards. This coincides with the time-lag between the emergence peak and increased dispersal in the field. Secondary effects on escape flights suggested that males tended to abandon low density areas.
• 4 Males flew relatively more southward than females.