Selection overrides gene flow to break down maladaptive mimicry

Predators typically avoid dangerous species, and batesian mimicry evolves when a palatable species (the 'mimic') co-opts a warning signal from a dangerous species (the 'model') and thereby deceives its potential predators. Because predators would not be under selection to avoid the model and any of its look-alikes in areas where the model is absent (that is, allopatry), batesian mimics should occur only in sympatry with their model. However, contrary to this expectation, batesian mimics often occur in allopatry. Here we focus on one such example--a coral snake mimic. Using indirect DNA-based methods, we provide evidence suggesting that mimics migrate from sympatry, where mimicry is favoured, to allopatry, where it is disfavoured. Such gene flow is much stronger in nuclear genes than in maternally inherited mitochondrial genes, indicating that dispersal by males may explain the presence of mimetic phenotypes in allopatry. Despite this gene flow, however, individuals from allopatry resemble the model less than do individuals from sympatry. We show that this breakdown of mimicry probably reflects predator-mediated selection acting against individuals expressing the more conspicuous mimetic phenotype in allopatry. Thus, although gene flow may explain why batesian mimics occur in allopatry, natural selection may often override such gene flow and promote the evolution of non-mimetic phenotypes in such areas.     

Co-mimics have a mutualistic relationship despite unequal defences

In the first clear mathematical treatment of natural selection, Müller proposed that a shared warning signal (mimicry) would benefit defended prey species by sharing out the per capita mortality incurred during predator education. Although mimicry is a mainstay of adaptationist thinking, there has been repeated debate on whether there is a mutualistic or a parasitic relationship between unequally defended co-mimic species. Here we show that the relationship between unequally defended species is mutualistic. We examined this in a 'novel world' of artificial prey with wild predators (great tit, Parus major). We kept the abundance of a highly defended prey ('model') constant and increased the density of a moderately defended prey ('defended mimic') of either perfect or imperfect mimetic resemblance to the model. Both model and defended mimic showed a net benefit from a density-dependent decrease in their per capita mortality. Even when the effect of dilution through density was controlled for, defended mimics did not induce additional attacks on the model, but we found selection for accurate signal mimicry. In comparison, the addition of fully edible (batesian) mimics did increase additional attacks on the model, but as a result of dilution this resulted in no overall increase in per capita mortality. By ignoring the effects of density, current theories may have overestimated the parasitic costs imposed by less defended mimics on highly defended models.     

The evolution of inaccurate mimics

Instances of strikingly accurate Batesian mimicry (in which a palatable prey organism closely resembles an aversive model) are often cited to illustrate the power of natural selection. Less attention has been paid to those mimics, such as many hoverfly (Syrphidae) mimics of wasps or bees, that resemble their models only poorly. Attempts to provide an adaptive explanation for imperfect mimicry have suggested that what seems a crude resemblance to human observers may appear a close match to predators, or that inaccurate mimics may bear a general resemblance to several different model species. I show here, however, that truly inaccurate mimicry of a single model organism may be favoured over perfect resemblance, by kin selection. Signal detection theory predicts that predators will modify their level of discrimination adaptively in response to the relative frequencies and similarity of models and mimics. If models are rare and/or weakly aversive, greater local similarity of mimics can thus lead to greater attack rates. Where individual mimics are related to others in their vicinity, kin selection will then oppose the evolution of accurate mimicry.     

Three-butterfly system provides a field test of müllerian mimicry

In 1879, Müller proposed that two brightly coloured distasteful butterfly species (co-models) that share a single warning-colour pattern would benefit by spreading the selective burden of educating predators. The mutual benefit of sharing warning signals among distasteful species, so-called müllerian mimicry, is supported by comparative evidence, theoretical studies and laboratory simulations; however, to date, this key exemplar of adaptive evolution has not been experimentally tested in the field. To measure natural selection generated by müllerian mimicry, I exploited the unusual polymorphism of Heliconius cydno (Lepidoptera: Nymphalidae). Here I show increased survival of H. cydno morphs that match locally abundant monomorphic co-model species. This study demonstrates müllerian mimicry in the field. It also shows that müllerian mimicry with several co-models generates geographically divergent selection, which explains the existence of polymorphism in distasteful species with warning coloration.     

A comparative analysis of the evolution of imperfect mimicry

Although exceptional examples of adaptation are frequently celebrated, some outcomes of natural selection seem far from perfect. For example, many hoverflies (Diptera: Syrphidae) are harmless (Batesian) mimics of stinging Hymenoptera. However, although some hoverfly species are considered excellent mimics, other species bear only a superficial resemblance to their models and it is unclear why this is so. To evaluate hypotheses that have been put forward to explain interspecific variation in the mimetic fidelity of Palearctic Syrphidae we use a comparative approach. We show that the most plausible explanation is that predators impose less selection for mimetic fidelity on smaller hoverfly species because they are less profitable prey items. In particular, our findings, in combination with previous results, allow us to reject several key hypotheses for imperfect mimicry: first, human ratings of mimetic fidelity are positively correlated with both morphometric measures and avian rankings, indicating that variation in mimetic fidelity is not simply an illusion based on human perception; second, no species of syrphid maps out in multidimensional space as being intermediate in appearance between several different hymenopteran model species, as the multimodel hypothesis requires; and third, we find no evidence for a negative relationship between mimetic fidelity and abundance, which calls into question the kin-selection hypothesis. By contrast, a strong positive relationship between mimetic fidelity and body size supports the relaxed-selection hypothesis, suggesting that reduced predation pressure on less profitable prey species limits the selection for mimetic perfection.     

The evolution of müllerian mimicry in multispecies communities

Prey species that are unprofitable to attack often share conspicuous colours and patterns with other coexisting defended species. This phenomenon, termed müllerian mimicry, has long been explained as a consequence of selection on defended prey to adopt a common way of advertising their unprofitability. However, studies using two unpalatable prey types have not always supported this theory. Here we show, using a system of humans hunting for computer-generated prey, that predators do not always generate strong selection for mimicry when there are two unprofitable prey types. By contrast, we demonstrate that when predators are faced with a range of different prey species, selection on unprofitable prey to resemble one another can be intense. Here the primary selective force is not one in which predators evaluate the profitabilities of distinct prey types independently, but one in which predators learn better to avoid unprofitable phenotypes that share traits distinguishing them from profitable prey. This need to simplify decision making readily facilitates the spread of imperfect mimetic forms from rarity, and suggests that müllerian mimicry is more likely to arise in multispecies communities.     

Female mimicry in garter snakes

In many diverse taxa, males of the same species often exhibit multiple mating strategies. One well-documented alternative male reproductive pattern is 'female mimicry', whereby males assume a female-like morphology or mimic female behaviour patterns. In some species males mimic both female morphology and behaviour. We report here female mimicry in a reptile, the red-sided garter snake (Thamnophis sirtalis parietalis). This form of mimicry is unique in that it is expressed as a physiological feminization. Courting male red-sided garter snakes detect a female-specific pheromone and normally avoid courting other males. However, a small proportion of males release a pheromone that attracts other males, as though they were females. In the field, mating aggregations of 5-17 males were observed formed around these individual attractive males, which we have termed 'she-males'. In competitive mating trails, she-males mated with females significantly more often than did normal males, demonstrating not only reproductive competence but also a possible selective advantage to males with this female-like pheromone.     

重金属联合毒性对蚤类与鱼类敏感性的影响及预测模型研究进展

通过阅读文献了解各类重金属在联合作用情况下对水生生物产生的毒性效应并讨论了联合毒性的作用机制.研究了水环境中重金属污染对水生生物的敏感性影响,介绍了联合毒性作用的具体表现形式,总结了包括蚤类、鱼类等常见水生生物的收集与培养、联合毒性实验的具体步骤与结果讨论,对联合毒性的两种基本模型原理与预测结果进行了阐述.结果表明,水...     

Animal mimicry: choosing when to be a cleaner-fish mimic

Mimicry in vertebrates is usually a permanent state--mimics resemble and normally accompany their model throughout the life stages during which they act as mimics. Here we show that the bluestriped fangblenny fish (Plagiotremus rhinorhynchos), which aggressively attacks other coral-reef fish, can turn off the mimetic colours that disguise it as the benign bluestreak cleaner wrasse, Labroides dimidiatus, and assume a radically different appearance. This opportunistic facultative mimicry extends the fangblenny's scope by allowing it to blend into shoals of small reef fish as well as to remain inconspicuous at cleaning stations.     

Competition and phylogeny determine community structure in Müllerian co-mimics

Until recently, the study of negative and antagonistic interactions (for example, competition and predation) has dominated our understanding of community structure, maintenance and assembly. Nevertheless, a recent theoretical model suggests that positive interactions (for example, mutualisms) may counterbalance competition, facilitating long-term coexistence even among ecologically undifferentiated species. Müllerian mimics are mutualists that share the costs of predator education and are therefore ideally suited for the investigation of positive and negative interactions in community dynamics. The sole empirical test of this model in a Müllerian mimetic community supports the prediction that positive interactions outweigh the negative effects of spatial overlap (without quantifying resource acquisition). Understanding the role of trophic niche partitioning in facilitating the evolution and stability of Müllerian mimetic communities is now of critical importance, but has yet to be formally investigated. Here we show that resource partitioning and phylogeny determine community structure and outweigh the positive effects of Müllerian mimicry in a species-rich group of neotropical catfishes. From multiple, independent reproductively isolated allopatric communities displaying convergently evolved colour patterns, 92% consist of species that do not compete for resources. Significant differences in phylogenetically conserved traits (snout morphology and body size) were consistently linked to trait-specific resource acquisition. Thus, we report the first evidence, to our knowledge, that competition for trophic resources and phylogeny are pivotal factors in the stable evolution of Müllerian mimicry rings. More generally, our work demonstrates that competition for resources is likely to have a dominant role in the structuring of communities that are simultaneously subject to the effects of both positive and negative interactions.     

基于多层CatBoost的电力系统暂态稳定评估

随着大规模新能源并网以及新装置的不断应用,电力系统暂态稳定问题日益复杂,为进一步提升暂态稳定评估(transient stability assessment, TSA)的精确性和可靠性,提出一种基于多层CatBoost的TSA方法。首先,以电力系统故障前的稳态运行变量作为输入特征,采用一种最大相关最小冗余(maximal relevance minial redundancy, mRMR)集成方案,从输入特征中筛选出多组不同的关键特征集。然后,利用这些关键特征分别单独训练多个CatBoost模型,建立多个CatBoost驱动的TSA模型,并结合多个训练好的CatBoost模型构建TSA综合模型。在暂态稳定分析时,综合多个CatBoost模型的分析,通过多数投票表决方式判定最终评估结果。最后,在IEEE 39节点系统和某省级电力系统上进行性能测试实验。测试结果表明:所提出的TSA综合模型不仅具有极高的预测精度,而且拥有良好的泛化能力和鲁棒性。     

The combined effects of pathogens and predators on insect outbreaks

The economic damage caused by episodic outbreaks of forest-defoliating insects has spurred much research, yet why such outbreaks occur remains unclear. Theoretical biologists argue that outbreaks are driven by specialist pathogens or parasitoids, because host-pathogen and host-parasitoid models show large-amplitude, long-period cycles resembling time series of outbreaks. Field biologists counter that outbreaks occur when generalist predators fail, because predation in low-density defoliator populations is usually high enough to prevent outbreaks. Neither explanation is sufficient, however, because the time between outbreaks in the data is far more variable than in host-pathogen and host-parasitoid models, and far shorter than in generalist-predator models. Here we show that insect outbreaks can be explained by a model that includes both a generalist predator and a specialist pathogen. In this host-pathogen-predator model, stochasticity causes defoliator densities to fluctuate erratically between an equilibrium maintained by the predator, and cycles driven by the pathogen. Outbreaks in this model occur at long but irregular intervals, matching the data. Our results suggest that explanations of insect outbreaks must go beyond classical models to consider interactions among multiple species.     

应用logk_(ow)计算二噁英毒性logTEF及QSAR研究

目的研究二口恶英毒性logTEP及QSAR。方法应用分子疏水常数logkow和分子前沿轨道能EHOMO逐步回归,建立简单的量化毒性方程。结果量化毒性方程为:logTEF=-1.207 3 logkow-0.071 6EHOMO。应用该模型计算了40种典型二口恶英毒性logTEF,同已报道的实验值吻合,结论该数学模型对二口恶英类化合物具有良好的预测能力。     

青光眼动物模型研究进展

青光眼是一种不可逆性视神经退行性病变,为全球第二位致盲眼病。在青光眼研究领域,动物模型已成为重要的研究工具。青光眼动物模型对于更好的理解青光眼性视神经病变的损伤机制及治疗措施有着重要的作用。目前研究中使用最多的动物主要有鼠、兔、猴。本综述较全面系统地概述了各种青光眼动物模型的研究进展,包括近年来发展的转基因鼠青光眼模型,如急性高眼压转基因小鼠CLR(calcitonin receptor-like receptor)、利用基因打靶技术构建的自然青光眼模型等,并分别对各种模型在视网膜神经节细胞(RGCs)、视神经、视网膜功能方面的研究做了介绍,分析各种模型的利与弊,为在青光眼研究中更好地选择合适的模型提供依据。     

基于有机物超声降解的动力学共振模型

为了深化对声化学机理的认识,从声场下空化泡的微观动力学出发,在研究分析现有模型基础上,进一步考虑空化泡的振荡过程及崩溃时界面的传质,提出以共振空化泡为中心的假设,经理论推导建立了新的模型．该模型较深刻表述了实际声化学作用过程,能较准确地反映实际声化学效应和解释各种实验结果．尽管新模型的推导机理与现有模型不同,然而所得到的数学方程与其是等价的,而且从化学动力学深度上拓宽了模型的应用范围,更具普适性．     

含硫芳香族化合物发光菌毒性的3D—QSAR研究

利用比较分子力场分析法（CoMFA)与比较分子相似指数分析法（COMSIA）研究了29种含硫芳香族化合物对发光菌的急性毒性与其结构间的三维构效关系（3D－QSAR）,得到了具有较强预测能力的3D－QSAR模型,并在此基础上剖析了这批含硫芳香族化合物结构与活性之间的内在关系,深入探讨化合物的毒性作用机理。     

一种基于注意力机制的绝缘子状态反馈认知方法

针对已有绝缘子状态识别模型,以及细节识别深层网络开环认知模式和损失函数泛化能力不足的缺陷,模仿人工巡检模式,即实时评估认知结果可信度自寻优调节多尺度图像知识空间决策,提出一种基于注意力机制的绝缘子状态反馈认知方法。首先,针对预处理后的绝缘子图像,设计自适应尺度堆叠的卷积神经网络架构,使得网络输入由整体图像缩放至细节局部区域,每个尺度的网络共享相同的架构具有不同的参数,确保不同分辨率输入的可区分能力并为下一尺度生成一个细节注意区域。其次,随机配置网络面向多个尺度特征,建立具有强泛化能力的绝缘子状态分类准则。再次,构建类间分类和类内尺度间排序损失函数优化注意力网络,较前次预测生成更高置信度得分排名。最后,借鉴闭环控制思想,定义广义误差熵性能指标实时评测绝缘子不确定状态认知结果可信度,动态调节网络尺度等级,实现不确定认知结果约束下的特征空间自优化调节和分类准则重构,反馈再认知绝缘子状态。实验结果表明了本文方法与其他网络架构相比,增强了模型的泛化能力,提升了模型的认知精度。     

武器系统费用估算的参数法研究

提出了武器系统费用估算中参数法的形式化研究方法,对参数模型的建立、目标函数的建立以及优化参数的求取进行分析.考虑到模型对样本数据的适应能力,采用径向基神经网络建立参数模型;针对模型的拟合精度和推广能力之间的矛盾以及两者的要求,提出建立一种折中的目标函数;针对目标函数的参数较多、形式较为复杂的特点,采用粒子群优化算法计算得到模型的优化参数,最后通过实例加以分析验证.理论研究和计算分析表明,该方法从本质上解决了参数法的模型建立、参数优化等问题,既可以对新参数模型的建立在理论上提供指导,也可以在实践中推广应用,通用性较好.     

类器官芯片在疾病体外模型中的应用

 类器官芯片是利用器官芯片独有的优势,体外构建类器官可控的理化微环境,使得类器官更能反应来源组织器官的结构和功能,从而更好地模拟器官的生理和疾病状态,是目前最具潜力的疾病体外模型之一。概述了传统类器官、器官芯片以及类器官芯片在疾病体外模型构建中的应用进展,提出了类器官芯片在疾病模型构建中存在的问题及可能解决的方案。     

基于自监督信息增强的图表示学习

针对图表示学习模型依赖具体任务进行特征保留以及节点表示的泛化性有限等问题,本文提出一种基于自监督信息增强的图表示学习模型(Self-Variational Graph Auto Encoder,Self-VGAE)。Self-VGAE首先使用图卷积编码器和节点表示内积解码器构建变分图自编码器(Variational Graph Auto Encoder,VGAE),并对原始图进行特征提取和编码;然后,使用拓扑结构和节点属性生成自监督信息,在模型训练过程中约束节点表示的生成。在多个图分析任务中,Self-VGAE的实验表现均优于当前较为先进的基线模型,表明引入自监督信息能够增强对节点特征相似性和差异性的保留能力以及对拓扑结构的保持、推断能力,并且Self-VGAE具有较强的泛化能力。