Impact of the field slug Deroceras reticulatum on establishment of ryegrass and white clover in mixed swards

The relationship between numbers of Deroceras reticulatum and the establishment of ryegrass cv. Melle and white clover cv. Milkanova was studied on a mini-plot experiment. Assessments 12 and 33 days after sowing showed that Deroceras reticulatum had a proportionally greater impact on survival and growth of clover than on ryegrass. Slugs had no apparent effect on numbers or growth of three species of broad-leaved weeds (Senecio vulgaris, Cardamine hirsuta and Epilobium sp.) which occurred in the field experiment. In pot experiments where seedlings of ryegrass together with one of three clover cultivars, with or without chickweed (Stellaria media), were exposed to Deroceras reticulatum, seedlings of white clover cv. Aran were less affected by slug grazing than cvs S184 or Milkanova. The presence of different clover cultivars did not significantly influence the impact of slugs on growth of ryegrass or chickweed, nor did the presence or absence of chickweed influence the effect of slugs on ryegrass and clover seedlings. Slugs had less impact on the growth of chickweed than on ryegrass or clover. Thus slug grazing would make clover less able to compete with chickweed as well as the other weeds found in the mini-plot experiment.     

Temporal relationships betweenZea mays,ostrinia nubilalis (Lep.: Pyralidae) and endophyticBeauveria bassiana

The entomopathogenic fungus,Beauveria bassiana (Balsamo) Vuillemin, was applied to whorl-stage (V7) corn,Zea mays L., by foliar application of a granular formulation of corn grits containing conidia or by injection of a conidial suspension. All plants were infested with European corn borer larvae,Ostrinia nubilalis (Hübner), at the V7 (whorl), V12 (late-whorl), or V17 (pretassel) stage of plant development. Plants infested at whorl and late-whorl stages had significantly more European corn borer tunneling than did plants infested at the pretassel stage. The percentage of plants colonized byB. bassiana did not differ significantly among the whorl, late-whorl, and pretassel stages. As the plants matured,B. bassiana was isolated from different plant areas, with the pith more frequently colonized than the leaf collars. Foliar application ofB. bassiana provided immediate suppression ofO. nubilalis in those plants infested at whorl stage. The reduced efficacy ofB. bassiana at the intermediate plant stages relative to efficacy at harvest is discussed. The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Microsite differentiation in a Mediterranean oak savanna

Abstract. Microscale variation of vegetation was studied in a Mediterranean oak savanna dominated by annual plants at Neve Ya'ar Experimental Station, in the lower Galilee of Israel. Species presence/absence data were recorded in 20 cm x 20 cm quadrats on a 500-quadrat transect. These data were ordinated with Detrended Correspondence Analysis. Soil nitrate, phosphorous, potassium, pH, soil moisture and salinity were determined at 2-m intervals on the 100-m transect, at monthly intervals from November 1981 to April 1982. Litter cover and canopy shade were surveyed in October 1981 and April 1982. A sharp rise in available nitrate occurred in November, following the first winter rains. Patterns in herbaceous vegetation, as expressed by sample ordination scores, correlated best with litter cover in October. This suggested that vegetation pattern in this community may be strongly influenced by environmental conditions at the time of seedling germination and establishment.     

进化距离与相对替代率的比较研究

系统树是描述物种、人种甚至基因间亲缘关系和演化的重要工具,必须以进化距离或(相对)替代率作为重要的参数。但以哪一个参数构建的树更能反映真实的系统树呢?事实上迄今并无人对此作过认真的研究。本文以模拟数据并用方差分析法检验两个参数的异同并讨论其包含的生物学意义。研究结果表明,当氨基酸的替代率和核苷酸的替代率分别为0.18和0.13时,它们的进化距离分别为0.199和0.143。经方差分析证实,若检验的氨基酸和核苷酸最大数目均为75只时,不论以替代率或进化距离中那一个作为构树参数,拓扑树事实上几乎只有一个。这就是说,该时拓扑树可靠性很大,而且随着它们替代率的减少,则检验的氨基酸和核苷酸的数目会随之增加。但是一旦氨基酸的替代率和核苷酸的替代率超过上述数字,则两个参数构建的树在拓扑长度上是不等价的。经分析,若进化距离大致上与进化时间成线性关系的话,则应选用进化距离。用进化距离重建的系统树事实上支持中性学说;若进化距离与进化时间显著地不存在线性关系的话,则可选用替代率,该情况表明中性学说不适用,似更倾向于新达尔文主义。     

Preliminary observations on plant-rock type relationships in the Shiraz-Dashte Arjan area,South-West Iran

Summary In the Dashte-Arjan area near Shiraz, rock formations appear to control the distribution of various plant species. The Fars formation (Miocene) and the Asmari-Jahrom formation (Eocene-Oligocen) sediments are characterized by distinet plant species and life forms. Among the characteristic calciphytes of Asmari-Jahrom limestones are Astragalus acutus, Amygdalus lyciodes, Cerasus microcarpa, and Fraxinus rotundifolia. The Fars formation limestones are characterized by Astragulus gossypinus, Acantholimon flexuosum, Noaea mucronata and Phlomis bruguieri, Except for Glycrrhiza glabra, white and red marls seem to have similar species, such as Alhagi maurorum and Carthamus oxyacantha. Gypsum of Fars formation has Berberis integerrima and Rosa beggeriana. Various life forms have been distinguished and were found to be confined to different rock types as well.Nomenclature of species is given in table 1.We are greately indebted to Dr. P.H. Davis and Prof. G. Pontecorvo F.R.S. for critically reading this paper and making some invaluable suggestions. We are grateful to the University Research Grant Commission for providing us a grant for this work. We are also indebted to the Dean, College of Arts & Sciences, Pahlavi University, Shiraz, Iran for providing us with a vehicle during this work.     

Amino acid sequence and immunological properties of chachalaca egg white lysozyme

Summary The amino acid sequence of lysozyme c from chachalaca egg white was determined. Like other bird lysozymes c, that of the chachalaca has 129 amino acid residues. It differs from other avian lysozymes c by 27 to 31 amino acid substitutions as well as by being devoid of phenylalanine. It contains substitutions at 9 positions which are invariant in the other 7 bird lysozymes of known sequence. Although the chachalaca is classified zoologically in the order Galliformes, which includes chickens and other pheasant-like birds, its lysozyme differs more from those of pheasant-like birds than do the lysozymes c of ducks. Phylogenetic analysis of the sequence comparisons confirms that the lineage leading to chachalaca lysozyme c separated from that leading to other galliform lysozymes c before the duck lysozyme c lineage did. This indicates a contrast between protein evolution and evolution at the organismal level. Immunological comparison of chachalacalysozyme c with other lysozymes of known sequence provides further support for the proposal that immunological cross-reactivity is strongly dependent on degree of sequence resemblance among bird lysozymes.103rd communication on lysozymes from the Laboratory of P. Jollès. Supported in part by grants from C.N.R.S. (ER 102), I.N.S.E.R.M. (Groupe de recherche U-116), N.S.F. (GB-42028X), and N.I.H. (GM-21509).     

Aldolases of the lactic acid bacteria

Reciprocal qualitative and quantitative immunological experiments employing an anti-Pediococcus cerevisiae aldolase serum confirmed many of the interspecific relationships demonstrated previously among lactic acid bacteria with antisera prepared against the Streptococcus faecalis fructose diphosphate aldolase. The extent of immunological relatedness observed between the Lactobacillus and Pediococcus aldolases was markedly greater than that noted between Pediococcus and Streptococcus aldolases indicating that the pediococci share closer phylogenetic ties with the rod-shaped lactobacilli than with their spherical counterparts in the streptococci. In addition to confirming the existence of definitive, but distant, relationships between the lactic acid bacteria and certain gram positive nonsporeforming anaerobes, immunological cross-reactivity was also demonstrated between the pediococcal aldolases and those of Aerococcus viridans.This paper is dedicated with deepest appreciation to Prof. Roger Y. Stanier on the occasion of his 60th birthday in token of what his friendship and guidance have meant to me. — J. L.     

Ammonia-nitrogen excretion in Daphnia pulex

Ammonia-nitrogen excretion rates were measured in natural summer and cultured populations of Daphnia pulex from Silver Lake, Clay County, Minnesota, USA during 1973. The mean rate of ammonia-nitrogen excretion for the summer populations was 0.20 µg N animal^–1 day^–1 or 5.11 µg N mg^–1 dry body weight day^–1 (N = 80) measured at 15°, 20°, and 25°C. These rates appear to be temperature and weight dependent, but they are probably affected by factors other than temperature and dry body weight. Ammonia-nitrogen excretion rates of Daphnia pulex cultured on Chlamydomonas reinhardi yielded the following relationship with temperature: Log₁₀E = (0.061) T 1.773, where E is µg N animal^–1 day^–1 and T is temperature °C. The ammonia-nitrogen excretion on a mg^–1 dry body weight day^–1 basis was related to temperature according to the following similar expression Log₁₀E = (0.043) T + 0.153, where E is µg N mg^–1 dry body weight day^–1, and T is temperature °C. The length-weight relationship of Daphnia pulex for the summer populations (N = 1583) was log₁₀W = (0.526) Log₁₀L + 1.357, where W is weight in µg and L is length in mm.     

The fine structure of Culicinomyces clavisporus invading mosquito larvae

Electron microscope observations were made of the Australian and U.S. strains of Culicinomyces clavisporus infecting mosquito larvae. The wall of the conidium is composed of an inner (primary) layer, an outer (secondary) layer, and an exterior coating of a mucopolysaccharide substance believed responsible for conidial adhesion to the host cuticle prior to germination and penetration. In some instances the wall of the conidium is ruptured during germination and new wall layers and mucoid coating form around the germ tube whereas in other specimens the conidial wall layers extend around the germ tube without fracturing. The most common invasion site is through the larval foregut following ingestion of conidia. The apex of the germ tube presses tightly against the surface of the foregut cuticle and the mucilaginous coating is stripped away. There is evidence to suggest that the host epicuticle, which disappears across the zone of contact with the germ tube, is utilized for nutrition of the invading fungus. A collar of cuticle forms around the germ tube apex and a narrow penetrant hyphae extends into the procuticle. It is believed that cuticular penetration is primarily enzymatic assisted by mechanical pressure. The penetrant hypha swells into an oval cell in the hypodermal region and vegetative hypha then invade the hemocoel. The cells of the hypodermis develop signs of degeneration presumably due to the secretion of toxic substances from the invading hyphae. Host reactions, involving melanization of the host tissues, are sometimes evident among the invading penetrant hyphae in the cuticle or in the hypodermal cells in contact with the fungus. Melanized capsules form around some of the hyphae within the hemocoel. These latter reactions do not directly involve host blood cells and are examples of “humoral encapsulation” similar to that described by other authors during invasion of pathogenic organisms into mosquito larvae and chironomid larvae.