The effect of colchicine on synaptonemal complex formation in Allium ursinum

Interference of colchicine with meiotic chromosome pairing in the wild garlic, Allium ursinum, was studied using a whole-mount spreading technique for synaptonemal complexes. Colchicine was found to cause (i) pairing suppression (arrest of leptotene) and (ii) deficient pairing initiation at zygotene in connection with morphologically anomalous, malfunctioning pairing initiation sites. Both of these phenomena could be responsible for the reduction of chiasma frequency by colchicine previously reported in the literature.     

Effects of elevated temperature on meiotic chromosome synapsis in Allium ursinum

Synaptonemal complex (SC) formation in microsporocytes of Allium ursinum is severely affected by exposure of plants to 35° C for 30 h or longer. In spread preparations made from fresh and freeze-conserved material it was found that a high proportion of meiocytes is arrested at leptotene and shows no synapsis at all. In another group of nuclei synaptonemal polycomplex-like structures do occur between converging axial elements at presumed rudimentary SC initiation sites. Axial elements are virtually always thickened at these sites which seem to involve primarily heterologous chromosomes. A third situation is seen in nuclei where two or more lateral elements are engaged in the formation of longer stretches of aberrant SCs. These feature surplus material filling the central space. It may be assumed that this abnormal condition precludes crossing over and hence may be one of several ways by which elevated temperatures cause the chiasma reduction described here for A. ursinum and reported for several other organisms in the literature.     

Influence of conspecific and heterospecific adults on riparian tree species establishment during encroachment of a humid palm savanna

Woody plant encroachment of savanna ecosystems has been related to altered disturbance regimes, mainly fire suppression and herbivore exclusion. In contrast, neighbourhood interactions among resident and colonising woody species have received little attention, despite their likely influence on the pattern and rate of tree establishment. We examined how resident palm trees (Butia yatay) and established adults of two riparian forest tree species (Allophylus edulis and Sebastiania commersoniana) influenced seed arrival and seedling performance of the latter two species in a humid savanna of east-central Argentina. Seed traps and seedlings of both riparian species were placed in herbaceous openings, and beneath palm, conspecific and heterospecific adult trees in two unburned savanna patches, and were monitored for 2 years. Only seeds of the bird-dispersed Allophylus arrived in palm microsites, yet survival of Allophylus seedlings near adult palms was limited by animal damage through trampling and burrowing, a non-trophic mechanism of apparent competition. Seeds of both riparian species dispersed into conspecific microsites, although adult trees selectively reduced growth of conspecific seedlings, a pattern consistent with the “escape hypothesis”. Further, survival of Sebastiania increased in the moister Allophylus microsites, suggesting a one-way facilitative interaction between woody colonisers. Our results indicate that dispersal facilitation by resident savanna trees may be critical to riparian species invasion after fire suppression. Distance-dependent effects of conspecific and heterospecific adult trees could contribute to shape the subsequent dynamics of woody seedling establishment. Overall, we show that indirect interactions can play a prominent role in savanna encroachment by non-resident woody species.     

Population studies of Cheilosia fasciata (Diptera: Syrphidae), a leaf miner of Allium ursinum

Abstract.

• 1 Population dynamics of Cheilosia fasciata were described based on a sampling programme covering all developmental stages.
• 2 Failure to oviposit and mortality which was due to parasitization of pupae contributed most to total generation mortality.
• 3 Abundance of older larvae was regulated by density-dependent intraspecific competition for food.
• 4 These findings were reinforced by a field experiment which manipulated food levels and suggested that losses in numbers on ‘low food’ plots were in part compensated for by producing low-sized adults.

     

Taxonomy and distribution of Allium ursinum (Liliaceae) in Poland and adjacent countries

The paper presents distribution data on Allium ursinum L. in Poland, with additional records from the other European countries. The study comprised 367 herbarium specimens, drawn from most of Polish herbaria and individuals obtained during field investigations. Two subspecies have been recorded: A. ursinum L. subsp. ursinum and A. ursinum subsp. ucrainicum Kleop. et Oxner. The study also documents the presence of intermediate populations at the border of the distribution ranges for both subspecies. In addition, the paper presents the pedicel structure and pollen grains ultrasculpture of each subspecies under a scanning electron microscope (SEM). Finally, questions in respect of the distribution data and habitat preferences are discussed.     

Isolation,characterization and molecular cloning of a leaf-specific lectin from ramsons (Allium ursinum L.).

Lectins were isolated from roots and leaves of ramsons and compared to the previously described bulb lectins. Biochemical analyses indicated that the root lectins AUAIr and AUAIIr are identical to the bulb lectins AUAI and AUAII, whereas the leaf lectin AUAL has no counterpart in the bulbs. cDNA cloning confirmed that the leaf lectin differs from the bulb lectins. Northern blot analysis further indicated that the leaf lectin is tissue-specifically expressed. Sequence comparisons revealed that the ramsons leaf lectin differs considerably from the leaf lectins of garlic, leek, onion and shallot.     

Comparative study of the post-translational processing of the mannose-binding lectins in the bulbs of garlic (Allium sativum L.) and ramsons (Allium ursinum L.)

The biosynthesis and processing of the homodimeric and heterodimeric lectins from the bulbs of garlic (Allium sativum) and ramsons (wild garlic;Allium ursinum) were studied using pulse and pulse-chase labelling experiments on developing bulbs. By combining the results of thein vivo biosynthesis studies and the cDNA cloning of the respective lectins, the sequence of events leading from the primary translation products into the mature lectin polypeptides could be reconstructed. From this it is demonstrated that garlic and ramsons use different schemes of post-translational modifications in order to synthesize apparently similar lectins from totally different precursors. Both the homomeric garlic lectin (ASAII) and its homologue in ramsons (AUAII) are synthesized on the endoplasmic reticulum (ER) as nonglycosylated 13.5 kDa precursors, which, after their transport out of the ER are converted into the mature 12.0 kDa lectin polypeptides by the cleavage of a C-terminal peptide. The heterodimeric garlic lectin ASAI is synthesized on the ER as a single glycosylated precursor of 38 kDa, which after its transport out of the ER undergoes a complex processing which gives rise to two mature lectin subunits of 11.5 and 12.5 kDa. In contrast, both subunits of the heterodimeric ramsons lectin AUAI are synthesized separately on the ER as glycosylated precursors, which after their transport out of the ER are deglycosylated and further processed into the mature lectin polypeptides by the cleavage of a C-terminal peptide.     

The influence of predation and conspecific adults on the abundance of juvenile Evechinus chloroticus (Echinoidea:Echinometridae)

Summary Reefs dominated by red algae, associated with high echinoid densities, are consistent features of the shallow subtidal around northeastern New Zealand. Factors determining the abundance of juvenile Evechinus chloroticus were investigated in such a habitat. Using a factorial design, a field experiment was used to assess the influence of predators and adult E. chloroticus on juvenile abundance. The use of 2 m² exclusion cages enhanced juvenile E. chloroticus abundance over a 16 month period, an effect independent of conspecific adults. We attributed this effect to the exclusion of benthic-feeding, predatory fish. Several species forage over the study area at high densities and are known from gut content analysis to prey on juvenile E. chloroticus in the field. Invertebrate predators are at very low densities in the area. The possibility of caging and site artefacts confounding this interpretation is discussed.Adult E. chloroticus did not directly affect conspecific juvenile densities during the experimental period. However their removal produced a significant change in community structure toward one dominated by macroscopic brown algae. Echinoid removal led to rapid recruitment of laminarian and fucoid algae, predominantly Ecklonia radiata and Sargassum sinclairii. In addition, densities of herbivorous gastropods, particularly the limpet Cellana stellifera decreased in the echinoid exclusion area, as did the feeding rates of predatory fish. The consequences of E. chloroticus removal may be dependent upon the size of the area from which they are excluded.Despite the high densities of predatory fish, a low though consistent number of juvenile E. chloroticus escape predation. We suggest that these represent sufficient input into the adult grazing population to maintain the habitat. This interpretation argues against a key role for predators in structuring shallow water reef communities in northeastern New Zealand.     

Top-down and bottom-up impacts of juvenile fish in a littoral reed stand

1. Research has often focused on pelagic food chains and processes of lakes; less is known about the contribution of benthic energy flows to whole‐lake ecosystem energetics. This stems from the fact that the shoreline and littoral habitats, which provide a key linkage between sediment and water column, have only recently become a significant focus for study. 2. This study aimed to quantify the feeding and phosphorus allocation of a juvenile fish community in a littoral zone of a shallow lake in response to the biomass succession of the invertebrate prey community. Habitats comprising reed and adjacent open water were sampled over two consecutive years during day and night. 3. Although there were substantial year‐to‐year differences in the biomass of invertebrates, the fish community composition, diet consumption rates and phosphorus allocations were very similar in both study years. Biomasses and predation impacts by juvenile fish on prey groups were substantially higher within the reeds than in the adjacent open water habitat. This may be explained by the refuge‐seeking behaviour of the fish. 4. In general, invertebrates were negligibly influenced by fish feeding, with the exception for a strong top‐down control of large cladocerans. In response to the resulting low Daphnia biomass, fish were forced to switch to a higher degree of benthivory. Consequently, juvenile fish in littoral reed stands may shift benthic‐derived energy and phosphorus via the excretion of soluble reactive phosphorus into the open water.     

Consequences for a specialist insect and its parasitoid of the response of Allium porrum to conspecific herbivore attack

Abstract.  Recent studies on the leek Allium porrum L. demonstrate that a sharp increase in the release of volatile and nonvolatile sulphur compounds occurs in response to attack by the specialist phytophage, the leek moth Acrolepiopsis assectella (Zeller). The consequences of that response on the developmental capacity and behaviour of the leek moth and on the host-searching behaviour of the parasitoid hymenoptera Diadromus pulchellus Wesmael have been studied. No immediate adverse effect on larval development is seen, but the duration of male development is significantly longer. In addition, an almost 20% decrease is observed in the number of oocytes produced by adult females that developed on attack-damaged leek plants. Leek moths do not avoid damaged plants systematically. On attacked plants, larvae tend to consume more and females to lay more eggs, although the latter tendency disappears after intensive attack. Concerning host-searching by D. pulchellus , the data indicate that females make use of the induced leek response. Parasitoids are attracted more strongly to attacked plants than to undamaged plants and mechanically damaged plants. The results of this study in a tritrophic system involving a biannual plant suggest a complex defence system combining direct and indirect mechanisms. Sulphur compounds may act by reducing second-generation pests, thereby preventing the specialist insect population from exploding at the expense of the leek.     

Nitrogen uptake and use by competing individuals in a Xanthium canadense stand

We studied differences in nitrogen uptake and use for plant growth among individuals competing in a natural dense stand of an annual herb, Xanthium canadense. Larger individuals took up more nitrogen than proportionately to their size, indicating that the competition for soil nitrogen was asymmetric among individuals, although it was more symmetric than the competition for light. The rate of nitrogen loss of individuals also increased with plant size. While smaller individuals shared smaller fractions of total plant nitrogen in the stand, they had higher nitrogen concentrations per unit mass. "Turnover" rates of nitrogen influx (r_in) and outflux (r_out) were defined as the rates of nitrogen uptake and loss per unit aboveground nitrogen, respectively. r_in was higher in larger individuals, whereas r_out was higher in smaller individuals. Consequently, the relative rate of nitrogen increment (r_in-r_out) was higher in larger individuals, whereas it was around zero in the smallest individuals. The mean residence time of nitrogen (MRT), defined as the inverse of r_out, was longer in larger individuals. Nitrogen productivity (NP), i.e. the growth rate per unit aboveground nitrogen, was higher in larger individuals. As the product of lifetime MRT and NP gives the nitrogen use efficiency (NUE), defined as biomass production per unit flux of nitrogen, higher MRT and NP observed in larger individuals would have contributed to their higher lifetime NUE. Shorter MRT in smaller individuals was caused by the abscission of leaves which contained relatively large fractions of total plant nitrogen. Xanthium canadense, as a competitive ruderal, tended to produce leaves at higher positions to acquire higher light levels at the expense of older leaves rather than to modify their productive structure to efficiently use low light levels as observed in shade-tolerant species.     

Soil properties and seedling establishment in soils from monodominant and high-diversity stands of the tropical deciduous forests of México

Abstract. The hypothesis that soils from mature monodominant forests are unfavourable for establishment of tree species other than the dominant was tested for a lowland tropical deciduous forest with stands dominated by Celaenodendron mexicanum Standl. (CS). This species of Euphorbiaceae occurs almost exclusively in monodominant stands in which recruitment of other species appears to be poor. Soil properties were examined and experiments were conducted on germination and establishment of Celaenodendron mexicanum and three other species common in adjacent high-diversity mixed stands (MS): Recchia mexicana Moc. & Sessé, Caesalpinia eriostachys Benth., and Cordia alliodora (Ruiz & Pav.) Oken. Soil moisture regimes are affected by topographic position in the study area, but Celaenodendron mexicanum was found occupying hillsides as well as flatlands, and slope gradients of its stands were typical of the region. The microsites occupied in relation to soil moisture and light availability also appear to be undistinctive. There were no significant differences between stand types in any soil property (pH, O.C., total N, total P, avail. P, K, Ca, Mg, Na, Mn, Fe, Cu, Zn concentrations). A stand of intermediate dominance of Celaenodendron (ICS) did not differ from its adjacent mixed stand (MS) in soil texture or most of the nutrients tested; however, seasonally restricted differences in the contents of Fe and Mn (ICSCaesalpinia eriostachys established in both stand types. The results suggest that the distinction between monodominance and high diversity is not maintained by some simple physiological restriction on the establishment of new seedlings.     

Density-dependence in single-species populations of plants

The general form of yield-density relationships in plant populations is discussed with reference to reciprocal equations and the $\text{3}\text{2}$ power law, which describes the concomitant changes in plant weight and density during self-thinning. A model to describe the pattern of mortality in high density populations is also discussed with particular reference to the nature of intraspecific competition within plant populations.A reparameterized version of a reciprocal equation proposed by Bleasdale & Nelder is used to describe the relationship between individual plant weight and surviving plant density. The biological interpretation of the parameters is discussed in relation to the dry matter production of isolated plants, the density at which mutual interference between neighbours becomes appreciable, and the efficiency of resource utilization at high densities.The reparameterized equation is then used together with an equation which describes mortality during self-thinning as the basis for a new model to describe the relation between total plant yield and sowing density. The law of allometry is used in conjunction with the model to describe the relationship between the weight of a plant part and density, and this then forms the basis for a model of the population dynamics of annual plants with effectively discrete generations. Finally the dynamical behaviour of plant populations is discussed. It is concluded that most plant populations will show neighbourhood stability with exponential or perhaps oscillatory damping towards an equilibrium.     

Discrimination of conspecific individuals via cuticular pheromones by males of the cricket Gryllus bimaculatus

Cuticular substances on the body surface of crickets serve as pheromones that elicit a variety of different behaviors in male crickets. Antennal contact between males and females resulted in courtship behavior, and that between two males resulted in aggressive displays. As a first step in elucidating how crickets recognize and discriminate individuals, behavioral responses of male individuals to cuticular substances of conspecific males or females were investigated. The behavioral responses of males to antennal or palpal stimulation with an isolated antenna from a male or a female were recorded. To both antennal and palpal stimulation with female antennae, the majority of males responded with courtship behavior; to stimulation with male antennae, males responded with aggressive displays. To gain insight into the chemical nature of the behaviorally relevant components, isolated antennae were washed in either n-hexane, acetone or ethanol before behavior assays. Washed antennae no longer elicited courtship or aggressive responses in males. Next, polypropylene fibers were smeared with substances from the body surface of females and used for antennal stimulation. This experiment showed that the quality and quantity of cuticular substances appear to be highly age-dependent. Significantly more males responded with courtship behavior to cuticular substances from younger females. Isolated males generally showed higher levels of aggression than males reared in groups. Grouped males also were more likely to display courtship behavior towards antennae from younger females, and aggressive behavior towards antennae from older females. These results suggest that male discrimination of mating partners depends on the nature of female cuticular substances.     

Effect of a dense Allium ursinum (L.) ground cover on nutrient dynamics and mesofauna of a Fagus sylvatica (L.) woodland

The aboveground biomass built up annually by Allium ursinum (L.) contains similar amounts of nutrients as the foliage of mature Fagus sylvatica (L.) stands. The decomposition of the A. ursinum stand in early summer provides N rich forage for grazing mesofauna, especially favouring collembolans and accelerating mineralization of soil organic matter. Short term decreases of soil pH had no negative effect on populations of collembolans. Synergistic effects from soil fauna and microbes may accelerate nitrogen release from decomposing leaf litter. A positive feed back may have emerged. High animal abundance and diverse mesofauna populations are capable of high rates of litter fragmentation. Consequently, favourable conditions for microorganisms are created and allow high rates of mineralization and release of nutrients. Our data show that substantial amounts of nitrogen are lost from the system. Undisturbed forest ecosystems are considered to recycle mineralized nitrogen efficiently though. But temporal uncoupling of the N cycle due to microbial activity and delayed or decreased N uptake of higher plants can cause enhanced leaching even from undisturbed systems. The tendency to loose nutrients is apparent from high nitrate concentrations in the soil solution throughout the year. When nutrient losses from A. ursinum subsystems are considered, lateral nutrient imports from adjacent parts of the ecosystem have to be taken into account. If lateral import does not counterbalance losses, maintenance of the soil nutrient status must occur by weathering or a decline is to be expected.     

Influence of larvae of Gastrophysa viridula on the distribution of conspecific adults in the field

1. Previous laboratory bioassays indicate that exocrine glandular secretions of larvae of Gastrophysa viridula repel conspecific adults and deter them from feeding and oviposition. The present study was conducted to investigate the influence of larvae of G. viridula on conspecific adults in the field.
2. Within the G. viridula population studied, two generations were observed in a year. Occurrence of the different developmental stages overlapped temporally.
3. Some individual plants of Rumex obtusifolius , the host of the G. viridula population studied, grew so close to each other that they were considered as a plant group. When investigating the spatial distribution of larvae and adults within such plant groups, larvae were rarely found on plant groups on which adults were feeding.
4. A field experiment revealed that adults avoided plants of R. obtusifolius infested by conspecific larvae of the second and third instar. Adults still avoided these damaged plants when larvae had left them for pupation.
5. Gastrophysa viridula avoided oviposition on leaves and plants infested by conspecific larvae. Larvae of the second instar significantly deterred oviposition when present at a high density (33.3 larvae/dm²), whereas larvae of the first instar did not deter oviposition of conspecifics at either density tested. The oviposition deterring effect was also observed when just exocrine glandular secretion of larvae of the second instar was applied to the leaves in amounts equivalent to a density of 33.3 larvae/dm².
6. Availability of food ( R. obtusifolius ) largely exceeded its exploitation in each group of plants examined. This may be due to either the spatial separation of adults and larvae or the low population density observed on these plant groups.