生物的竞争与适应

竞争和适应是生物生存过程中的两个现象。竞争是种内或种间争夺有限共同资源产生的,是一种生存斗争,整体来说是不利的。适应是通过本身的变化使其能在环境中更好地生存或保存自己,对生物来说是有利的。探讨物种竞争和适应的形式、特点等,对于生物多样性保护具有重要的意义。     

细菌群体的异质性

发生在由一祖先细胞形成的菌悬液、菌落或生物膜中的细菌群体异质性,可以使群体在面临多种胁迫环境时,通过各亚群间的协同作用生存下去。这种分化不仅有表型差异,而且还通过细胞间的遗传物质交换和细胞内的自发突变在群体水平上产生遗传差异。细菌群体的这种异质性分化可能是细菌适应环境的的根本源泉。     

Cell:科学家发现可以产生HIV高亲和力抗体的方法

<正>B细胞是人体在生理状态下唯一可以发生体细胞高频突变的场所,而这一过程正是B细胞产生高效抗体的过程。近日,科学家通过在硅载体上的研究发现了可以产生HIV高亲和力抗体的方法。相关研究结果发表于国际生命科学顶尖杂志Cell上。抗体是由成熟的B细胞或记忆性B细胞分化成浆细胞后分泌产生的免疫球蛋白,可以特异性地结合相应的抗原。亲和力成熟是指浆细胞内     

Leptin基因多态性与绵羊季节性发情的相关分析

根据leptin基因在GenBank中的已知序列设计两对引物,采用PCR-SSCP技术在常年发情的湖羊和季节性发情的阿勒泰羊群体中进行单核苷酸多态性(SNPs)检测,对筛查到的SNP位点进行基因型与绵羊季节性发情的关联分析。结果表明,与湖羊相比,阿勒泰羊leptin基因第1内含子上有3个连续碱基TTG的插入和C/T碱基突变;第3外显子3上发生G/T碱基突变,编码氨基酸由缬氨酸变成亮氨酸。Leptin外显子2扩增片段上检测到AA、AB、BB三种基因型,BB基因型在阿勒泰羊群体中属于优势基因型;对两个群体进行基因型频率独立性χ2检验,差异极显著(P0.001),说明BB基因型是影响季节性发情的有利基因型。研究结果提示,绵羊品种中Leptin基因序列的差异性可能是造成绵羊季节性发情的原因之一,可作为常年发情绵羊品种选育的辅助标记。     

作物群体边际效应规律及其应用

对作物边际效应的研究表明,有利生态因子的作用大于不利生态因子的作用时,作物群体发生正边际效应,表现为边际优势;不利生态因子的作用大于有利生态因子的作用时,作物群体发生负边际效应,表现为边际劣势．在作物群体内部条件一致的情况下,边际效应的绝对值随边距递增而递减．     

鲸类低氧耐受的分子机制初探:基于HIF1α和TSC1基因的生物信息学分析

鲸类（Cetacea）具有超强潜水能力,长时间潜水造成的体内低氧是其适应完全水生生活面临的挑战之一。为了克服体内低氧环境,鲸类产生了一系列低氧耐受相关的解剖和生理等方面的适应特征,然而这一适应的分子机制仍不清楚。本研究选择在细胞感知和适应内环境氧分压变化的过程中发挥重要作用的低氧诱导因子（Hypoxia-inducible factor 1α,HIF1α）和低氧环境下抑制能量代谢的结节性复合物1（Tuberous sclerosis complex 1,TSC1）基因为候选基因,选择压力检测发现鲸类TSC1基因的6个正选择位点至少被两种最大似然法（Maximum Likelihood,ML）检测到,且通过与陆生哺乳动物同源序列比较分析,鲸类鉴定出7个特异的氨基酸突变。这些正选择和特异突变位点有30.77%（4/13）发生了激进氨基酸性质改变,且正选择位点位于重要结构域附近。正选择信号主要集中在鲸类内部各支系中,提示鲸类为了适应低氧环境,这两个基因可能发生了功能改变,以保护细胞免受低氧损伤。我们在低氧耐受不同类群间共检测到66个平行/趋同进化位点,为低氧耐受不同类群的趋同的低氧适应提供了分子证据。     

鸽黑素皮质素受体3、4(MC3R、MC4R)基因多态性与生长性状的相关分析

利用PCR-SSCP技术和DNA测序方法检测广东石岐肉鸽和哈尔滨地区灰色家鸽MC3R和MC4R基因部分编码区序列的单核苷酸多态性, 分析了MC3R基因T91G突变位点和MC4R基因A903G突变位点导致的基因型与两群体鸽生长和体组成性状的关系。结果表明, 这两个多态位点所导致的基因型对石岐肉鸽活重、屠体重、全净膛重均有显著影响(P<0.05); 另外, 利用这两个突变位点所产生的合并基因型在鸽群体中与生长和体组成性状作最小二乘分析, 结果表明, 两位点合并后的基因型对全净膛重影响显著(P<0.05)。多重比较结果表明, BBAA型全净膛重显著大于AABB型, BBAA型对于体重增长是有利基因型。     

野兔与家兔

野兔一般指兔属、粗毛兔属和岩兔属中的部分种类。野兔能适应许多不同的环境,只要有足够的青草,就可以在从极地到赤道的各种地方生存。一般生活在热带的野兔毛比较短,耳朵更大：寒带生活的野兔毛长而厚密,耳朵比较短。因为一般兔子的被毛较浓密,汗腺很少,故散热的主要途径是呼吸。当外界温度升高时,兔子通过增加呼吸次数,呼出气体蒸发水分散热,同时,长而大的耳朵也能起到协助散热的作用。兔子的排尿机制属浓缩性,对水分的需求比其他动物少。有些野免只靠草上的露水就可以生存,故很少看到兔子到河边喝水。     

GHR基因第10外显子与塞北兔生长发育性能相关性研究

本研究利用单链构象多态性(SSCP)和测序技术,对塞北兔群体GHR基因第10外显子进行多态性研究,并与生长发育性能进行关联性分析。结果发现:有两处点突变,214处为同义突变,均编码苯丙氨酸;AB基因型在255处出现A位点的缺失,引起移码突变;塞北兔整个群体呈现哈代-温伯格平衡状态,但母兔群体不平衡;AA基因型比AB基因型对塞北兔活体重,胴体重,前腿重均有提高,差异显著(p0.05)。表明:母兔群体在育种过程中受到人工选择而引起遗传漂变,AA基因型为有利基因型,因此可作为影响塞北兔生长性状的主效候选基因,进行早期辅助选择。     

适应性突变中的DNA重组事件

适应性突变 (ａｄａｐｔｉｖｅｍｕｔａｔｉｏｎ)或定向突变 (ｄｉｒｅｃｔｅｄｍｕｔａｔｉｏｎ)最先是指大肠杆菌 (Ｅｓｃｈｅｒｉｃｈｉａｃｏｌｉ)ｌａｃ-突变细胞在以乳糖为唯一碳源的培养基上 ,随选择时间延长ｌａｃ 回复子数量不断增加的现象 .由于当时认为ｌａｃ 回复子仅在乳糖存在的情况下才发生 ,且没有发现其他同选择无关的突变 ,因此猜测细菌具有针对选择环境定向地发生有利突变的能力 .后来的研究结果表明 ,在乳糖选择条件下 ,回复突变细胞除产生ｌａｃ 突变外 ,还产生与乳糖利用无关的突变 ,因此 ,突变并不是定向的 ,现又…     

A numerical method for calculating moments of coalescent times in finite populations with selection

A numerical method is developed for solving a nonstandard singular system of second-order differential equations arising from a problem in population genetics concerning the coalescent process for a sample from a population undergoing selection. The nonstandard feature of the system is that there are terms in the equations that approach infinity as one approaches the boundary. The numerical recipe is patterned after the LU decomposition for tridiagonal matrices. Although there is no analytic proof that this method leads to the correct solution, various examples are presented that suggest that the method works. This method allows one to calculate the expected number of segregating sites in a random sample of n genes from a population whose evolution is described by a model which is not selectively neutral.     

Screening differentially expressed cDNA clones obtained by differential display using amplified RNA.

The major obstacle of differential display is not the technique itself but rather the post-differential display issueof discriminating between false positives and the truly differentially expressed mRNAs. This process is arduous and requires large amounts of RNA. We present and validate a method which allows one to screen putative positives from differential display analysis using only micrograms of total RNA. More importantly, we demonstrate that cDNA probes generated from amplified RNA are representative of the starting mRNA population and can be used for differential screening of mRNA species at a detectable limit of sensitivity of>/=1/40 000.     

A note on modelling the dynamics of budding yeast populations using branching processes

A multitype branching process is proposed as a model for the behaviour of populations of the budding yeast Saccharomyces Cerevisiae. Using the idea of branching processes counted by random characteristics, we are able to obtain explicit expressions describing different aspects of the asymptotic composition of such populations. The main purpose of this note is to show that the branching process approach is an alternative to deterministic population models based on differential equation methods.Supported by the Swedish Natural Science Research Council     

Trait Substitution Sequence process and Canonical Equation for age-structured populations

We are interested in a stochastic model of trait and age-structured population undergoing mutation and selection. We start with a continuous time, discrete individual-centered population process. Taking the large population and rare mutations limits under a well-chosen time-scale separation condition, we obtain a jump process that generalizes the Trait Substitution Sequence process describing Adaptive Dynamics for populations without age structure. Under the additional assumption of small mutations, we derive an age-dependent ordinary differential equation that extends the Canonical Equation. These evolutionary approximations have never been introduced to our knowledge. They are based on ecological phenomena represented by PDEs that generalize the Gurtin–McCamy equation in Demography. Another particularity is that they involve an establishment probability, describing the probability of invasion of the resident population by the mutant one, that cannot always be computed explicitly. Examples illustrate how adding an age-structure enrich the modelling of structured population by including life history features such as senescence. In the cases considered, we establish the evolutionary approximations and study their long time behavior and the nature of their evolutionary singularities when computation is tractable. Numerical procedures and simulations are carried.      

A study of some diffusion models of population growth

The stochastic differential equations of many diffusion processes which arise in studies of population growth in random environments can be transformed, if the Stratonovich stochastic calculus is employed, to the equation of the Wiener process. If the transformation function has certain properties then the transition probability density function and quantities relating to the time to first attain a given population size can be obtained from the known results for the Wiener process. Some other random growth processes can be derived from the Ornstein-Uhlenbeck process. These transformation methods are applied to the random processes of Malthusian growth, Pearl-Verhulst logistic growth and a recent model of density independent growth due to Levins.     

A stochastic model of a cell population with quiescence

A cell population in which cells are allowed to enter a quiescent (nonproliferating) phase is analyzed using a stochastic approach. A general branching process is used to model the population which, under very mild conditions, exhibits balanced exponential growth. A formula is given for the asymptotic fraction of quiescent cells, and a numerical example illustrates how convergence toward the asymptotic fraction exhibits a typical oscillatory pattern. The model is compared with deterministic models based on semigroup analysis of systems of differential equations.     

A stochastic model of a cell population with quiescence

A cell population in which cells are allowed to enter a quiescent (nonproliferating) phase is analyzed using a stochastic approach. A general branching process is used to model the population which, under very mild conditions, exhibits balanced exponential growth. A formula is given for the asymptotic fraction of quiescent cells, and a numerical example illustrates how convergence toward the asymptotic fraction exhibits a typical oscillatory pattern. The model is compared with deterministic models based on semigroup analysis of systems of differential equations.     

Traveling wave solutions of a nonlinear reaction–advection equation

 We establish the existence of traveling wave solutions for a nonlinear partial differential equation that models a logistically growing population whose movement is governed by an advective process. Conditions are presented for which traveling wave solutions exist and for which they are stable to small semi-finite domain perturbations. The wave is of mathematical interest because its behavior is determined by a singular differential equation and those with small speed of propagation steepen into a shock-like solutions. Finally, we indicate that the smoothing presence of diffusion allows wave persistence when an advective slow moving wave may collapse. Received: 24 November 1997 / Revised version: 13 July 1998     

Population regulation of territorial species: both site dependence and interference mechanisms matter

Spatial patterns of site occupancy are commonly driven by habitat heterogeneity and are thought to shape population dynamics through a site-dependent regulatory mechanism. When examining this, however, most studies have only focused on a single vital rate (reproduction), and little is known about how space effectively contributes to the regulation of population dynamics. We investigated the underlying mechanisms driving density-dependent processes in vital rates in a Mauritius kestrel population where almost every individual was monitored. Different mechanisms acted on different vital rates, with breeding success regulated by site dependence (differential use of space) and juvenile survival by interference (density-dependent competition for resources). Although territorial species are frequently assumed to be regulated through site dependence, we show that interference was the key regulatory mechanism in this population. Our integrated approach demonstrates that the presence of spatial processes regarding one trait does not mean that they necessarily play an important role in regulating population growth, and demonstrates the complexity of the regulatory process.     

A model of proliferating cell populations with inherited cycle length

A mathematical model of cell population growth introduced by J. L. Lebowitz and S. I. Rubinow is analyzed. Individual cells are distinguished by age and cell cycle length. The cell cycle length is viewed as an inherited property determined at birth. The density of the population satisfies a first order linear partial differential equation with initial and boundary conditions. The boundary condition models the process of cell division of mother cells and the inheritance of cycle length by daughter cells. The mathematical analysis of the model employs the theory of operator semigroups and the spectral theory of linear operators. It is proved that the solutions exhibit the property of asynchronous exponential growth.