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.     

Herbivore effects on developmental instability and fecundity of holm oaks

Plants are able to compensate for loss of tissue due to herbivores at a variety of spatial and temporal scales, masking detrimental effects of herbivory on plant fitness at these scales. The stressing effect of herbivory could also produce instability in the development of plant modules, and measures of such instability may reflect the fitness consequences of herbivory if instability is related to components of plant fitness. We analyse the relationships between herbivory, developmental instability and production of female flowers and fruits of holm oak Quercus ilex trees by means of herbivore removal experiments. Removal of leaf herbivores reduced herbivory rates at the tree level, but had no effect on mean production of female flowers or mature fruits, whereas herbivory tended to enhance flower production and had no effect on fruit abortion at the shoot level. Differences in herbivory levels between shoots of the same branch did not affect the size and fluctuating asymmetry of intact leaves. These results indicate compensation for herbivory at the tree level and over-compensation at the shoot level in terms of allocation of resources to female flower production. Removal of insect herbivores produced an increase in the mean developmental instability of leaves at the tree level in the year following the insecticide treatment, and there was a direct relationship between herbivory rates in the current year and leaf fluctuating asymmetry the following year irrespective of herbivore removal treatment. Finally, the production of pistillate flowers and fruits by trees was inversely related to the mean fluctuating asymmetry of leaves growing the same year. Leaf fluctuating asymmetry was thus an estimator of the stressing effects of herbivory on adult trees, an effect that was delayed to the following year. As leaf fluctuating asymmetry was also related to tree fecundity, asymmetry levels provided a sensitive measure of plant performance under conditions of compensatory responses to herbivory.     

Riparian zones as havens for exotic plant species in the central grasslands

In the Central Grasslands of the United States, we hypothesized that riparian zones high in soil fertility would contain more exotic plant species than upland areas of low soil fertility. Our alternate hypothesis was that riparian zones high in native plant species richness and cover would monopolize available resources and resist invasion by exotic species. We gathered nested-scale vegetation data from 40 1 m²subplots (nested in four 1000 m² plots) in both riparian and upland sites at four study areas in Colorado, Wyoming, and South Dakota (a total of 320 1 m² subplots and 32 1000 m² plots). At the 1 m² scale, mean foliar cover of native species was significantly greater (P<0.001) in riparian zones (36.3% ± 1.7%) compared to upland sites (28.7% ± 1.5%), but at this small scale there were no consistent patterns of native and exotic species richness among the four management areas. Mean exotic species cover was slightly higher in upland sites compared to riparian sites (9.0% ± 3.8% versus 8.2% ± 3.0% cover). However, mean exotic species richness and cover were greater in the riparian zones than upland sites in three of four management areas. At the 1000 m² scale, mean exotic species richness was also significantly greater (P<0.05) in riparian zones (7.8 ± 1.0 species) compared to upland sites (4.8 ± 1.0 species) despite the heavy invasion of one upland site. For all 32 plots combined, 21% of the variance in exotic species richness was explained by positive relationships with soil % silt (t =1.7, P=0.09) and total foliar cover (t = 2.4, P=0.02). Likewise, 26% of the variance in exotic species cover (log₁₀ cover) was explained by positive relationships with soil % silt (t =2.3, P=0.03) and total plant species richness (t = 2.5, P=0.02). At landscape scales (four 1000 m² plots per type combined), total foliar cover was significantly and positively correlated with exotic species richness (r=0.73, P<0.05) and cover (r=0.74, P<0.05). Exotic species cover (log₁₀ cover) was positively correlated with log₁₀% N in the soil (r=0.61, P=0.11) at landscape scales. On average, we found that 85% (±5%) of the total number of exotic species in the sampling plots of a given management area could be found in riparian zones, while only 50% (±8%) were found in upland plots. We conclude that: (1) species-rich and productive riparian zones are particularly invasible in grassland ecosystems; and (2) riparian zones may act as havens, corridors, and sources of exotic plant invasions for upland sites and pose a significant challenge to land managers and conservation biologists.     

Actual vs perceived profitability: A study of floral choice of honey bees

The relationship between actual and perceived profitability was investigated by quantifying choice behavior of foraging honey bees (Apis mellifera).Rate of net energy gain was used as a measure of profitability. Individual bees repeatedly chose between a yellow and a blue tubular artificial flower which had different associated profitabilities. Handling costs were manipulated by using flowers of different depth;energy gains were manipulated by using different volumes of a 20% (w/w) sucrose solution. Bees' discrimination between the two flowers increased as the absolute difference in profitabilities increased and discrimination decreased as profitabilities of both flowers increased. Therefore, discrimination depended on the relative difference in profitability between flowers, and therefore, perception was a nonlinear function of actual rates of net energy gain. The results also suggested that motivation to choose between flowers depended on the level of profitability. We suggest that nonlinear perceptual scales and motivation should be incorporated into models of food choice as constraints and should be considered in the design of experiments used to test predictions of models and in the interpretation of experimental results.     

昆虫濒危等级和保护级别

介绍了国际上目前普遍通用的物种濒危等级系统“IUCN红色名录等级 ( 1994年版 )”来源和结构及使用注意事项 ,对我国 1989年公布生效的《国家重点保护野生动物名录》保护级别和昆虫收录情况进行了评介 ,最后就保护名录与红皮书或红色名录的关系及国家重点保护昆虫的遴选和定级原则提出讨论和建议     

阿特拉津降解菌ATR3的分离鉴定与土壤修复

阿特拉津因效率高、价格低廉,是我国玉米田施用最广泛的除草剂之一,但其结构稳定,残留时间长,因此对生态环境和人类健康造成了一定的危害。从长期受阿特拉津污染的玉米田土壤中筛选并鉴定阿特拉津降解菌,明确其在不同类型土壤中的去除能力。对分离出的阿特拉津降解菌ATR3进行生理生化分析和16S rRNA序列鉴定,确定菌株ATR3为节杆菌属（Arthrobacter sp.）。该菌株以阿特拉津为唯一氮源,培养48 h后对1 000 mg/L阿特拉津的去除率达到97%以上。敏感作物盆栽试验结果表明,阿特拉津在棕壤上去除最快,褐土次之,黑土最慢,说明阿特拉津在土壤中的去除过程与土壤本身的理化性质呈相关关系。同时,该菌株处理14 d后,能明显恢复玉米的各项生物学指标,说明该菌株对阿特拉津污染土壤具有良好的修复能力。为阿特拉津降解菌剂的推广利用提供参考。     

基于特征属性的中国自然保护区分类体系

基于114个自然保护区典型样本的特征属性,采用聚类分析方法建立了新的中国自然保护区分类体系.结果表明:与现行的国家分类标准相比,新的分类体系更具简明性和实用性;同时,新体系中的C1、C2、C3、C4类型分别与世界自然保护联盟(IUCN)分类体系中的Ⅰ、Ⅱ、Ⅳ、Ⅴ类保护区相对应.新体系保持了分类标准和尺度的一致性,一定程度上避免了主观分类的偏差,为中国自然保护区的分类提供了量化依据.     

Limited influence of local and landscape factors on finescale gene flow in two pond‐breeding amphibians

Dispersal and gene flow within animal populations are influenced by the composition and configuration of the landscape. In this study, we evaluated hypotheses about the impact of natural and anthropogenic factors on genetic differentiation in two amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Lithobates sylvaticus) in a commercial forest in central Maine. We conducted this analysis at two scales: a local level, focused on factors measured at each breeding pond, and a landscape level, focused on factors measured between ponds. We investigated the effects of a number of environmental factors in six categories including Productivity, Physical, Land Composition, Land Configuration, Isolation and Location. Embryos were sampled from 56 spotted salamander breeding ponds and 39 wood frog breeding ponds. We used a hierarchical Bayesian approach in the program GESTE at each breeding pond and a random forest algorithm in conjunction with a network analysis between the ponds. We found overall high genetic connectivity across distances up to 17 km for both species and a limited effect of natural and anthropogenic factors on gene flow. We found the null models best explained patterns of genetic differentiation at a local level and found several factors at the landscape level that weakly influenced gene flow. This research indicates multiscale investigations that incorporate local and landscape factors are valuable for understanding patterns of gene flow. Our findings suggest that dispersal rates in this system are high enough to minimize genetic structuring and that current forestry practices do not significantly impede dispersal.     

Ring formation on otoliths and scales of Pagrus pagrus: a comparative study

One annulus formed on the scales of farmed red porgy Pagrus pagrus each year during March and one opaque zone on the otoliths during June. Scales proved to be more sensitive than otoliths in recording the life history of the red porgy. A false annulus (ring of capture) was observed on the scales of the 0+ age group, but not on the otoliths. A gradual lengthening of the period of annulus formation was observed, from the younger to the older fish. The annulus formation in fish older than 2+ was less synchronized, due to the aquaculture conditions. Scales were more accurate than otoliths in annuli formation. A high percentage of missing or additional opaque zones were observed on otoliths of older fish. These irregularities were related to fish maturation and/or farming conditions. Farmed fish grew three times as fast as the wild fish.