A general approach for the study of a population of testcross progenies and consequences for recurrent selection

Summary A model to study genetic effects at the level of a population of testcross progenies is presented. As there is no dominance for the testcross value, with the restriction of epistasis to pairs of loci, only additive x additive epistasis can contribute to the variance among progenies. To estimate the variance among progenies due to epistasis, it is necessary to have the population structured in families of full sibs, half sibs or S₁, with only a few plants per family tested in combination with the tester. Using a two-way mating design to produce the families, it is possible to estimate the variance due to additive x additive epistasis. The consequence of the presence of epistasis is studied at the level of recurrent selection for combining ability with the tester. It seems that epistasis itself does not change the efficiency of the breeding methods considered. However, when the population from intercrossing is structured in families, it could be efficient to use a combined selection when the heritability is very low. In this case it would be efficient to produce full-sib families (by single-pair matings) at the level of intercrossing. The best procedure is to produce such families at the same time as crossing with the tester. In comparison to the classical scheme of selection for combining ability with a tester, such a modification increases the efficiency of selection 41.1% if an off-season generation can be used.     

Selection response and efficiency of doubled-haploid recurrent selection in a cross-fertilized species

Summary Computer simulation was used to compare the simulated response to doubled-haploid (DH) mass selection with the response predicted by mathematical formulae. The efficiency of DH versus diploid mass selection in a cross-fertilized species was also studied by means of theoretical consideration and computer simulation. Simulated gain was in agreement with the predicted gain in the DH population under both additive and complete dominance models. The simulated variance of response to DH mass selection was close to the predicted variance at both the 5% and 25% selection regimes under additive and complete dominance models. The efficiency of DH over diploid mass selection was shown to be dependent upon the allelic frequency, the degree of dominance, and the amount of environmental variance. In theory the efficiency can range from zero to infinity, but in reality it should be greater than one. The efficiency ranges from 2 to 2 in the absence of dominance; it can be greater than two only in the presence of dominance and a small environmental variance. The variance of response to DH mass selection can be smaller than or up to twice as large as the variance of response to diploid mass selection. Computer simulation results agreed with the predicted efficiency of DH mass selection and with the predicted variance-of-response ratio of DH mass selection to diploid mass selection.Joint Contribution from the Charlottetown Research Station, contribution no. 604 and Department of Crop Science, University of Guelph     

Two-locus theory in recurrent selection for general combining ability in maize

Summary Two-locus theory for recurrent selection for general combining ability in maize was developed. The theory featured: (a) recombination of the selfed progeny of selected parents; and (b) linkage disequilibrium in the initial gametic array. The theory indicated: (a) that initial linkage disequilibrium exerts a permanent influence upon selection progress; (b) that interposition of one or more generations of random mating before each cycle reduces the permanent effect in ensuing cycles; and (c) that random mating done before initiation of selection is more efficient in removing the influence of linkage disequilibrium on selection progress than random mating done between subsequent cycles.     

基于层次分析法的旗舰物种遴选方法

旗舰物种是保护生物学中一个广泛应用的概念, 用于获得公众对保护行为的支持, 在生物多样性保护领域发挥着重要作用。但目前尚未见量化分析遴选和确定旗舰物种的公开报道, 致使学术界对旗舰物种的定义和使用相对主观, 缺乏科学依据。本文对旗舰物种的定义进行了梳理, 探讨了旗舰物种的内涵, 确定了旗舰物种的属性, 制定了遴选标准和量化遴选方法, 以便读者更好地理解和运用这一概念。目前旗舰物种的定义仍然局限在其社会学属性, 作者建议今后应加强其生物生态学属性。作者认为除了公众的关注度和认可度之外, 旗舰物种还应具备以下3个生态生物学和社会文化特征: (1)物种在当地的濒危程度及生存现状; (2)物种在当地生态系统中的重要性; (3)物种在当地民众中的影响力和认可度。基于此, 本文确定了表征旗舰物种社会文化属性和生态生物学属性的8个要素, 基于层次分析法提出了一种量化的旗舰物种遴选方法。该方法综合上述8个要素进行评判和计算分值, 以塔吉克斯坦境内分布的14种大型濒危哺乳动物的生态生物学属性和社会文化影响力为基础, 描述基于层次分析法遴选塔吉克斯坦哺乳类旗舰物种的方法和过程, 最终依据每个备选物种所得分值高低排序, 得到塔吉克斯坦旗舰物种的优先备选物种。本文首次提出了一种量化遴选旗舰物种的方法, 期望今后可基于该方法开发更加合理的旗舰物种遴选模型和算法。     

小麦新品种皖麦17选育的理论与实践

本文对一个高产小麦新品种选育实践进行了剖析。结果表明：在Ｆ１按杂种的综合性状进行指数估算,然后把指数当作一个性状,估算各组合的杂种优势和配合力,并以此评判组合,可以增加对组合认识的预见性。再根据单株表现分别种植,可以在Ｆ３形成系统群。Ｆ２株系间则可表现出遗传差异,结合测产选择单株,并以对照单株综合指数为标准,再把高产组合作为选择（株行或单株）重点,可提高杂种的选择效率。Ｆ３以后一边鉴定株系,一边继续单株选择,可使品系纯化和提高同步深化。Ｆ６以后继续优中选优仍然能使增效基因积累。     

Genome‐wide selection components analysis in a fish with male pregnancy

A major goal of evolutionary biology is to identify the genome‐level targets of natural and sexual selection. With the advent of next‐generation sequencing, whole‐genome selection components analysis provides a promising avenue in the search for loci affected by selection in nature. Here, we implement a genome‐wide selection components analysis in the sex role reversed Gulf pipefish, Syngnathus scovelli. Our approach involves a double‐digest restriction‐site associated DNA sequencing (ddRAD‐seq) technique, applied to adult females, nonpregnant males, pregnant males, and their offspring. An F_ST comparison of allele frequencies among these groups reveals 47 genomic regions putatively experiencing sexual selection, as well as 468 regions showing a signature of differential viability selection between males and females. A complementary likelihood ratio test identifies similar patterns in the data as the F_ST analysis. Sexual selection and viability selection both tend to favor the rare alleles in the population. Ultimately, we conclude that genome‐wide selection components analysis can be a useful tool to complement other approaches in the effort to pinpoint genome‐level targets of selection in the wild.     

Host selection behavior of a thistle-feeding fly: choices and consequences

Summary Female Canada thistle seed flies (Orellia ruficauda) preferentially oviposit into seed heads which are a single day from opening. When flies are forced to oviposit into flower heads at other stages of development, offspring typically do slightly poorer: they attain a mature mass of about 15% less than do larvae derived from preferred hosts. Larval mass correlates strongly with reproductive success: heavy larvae develop into adults that produce eggs at a faster rate than do those developing from small larvae. After laying a clutch of eggs, flies circumscribe the rim of the flowerhead with their extended ovipositor and deposit a clear fluid. Flies reject previously-attacked hosts, bearing this apparent marking pheromone, significantly more often than they reject unattacked hosts. Costs of superparasitism in this system are relatively small, inasmuch as there is only a weak relationship between clutch size and larval success at the densities measured in this study. We speculate that flies are highly selective, when the apparent costs of making a mistake are rather low, because the information provided by phenological cues and by the putative marking pheromone is highly reliable, and low fecundity and time costs allow sufficient time to express a high level of discrimination.     

Lifetime selection on adult body size and components of body size in a waterstrider: opposing selection and maintenance of sexual size dimorphism

Abstract.— Sexual size dimorphism (SSD), the difference in body size between males and females, is common in almost all taxa of animals and is generally assumed to be adaptive. Although sexual selection and fecundity selection alone have often been invoked to explain the evolution of SSD, more recent views indicate that the sexes must experience different lifetime selection pressures for SSD to evolve and be maintained. We estimated selection acting on male and female adult body size (total length) and components of body size in the waterstrider Aquarius remigis during three phases of life history. Opposing selection pressures for overall body size occurred in separate episodes of fitness for females in both years and for males in one year. Specific components of body size were often the targets of the selection on overall body size. When net adult fitness was estimated by combining each individual's fitnesses from all episodes, we found stabilizing selection in both sexes. In addition, the net optimum overall body size of males was smaller than that of females. However, even when components of body size had experienced opposing selection pressures in individual episodes, no components appeared to be under lifetime stabilizing selection. This is the first evidence that contemporary selection in a natural population acts to maintain female size larger than male size, the most common pattern of SSD in nature.     

Additive main effect and multiplicative interaction model for a diallel-cross analysis

Diallel mating designs have proved informative in determining the inheritance of quantitative traits of interest to plant breeders. Apart from the well-established analyses of a complete diallel, the two-way factorial data structure of this design lends itself to analysis by the additive-main-effects-and-multiplicative-interaction (AMMI) model. This research article describes the joint application of the AMMI model and Griffing’s method 1, model I, to gain insight into the breeding value of inbred lines in a self-pollinated crop such as disomic, hexaploid bread wheat. Data from a multi-environment trial of a complete diallel cross between eight lines adapted to the East African highlands were analyzed to provide an example of this joint analysis. This combined approach identified not only the direction of a cross, i.e. which parent should be male or female, but also which crosses produce offspring showing F₁ heterosis. Received: 10 June 2000 / Accepted: 31 July 2000     

Habitat selection and potential fitness consequences of two early‐successional species with differing life‐history strategies

Habitat selection and its relationship to fitness is a fundamental concept in ecology, but the mechanisms driving this connection are complex and difficult to detect. Despite the difficulties in understanding such intricate relationships, it is imperative that we study habitat selection and its relationship with fitness. We compared habitat selection of least terns (Sternula antillarum) and piping plovers (Charadrius melodus) on the Missouri River (2012–2014) to examine the consequences of those choices on nest and chick survival. We hypothesized that plovers and terns would select habitat that minimized the chance of flooding and predation of eggs, chicks, and adults, but that plovers would also select habitat that would provide foraging habitat for their chicks. We developed an integrated habitat selection model that assessed selection across multiple scales (sandbar and nest scales) and directly modeled the effect of selection on nest and chick survival. In general, the species selected habitat in keeping with our hypotheses, such that predation and flooding, in particular, may have been reduced. Sandbar selection had either a negative or no appreciable effect on nest survival for both species across years. Nest‐site selection in 2012 had a generally positive effect on nest survival and chick survival for both terns and plovers, and this trended toward a negative effect by 2014. This result suggested that early selection decisions appeared to be adaptive, but we speculate that relatively high site fidelity and habitat degradation led to reduced benefit over time. Our results highlight the complex nature of habitat selection and its relationship to fitness.     

Phenotypic selection and response to selection in Lobularia maritima: importance of direct and correlational components of natural selection

By using selection differentials, gradients and structural equation modelling (SEM), I have quantified the phenotypic selection acting on Lobularia maritima (Cruciferae) flower size, display, colour and density, using data on lifetime female fitness. Furthermore, by analysing the resulting F₁ generation in field and greenhouse conditions, I estimated the actual intergenerational change in the value of these traits. Both pollinators preferred plants with many and large flowers. Strong directional selection for increased flower display was found in all years of the study, regardless of the technique used. Indirect selection due to a high significant correlation with flower display occurred on flower colour and size. SEM showed that pollinators played only a minor role in this observed phenotypic selection. The analysis of the phenotypes of F₁ plants showed that flower display actually increased across generations. In addition, white flowers were significantly more frequent in the offspring population than in the parental one, mostly due to the association between flower display and white coloured flowers. This suggests that both direct and indirect selection can play a role in the evolution of correlated traits in this crucifer.     

几个优良籼稻亲本品质性状的配合力和杂种优势分析

以3个不育系和10个恢复系为材料,采用NCII交配设计研究10个米质性状的配合力和杂种优势。结果表明：①大多数品质性状的量值介于双亲之间,除粒重表现一定的超亲优势、垩白度和粒宽表现一定的正向平均优势外,其他品质性状优势不明显。②杂种稻米的品质性状主要受不育系或恢复系的影响,其中粒长、粒宽和直链淀粉含量3个性状,不育系的影响要高于恢复系;而对于整精米率、粒重、垩白率、垩白度和糊化温度,则恢复系的影响要高于不育系。③就优质育种的利用价值而言,不育系以广占63-4S为好,恢复系以扬稻6号为好,R527、镇恢084次之,用上述亲本选配的杂交组合米质较好;恢复系特青、盐恢559表现为一般配合力效应低,特殊配合力方差小,优质育种利用价值不大。     

Comparing measures of breeding inequality and opportunity for selection with sexual selection on a quantitative character in bighorn rams

The reliability and consistency of the many measures proposed to quantify sexual selection have been questioned for decades. Realized selection on quantitative characters measured by the selection differential i was approximated by metrics based on variance in breeding success, using either the opportunity for sexual selection I_s or indices of inequality. There is no consensus about which metric best approximates realized selection on sexual characters. Recently, the opportunity for selection on character mean OSM was proposed to quantify the maximum potential selection on characters. Using 21 years of data on bighorn sheep (Ovis canadensis), we investigated the correlations between seven indices of inequality, I_s, OSM and i on horn length of males. Bighorn sheep are ideal for this comparison because they are highly polygynous and sexually dimorphic, ram horn length is under strong sexual selection, and we have detailed knowledge of individual breeding success. Different metrics provided conflicting information, potentially leading to spurious conclusions about selection patterns. I_δ, an index of breeding inequality, and, to a lesser extent, I_s showed the highest correlation with i on horn length, suggesting that these indices document breeding inequality in a selection context. OSM on horn length was strongly correlated with i, I_s and indices of inequality. By integrating information on both realized sexual selection and breeding inequality, OSM appeared to be the best proxy of sexual selection and may be best suited to explore its ecological bases.     

玉米重金属铅含量的配合力分析与育种对策

选择有代表性的12个玉米自交系,按Griffing4模式组配获得66个组合(F1),用温室盆栽,在3个Pb2+污染水平下对叶片和子粒Pb2+含量配合力和遗传参数进行分析。结果表明:玉米叶片和子粒的Pb2+含量一般配合力与特殊配合力差异均达到显著水平,非加性方差大于加性方差,遗传方差大于环境方差,广义遗传率大于狭义遗传率,该性状的变异主要来自遗传因素,遗传力较强。玉米种质筛选过程中,土壤Pb2+浓度在333.32 mg/kg以下,用亲本郑58组配的组合在筛选时不仅注重子粒Pb2+含量未超标而且要注重叶片Pb2+高富集,其主要是兼顾饲料和粮食安全的同时进行土壤Pb2+污染的生物修复;土壤Pb2+浓度高于715.46 mg/kg时,用亲本178组配的组合筛选应注意叶片和子粒低Pb2+积累的种质选育,对今后在不同Pb2+污染土壤中开展玉米品种筛选和规避污染育种策略的选择具有一定的指导意义。     

三个玉米合成群体选系的配合力及杂种优势分析

采用NCⅡ遗传交配设计,通过在黑龙江省哈尔滨和泰来的两点试验,以玉米自交系Mo17、B73、444和丹340为测验种,对从群体品综1号、中综3号和陕综5号选育的18份自交系进行配合力及杂种优势分析,以探讨群体选系在我国东北早熟玉米区的利用途径。结果表明,供试自交系间一般配合力存在较大差异;陕综5号群体选系HR14、HR17和HR15、中综3号选系HR9和HR8、品综1号选系HR4的一般配合力较高。在供试的72个组合中HR15×丹340、HR17×丹340、HR9×Mo17、HR14×丹340、HR7×B73、HR8×B73、HR6×444、HR5×丹340产量的特殊配合力及对照优势较高,表现出较高的利用潜力。依据特殊配合力及对照优势分析,中综3号选系与旅大红骨群、陕综5号选系与兰卡斯特群、品综1号选系与瑞德群遗传关系较近。结合育种实践,在我国北方早熟春玉米区陕综5号×旅大红骨、中综3号×瑞德或兰卡斯特、品综1号×旅大红骨或唐四平头可能组成较大利用潜力的杂种优势模式。     

Gametic models for multitrait selection schemes to study variance of response and drift under adverse genetic correlations

A major issue faced by breeders is how to effectively manage adverse correlations in breeding programs. We present results of a Monte Carlo allele-based simulation of the changes in response and variance of response under adverse genetic correlations by using the examples of two contrasting selection methods: the ‘Smith-Hazel’ selection index (SH) and independent culling (IC). We assumed several gene models, which included linkage and antagonistic pleiotropy as the primary drivers of adverse genetic correlations. The different behaviors of these selection methods allowed us to identify the mechanism behind the generation of uncertainty under antagonistic trait selection: IC had the properties of stabilizing selection, while SH behaved more similar to disruptive selection. Although SH outperformed IC in terms of genetic gain, this advantage happened at the cost of higher variance of response and loss of heterozygosity. Using an optimum selection algorithm (OS) to prevent the loss of heterozygosity through a constraint on inbreeding in SH/OS increased marginally the reliability, remaining still below that of IC under equal conditions. However, SH/OS had lower inbreeding (ΔF) than IC for equivalent levels of genetic gain, so a compromise between high selection reliability, low ΔF, and gain must be made by a breeder under antagonistic trait selection even with the use of optimization tools.     

A measure of sexual selection for interspecific comparisons of species with diversified mating systems and different mortality schedules

Based on variances in components of lifetime reproductive success (LRS), a new index of the intensity of sexual selection was proposed mainly useful for interspecific comparisons. The index was defined as the male to female ratio of the standardized variance in mating efficiency during mating period. The index can to a large extent exclude the effect from natural selection which commonly act on both sexes in mating period and also from mortality in pre-reproductive period. This empirical measure has some defects in the strict sense (i.e., dichotomy of natural and sexual selection), however, it enables interspecific comparisons of the intensity of sexual selection among different taxonomic groups of animals with various mating systems and mortality schedules.     

小麦蛋白质组分含量的配合力和遗传力分析

利用5个小麦亲本,按Griffing方法4组配一套完全双列杂交,研究小麦籽粒蛋白质组分的配合力和遗传力。结果表明,同一性状不同亲本的一般配合力效应和不同组合间的特殊配合力效应差异都较大。球蛋白、醇溶蛋白和谷蛋白含量的遗传主要受加性基因控制,清蛋白含量的遗传不存在加性基因作用,以显性基因作用为主。 Abstract：　A set of diallel crosses involving 5 wheat parents, according to the random model of Griffing Method 4, was made to study the combining ability and heritability of grain protein components in wheat. The results indicated that GCA effects of different parents for the same trait varied significantly. And SCA effects of different combination studied varied obviously. The inheritance of globulin, gliadin and glutenin contents were mainly controlled by additive genes. Dominant genes functioned mainly on albumin content without additive gene.     

Fluctuating selection and its (elusive) evolutionary consequences in a wild rodent population

Temporal fluctuations in the strength and direction of selection are often proposed as a mechanism that slows down evolution, both over geological and contemporary timescales. Both the prevalence of fluctuating selection and its relevance for evolutionary dynamics remain poorly understood however, especially on contemporary timescales: unbiased empirical estimates of variation in selection are scarce, and the question of how much of the variation in selection translates into variation in genetic change has largely been ignored. Using long‐term individual‐based data for a wild rodent population, we quantify the magnitude of fluctuating selection on body size. Subsequently, we estimate the evolutionary dynamics of size and test for a link between fluctuating selection and evolution. We show that, over the past 11 years, phenotypic selection on body size has fluctuated significantly. However, the strength and direction of genetic change have remained largely constant over the study period; that is, the rate of genetic change was similar in years where selection favoured heavier vs. lighter individuals. This result suggests that over shorter timescales, fluctuating selection does not necessarily translate into fluctuating evolution. Importantly however, individual‐based simulations show that the correlation between fluctuating selection and fluctuating evolution can be obscured by the effect of drift, and that substantially more data are required for a precise and accurate estimate of this correlation. We identify new challenges in measuring the coupling between selection and evolution, and provide methods and guidelines to overcome them.