Dispersal and the sex ratio at birth in primates

The females of many species of primates settle for life within the home ranges of their mothers, whereas males disperse as immatures. According to the theory of sex allocation, the costs incurred by mothers through local competition for resources with their philopatric daughters should favour the evolution of male-biased sex ratios at birth. I report here two tests of this hypothesis based on data from 15 genera of primates. First, I show that the intensity of competition for resources within kin groups is strongly and positively correlated with sex ratios at birth. Second, I show that sex ratios at birth are higher in genera with female-biased philopatry than in genera in which philopatry is not female-biased. These analyses suggest that local resource competition among kin powerfully influences the evolution of sex ratios in primates.     

红姜花Hedychium coccineum依赖个体大小的性分配研究

 性分配理论假定雌雄功能间存在一种权衡关系,依赖个体大小的资源分配策略是解释种群内性分配变化的主要机制之一,已经引起了许多学者的关注,然而在姜科植物中缺乏对其的研究.为了验证依赖个体大小的性分配理论预测,研究通过对姜科植物红姜花Hedychium coccineum不同种群花期和果期的繁殖特征与个体大小的回归关系发现:①红姜花对繁殖结构的资源分配策略与SDS理论预测的一致,然而花期的繁殖分配却和预测不一致;②花设计大小、吸引结构、性分配和雌雄适合度都不依赖个体大小,暗示了这种性分配格局具有特殊的适应意义.     

Climate-driven population divergence in sex-determining systems

Sex determination is a fundamental biological process, yet its mechanisms are remarkably diverse. In vertebrates, sex can be determined by inherited genetic factors or by the temperature experienced during embryonic development. However, the evolutionary causes of this diversity remain unknown. Here we show that live-bearing lizards at different climatic extremes of the species' distribution differ in their sex-determining mechanisms, with temperature-dependent sex determination in lowlands and genotypic sex determination in highlands. A theoretical model parameterized with field data accurately predicts this divergence in sex-determining systems and the consequence thereof for variation in cohort sex ratios among years. Furthermore, we show that divergent natural selection on sex determination across altitudes is caused by climatic effects on lizard life history and variation in the magnitude of between-year temperature fluctuations. Our results establish an adaptive explanation for intra-specific divergence in sex-determining systems driven by phenotypic plasticity and ecological selection, thereby providing a unifying framework for integrating the developmental, ecological and evolutionary basis for variation in vertebrate sex determination.     

The optimal sex ratio in cooperatively breeding populations

In some cooperatively breeding species, elder siblings remain within their home ranges to assist their parents in raising their younger siblings by providing protection or food. Previous attempts to model the popu- lation sex ratios of such species have assumed that helping is cost-free and only involves benefits to parents, resulting in offspring sex ratio biases towards the helping sex. However, parents may also incur costs in maintaining helpers. We incorporated costs and benefits of helping to predict the sex ratio of offspring in a theoretical model. Our model showed that the evolutionary stable strategy （ESS） sex ratio strongly depends on three parameters： （1） the average number of helpers per female; （2） the benefits that a helper brings to its mother＇s offspring production （MOP）; and （3） the cost-benefit ratio of helping. When one sex of elder siblings provides help, the ESS sex ratio is biased towards the helping sex if MOP costs are less than the benefits, （i.e., the cost-benefit ratio 〈1）. However, the ESS sex ratio becomes biased towards the non-helping sex if MOP costs exceed the benefits （i.e., the cost-benefit ratio 〉1）. Additionally, our model shows that the ESS sex ratio becomes biased in favor of the more helpful sex when both male and female elder siblings provide help. These results explain why sex ratios may become biased towards the helping sex, as well as the non-helping sex, in some species.     

Coevolution in multidimensional trait space favours escape from parasites and pathogens

Almost all species are subject to continuous attack by parasites and pathogens. Because parasites and pathogens tend to have shorter generation times and often experience stronger selection due to interaction than their victims do, it is frequently argued that they should evolve more rapidly and thus maintain an advantage in the evolutionary race between defence and counter-defence. This prediction generates an apparent paradox: how do victim species survive and even thrive in the face of a continuous onslaught of more rapidly evolving enemies? One potential explanation is that defence is physiologically, mechanically or behaviourally easier than attack, so that evolution is less constrained for victims than for parasites or pathogens. Another possible explanation is that parasites and pathogens have enemies themselves and that victim species persist because parasites and pathogens are regulated from the top down and thus generally have only modest demographic impacts on victim populations. Here we explore a third possibility: that victim species are not as evolutionarily impotent as conventional wisdom holds, but instead have unique evolutionary advantages that help to level the playing field. We use quantitative genetic analysis and individual-based simulations to show that victims can achieve such an advantage when coevolution involves multiple traits in both the host and the parasite.     

Optimal nitrogen-to-phosphorus stoichiometry of phytoplankton

Redfield noted the similarity between the average nitrogen-to-phosphorus ratio in plankton (N:P = 16 by atoms) and in deep oceanic waters (N:P = 15; refs 1, 2). He argued that this was neither a coincidence, nor the result of the plankton adapting to the oceanic stoichiometry, but rather that phytoplankton adjust the N:P stoichiometry of the ocean to meet their requirements through nitrogen fixation, an idea supported by recent modelling studies. But what determines the N:P requirements of phytoplankton? Here we use a stoichiometrically explicit model of phytoplankton physiology and resource competition to derive from first principles the optimal phytoplankton stoichiometry under diverse ecological scenarios. Competitive equilibrium favours greater allocation to P-poor resource-acquisition machinery and therefore a higher N:P ratio; exponential growth favours greater allocation to P-rich assembly machinery and therefore a lower N:P ratio. P-limited environments favour slightly less allocation to assembly than N-limited or light-limited environments. The model predicts that optimal N:P ratios will vary from 8.2 to 45.0, depending on the ecological conditions. Our results show that the canonical Redfield N:P ratio of 16 is not a universal biochemical optimum, but instead represents an average of species-specific N:P ratios.     

Excess digestive capacity in predators reflects a life of feast and famine

A central challenge for predators is achieving positive energy balance when prey are spatially and temporally heterogeneous. Ecological heterogeneity produces evolutionary trade-offs in the physiological design of predators; this is because the ability to capitalize on pulses of food abundance requires high capacity for food-processing, yet maintaining such capacity imposes energetic costs that are taxing during periods of food scarcity. Recent advances in physiology show that when variation in foraging opportunities is predictable, animals may adjust energetic trade-offs by rapidly modulating their digestive system to track variation in foraging opportunities. However, it is increasingly recognized that foraging opportunities for animals are unpredictable, which should favour animals that maintain a capacity for food-processing that exceeds average levels of consumption (loads). Despite this basic principle of quantitative evolutionary design, estimates of digestive load:capacity ratios in wild animals are virtually non-existent. Here we provide an extensive assessment of load:capacity ratios for the digestive systems of predators in the wild, compiling 639 estimates across 38 species of fish. We found that piscine predators typically maintain the physiological capacity to feed at daily rates 2-3 times higher than what they experience on average. A numerical simulation of the trade-off between food-processing capacity and metabolic cost suggests that the observed level of physiological opportunism is profitable only if predator-prey encounters, and thus predator energy budgets, are far more variable in nature than currently assumed.     

Mammalian chiasma frequencies as a test of two theories of recombination

A broad survey of asexuality in the animal kingdom is sufficient to reject all theories of sex and recombination except two: the Red Queen and the Tangled Bank. The Red Queen theory states that an organism's biotic environment tends to be 'contrary', consistently evolving to the detriment of the organism; sex and recombination result in progeny genetically distinct from their parents and grandparents and thus less susceptible to the antagonistic advances made during the previous generations, particularly by their parasites. The alternative theory, the Tangled Bank, states that sex and recombination function to diversify the progeny from each other, thus reducing competition between them. An extensive survey of mammalian recombination shows that the total number of chiasmata in excess of one per bivalent is strongly correlated with generation time but uncorrelated with fecundity. We conclude that crossing-over may function to combat antagonists with short generation times but does not function to reduce sib competition. Chromosome number is selectively neutral with respect to these factors.     

Transgenic anopheline mosquitoes impaired in transmission of a malaria parasite

Malaria is estimated to cause 0.7 to 2.7 million deaths per year, but the actual figures could be substantially higher owing to under-reporting and difficulties in diagnosis. If no new control measures are developed, the malaria death toll is projected to double in the next 20 years. Efforts to control the disease are hampered by drug resistance in the Plasmodium parasites, insecticide resistance in mosquitoes, and the lack of an effective vaccine. Because mosquitoes are obligatory vectors for malaria transmission, the spread of malaria could be curtailed by rendering them incapable of transmitting parasites. Many of the tools required for the genetic manipulation of mosquito competence for malaria transmission have been developed. Foreign genes can now be introduced into the germ line of both culicine and anopheline mosquitoes, and these transgenes can be expressed in a tissue-specific manner. Here we report on the use of such tools to generate transgenic mosquitoes that express antiparasitic genes in their midgut epithelium, thus rendering them inefficient vectors for the disease. These findings have significant implications for the development of new strategies for malaria control.     

Evidence for immunological cross-reaction between sporozoites and blood stages of a human malaria parasite

Malaria parasites (Plasmodium spp.) show a complex pattern of development in the mammalian host and many studies support the view that the surface of the sporozoite, injected by the mosquito, has no antigens in common with the erythrocytic stage of development. For example, immunization with the erythrocytic parasites generates antisera with negligible titre by indirect immunofluorescence to the sporozoite surface. Although monoclonal antibodies prepared against erythrocytic stages were reported to show cross-reaction to the sporozoite stage, this appeared to be due to cytoplasmic antigens exposed by the method of sporozoite preparation, and in Plasmodium knowlesi, a cDNA clone coding for the circumsporozoite antigen, the major protein of the sporozoite surface, showed no hydridization to mRNA isolated from the erythrocytic stages. Here, however, we present evidence for an antigenic determinant shared by the sporozoite surface and the erythrocytic stages of the human malaria parasite, P. falciparum. Moreover, our studies show that the antigen(s) elicit a strong immune response in man.     

Sex releases the speed limit on evolution

Explaining the evolutionary maintenance of sex remains a key problem in evolutionary biology. One potential benefit of sex is that it may allow a more rapid adaptive response when environmental conditions change, by increasing the efficiency with which selection can fix beneficial mutations. Here I show that sex can increase the rate of adaptation in the facultatively sexual single-celled chlorophyte Chlamydomonas reinhardtii, but that the benefits of sex depend crucially on the size of the population that is adapting: sex has a marked effect in large populations but little effect in small populations. Several mechanisms have been proposed to explain the benefits of sex in a novel environment, including stochastic effects in small populations, clonal interference and epistasis between beneficial alleles. These results indicate that clonal interference is important in this system.     

信息不对称条件下企业集团税后利润的优化

研究了信息不对称条件下一个既有内部关联交易又有外部交易的企业集团 ,如何通过转移价格、运输费用分配率等因素 ,减少信息不对称子公司的道德风险 ,实现企业集团整体税后利润最大化的问题·根据委托代理理论 ,从最大化企业集团期望税后利润的角度出发 ,考虑了信息不对称子公司的个体理性约束和激励相容约束 ,以转移价格和运输费用分配率为决策变量 ,建立了企业集团税后利润优化模型 ,并应用进化规划算法对模型作了仿真计算·结果表明 ,企业集团可以通过转移价格、运输费用分配率等变量的适当选择来优化自己的税后利润     

云制造模式下分布式资源共享激励机制研究

针对云制造模式下分布式企业间迫切需要开展大规模开放式协作及资源共享的需求，结合演化博弈理论，建立分布式环境下资源共享激励机制，分析了不同情况下资源共享的演化博弈趋势.通过理论分析及仿真实验可知:资源可共享总量、资源共享水平、资源利用能力、协同收益系数、评价收益系数、共享激励系数及投机惩罚系数对资源共享起促进作用，共享成本系数起阻碍作用，直接收益系数无影响，协同收益分配系数与资源共享演化稳定状态呈倒U型关系.本文研究内容为促进分布式资源共享，加速未来云制造模式下产业创新研发提供借鉴意义.     

面向群体性事件的三方两两博弈演化模型

为更好地应对航班延误引发的群体性事件,以机场、旅客、航空公司为群体性事件的博弈主体,明确各个主体在群体性事件中的策略选择,分析其对于群体性事件的影响机理。并基于演化博弈理论,利用复制动态方程,构建三方两两博弈演化模型,采用三个两方博弈模型对航班延误的旅客群体性事件进行分析。在航空公司与旅客、机场与旅客两个博弈模型中,多数情况下,博弈双方在多次博弈后会调整各自的策略,形成一个循环的闭合博弈圈。在机场与航空公司的博弈模型分析中,引入了契约下的核战略的囚徒困境,并得出结论：博弈双方会同时积极应对旅客群体性事件。     

The adaptive significance of temperature-dependent sex determination in a reptile

Understanding the mechanisms that determine an individual's sex remains a primary challenge for evolutionary biology. Chromosome-based systems (genotypic sex determination) that generate roughly equal numbers of sons and daughters accord with theory, but the adaptive significance of environmental sex determination (that is, when embryonic environmental conditions determine offspring sex, ESD) is a major unsolved problem. Theoretical models predict that selection should favour ESD over genotypic sex determination when the developmental environment differentially influences male versus female fitness (that is, the Charnov-Bull model), but empirical evidence for this hypothesis remains elusive in amniote vertebrates--the clade in which ESD is most prevalent. Here we provide the first substantial empirical support for this model by showing that incubation temperatures influence reproductive success of males differently than that of females in a short-lived lizard (Amphibolurus muricatus, Agamidae) with temperature-dependent sex determination. We incubated eggs at a variety of temperatures, and de-confounded sex and incubation temperature by using hormonal manipulations to embryos. We then raised lizards in field enclosures and quantified their lifetime reproductive success. Incubation temperature affected reproductive success differently in males versus females in exactly the way predicted by theory: the fitness of each sex was maximized by the incubation temperature that produces that sex. Our results provide unequivocal empirical support for the Charnov-Bull model for the adaptive significance of temperature-dependent sex determination in amniote vertebrates.     

Sexual selection and the maintenance of sexual reproduction

The maintenance of sexual reproduction is a problem in evolutionary theory because, all else being equal, asexual populations have a twofold fitness advantage over their sexual counterparts and should rapidly outnumber a sexual population because every individual has the potential to reproduce. The twofold cost of sex exists because of anisogamy or gamete dimorphism-egg-producing females make a larger contribution to the zygote compared with the small contribution made by the sperm of males, but both males and females contribute 50% of the genes. Anisogamy also generates the conditions for sexual selection, a powerful evolutionary force that does not exist in asexual populations. The continued prevalence of sexual reproduction indicates that the 'all else being equal' assumption is incorrect. Here I show that sexual selection can mitigate or even eliminate the cost of sex. If sexual selection causes deleterious mutations to be more deleterious in males than females, then deleterious mutations are maintained at lower equilibrium frequency in sexual populations relative to asexual populations. The fitness of sexual females is higher than asexuals because there is no difference in the fecundity of sexual females and asexuals of the same genotype, but the equilibrium frequency of deleterious mutations is lower in sexual populations. The results are not altered by synergistic epistasis in males.     

毛茛科植物交配系统的特征与花期资源分配对策

以青藏高原东部高寒草甸的毛茛科为对象，研究处于进化树不同位置8个种(6个属)的交配系统的差异对资源分配对策的影响，发现随着自交率的提高，植物对性分配的投入减小，对花的吸引结构(如花被)的资源分配也减小，表明在个体水平上的结论同样符合性分配理论的预测(指花的水平)；花期繁殖分配随自交率的增加而降低；并且揭示了物种的系统起源与交配系统的进化、资源分配对策之间的功能联系．     

Higher rates of sex evolve in spatially heterogeneous environments

The evolution and maintenance of sexual reproduction has puzzled biologists for decades. Although this field is rich in hypotheses, experimental evidence is scarce. Some important experiments have demonstrated differences in evolutionary rates between sexual and asexual populations; other experiments have documented evolutionary changes in phenomena related to genetic mixing, such as recombination and selfing. However, direct experiments of the evolution of sex within populations are extremely rare (but see ref. 12). Here we use the rotifer, Brachionus calyciflorus, which is capable of both sexual and asexual reproduction, to test recent theory predicting that there is more opportunity for sex to evolve in spatially heterogeneous environments. Replicated experimental populations of rotifers were maintained in homogeneous environments, composed of either high- or low-quality food habitats, or in heterogeneous environments that consisted of a mix of the two habitats. For populations maintained in either type of homogeneous environment, the rate of sex evolves rapidly towards zero. In contrast, higher rates of sex evolve in populations experiencing spatially heterogeneous environments. The data indicate that the higher level of sex observed under heterogeneity is not due to sex being less costly or selection against sex being less efficient; rather sex is sufficiently advantageous in heterogeneous environments to overwhelm its inherent costs. Counter to some alternative theories for the evolution of sex, there is no evidence that genetic drift plays any part in the evolution of sex in these populations.     

The circumsporozoite protein is an immunodominant protective antigen in irradiated sporozoites

Malaria infection starts when mosquitoes inject sporozoites into the skin. The parasites enter the blood stream and make their way to the liver where they develop into the exo-erythrocytic forms (EEFs). Immunization with irradiated sporozoites (IrSp) leads to robust protection against malaria infection in rodents, monkeys and humans by eliciting antibodies to circumsporozoite protein (CS) that inhibit sporozoite infectivity, and T cells that destroy the EEFs. To study the role of non-CS antigens in protection, we produced CS transgenic mice that were tolerant to CS T-cell epitopes. Here we show that in the absence of T-cell-dependent immune responses to CS, protection induced by immunization with two doses of IrSp was greatly reduced. Thus, although hundreds of other Plasmodium genes are expressed in sporozoites and EEFs, CS is a dominant protective antigen. Nevertheless, sterile immunity could be obtained by immunization of CS transgenics with three doses of IrSp.     

近期科学调整邮电人才结构的研究

以产业结构和人才资源优化配置理论为指导，从宏观经济角度，以翔实的数据和确凿的论据，论述了近期邮电人才结构存在的弊端。深入论证了如何科学调整邮电人才结构的策略