The functional morphology and role of the thelycum in insemination,and its relation to the mating system in the seagrass shrimp Ambidexter symmetricus (Decapoda: Processidae)

There is considerable variation in structures known to function in the transfer and storage of sperm in female decapod crustaceans. The thelycum is a secondary sexual character that forms from the posterior thoracic sterna of female shrimps (especially penaeoids and sergestoids). Females in the caridean shrimp family Processidae have a thelycum‐like structure which rarely occurs in other caridean females. We tested the hypothesis that the processid thelycum serves as a spermatheca for either short‐term attachment or long‐term sperm storage. When inseminated females of the processid Ambidexter symmetricus were isolated after mating, newly spawned and then incubated embryos hatched, but in the continued absence of a male, females were unable to fertilize a subsequent spawn. Our observations on A. symmetricus show that sperm were not retained after female spawning, and thus the thelycum is not used for long‐term sperm storage as in many penaeoids. In A. symmetricus, the thelycum may serve as an external median spermatheca (seminal receptacle) for temporary attachment and storage of a sperm mass during the 2–3 h interval between mating and spawning. Observations on mating behavior support the hypothesis of a pure‐search (promiscuous) mating system in A. symmetricus, with males showing little interest before, and copulating with females only after, the female parturial molt. Mating encounters were short (<2 min). This mating system is like that of other caridean shrimps with populations structured similarly to those in A. symmetricus: a relatively high density of mobile individuals and sexual dimorphism in body size (reproductive females larger than males) but not in cheliped weaponry (similar in males and females).     

Study on the ability of 1,2,3,4-tetrahydropapaveroline to cause oxidative stress: Mechanisms and potential implications in relation to parkinson's disease

Tetrahydropapaveroline (THP) is a compound derived from dopamine monoamine oxidase-mediated metabolism, particularly present in the brain of parkinsonian patients receiving L-dopa therapy, and is capable of causing dopaminergic neurodegeneration. The aim of this work was to evaluate the potential of THP to cause oxidative stress on mitochondrial preparations and to gain insight into the molecular mechanisms responsible for its neurotoxicity. Our data show that THP autoxidation occurs with a continuous generation of hydroxyl radicals (*OH) and without the involvement of the Fenton reaction. The presence of ascorbate enhances this process by establishing a redox cycle, which regenerates THP from its quinolic forms. It has been shown that the production of *OH is not affected by the presence of either ferrous or ferric iron. Although THP does not affect lipid peroxidation, it is capable of reducing the high levels of thiobarbituric acid-reactive substances obtained in the presence of ascorbate and/or iron. However, THP autoxidation in the presence of ascorbate causes both an increase in protein carbonyl content and a reduction in protein-free thiol content. THP also increases protein carbonyl content when the autoxidation occurs in the presence of iron. The remarkable role played by ascorbate in the production of oxidative stress by THP autoxidation is of particular interest.     

How to stay on mummy's back: Morphological and functional changes of the pretarsus in arachnid postembryonic stages

A specific type of maternal care occurs in several groups of Arachnida: mothers carry their offspring on their back (pulli-carrying behaviour). In scorpions, whip scorpions and whip spiders it is the prenymphal stage that settles on the mother. The prenymph is not yet fully developed for a free life and very limited in its mobility, but its feet are equipped with special adhesive organs (arolia) that become lost at the nymphal stage. Here we study the morphology, ultrastructure and mechanical function of the arolia. In scorpions (Scorpiones) the contact area between arolia and substrate and thus adhesion of the pad is controlled by the antagonistic work of hydrostatic pressure and muscular retraction. Arolia of whip scorpions (Thelyphonida) do not require muscular action for strong attachment. Arrays of long, branching fibres in the mesocuticle lead to high compliancy of the pad. In whip spiders (Amblypygi) the prenymphal pretarsus is already equipped with sclerites and claws. Its arolium is retained in nymphs and adults in some taxa, but acquires a more complex structure. These results contribute to our knowledge on the postembryonic development of arachnids and to the understanding of attachment pad evolution among arthropods. Some of the described developmental, structural, and mechanical phenomena are not known from other animals and might be of potential interest for further biomimetic developments.     

Update on the possible mode of action of the jasmonates: Focus on the metabolism of cell wall polysaccharides in relation to growth and development

Jasmonic acid (JA) and its related compounds (jasmonates) applied to plant tissues exert either inhibitory or promotive effects in growth and developmental processes, which in some ways are similar to abscisic acid. However, little is known about the mode of action of the jamonates at the tissue or organ levels. Here, we review partial evidence for the physiological action of the jasmonates on cell elongation and abscission.
Jasmonates inhibit the IAA-induced cell elongation of oat coleoptile segments not by affecting energy production, osmoregulation and cell wall loosening, but by inhibiting the synthesis of cell wall polysaccharides. The inhibition is partially reversed by simultaneous application of sucrose. Inhibition of IAA-induced elongation by JA is only observed in monocotyledons, not in dicotyledons. These effects suggest that jasmonates exert their inhibitory effect on cell elongation by affecting the metabolism of the cell wall polysaccharides in monocotyledons.
Jasmonates promote the abscission of bean petiole explants without enhancing ethylene production. Cells in the petiole adjacent to the abscission zone expand during abscission. In the abscission zone, jasmonates decrease the amount of cellulosic but not that of noncellulosic polysaccharides. Jasmonates increase the activities of cellulase and decrease the levels of UDP-sugars, which are important intermediates for the synthesis of cell wall polysaccharides in the abscission zone, probably resulting in the decreased level of cellulose and the mechanical weakness of cell walls.
Thus, it is suggested that jasmonates exert their multiple physiological effects by affecting the metabolic processes of cell wall polysaccharides.     

Leaf miners on Ochna ciliata (Ochnaceae) growing on Aldabra Atoll: patterns of herbivory in relation to goat browsing and exposure to the sun

Abstract.

• 1 The patterns of herbivory by leaf miners on the shrub Ochna ciliata growing on Aldabra Atoll were studied in relation to browsing by feral goats and exposure to the tropical sun versus shading.
• 2 Damage due to both tunnelling (Diptera) and ‘blotch-making’ (Lepidoptera) leaf miners was statistically greater on trees that had been browsed and on those that received more extensive exposure to the sun.
• 3 Effects of exposure and browsing were additive, as evidenced by the lack of statistical interaction between these factors.
• 4 There was a significant negative correlation between the numbers of tunnelling and blotch-making miners in trees that had been browsed, but not in unbrowsed trees.
• 5 Three geographical areas were sampled to test whether the effects of browsing on leaf mining were invariant or influenced by as yet unknown environmental factors. A statistically significant interaction between browsing and geographical region indicated that, while browsed trees had significantly more mines whatever the habitat, the extent of this effect differed across the habitats.

     

Effects of ouabain and isoproterenol on potassium influx in the turkey erythrocyte: Quantitative relation to ligand binding and cyclic AMP generation

Studies have been carried out in the turkey erythrocyte to examine: (1) the influence of external K⁺ concentration on both [³H]ouabain binding and the sensitivity of potassium influx to inhibition by ouabain and (2) the quantitative relation between β-adrenergic receptor site occupancy, agonist-directed cyclic AMP generation and potassium influx rate. Both [³H]ouabain binding and the ability of ouabain to inhibit potassium influx are markedly reduced at increasing external K⁺ concentrations, and at each K⁺ concentration the concentrations of ouabain required for half-maximal binding to the erythrocyte membrane and for half-maximal inhibition of potassium influx are identical. Both basal and isoproterenol-stimulated potassium influx rise with increasing external K⁺ concentrations. In contrast to basal potassium influx, which is 50–70% inhibitable by ouabain, the isoproterenol-stimulated component of potassium influx is entirely insensitive to ouabain. At all concentrations of K⁺, inhibition of basal potassium influx by ouabain is linear with ouabain binding, indicating that the rate of transport per unoccupied ouabain binding site is unaffected by simultaneous occupancy of other sites by ouabain. Similarly, the rate of isoproterenol-stimulated cyclic AMP synthesis is directly proportional to β-adrenergic receptor occupancy over the entire concentration-response relationship for isoproterenol, showing that at all levels of occupancy β-adrenergic receptor sites function independently of each other.Analysis of the relation of catecholamine-dependent potassium transport to the number of β-adrenergic receptor sites occupied indicates an extremely sensitive physiological system, in which 50%-maximal stimulation of potassium transport is achieved at less than 3% receptor occupancy, corresponding to fewer than ten occupied receptors per cell.     

Impact of dietary protein on microbiota composition and activity in the gastrointestinal tract of piglets in relation to gut health: a review

In pigs, the microbial ecosystem of the gastrointestinal tract (GIT) is influenced by various factors; however, variations in diet composition have been identified as one of the most important determinants. Marked changes in fermentation activities and microbial ecology may occur when altering the diet, for example, from milk to solid feed during weaning. In that way, access of pathogens to the disturbed ecosystem is alleviated, leading to infectious diseases and diarrhea. Thus, there is increasing interest in improving intestinal health by use of dietary ingredients suitable to beneficially affect the microbial composition and activity. For example, fermentable carbohydrates have been shown to promote growth of beneficial Lactobacillus species and bifidobacteria, thereby enhancing colonization resistance against potential pathogens or production of short-chain fatty acids, which can be used as energy source for epithelial cells. On the other hand, fermentation of protein results in the production of various potentially toxic products, such as amines and NH₃, and is often associated with growth of potential pathogens. In that way, excessive protein intake has been shown to stimulate the growth of potentially pathogenic species such as Clostridium perfringens, and to reduce fecal counts of beneficial bifidobacteria. Therefore, it seems to be a promising approach to support growth and metabolic activity of the beneficial microbiota by developing suitable feeding strategies. For example, a reduction of dietary CP content and, at the same time, dietary supplementation with fermentable carbohydrates have proven to successfully suppress protein fermentation. In addition, the intestinal microbiota seems to be sensible to variations in dietary protein source, such as the use of highly digestible protein sources may reduce growth of protein-fermenting and potentially pathogenic species. The objective of the present review is to assess the impact of dietary protein on microbiota composition and activity in the GIT of piglets. Attention will be given to studies designed to determine the effect of variations in total protein supply, protein source and supplementation of fermentable carbohydrates to the diet on composition and metabolic activity of the intestinal microbiota.     

Studies on the leaf of Amaranthus retroflexus (Amaranthaceae): ultrastructure,plasmodesmatal frequency,and solute concentration in relation to phloem loading

Both the mesophyll and bundle-sheath cells associated with the minor veins in the leaf of Amaranthus retroflexus L. contain abundant tubular endoplasmic reticulum, which is continuous between the two cell types via numerous plasmodesmata in their common walls. In bundle-sheath cells, the tubular endoplasmic reticulum forms an extensive network that permeates the cytoplasm, and is closely associated, if not continuous, with the delimiting membranes of the chloroplasts, mitochondria, and microbodies. Both the number and frequency of plasmodesmata between various cell types decrease markedly from the bundle-sheath — vascular-parenchyma cell interface to the sicve-tube member — companion-cell interface. For plants taken directly from lighted growth chambers, a stronger mannitol solution (1.4 M) was required to plasmolyze the companion cells and sieve-tube members than that (0.6 M) necessary to plasmolyze the mesophyll, bundle-sheath, and vascular-parenchyma cells. Placing plants in the dark for 48 h reduced the solute concentration in all cell types. Judging from the frequency of plasmodesmata between the various cell types of the vascular bundles, and from the solute concentrations of the various cell types, it appears that assimilates are actively accumulated by the sieve-tube — companion-cell complex from the apoplast.     

Influence of epiphytic micro-organisms on leaf wettability: wetting of the upper leaf surface of Juglans regia and of model surfaces in relation to colonization by micro-organisms

Wetting of the upper leaf surface of Juglans regia L. and of model surfaces colonized by epiphytic micro-organisms was investigated by measuring contact angles of aqueous solutions buffered at different pH values. During June to October 1995, contact angles of aqueous solutions on the leaf surface of J. regia decreased by angles ranging from 12° (low pH values) to 25° at high pH values. At the end of this vegetation period, wetting was strongly dependent on pH showing significantly lower contact angles with alkaline solutions (pH 9·0) than with acidic solutions (pH 3·0). Contact angle titration measured angles on the leaf surface as a function of the pH of buffered aqueous solutions, covering a pH range from 3·0 to 11·0. Titration curves revealed inflection points around 7·5, indicating the existence of ionizable carboxylic groups at the interface of the phylloplane. Altered leaf-surface wetting properties observed on the intact leaf surface could be simulated in model experiments by measuring contact angles on artificial surfaces colonized by Pseudomonas fluorescens and by epiphytic micro-organisms isolated from the phylloplane of J. regia . Strong evidence is provided that interfacial carboxylic groups derive from epiphytic micro-organisms present on the phylloplane. Results suggest that the age-dependent increase in, and pH dependence of, wetting as leaves mature are related to the presence of epiphytic micro-organisms on the phylloplane. Ecological consequences of increased leaf-surface wetting, concerning the structure of the leaf surface as a microhabitat for epiphytic micro-organisms, are discussed.     

The hydrogeomorphic approach to functional assessment of riparian wetlands: evaluating impacts and mitigation on river floodplains in the U.S.A.

1. The ’hydrogeomorphic‘ approach to functional assessment of wetlands (HGM) was developed as a synthetic mechanism for compensatory mitigation of wetlands lost or damaged by human activities. The HGM approach is based on: (a) classification of wetlands by geomorphic origin and hydrographic regime (b) assessment models that associate variables as indicators of function, and (c) comparison to reference wetlands that represent the range of conditions that may be expected in a particular region. In this paper, we apply HGM to riparian wetlands of alluvial rivers. 2. In the HGM classification, riverine wetlands are characterized by formative fluvial processes that occur mainly on flood plains. The dominant water sources are overbank flooding from the channel or subsurface hyporheic flows. Examples of riverine wetlands in the U.S.A. are: bottomland hardwood forests that typify the low gradient, fine texture substratum of the south-eastern coastal plain and the alluvial flood plains that typify the high gradient, coarse texture substratum of western montane rivers. 3. Assessment (logic) models for each of fourteen alluvial wetland functions are described. Each model is a composite of two to seven wetland variables that are independently scored in relation to a reference data set developed for alluvial rivers in the western U.S.A. Scores are summarized by a ’functional capacity index‘ (FCI), which is multiplied by the area of the project site to produce a dimensionless ’functional capacity unit‘ (FCU). When HGM is properly used, compensatory mitigation is based on the FCUs lost that must be returned to the riverine landscape under statutory authority. 4. The HGM approach also provides a framework for long-term monitoring of mitigation success or failure and, if failing, a focus on topical remediation. 5. We conclude that HGM is a robust and easy method for protecting riparian wetlands, which are critically important components of alluvial river landscapes.     

Response of soil respiration to temperature and soil moisture: Effects of different vegetation types on a small scale in the eastern Loess Plateau of China

Soil respiration is affected by vegetation and environmental conditions. The purpose of this study was to investigate the effect of vegetation type on soil respiration, temperature and water content, and their correlations on a small scale. We measured soil respiration rate (R_s) over a 3-year period at biweekly intervals in three plots in the eastern Loess Plateau of China, with the same soil texture but different vegetation types: pine forest, grassland, and shrub land. Simultaneously, soil temperature (T_s) at 10 cm depth and soil water content (W_s) within 10 cm depth were measured. The seasonal course of R_s and T_s showed a similar temporal variation in the three plots, with higher values in summer and autumn and lower values in winter and spring. No significant differences (P>0.05) were found between plots, except for W_s. The mean cumulative release of CO₂ efflux from March to December was 962.5, 1027.5, and 1166.5 g C m^? 2 a^? 1 for plots 1, 2, and 3, respectively, with no significant difference between plots. The fitted exponential equations of R_s versus T_s from the 3-year data-set were significant (P < 0.05) with an R² of 0.72, 0.64, and 0.72 for plots 1, 2, and 3, respectively. The calculated Q₁₀ from the parameters of the fitted equation was 3.57, 3.52, and 3.61, and the R₁₀ was 2.36, 2.03, and 2.37 μmol CO₂ m^? 2 s^? 1 for plots 1, 2, and 3, respectively. Compared with the T_s, the correlations between R_s and W_s were not significant for the three plots. However, if the T_s was above 10°C, then their correlation was significant, and W_s had an impact on R_s. Four combined regression equations including two variables of T_s and W_s could be well established to model correlations between R_s and both T_s and W_s. Our study demonstrated that the exponential and power model fitted best and no significant different correlations of combined equations existed between the three plots. These results show that vegetation type had little impact on R_s, T_s, W_s, and their correlations, as well as on related parameters such as Q₁₀ and R₁₀. Therefore, while doing R_s research in a horizontal patchy vegetation conditions on a small area, the sampling location of measurements should focus on vertical dominant vegetation and ignore patch vegetation so as to reduce field work load.     

The influence of host plant genotype on variation in population densities of the gorse thrips,Sericothrips staphylinus (Thysanoptera: Thripidae), and its consideration in relation to release strategies

Large variations in population densities of Sericothrips staphylinus were observed between gorse bushes at a field site in an earlier Tasmanian study. A replicated potted plant experiment was conducted to assess whether genetic variation between gorse bushes could affect densities of S. staphylinus. There were significant differences in the number of S. staphylinus recovered from the individual bushes sampled within sites and individual bushes across all sites. This provides evidence that genetic variation between gorse bushes is at least partly responsible for the observed variability in field populations. The result validates the current release strategy used for the field establishment of S. staphylinus in south-eastern Australia. This strategy involves making multiple small releases (ca. 250 adults per bush per site) instead of a small number of large releases (ca. 1000 per bush per site), thereby reducing variation in numbers due to genetic affects. Genetic variation between individual plants of the same species and associated effects on herbivore densities should be considered when devising release strategies for biological control agents.     

Occurrence of epibenthic dinoflagellates in relation to biotic substrates and to environmental factors in Southern Mediterranean (Bizerte Bay and Lagoon,Tunisia): An emphasis on the harmful Ostreopsis spp., Prorocentrum lima and Coolia monotis

Harmful events associated with epibenthic dinoflagellates, have been reported more frequently over the last decades. Occurrence of potentially toxic benthic dinoflagellates, on the leaves of two magnoliophytes (Cymodocea nodosa and Zostera noltei) and thalli of the macroalgae (Ulva rigida), was monitored over one year (From May 2015 to April 2016) in the Bizerte Bay and Lagoon (North of Tunisia, Southern Mediterranean Sea). The investigated lagoon is known to be highly anthropized. This is the first report on the seasonal distribution of epibenthic dinoflagellates hosted by natural substrates, from two contrasted, adjacent coastal Mediterranean ecosystems. The environmental factors promoting the development of the harmful epibenthic dinoflagellates Ostreopsis spp., Prorocentrum lima and Coolia monotis were investigated. The highest cell densities were reached by Ostreopsis spp. (1.9 × 10³ cells g⁻¹ FW, in October 2015), P. lima (1.6 × 10³ cells g⁻¹ FW, in June 2015) and C. monotis (1.1 × 10³ cells g⁻¹ FW, in May 2015). C. nodosa and Z. noltei were the most favorable host macrophytes for C. monotis (in station L2) and Ostreopsis spp. (in station L3), respectively. Positive correlations were recorded between Ostreopsis spp. and temperature. Densities of the epibenthic dinoflagellates varied according to the collection site, and a great disparity was observed between the Bay and the Lagoon. Maximum concentrations were recorded on C. nodosa leaves from the Bizerte Bay, while low epiphytic cell abundances were associated with macrophytes sampled from the Bizerte Lagoon. The observed differences in dinoflagellate abundances between the two ecosystems (Bay-Lagoon) seemed not related to the nutrients, but rather to the poor environmental conditions in the lagoon.     

Biological diversity of the Yala Swamp lakes, with special emphasis on fish species composition, in relation to changes in the Lake Victoria Basin (Kenya): threats and conservation measures

During the second half of the last century, the Lake Victoria ecosystem has undergone drastic ecological changes. Most notable has been the decline in the populations of many endemic cichlid fishes. The lake has lost nearly 200 haplochromines and one tilapiine, Oreochromis esculentus. The above changes have been attributed to effects of species stocking and, in particular, from predation pressure by the introduced Nile perch, Lates niloticus. Other factors that have led to the decline of the endemic species include intensive non-selective fishing, extreme changes in the drainage basin, increased eutrophication, and the invasion of the lake by the water hyacinth, Eichhornia crassipes. However, the remnants of some species that had disappeared from Lake Victoria occur abundantly in the Yala Swamp lakes (Kanyaboli, Sare and Namboyo). This paper discusses the biodiversity of the swamp and the three lakes and gives suggestions for their conservation.     

Ecological impact of solar ultraviolet-B (UV-B: 320-290 nm) radiation on Corynebacterium aquaticum and Xanthomonas sp. colonization on tea phyllosphere in relation to blister blight disease incidence in the field

AIMS: To assess the effects of solar UV-B radiation on phyllosphere bacteria of tea leaves in relation to blister blight disease in the field. METHODS AND RESULTS: The effects of UV-B radiation on the phyllosphere microbiology of tea (Camellia sinensis) were studied in contrasting wet and dry seasons at a tropical site. Wavelength-selective filters were used to separate the effects of UV-B from those of other factors. Bacterial populations were quantified in relation to the incidence of blister blight disease. Attenuation of UV-B increased the survival of Xanthomonas sp. when populations were not water limited, and increased the incidence of blister blight, but had no effect on Corynebacterium aquaticum. CONCLUSIONS: The effects of solar UV-B on phyllosphere bacteria were substantial but depended on both species and interactions with other environmental variables. Xanthomonas sp. was more sensitive to UV-B than C. aquaticum, but this did not result in differences in population density under high radiation conditions (dry season), but only in the wet season when other factors were not limiting. SIGNIFICANCE AND IMPACT OF THE STUDY: The role of UV-B on leaf surface microbiology in the tropics is marked but depends on other conditions, and the contrasting UV-B responses of different organisms can be masked by other limiting factors.     

Phylogeography in continuous space: coupling species distribution models and circuit theory to assess the effect of contiguous migration at different climatic periods on genetic differentiation in Busseola fusca (Lepidoptera: Noctuidae)

Current population genetic models fail to cope with genetic differentiation for species with large, contiguous and heterogeneous distribution. We show that in such a case, genetic differentiation can be predicted at equilibrium by circuit theory, where conductance corresponds to abundance in species distribution models (SDMs). Circuit‐SDM approach was used for the phylogeographic study of the lepidopteran cereal stemborer Busseola fuscaFüller (Noctuidae) across sub‐Saharan Africa. Species abundance was surveyed across its distribution range. SDMs were optimized and selected by cross‐validation. Relationship between observed matrices of genetic differentiation between individuals, and between matrices of resistance distance was assessed through Mantel tests and redundancy discriminant analyses (RDAs). A total of 628 individuals from 130 localities in 17 countries were genotyped at seven microsatellite loci. Six population clusters were found based on a Bayesian analysis. The eastern margin of Dahomey gap between East and West Africa was the main factor of genetic differentiation. The SDM projections at present, last interglacial and last glacial maximum periods were used for the estimation of circuit resistance between locations of genotyped individuals. For all periods of time, when using either all individuals or only East African individuals, partial Mantel r and RDA conditioning on geographic distance were found significant. Under future projections (year 2080), partial r and RDA significance were different. From this study, it is concluded that analytical solutions provided by circuit theory are useful for the evolutionary management of populations and for phylogeographic analysis when coalescence times are not accessible by approximate Bayesian simulations.