昆虫抗药性与适合度

昆虫抗药性的产生常伴有适合度劣势(即适合度代价),即抗性个体常表现出发育速率较慢、存活率和生殖力较低。文章主要阐述害虫抗药性与生物适合度和适合度代价的关系以及适合度代价产生的机制、特性及影响因素。并从生态学角度论述害虫抗药性的进化,为探索抗性发展规律及害虫抗性治理提供理论依据。     

Insecticide resistance in the mosquito Culex pipiens: what have we learned about adaptation?

Resistance to organophosphate (OP) insecticide in the mosquito Culex pipiens has been studied for ca. 30 years. This example of micro-evolution has been thoroughly investigated as an opportunity to assess precisely both the new adapted phenotypes and the associated genetic changes. A notable feature is that OP resistance is achieved with few genes, and these genes have generally large effects. The molecular events generating such resistance genes are complex (e.g., gene amplification, gene regulation) potentially explaining their low frequency of de novo occurrence. In contrast, migration is a frequent event, including passive transportation between distant populations. This generates a complex interaction between mutations and migration, and promotes competition among resistance alleles. When the precise physiological action of each gene product is rather well known, it is possible to understand the dominance level or the type of epistasis observed. It is however difficult to predict a priori how resistance genes will interact, and it is too early to state whether or not this will be ever possible. These resistance genes are costly, and the cost is variable among them. It is usually believed that the initial fitness cost would gradually decrease due to subsequent mutations with a modifier effect. In the present example, a particular modifier occurred (a gene duplication) at one resistance locus, whereas at the other one reduction of cost is driven by allele replacement and apparently not by selection of modifiers.     

The effects of habitat,density, gender and duration on overwintering success in Bembidion lampros (Coleoptera: Carabidae)

In temperate climates, winter mortality is a key factor influencing insect survival. In Bembidion lampros (Coleoptera: Carabidae), an abundant polyphagous predator in arable farmland, we investigated how habitat, population density, gender and duration of overwintering affect the winter mortality and body condition of survivors. In a field experiment, we introduced beetles at two population densities into isolators placed either in the interior of the field or in the grassy boundary. Half of the isolators were collected in mid‐March, and the remaining half were collected in mid‐April. Across all treatments, 44–92% of the beetles survived until spring. Survival was significantly higher in the field interior than in the boundary. The longevity of individuals starved after overwintering was higher in females than in males and was positively related to the length of time spent at the overwintering site. Population density was positively related to percentage survival but did not affect body condition. Our results suggest that biotic factors such as population density and predation, though little studied, may have a similar significance as abiotic factors. Even ubiquitous carabid species inhabiting agroecosystems have specific requirements for overwintering. Understanding these requirements is useful for developing techniques to support their overwintering success.     

The in vitro fitness cost of antimicrobial resistance in Escherichia coli varies with the growth conditions

The objective of this study was to investigate the influence of stressful growth conditions on the fitness cost of antimicrobial resistance in Escherichia coli BJ4 caused by chromosomal mutations and plasmid acquisition. The fitness cost of chromosomal streptomycin resistance increased significantly when the bacteria were grown under all stress conditions tested, while the cost in 1/3 Luria–Bertani was not significantly changed in a streptomycin+rifampicin mutant. The increase in the fitness cost depended in a nonregular manner on the strain/stress combination. The fitness cost of plasmid-encoded resistance on R751 did not differ significantly, and was generally less under stressful growth conditions than in rich media. The fitness cost associated with R751 with the multiple drug resistance cassette from Salmonella Typhimurium DT104 increased significantly only under stressful conditions at low pH and at high-salt concentrations. Strains with an impaired rpoS demonstrated a reduced fitness only during growth in a high-salt concentration. In conclusion, it was demonstrated that bacterial fitness cost in association with antimicrobial resistance generally increases under stressful growth conditions. However, the growth potential of bacteria with antimicrobial resistances did not increase in a straightforward manner in these in vitro experiments and is therefore probably even more difficult to predict in vivo .     

韭菜迟眼蕈蚊的抗药性监测及对灭蝇胺的抗性风险和亚致死效应分析

【目的】明确韭菜迟眼蕈蚊Bradysia odoriphaga对10种杀虫剂的抗性现状及对灭蝇胺的抗性风险和灭蝇胺对韭菜迟眼蕈蚊的亚致死效应。【方法】采用胃毒触杀联合毒力法测定了5类（新烟碱类、拟除虫菊酯类、吡咯类、昆虫生长调节剂类和有机磷类）共10种杀虫剂对河南省濮阳市、安徽省亳州市、河北省唐山市及山东省济宁市4个地区韭菜迟眼蕈蚊2龄幼虫的毒力,用亚致死浓度(LC₁₅和LC₃₀)灭蝇胺处理韭菜迟眼蕈蚊观察对其幼虫历期、化蛹率、羽化率及单雌产卵量等指标的影响,评估了韭菜迟眼蕈蚊对灭蝇胺的抗性风险,并通过Tabashnik域性状分析法计算抗性现实遗传力（realized heritability,h²）和基于选择数据预测不同选择压力下的抗性发展速率。【结果】监测数据表明,韭菜迟眼蕈蚊田间种群对灭蝇胺、氟啶脲、氟铃脲和吡丙醚处于敏感至低水平抗性,对辛硫磷产生低至中等水平抗性,对高效氯氰菊酯处于低水平抗性,对吡虫啉、噻虫嗪和噻虫胺处于敏感或低至中等水平抗性。当抗性现实遗传力（h²）为0.073,在不同的选择压力下（死亡率分别为50%, 60%, 70%, 80%和90%）,韭菜迟眼蕈蚊对灭蝇胺的抗性上升至10倍分别需要25.2, 20.7, 17.2, 14.4和11.4代;采用LC₁₅和LC₃₀浓度灭蝇胺处理韭菜迟眼蕈蚊2龄幼虫后,F₀和F₁代的羽化率和单雌产卵量显著降低。【结论】韭菜迟眼蕈蚊对灭蝇胺具有较低的抗性风险,亚致死浓度灭蝇胺显著抑制韭菜迟眼蕈蚊的化蛹率、羽化率及单雌产卵量。     

Natural selection on the genetical component of variance in body condition in a wild bird population

Although there is substantial evidence that skeletal measures of body size are heritable in wild animal populations, it is frequently assumed that the nonskeletal component of body weight (or ‘condition’) is determined primarily by environmental factors, in particular nutritional state. We tested this assumption by quantifying the genetic and environmental components of variance in fledgling body condition index (=relative body weight) in a natural population of collared flycatchers (Ficedula albicollis), and compared the strength of natural selection on individual breeding values with that on phenotypic values. A mixed model analysis of the components of variance, based on an ‘animal model’ and using 18 years of data on 17 717 nestlings, revealed a significant additive genetic component of variance in body condition, which corresponded to a narrow sense heritability (h²) of 0.30 (SE=0.03). Nongenetic contributions to variation in body condition were large, but there was no evidence of dominance variance nor of contributions from early maternal or common environment effects (pre‐manipulation environment) in condition at fledging. Comparison of pre‐ and post‐selection samples revealed virtually identical h² of body condition index, despite the fact that there was a significant decrease (35%) in the levels of additive genetic variance from fledging to breeding. The similar h² in the two samples occurred because the environmental component of variance was also reduced by selection, suggesting that natural selection was acting on both genotypic and environmental variation. The effects of selection on genetic variance were confirmed by calculation of the selection differentials for both phenotypic values and best linear unbiased predictor (BLUP) estimates of breeding values: there was positive directional selection on condition index both at the phenotypic and the genotypic level. The significant h² of body condition index is consistent with data from human and rodent populations showing significant additive genetic variance in relative body mass and adiposity, but contrasts with the common assumption in ecology that body condition reflects an individual’s nongenetic nutritional state. Furthermore, the substantial reduction in the additive genetic component of variance in body condition index suggests that selection on environmental deviations cannot alone explain the maintenance of additive genetic variation in heritable traits, but that other mechanisms are needed to explain the moderate to high heritabilities of traits under consistent and strong directional selection.     

广大腿小蜂对菜粉蝶蛹体型大小的产卵选择及后代发育表现

产卵选择与后代发育适合度之间的相关性是进化生态学的主要科学问题之一。为探究广大腿小蜂(Brachymeria lasus)对不同体型大小寄主的选择和后代发育表现的关系,采用饥饿方法处理4龄菜粉蝶(Pieris rapae)幼虫以获得体型大小(用体质量表示)差异较大的寄主蛹,供寄生蜂选择寄生。结果表明,广大腿小蜂显著偏好体型较大的寄主蛹,而且在体型较大的蛹内产雌性后代的概率更大;子代蜂体型大小与寄主蛹大小存在显著的正相关性,但子代蜂发育历期与寄主蛹大小无相关性。研究说明,广大腿小蜂对菜粉蝶蛹的寄生选择与后代发育表现,符合寄主大小-质量模型的预测。     

What does body size mean,from the “plant's eye view”?

Alternative metrics exist for representing variation in plant body size, but the vast majority of previous research for herbaceous plants has focused on dry mass. Dry mass provides a reasonably accurate and easily measured estimate for comparing relative capacity to convert solar energy into stored carbon. However, from a “plant's eye view”, its experience of its local biotic environment of immediate neighbors (especially when crowded) may be more accurately represented by measures of “space occupancy” (S–O) recorded in situ—rather than dry mass measured after storage in a drying oven. This study investigated relationships between dry mass and alternative metrics of S–O body size for resident plants sampled from natural populations of herbaceous species found in Eastern Ontario. Plant height, maximum lateral canopy extent, and estimated canopy area and volume were recorded in situ (in the field)—and both fresh and dry mass were recorded in the laboratory—for 138 species ranging widely in body size and for 20 plants ranging widely in body size within each of 10 focal species. Dry mass and fresh mass were highly correlated (r² > .95) and isometric, suggesting that for some studies, between‐species (or between‐plant) variation in water content may be unimportant and fresh mass can therefore substitute for dry mass. However, several relationships between dry mass and other S–O body size metrics showed allometry—that is, plants with smaller S–O body size had disproportionately less dry mass. In other words, they have higher “body mass density” (BMD) — more dry mass per unit S–O body size. These results have practical importance for experimental design and methodology as well as implications for the interpretation of “reproductive economy”—the capacity to produce offspring at small body sizes—because fecundity and dry mass (produced in the same growing season) typically have a positive, isometric relationship. Accordingly, the allometry between dry mass and S–O body size reported here suggests that plants with smaller S–O body size—because of higher BMD—may produce fewer offspring, but less than proportionately so; in other words, they may produce more offspring per unit of body size space occupancy.     

Measuring Natural Selection on Proportional Traits: Comparisons of Three Types of Selection Estimates for Resistance and Susceptibility to Herbivore Damage

To compare the strength of natural selection on different traits and in different species, evolutionary biologists typically estimate selection differentials and gradients in standardized units. Measuring selection differentials and gradients in standard deviation units or mean-standardized units facilitates such comparisons by converting estimates with potentially varied units to a common scale. In this note, I compare the performance of variance- and mean-standardized selection differentials and gradients for a unique and biologically important class of traits: proportional traits, that can only vary between zero and one, and their complements (1 minus the trait) using simple algebra and analysis of data from a field-study using morning glories. There is a systematic, mathematical relationship between unstandardized and variance-standardized selection gradients for proportional traits and their complements, but such a general relationship is lacking for mean-standardized gradients, potentially leading investigators to mistakenly conclude that a proportional change in a trait would have little effect on fitness. Despite this potential limitation, mean-standardized selection differentials and gradients represent a useful tool for studying natural selection on proportional traits, because by definition they measure how proportional changes in the mean of a trait lead to proportional changes in relative fitness.Co-ordinating editor: I. Olivieri