First come,first served: superinfection exclusion in Deformed wing virus is dependent upon sequence identity and not the order of virus acquisition

Deformed wing virus (DWV) is the most important globally distributed pathogen of honey bees and, when vectored by the ectoparasite Varroa destructor, is associated with high levels of colony losses. Divergent DWV types may differ in their pathogenicity and are reported to exhibit superinfection exclusion upon sequential infections, an inevitability in a Varroa-infested colony. We used a reverse genetic approach to investigate competition and interactions between genetically distinct or related virus strains, analysing viral load over time, tissue distribution with reporter gene-expressing viruses and recombination between virus variants. Transient competition occurred irrespective of the order of virus acquisition, indicating no directionality or dominance. Over longer periods, the ability to compete with a pre-existing infection correlated with the genetic divergence of the inoculae. Genetic recombination was observed throughout the DWV genome with recombinants accounting for ~2% of the population as determined by deep sequencing. We propose that superinfection exclusion, if it occurs at all, is a consequence of a cross-reactive RNAi response to the viruses involved, explaining the lack of dominance of one virus type over another. A better understanding of the consequences of dual- and superinfection will inform development of cross-protective honey bee vaccines and landscape-scale DWV transmission and evolution.Subject terms: Viral genetics, Microbial ecology, Virus-host interactions, Small RNAs     

Response to begging calls by Zebra Finch parents: "first come, first served" rule may overcome a parental preference between chicks

In birds, parents may provide differential food provisioning among offspring according to their sex. Here, we test the hypothesis that events linked to the fine dynamics of begging behaviour could modulate parental preferences. After evaluating the preference related to chick sex for each parent of six Zebra Finch Taeniopygia guttata pairs, we studied the possible modifications of this preference when offspring begging was asynchronous. Our observations show that male parents follow a "first come, first served" rule, whereas females keep their initial choice. Although this study remains preliminary due to the sample size, it underlines the potential importance of investigating fine temporal features of begging behaviour to fully understand parents' provisioning strategies.     

Effects of fire and water availability on the emergence and recruitment of grasses,forbs and woody species in a semiarid Chaco savanna

In the semiarid Chaco savannas, the balance between herbaceous and woody species affects landscape configuration and ecosystem services such as forage production. Therefore, understanding the factors that control this balance is crucial for management. In a factorial experiment, we assessed the effects of fire and water availability on the emergence and recruitment of grasses, forbs and woody species. The results showed that the effects of fire and water availability on early regeneration stages differed among the three functional groups. For grasses, fire and water addition enhanced emergence when acted solely, but only the positive effects of fire were translated into a greater recruitment, irrespective of the water availability. For forbs, only water addition, when acted solely, promoted the emergence, although this effect was not translated into a greater recruitment. Lastly, in the case of woody species, both fire and water addition reduced emergence and recruitment. Our results support the notion that both fire and greater water availability would contribute to the maintenance and recovery of a grass‐dominated state of vegetation through a positive effect of fire on grasses recruitment and a general negative effect of fire and water on woody species emergence and recruitment.     

Getting a head start: diet, sub-adult growth, and associative learning in a seed-eating passerine

Developmental stress, and individual variation in response to it, can have important fitness consequences. Here we investigated the consequences of variable dietary protein on the duration of growth and associative learning abilities of zebra finches, Taeniopygia guttata, which are obligate graminivores. The high-protein conditions that zebra finches would experience in nature when half-ripe seed is available were mimicked by the use of egg protein to supplement mature seed, which is low in protein content. Growth rates and relative body proportions of males reared either on a low-protein diet (mature seed only) or a high-protein diet (seed plus egg) were determined from body size traits (mass, head width, and tarsus) measured at three developmental stages. Birds reared on the high-protein diet were larger in all size traits at all ages, but growth rates of size traits showed no treatment effects. Relative head size of birds reared on the two diets differed from age day 95 onward, with high-diet birds having larger heads in proportion to both tarsus length and body mass. High-diet birds mastered an associative learning task in fewer bouts than those reared on the low-protein diet. In both diet treatments, amount of sub-adult head growth varied directly, and sub-adult mass change varied inversely, with performance on the learning task. Results indicate that small differences in head growth during the sub-adult period can be associated with substantial differences in adult cognitive performance. Contrary to a previous report, we found no evidence for growth compensation among birds on the low-protein diet. These results have implications for the study of vertebrate cognition, developmental stress, and growth compensation.     

Species effects on nitrogen cycling: a test with perennial grasses

Summary To test for differing effects of plant species on nitrogen dynamics, we planted monocultures of five perennial grasses (Agropyron repens, Agrostis scabra, Poa pratensis, Schizachyrium scoparium, and Andropogon gerardi) on a series of soils ranging from sand to black soil. In situ net N mineralization was measured in the monocultures for three years. By the third year, initially identical soils under different species had diverged up to 10-fold in annual net mineralization. This divergence corresponded to differences in the tissue N concentrations, belowground lignin concentrations, and belowground biomasses of the species. These results demonstrate the potential for strong feedbacks between the species composition of vegetation and N cycling. If individual plant species can affect N mineralization and N availability, then competition for N may lead to positive or negative feedbacks between the processes controlling species composition and ecosystem processes such as N and C cycling. These feedbacks create the potential for alternative stable states for the vegetation-soil system given the same initial abiotic conditions.     

Giving offspring a head start in life: field and experimental evidence for selection on maternal basking behaviour in lizards

The timing of birth is often correlated with offspring fitness in animals, but experimental studies that disentangle direct effects of parturition date and indirect effects mediated via variation in female traits are rare. In viviparous ectotherms, parturition date is largely driven by female thermal conditions, particularly maternal basking strategies. Our field and laboratory studies of a viviparous lizard (Niveoscincus ocellatus) show that earlier‐born offspring are more likely to survive through their first winter and are larger following that winter, than are later‐born conspecifics. Thus, the association between parturition date and offspring fitness is causal, rather than reflecting an underlying correlation between parturition date and maternal attributes. Survival selection on offspring confers a significant advantage for increased maternal basking in this species, mediated through fitness advantages of earlier parturition. We discuss the roles of environmentally imposed constraints and parent–offspring conflict in the evolution of maternal effects on parturition date.     

Predation, competition, and nutrient recycling: a stoichiometric approach with multiple nutrients

A model for two competing prey species and one predator is formulated in which three essential nutrients can limit growth of all populations. Prey take up dissolved nutrients and predators ingest prey, assimilating a portion of ingested nutrients and recycling or respiring the balance. For all species, the nutrient contents of individuals vary and growth is coupled to increasing content of the limiting nutrient. This model was parameterized to describe a flagellate preying on two bacterial species, with carbon (C), nitrogen (N), and phosphorus (P) as nutrients. Parameters were chosen so that the two prey species would stably coexist without predators under some nutrient supply conditions. Using numerical simulations, the long-term outcomes of competition and predation were explored for a gradient of N:P supply ratios, varying C supply, and varying preference of the predator for the two prey. Coexistence and competitive exclusion both occurred under some conditions of nutrient supply and predator preference. As in simpler models of competition and predation these outcomes were largely governed by apparent competition mediated by the predator, and resource competition for nutrients whose effective supply was partly governed by nutrient recycling also mediated by the predator. For relatively small regions of parameter space, more complex outcomes with multiple attractors or three-species limit cycles occurred. The multiple constraints posed by multiple nutrients held the amplitudes of these cycles in check, limiting the influence of complex dynamics on competitive outcomes for the parameter ranges explored.     

Interaction between patch area and shape: lakes with different formation processes have contrasting area and shape effects on macrophyte diversity

Although both patch area and shape are key factors driving biodiversity in fragmented terrestrial landscapes, researchers have had limited and mixed success in documenting the effects of these two factors on aquatic ecosystems. Here we examined the effects of lake area and shape on macrophyte species richness in a lowland floodplain by considering the differences in lake types (i.e. marsh, oxbow, man-made lakes). We surveyed species richness of native macrophytes in 35 lakes including 11 marshes, 11 oxbows and 13 man-made lakes with various complex shapes covering from 0.25 to 46.3 ha. Model selection clearly supported the existence of interaction between area and shape effects: large-circular and small-complex lakes supported a higher macrophyte species richness, while it was lower in large-complex and small-circular lakes. Among the three lake types, marsh lakes were more circular and man-made lakes had more complex shapes, while oxbow lakes were intermediate between these two. Also, marsh lakes had positive species–area relationships, while man-made lakes had negative relationships. Our results suggest the opposing shape complexity and species–area relationships of these two contrasting lake types are the result of the interactions between lake area and shape. These results indicate that different lake types result in variations in their conservation value for preserving macrophyte diversity. We suggest that small complex-shaped patches (especially oxbow lakes), which are often given the lowest conservation priority in terrestrial ecosystems, cannot be disregarded when conserving macrophyte biodiversity in aquatic ecosystems.     

Amending soils of different texture with six compost types: impact on soil nutrient availability, plant growth and nutrient uptake

Background

Composts with different feedstocks may have differential effects on soil properties and plant growth which, may be further modulated by soil texture.

Materials and methods

In a 77-day pot experiment in the glasshouse, we investigated the effect of a single application as mulch of six types of composts derived from different starting feedstocks in two soils (13% and 46% clay, referred to as S13 and S46) on soil physical, chemical and biological properties, plant growth and nutrient uptake. Composts were placed as 2.5?cm thick mulch layer on the soil surface and wheat plants were grown and harvested at 42?days and at 77?days (grain filling).

Results

Composts differed in total and available N and P and particle size with C1, C3, C4 and C5 being fine-textured, whereas C2 and C6 were coarse-textured. Compost addition as mulch increased soil total organic C and EC, but had no effect on pH. In all treatments, cumulative soil respiration was higher in S13 than in S46 and was increased by compost addition with the greatest increase with C2 and C6. Compared to the unamended soil, most compost mulches (except C2) increased macroaggregate stability. Compost mulches significantly increased available P and N in both soils, except for C2. Compost mulches increased available N up to 6-fold in both soils with the strongest increase by C5. Most composts also increased wheat growth and shoot P and N concentrations with the greatest effect on plant N concentration by C5 and on plant P concentration by C4. However, C2 decreased shoot N and P concentrations compared to the unamended soil. Most compost mulches (except C2) increased mycorrhizal colonization by up to 50% compared to the unamended soil.

Conclusions

Fine-textured compost mulches generally had a greater effect on soil properties and plant growth than coarse-textured composts. Despite distinct differences between the soils with respect to clay content, TOC and available P, the effect of the compost mulches on soil and plant properties was quite similar.     

生态斑块重要性综合评价方法研究——以四川省为例

生态斑块为生物提供生存和发展的场所,城市化的推进引发生态斑块面积锐减且趋于破碎化,严重威胁生态系统服务。通过对生态斑块重要性的分析,可识别对保持景观连接度有关键作用的区域,是优化有限资金配置、实现高效生态保护和分级管理的有效途径。以2015年的四川省为例,从景观连接度出发,基于网络建模和拓扑指标计算,结合逼近理想点排序法(TOPSIS)和有序样品聚类进行了斑块重要性的综合评估和排序。研究结果表明,四川省内生态斑块呈现西北部相对连续,南部和东部零散而稀疏的分布特点,在此基础上构建的生态基础设施网络具有无标度性;所选拓扑指标结合综合评价方法后可有效评估斑块重要性,所有斑块可分为5个重要性层级,高层级斑块主要位于相对核心的位置,低层级斑块分布于全省边缘。针对不同层级斑块的特点提出了相应规划建议,从整体角度出发引导局部生态规划,以期为有限资源下省域尺度复合种群保护工作提供参考与借鉴。     

Soil nutrient input effects on seed longevity: a burial experiment with fen-meadow species

1. Effects of high nutrient input on the longevity and viability of buried seed are examined. Seeds of 17 fen-meadow species were buried in nylon mesh bags at four sites in the Netherlands and one site in Great Britain in plots to which N, P, K fertilizers are applied. Prior to burial germination tests were conducted on the seeds of each species. This paper describes the results of the viability tests on the seeds that were exhumed after one and 2 years of burial.
2. The percentage of seeds that germinated after 1 year of burial was significantly lower than the pre-burial percentage for the majority of the species. After 2 years of burial the germination percentage further decreased. A few species, such as the Carex species, did, however, show an increase in germination percentage indicating that the burial conditions allowed dormancy controls to be broken.
3. Differences in the edaphic conditions between the sites appeared to affect germination percentages after 1 year of burial. A difference in germination response between sites was observed for Carex acutiformis, Filipendula ulmaria and Lychnis flos-cuculi .
4. A significantly higher germination percentage was found at the Great Britain site for F. ulmaria in the phosphate treatment compared with the potassium treatment and the control after 1 year of burial. In contrast to many literature assessments no significant effects of fertilizer application was found after 2 years.
5. For all sites, except one in the Netherlands, the total number of seeds that germinated was lower in 1996 than in 1995.     

The influence of mesozooplankton on phytoplankton nutrient limitation: a mesocosm study with northeast Atlantic plankton

We used marine phytoplankton from mesocosms seeded with different zooplankton densities to study the impact of mesozooplankton on phytoplankton nutrient limitation. After 7 d of grazing (copepod mesocosms) or 9 d (appendicularian mesocosms) phytoplankton nutrient limitation was studied by enrichment bioassays. After removal of mesozooplankton, bioassay bottles received either no nutrients, phosphorus or nitrogen alone, or a combination of nitrogen and phosphorus and were incubated for 2 d. Phytoplankton reproductive rates in the bottles without nutrient addition were calculated after correction for grazing by ciliates and indicated increasing nitrogen limitation with increasing copepod abundance. No nutrient limitation was found in the appendicularian mesocosms. The increase of nutrient limitation with increasing copepod density seems to be mainly the result of a trophic cascade effect: Copepods released nanoplankton from ciliate grazing pressure, and thereby enhanced nitrogen exhaustion by nanophytoplankton and reduced nitrogen excretion by ciliates. Nitrogen sequestration in copepod biomass, the mechanism predicted by the ecological stoichiometry theory, seems to have been a weaker effect because there was only little copepod growth during the experiment.     

Gated, ion-selective channels observed with patch pipettes in the absence of membranes: novel properties of a gigaseal.

Gigaohm seals made between patch pipettes and hydrophobic substrates have a finite conductance which are cation-selective and capable of producing quantized gating indistinguishable from the gating of biological ion channels. The selectivity sequence and streaming potentials of these seals suggests the existence of a pore of similar dimensions to the nicotinic acetylcholine channel. The ionic selectivity of these seals appears similar to the seal selectivity observed with membrane patches (Fischmeister, R., R. K. Ayer, and R. L. DeHann. 1986. Pfluegers Arch. 406:73-82) and the possibility of discrete gating within the seal region suggests caution when interpreting patch clamp data from unfamiliar preparations. The data suggests that the permeation pathway is the narrow space between the hydrophobic substrate and the pipette. Since this space has one hydrophobic wall, a hydrophilic channel lining may not be essential for channel permeation and gating.