Adaptation to slow environmental change, with apparent anticipation of selection

We investigate a genetic model of a large population of sexual organisms in a changing environment. The organisms are subject to stabilising selection on a quantitative trait, with environmental change causing the fitness optimum to move. When the fitness optimum moves slowly, adaptation to the changing environment occurs by means of reasonably well-separated substitutions at the loci controlling the trait. In this way, the trait generally tracks the moving optimum, but in such a case, the population may exhibit periods of time where the mean trait value overshoots the moving optimal trait value, thereby exhibiting an apparent anticipation of selection. The mechanism underlying this phenomenon is determined from consideration of a simpler model that correctly captures the observed dynamical behaviour. We note that very slow rates of changes of traits are seen in the fossil record and the present work may be relevant to this topic.     

The frequency of the perfect genotype in a population subject to pleiotropic mutation

We consider a large population of asexual organisms characterised by a number of quantitative traits that are subject to stabilising selection. Mutation is taken to act pleiotropically, with every mutation generally changing all of the traits under selection. We focus on the equilibrium distribution of the population, where mutation and selection are in balance. It has been previously established that the equilibrium distribution of genotypic effects may be anomalous, as it may contain a singular spike--a Dirac delta function--corresponding to a non-zero proportion of the population having exactly optimal genotypic values. In the present work, we present exact results for the case where three traits are under selection. These results give the equilibrium genetic variance of the population, and the proportion of the population that have the optimal genotype. This is achieved for two different spherically symmetric distributions of mutant effects. Additionally, a simple and robust numerical approach is also presented that allows the treatment of some other mutation distributions, where there are an arbitrary number of selected traits.     

The balance between pleiotropic mutation and selection,when alleles have discrete effects

The theory of pleiotropic mutation and selection is investigated and developed for a large population of asexual organisms. Members of the population are subject to stabilising selection on Omega phenotypic characters, which each independently affect fitness. Pleiotropy is incorporated into the model by allowing each mutation to simultaneously affect all characters. To expose differences with continuous-allele models, the characters are taken to originate from discrete-effect alleles and thus have discrete genotypic effects. Each character can take the values nxDelta where n=0,+/-1,+/-2, em leader, and the splitting in character effects, Delta, is a parameter of the model. When the distribution of mutant effects is normally distributed around the parental value, and Delta is large, a "stepwise" model of mutation arises, where only adjacent trait effects are accessible from a single mutation. The present work is primarily concerned with the opposite limit, where Delta is small and many different trait effects are accessible from a single mutation.In contrast to what has been established for continuous-effect models, discrete-effect models do not yield a singular equilibrium distribution of genotypic effects for any value of Omega. Instead, for different values of Omega, the equilibrium frequencies of trait values have very different dependencies on Delta. For Omega=1 and 2, decreasing Delta broadens the width of the frequency distribution and hence increases the equilibrium level of polymorphism. For all sufficiently large values of Omega, however, decreasing Delta decreases the width of the frequency distribution and the equilibrium level of polymorphism. The connection with continuous trait models follows when the limit Delta-->0 is considered, and a singular probability density of trait values is obtained for all sufficiently large Omega.     

作物分子标记辅助选择的研究进展、影响因素及其发展策略

随着分子标记技术及其检测手段的发展,开发和应用成本的降低,分子标记辅助选择(MAS)在作物育种上的应用优势日益明显。本文综述了近年来MAS在基因聚合、基因转移和数量性状改良上的研究进展。总结了MAS的影响因素,包括标记与基因间的距离、目标性状的遗传率、群体大小、所用分子标记的数目、类型和相位等。并提出育种和定位同步进行、选择合适分子标记类型和数量、简化DNA提取方法、背景选择的逐步选择法、确定合适选择方案等MAS发展策略。     

黄海车牛山岛白腰雨燕的繁殖习性及种群动态

本文为作者于1980—1981年对黄海车牛山岛白腰雨燕Apuspacificus pacificus (Latham)的初步研究。内容包括对繁殖习性的观察;对繁殖周期、卵孵化率、雏鸟成活串以及出生率等的统计。并对海岛生态环境下白腰雨燕种群数量的变动及其影响因素,作初步探讨。     

Is Fisher's model necessary for the theory of population improvement?

Summary It is shown here that genetic advance in one cycle of recurrent selection can be formulated directly in terms of covariances between relatives by application of the general statistical principle of linear prediction. For practical use of such formulae it is necessary to estimate the corresponding covariance between relatives from the mating design used. With General Combining Ability selection such estimation is direct. For other types of selection, it is necessary to derive associated covariances from other types of covariances but it is not necessary to use classical results of covariances between relatives in terms of genetic effects. Indeed, covariances can be derived without factorial decomposition of the genetic effects at one locus, i.e., without the concept of additivity and dominance. This approach allows a simple derivation of the genetic advance after n cycles of selection, followed by m generations of intercrossing, with a minimum of assumptions.     

人工投食行为对非人灵长类社会生态的影响

近年来,国内开展了对几种非人灵长类投食群的研究。借鉴日本猴(Macaca fuscata)、恒河猴(M.mulatta)和黑猩猩(Pan troglodytes)长期积累的研究经验,有利于我们减少人工投食对非人灵长类带来的不利影响,也有利于推动国内非人灵长类社会生态学的深入研究。本文通过比较这三种灵长类野生群和投食群之间的差异,量化地分析了人工投食对灵长类动物社会生态学方面的影响。结果表明在社会行为方面,人工投食会导致灵长类动物的聚集、增加争斗频率、改变个体间等级关系、延缓分群现象、影响活动域和增加新兴行为。在种群数量方面,人工投食会缩短雌性性成熟时间、增加出生率和婴猴存活率、减少成年猴死亡率。而人工投食对雄性性成熟、出生间隔等方面的影响仍需要进一步考证。最后我们讨论了人工投食行为的利弊,并建议应谨慎和妥善地实施人工投食,和对非人灵长类投食群进行合理的监管。     

Regional behaviour among late Neanderthal groups in Western Europe: A comparative assessment of late Middle Palaeolithic bifacial tool variability

Population dynamics between and within Pleistocene groups are vital to understanding wider behavioural processes like social transmission and cultural variation. The late Middle Palaeolithic (MIS 5d-3, ca. 115,000–35,000 BP [years before present]) permits a novel, data-driven assessment of these concepts through a unique record: bifacial tools made by classic Neanderthals. Previously, studies of late Middle Palaeolithic bifacial tools were hampered by a convoluted plethora of competing terms, types and regional entities. This paper presents a large-scale intercomparison of this tool type, and bridges typo-technological and spatio-temporal data from across Western Europe (Britain, Belgium, the Netherlands, France and Germany).     

Near-periodic substitution and the genetic variance induced by environmental change

We investigate a model that describes the evolution of a diploid sexual population in a changing environment. Individuals have discrete generations and are subject to selection on the phenotypic value of a quantitative trait, which is controlled by a finite number of bialleic loci. Environmental change is taken to lead to a uniformly changing optimal phenotypic value. The population continually adapts to the changing environment, by allelic substitution, at the loci controlling the trait. We investigate the detailed interrelation between the process of allelic substitution and the adaptation and variation of the population, via infinite population calculations and finite population simulations. We find a simple relation between the substitution rate and the rate of change of the optimal phenotypic value.     

植物数量性状基因定位研究概述

植物重要的性状多为数量性状。长期以来,人类一直寻求解释植物数量性状的遗传规律以便对其进行遗传操纵。现代分子生物技术的发展为植物数量性状基因的定位、分离等研究提供了条件。本文从数量性状基因座(QTL)作图群体类型及其特点,QTL定位方法,植物QTL研究现状,以及QTL精细定位、克隆、利用等方面进行了综述,并对今后植物QTL研究进行了展望。     

Wood mice (Apodemus sylvaticus L.) as pioneers of recolonization in a reclaimed area

A population of wood mice, Apodemus sylvaticus, was studied by live-trapping for 15 months in an area recently reclaimed from lignite open-mining, where the species is a pioneer of recolonization. Population dynamics, spacing behaviour and feeding habits were compared with data in the literature in order to investigate how these characteristics were affected by the peculiar habitat conditions and the special situation of early colonization. Population density was remarkably high with a peak of 86 individuals/ha in autumn and a low of 20 individuals/ha in late spring. The sex-ratio was always biased towards males except during periods of low density, when the ratio was close to unity. Individual body weights and the annual course of weight class distribution showed no distinct peculiarities, although body weight increased relatively slowly in late winter. Low juvenile survival, relatively low litter sizes and early termination of breeding were special features of the population. Furthermore, very few juveniles matured in the year of birth, and the best winter survival was found in mice born in the middle of the breeding season. Activity ranges were small compared with those given in the literature, and space use was similar in both sexes. As a direct effect of the habitat conditions, the diet was largely dominated by weed seeds. The possible reasons for and causal relations of these features are discussed.     

Simultaneous marker-assisted selection for multiple traits in autogamous crops

A method is presented for the selection of parents with the aim of obtaining improved genotypes in the progeny of a cross. The procedure is designed to select in several unrelated traits simultaneously and is based on the selection of molecular markers that are linked to QTLs. The method was compared with conventional phenotypic selection in simulation experiments for a number of genetic structures underlying the traits and several types of parental populations. Although the method in general provides good results, some of the underlying assumptions may be violated quite easily, thereby reducing the applicability of the procedure in practice. Received: 10 September 1999 / Accepted: 24 August 2000     

Moments,cumulants, and polygenic dynamics

A new approach for describing the evolution of polygenic traits subject to selection and mutation is presented. Differential equations for the change of cumulants of the allelic frequency distribution at a particular locus and for the cumulants of the distributions of genotypic and phenotypic values are derived. The derivation is based on the assumptions of random mating, no sex differences, absence of random drift, additive gene action, linkage equilibrium, and Hardy-Weinberg proportions. Cumulants are a set of parameters that, like moments, describe the shape of a probability density. Compared with moments, however, they have properties that make them a much more convenient tool for investigating polygenic traits. Applications to directional and stabilizing selection are given.     

Activity, structure and dynamics of the methanogenic archaeal community in a flooded Italian rice field

Methane production was studied in an Italian rice field over two consecutive years (1998, 1999) by measuring the rates of total and acetate-dependent methanogenesis in soil and root samples. Population dynamics of methanogens were followed by terminal restriction fragment length polymorphism and real-time PCR targeting archaeal SSU rRNA genes. Rates of total and acetate-dependent methanogenesis in soil increased during the season, reached a maximum at about 70-80 days after flooding and then decreased again. In contrast, the size of the archaeal community remained relatively constant. Therefore, the seasonal changes in the methanogenic processes were probably not caused by changes in the size of the methanogenic community but in its activity. During the 1998/1999 winter period, a slight decrease in archaeal cell numbers was found. In both years, the dominant groups were methanogens affiliated with Rice cluster I, Methanosaetaceae, Methanosarcinaceae and Methanobacteriaceae. Correspondence analysis showed, however, that the archaeal community structure was different in 1998 and 1999. Methanogens with potential acetoclastic activity made up a larger fraction of the total archaeal community in 1999 (32-53%) than in 1998 (20-32%). Furthermore, the frequency of Methanosaetaceae relative to Methanosarcinaceae was significantly higher in 1999 than in 1998. This difference could be explained by the much lower soil acetate concentrations in 1999, to which Methanosaetaceae are physiologically better adapted than Methanosarcinaceae. Over the season, however, the composition of the archaeal community remained relatively constant and thus did not reflect the observed seasonal change in CH(4) production activity. The analysis of rice root samples in 1999 showed that the archaeal community structure on the roots was similar to that in soil but with acetoclastic methanogens being relatively less common. This observation is in agreement with domination of CH(4) production by H(2)/CO(2)-dependent methanogenesis on roots. Our study provided a link between size, structure and function of the methanogenic community in an Italian rice field.     

Population dynamics with a stable efficient equilibrium

We propose a game-theoretic dynamics of a population of replicating individuals. It consists of two parts: the standard replicator one and a migration between two different habitats. We consider symmetric two-player games with two evolutionarily stable strategies: the efficient one in which the population is in a state with a maximal payoff and the risk-dominant one where players are averse to risk. We show that for a large range of parameters of our dynamics, even if the initial conditions in both habitats are in the basin of attraction of the risk-dominant equilibrium (with respect to the standard replication dynamics without migration), in the long run most individuals play the efficient strategy.     

Marker-assisted selection in autogamous RIL populations: a simulation study

 Molecular markers may enable plant breeders to select indirectly for genes affecting quantitative traits by selecting for molecular markers closely linked to these genes (marker-assisted selection, MAS). We have assessed the effectiveness of MAS compared to phenotypic selection. Key variables in this assessment were: trait heritability, selection intensity, genetic architecture and uncertainty in QTL mapping. Simulation studies showed that the application of MAS in autogamous crops, with the objective of obtaining transgressive genotypes, can improve selection results when compared to conventional selection procedures. Marker-assisted selection appears particularly promising when dominant alleles at quantitative trait loci are present and linked in coupling phase. Uncertainty in estimated QTL map positions reduces the benefits of marker-assisted selection, but this reduction remains limited in most cases. Received: 5 September 1997 / Accepted: 6 October 1997