Transforming the dilemma

How does natural selection lead to cooperation between competing individuals? The Prisoner's Dilemma captures the essence of this problem. Two players can either cooperate or defect. The payoff for mutual cooperation, R, is greater than the payoff for mutual defection, P. But a defector versus a cooperator receives the highest payoff, T, where as the cooperator obtains the lowest payoff, S. Hence, the Prisoner's Dilemma is defined by the payoff ranking T > R > P > S . In a well‐mixed population, defectors always have a higher expected payoff than cooperators, and therefore natural selection favors defectors. The evolution of cooperation requires specific mechanisms. Here we discuss five mechanisms for the evolution of cooperation: direct reciprocity, indirect reciprocity, kin selection, group selection, and network reciprocity (or graph selection). Each mechanism leads to a transformation of the Prisoner's Dilemma payoff matrix. From the transformed matrices, we derive the fundamental conditions for the evolution of cooperation. The transformed matrices can be used in standard frameworks of evolutionary dynamics such as the replicator equation or stochastic processes of game dynamics in finite populations.     

Overlapping expression patterns among the genes encoding Arabidopsis chromosomal high mobility group (HMG) proteins

High mobility group (HMG) proteins are usually considered ubiquitous components of the eukaryotic chromatin. Using HMG gene promoter-GUS reporter gene fusions we have examined the expression of the reporter gene in transgenic Arabidopsis plants. These experiments have revealed that the different HMGA and HMGB promoters display overlapping patterns of activity, but they also show tissue- and developmental stage-specific differences. Moreover, leader introns that are present in some of the HMGB genes can modulate reporter gene expression. The differential HMG gene expression supports the view that the various HMG proteins serve partially different architectural functions in plant chromatin.     

Artificial selection of stable rhizosphere microbiota leads to heritable plant phenotype changes

Artificial selection of microbiota opens new avenues for improving plants. However, reported results lack consistency. We hypothesised that the success in artificial selection of microbiota depends on the stabilisation of community structure. In a ten-generation experiment involving 1,800 plants, we selected rhizosphere microbiota of Brachypodium distachyon associated with high or low leaf greenness, a proxy of plant performance. The microbiota structure showed strong fluctuations during an initial transitory phase, with no detectable leaf greenness heritability. After five generations, the microbiota structure stabilised, concomitantly with heritability in leaf greenness. Selection, initially ineffective, did successfully alter the selected property as intended, especially for high selection. We show a remarkable correlation between the variability in plant traits and selected microbiota structures, revealing two distinct sub-communities associated with high or low leaf greenness, whose abundance was significantly steered by directional selection. Understanding microbiota structure stabilisation will improve the reliability of artificial microbiota selection.     

互花米草入侵对红树林底栖甲壳动物和鱼类功能群及生态位的影响

为了解互花米草入侵对红树林湿地生态系统底栖甲壳动物和鱼类的影响,本研究利用地笼方式于2020年8月、2021年1月和4月对福建漳江口2个原生红树林样地(白骨壤和秋茄)、2个互花米草入侵样地以及1个光滩样地的底栖甲壳动物和鱼类进行采样调查。采用相对重要性指数、Shannon多样性指数、Pielou均匀度指数和Margalef丰富度指数分析底栖甲壳动物和鱼类的优势种及物种多样性,统计其功能群,并计算其生态位宽度和生态位重叠指数。结果表明: 3个季节共采集到底栖甲壳动物和鱼类种类37种,隶属于2门2纲8目17科,其中大多数为暖水性和广盐性物种,且以肉食性和杂食性功能群为主。双因素方差分析和非度量多维尺度分析结果表明,相比光滩,互花米草入侵后,底栖甲壳动物和鱼类的群落多样性指数变化不显著,但功能群发生了显著变化,浮游生物食性功能群以及肉食性和植食性功能群物种均有一定程度的增加。相比红树林样地,互花米草样地内底栖甲壳动物和鱼类物种丰富度更高。优势物种的时空生态位宽度变化范围在0～1.4186,其中棱鮻最高(1.4186),其次是中华乌塘鳢(1.0168)、刀额新对虾(0.9469)、脊尾白虾(0.8922)。     

土壤原生生物多样性及其生态功能研究进展

原生生物广泛分布在土壤和不同生境中, 其数量庞大、种类繁多, 在生态系统物质循环和能量流动以及维持土壤和植物健康中起着举足轻重的作用。与土壤其他生物类群相比, 原生生物分类体系和生态类型复杂, 分类鉴定困难且分子检测技术不够成熟, 目前对原生生物的认识相对不足。本文对当前原生生物的相关研究进展进行了总结和梳理, 系统阐述了原生生物的分类系统和营养功能群特征、土壤原生生物的多样性分布特征及影响因子, 重点介绍了原生生物群落在参与土壤养分循环、维持土壤和植物健康等中的功能作用, 并对未来的研究方向与应用前景进行了展望。对土壤原生生物的研究有助于我们深入认识土壤生物多样性资源, 并进行保护性地开发和利用, 维护土壤和生态系统健康。     

Individual‐ versus group‐optimality in the production of secreted bacterial compounds

How unicellular organisms optimize the production of compounds is a fundamental biological question. While it is typically thought that production is optimized at the individual‐cell level, secreted compounds could also allow for optimization at the group level, leading to a division of labor where a subset of cells produces and shares the compound with everyone. Using mathematical modeling, we show that the evolution of such division of labor depends on the cost function of compound production. Specifically, for any trait with saturating benefits, linear costs promote the evolution of uniform production levels across cells. Conversely, production costs that diminish with higher output levels favor the evolution of specialization–especially when compound shareability is high. When experimentally testing these predictions with pyoverdine, a secreted iron‐scavenging compound produced by Pseudomonas aeruginosa, we found linear costs and, consistent with our model, detected uniform pyoverdine production levels across cells. We conclude that for shared compounds with saturating benefits, the evolution of division of labor is facilitated by a diminishing cost function. More generally, we note that shifts in the level of selection from individuals to groups do not solely require cooperation, but critically depend on mechanistic factors, including the distribution of compound synthesis costs.     

Autophagy protects against redox-active trace metal-induced cell death in rabbit synovial fibroblasts through Toll-like receptor 4 activation

Reactive oxygen species (ROS) are implicated to play a role in initiating rheumatoid arthritis (RA) pathogenesis. We have investigated the mechanism(s) by which essential redox-active trace metals (RATM) may induce cell proliferation and cell death in rabbit synovial fibroblasts. These fibroblast-like synovial (FLS) cells, which express Toll-like receptor 4 (TLR4), were used as a model system that plays a role in potentially initiating RA through oxidative stress. Potassium peroxychromate (PPC, [Cr⁵⁺]), ferrous chloride (FeCl₂, [Fe²⁺]), and cuprous chloride (CuCl, [Cu⁺]) in the indicated valency states were used as exogenous pro-oxidants that can induce oxidative stress through TLR4 coupled activation that also causes HMGB1 release. We measured the proliferation index (PI) of FLS, and examined the effect of RATM oxidants on apoptosis and autophagy by fluorescence cell-sorting flow cytometry (FC). Cell cycle was analysed by FC and autophagy-related protein expression levels were measured by western blot. Our data showed that as RATM as prooxidants increased intracellular ROS (iROS) that can induce oxidative stress. Whereas iROS increased PI in FLS, these reactive species also protected cells against apoptosis by inducing autophagy. Our results indicate that ROS/TLR4-coupled activation may contribute to the pathogenesis of RA in FLS by induction of autophagy. The signalling pathway by which inflammation and its tissue destructive sequel may occur in RA underlies the need for developing therapeutic agents that can inhibit release of tissue-damaging high mobility group box 1 (HMGB1), cytokines, and possess both trace metal chelating capacity and oxidant scavenging properties in a directed combinatorial therapy for RA.     

Sexual differences in the behavioural response to a variation in predation risk

Predators may influence their prey populations not only through direct lethal effects, but also by causing behavioural changes. The natural expansion of the wolf (Canis lupus) into the Alps provided the rare opportunity to monitor the responses of a prey species to the return of a large predator. Density effects have rarely been considered in the study of antipredator strategies. We examined the effects of wolf recolonisation and density modifications on group size and use of safe areas by Alpine ibex (Capra ibex) in Gran Paradiso National Park (Italy), where no large terrestrial predator has been present for about a century. We documented that, in a few years, the variation in the factors affecting the landscape of fear caused significant modifications in ibex behavioural patterns that could not be accounted for by density changes only. Male groups decreased in size and moved closer to safer areas. The distance of female groups from refuge sites, instead, was not affected, and their propensity to live in groups was scarcely modified. Behavioural modifications likely caused a reduction in nutrient intake in adult male ibex, as they necessarily used lower‐quality feeding patches. Our results showed that male and female ibex, which are characterised by a strong dimorphism, adopted different strategies to solve the conflicting demands of foraging efficiently and avoiding predators.     

Bacillus cereus biofilm formation on central venous catheters of hospitalised cardiac patients

Formation of bacterial biofilms is a risk with many in situ medical devices. Biofilm-forming Bacillus species are associated with potentially life-threatening catheter-related blood stream infections in immunocompromised patients. Here, bacteria were isolated from biofilm-like structures within the lumen of central venous catheters (CVCs) from two patients admitted to cardiac hospital wards. Isolates belonged to the Bacillus cereus group, exhibited strong biofilm formation propensity, and mapped phylogenetically close to the B. cereus emetic cluster. Together, whole genome sequencing and quantitative PCR confirmed that the isolates constituted the same strain and possessed a range of genes important for and up-regulated during biofilm formation. Antimicrobial susceptibility testing demonstrated resistance to trimethoprim-sulphamethoxazole, clindamycin, penicillin and ampicillin. Inspection of the genome revealed several chromosomal β-lactamase genes and a sulphonamide resistant variant of folP. This study clearly shows that B. cereus persisting in hospital ward environments may constitute a risk factor from repeated contamination of CVCs.     

Impact of increased predation risk on vigilance behaviour in a gregarious waterfowl,the Egyptian goose Alopochen aegyptiaca

Vigilance is amongst the most universal of anti‐predator strategies and commonly declines with increasing group size. We experimentally manipulated predation risk in a system with a known relationship between group size and vigilance levels to explore whether this relationship changes in response to elevated predation risk. We investigated the vigilance levels of Egyptian geese Alopochen aegyptiaca at eight golf courses in the western Cape, South Africa, to assess the perception of and reaction to predation risk. We manipulated predation risk by introducing trained Harris's hawks Parabuteo unicintus where avian predation was otherwise low or absent. The study confirmed the typical reduction in vigilance with group size on control sites, where the risk of predation is low. However, at experimental sites with elevated predation risk, a positive relationship between vigilance and group size was observed. We hypothesize that the mechanism for this relationship might be linked to social information transfer via copying behaviour and manipulation to induce vigilance. Thus, larger groups will have a higher probability of containing individuals with experience of elevated predation risk and their increased vigilance behaviour is copied by naïve individuals. This prediction is based on the intended outcome of introducing avian predation to make the geese feel less safe and to eventually leave the site as a management tool for controlling nuisance geese.