The population genetics of ecological specialization in evolving Escherichia coli populations

When organisms adapt genetically to one environment, they may lose fitness in other environments. Two distinct population genetic processes can produce ecological specialization-mutation accumulation and antagonistic pleiotropy. In mutation accumulation, mutations become fixed by genetic drift in genes that are not maintained by selection; adaptation to one environment and loss of adaptation to another are caused by different mutations. Antagonistic pleiotropy arises from trade-offs, such that the same mutations that are beneficial in one environment are detrimental in another. In general, it is difficult to distinguish between these processes. We analysed the decay of unused catabolic functions in 12 lines of Escherichia coli propagated on glucose for 20,000 generations. During that time, several lines evolved high mutation rates. If mutation accumulation is important, their unused functions should decay more than the other lines, but no significant difference was observed. Moreover, most catabolic losses occurred early in the experiment when beneficial mutations were being rapidly fixed, a pattern predicted by antagonistic pleiotropy. Thus, antagonistic pleiotropy appears more important than mutation accumulation for the decay of unused catabolic functions in these populations.     

Divergent sexual selection enhances reproductive isolation in sticklebacks

Sexual selection may facilitate speciation because it can cause rapid evolutionary diversification of male mating signals and female preferences. Divergence in these traits can then contribute to reproductive isolation. The sensory drive hypothesis predicts that three mechanisms underlie divergence in sexually selected traits: (1) habitat-specific transmission of male signals; (2) adaptation of female perceptual sensitivity to local ecological conditions; and (3) matching of male signals to female perceptual sensitivity. I test these mechanisms in threespine sticklebacks (Gasterosteus spp.) that live in different light environments. Here I show that female perceptual sensitivity to red light varies with the extent of redshift in the light environment, and contributes to divergent preferences. Male nuptial colour varies with environment and is tuned to female perceptual sensitivity. The extent of divergence among populations in both male signal colour and female preference for red is correlated with the extent of reproductive isolation in these recently diverged species. These results demonstrate that divergent sexual selection generated by sensory drive contributes to speciation.     

The evolution of reproductive isolation through sexual conflict

Classical population-genetics theory suggests that reproductive isolation will evolve fastest in small isolated populations. In contrast, recent theory suggests that divergence should occur fastest in larger allopatric populations. The rationale behind this is that sexual conflict, potentially the strongest driver of speciation, is greater in larger, higher-density populations. This idea is highly controversial and has little experimental support. Here we show, using replicate fly populations with varying levels of sexual conflict, that larger, more dense populations with more sexual conflict diverged to a greater degree than small populations with relaxed conflict. This result strongly suggests that speciation can occur rapidly in large populations through increased sexual conflict.     

Genetic linkage between X-chromosome markers and bipolar affective illness

A pedigree study shows close linkage of bipolar affective illness (manic depression) to the X-chromosome markers colour blindness and glucose-6-phosphate dehydrogenase deficiency. The maximum lod score ranges from 7.52 (assuming homogeneity) to 9.17 (assuming heterogeneity); that is, the odds in favour of linkage range between 3 X 10(7) to 1 and 10(9) to 1. These results provide confirmation that a major psychiatric disorder can be caused by a single genetic defect. As a possible first step in characterizing the primary genetic abnormality, this finding may have important implications for the aetiology, nosology, pathophysiology and, possibly, prevention and treatment of bipolar affective disorder. It also provides a means for identifying and characterizing homogeneous populations of patients and may help in clarifying aetiological heterogeneity.     

Host-plant adaptation drives the parallel evolution of reproductive isolation

Parallel evolution of similar traits in independent populations that inhabit ecologically similar environments strongly implicates natural selection as the cause of evolution. Parallel speciation is a special form of parallel evolution where traits that determine reproductive isolation evolve repeatedly, in closely related populations, as by-products of adaptation to ecological conditions. The outcome of such parallel evolution is that ecologically divergent pairs of populations exhibit greater levels of reproductive isolation than ecologically similar pairs of populations of a similar or younger age. The parallel evolution of reproductive isolation provides strong evidence for natural selection in the process of speciation, but only one conclusive example from nature is known. Populations of the walking-stick insect Timema cristinae that use different host-plant species have diverged in body size and shape, host preference, behaviour and the relative frequency of two highly cryptic colour-pattern morphs. Here we report that divergent selection for host adaptation, and not genetic drift, has promoted the parallel evolution of sexual isolation in this species. Our findings represent a clear demonstration that host-plant adaptation can play a crucial and repeatable role in the early stages of speciation.     

Genetic selection for reproductive photoresponsiveness in deer mice

Seasonal breeding is common in mammals, particularly in habitats outside the tropics. Climate and availability of food are the ultimate factors that usually dictate the optimal time of year for a mammal to breed; however, day length (photoperiod) often serves as the proximal cue to signal the onset or cessation of seasonal reproduction. Some individuals in some populations of deer mice are reproductively responsive to photoperiod, while other individuals in the same population are not. As shown here, selection can dramatically alter the frequency of photoresponsiveness in a laboratory population in only two generations. To our knowledge this is the first demonstration of selection for reproductive photoresponsiveness in any mammal. By implication, some wild populations of deer mice must use multiple, genetic-based reproductive strategies, and the degree to which each such strategy is exhibited must be subject to rapid change in response to both seasonally and momentarily changing climatic and dietary conditions.     

Genetic cost of reproductive assurance in a self-fertilizing plant

The transition from outcrossing to self-fertilization is one of the most common evolutionary trends in plants. Reproductive assurance, where self-fertilization ensures seed production when pollinators and/or potential mates are scarce, is the most long-standing and most widely accepted explanation for the evolution of selfing, but there have been few experimental tests of this hypothesis. Moreover, many apparently adaptive floral mechanisms that ensure the autonomous production of selfed seed might use ovules that would have otherwise been outcrossed. This seed discounting is costly if selfed offspring are less viable than their outcrossed counterparts, as often happens. The fertility benefit of reproductive assurance has never been examined in the light of seed discounting. Here we combine experimental measures of reproductive assurance with marker-gene estimates of self-fertilization, seed discounting and inbreeding depression to show that, during 2 years in 10 Ontario populations of Aquilegia canadensis (Ranunculaceae), reproductive assurance through self-fertilization increases seed production, but this benefit is greatly outweighed by severe seed discounting and inbreeding depression.     

Microorganisms associated with chromosome destruction and reproductive isolation between two insect species

Microorganisms have been implicated in causing cytoplasmic incompatibility in a variety of insect species, including mosquitoes, fruitflies, beetles and wasps. The effect is typically unidirectional: incompatible crosses produce no progeny or sterile males, whereas the reciprocal crosses produce normal progeny. The parasitic wasp Nasonia vitripennis is one of the few species in which the cytogenetic mechanism of incompatibility is known. In this species the paternal chromosome set forms a tangled mass in a fertilized egg and is eventually lost. Here we report that cytoplasmic microorganisms are associated with complete bidirectional incompatibility between N. vitripennis and a closely related sympatric species, N. giraulti. Microorganisms can be seen in the eggs of both species. Hybrid offspring are normally not produced in crosses between the two species, but do occur after elimination of the microorganisms by antibiotic treatment. A cytogenetic and genetic study shows that bidirectional interspecific incompatibility is due to improper condensation of the paternal chromosomes. Microorganism-mediated reproductive isolation is of interest because it could provide a rapid mode of speciation. The mechanism of incompatibility in Nasonia is also of interest as a potential tool for studying chromosome imprinting and chromosome condensation.     

Genetic linkage of Werner's syndrome to five markers on chromosome 8.

Werner's syndrome (WS) is a rare autosomal recessive disease in which the affected individuals display symptoms of premature ageing. The substantial phenotypic overlap between WS and normal ageing indicates that these two conditions may have pathogenetic mechanisms in common. The WS mutation has pleiotropic effects, and patients and their cells show many differences compared with normals. Despite extensive study of the clinical and biochemical features of this disorder, the primary genetic defect remains unknown. We have undertaken a genetic linkage study in an effort to identify the locus of the primary defect. Here we report close genetic linkage of the WS mutation to a group of markers on chromosome 8.     

Genetic linkage of bilateral acoustic neurofibromatosis to a DNA marker on chromosome 22

Bilateral acoustic neurofibromatosis (BANF) is a severe autosomal dominant disorder involving development of multiple tumours of the nervous system including meningiomas, gliomas, neurofibromas and particularly bilateral acoustic neuromas. We have used genetic linkage analysis with DNA markers to establish that the defective gene causing BANF is on chromosome 22, and is therefore distinct from the gene for the von Recklinghausen form of neurofibromatosis, which maps to chromosome 17. Linked DNA markers will be particularly valuable in BANF, facilitating early detection of tumours and thereby permitting more effective surgical intervention. In view of the reported loss of genes on chromosome 22 in meningiomas and acoustic neuromas, the genetic localization of the primary BANF defect strongly supports the concept that the disease locus encodes a 'tumour suppressor' gene. Isolation of this gene should provide insights into the pathogenesis of acoustic neuromas and other nervous system tumours, as well as into the control of proliferation and differentiation of neural crest cells.     

蚜虫次级内共生菌的多样性和功能

内共生菌与其寄主之间的关系一直都是生物学研究的热点。蚜虫类昆虫的内共生菌分为初级内共生菌(Buchnera)和一些次级内共生菌。Buchnera与蚜虫寄主之间有密切的营养共生关系,对蚜虫寄主的生长发育至关重要。虽然次级内共生菌在蚜虫体内含量相对较少,但是随着研究的不断深入,次级内共生菌无论对蚜虫寄主的生态行为(抵御寄生蜂、耐高温特性、体色形成等)还是物种形成和进化的影响都不容忽视。此外,次级内共生菌基因组序列的测定,也促进了功能基因学的发展。在系统梳理已发表文献的基础上,本文主要综述了蚜虫次级内共生菌的基本特征、多样性、及其对蚜虫寄主的生态影响,进而对未来值得关注的问题进行了展望。     

对高校管理专业化的思考

我国新时期高等教育具有教学内容新且变化快、规模大、学科之间互相 融通、信息量大等特点。面对这种新的特点和管理内容的要求，高等学校的管理者应该具备高度的责任感和事业心、较高的素质、管理能力和优化的知识结构等条件，这些条件也要求高校管理应该专业化。     

油田环保工作的产业化专业化研究

环保产业被誉为朝阳产业和新的经济增长点,是环境保护的重要物质基础和技术保障,环保产业包括环保产品的生产与经营、资源综合利用、环境服务三大领域。论述了油田污染治理工作存在的问题及发展环保产业和推行专业化管理对提高污染治理水平的重要意义。     

基于NSGA-Ⅱ的层间隔震体系参数优化与能量响应分析

基于层间隔震体系两质点简化模型,建立了以基底剪力最小为优化目标的参数优化方法,采用NSGA-Ⅱ优化得到层间隔震体系在不同质量比下的最优频率比和最优阻尼比;建立了体系的能量和功率方程,从能量和功率角度分别分析了不同质量比下的层间隔震结构最优参数模型能量的传递、耗散和转化关系以及机理表现。     

西安市生态足迹和生态承载力动态测度分析

目的对西安市可持续发展状况进行定量评价。方法运用以生态足迹、生态承载力为理论基础测度生态赤字的一种生物物理学方法。结果西安市1997—2005年的人均生态足迹从1997年的0.8542hm2增加到2005年的1.7575hm2,表明生态承载力的供给不能满足生态足迹的需求,得出西安市9年来生态赤字由0.528hm2增加到1.4671hm2,表明西安市的发展已经处于一种不可持续状态。结论分析西安市发展不可持续的原因,提出实现可持续发展应从降低生态足迹和提高生态承载力入手的对策。     

湘西北奶牛繁殖性能与繁殖疾病调查

为了了解湘西北地区奶牛繁殖状况与繁殖性能,对常德地区某大型奶牛场700余头奶牛2017～2019年间的整体繁殖状况以及繁殖相关疾病进行调查,分析比较年度、月份、季节等因素对受胎率、产犊率等繁殖指标的影响.结果表明:该奶牛养殖场年平均受胎率、繁殖率分别为87.92％和83.26％;第一情期授胎率为47.37％,低于国内其...