Accuracy of genomic within-family selection in aquaculture breeding programmes

In aquaculture breeding programmes, selection within families cannot be applied for traits that cannot be recorded on the candidates (e.g., disease resistance or fillet quality). However, this problem can be overcome if genomic evaluation is used. Within-family genomic evaluation has been proposed for these programmes as large family sizes are available and substantial levels of linkage disequilibrium (LD) within families can be attained with a limited number of markers even in populations in global linkage equilibrium. Here, we compare by computer simulation: (i) within-family and population-wide LD; and (ii) the accuracy of within-family genomic selection when genomic evaluations are carried out either at the population level or within families. The population simulated was composed by a varying number of families of full-sibs (half for training and half for testing). The results indicate that, to practice within-family selection, performing the genomic evaluation separately for each family using only molecular information from the family could be recommended for populations either in linkage equilibrium or with a low level of disequilibrium.

The coefficient of dominance is not (always) estimable with biallelic markers

The genetic relationship among individuals at one locus is characterized by nine coefficients of identity. The coefficients of inbreeding, coancestry and dominance (or fraternity) are just linear functions of them. Here, it is shown how they can be estimated using biallelic and triallelic markers using the method of moments, and comparisons are made with other methods based on molecular coancestry or molecular covariance. It is concluded that in the general case of dominance and inbreeding with biallelic markers, only the coefficients of inbreeding and coancestry can be estimated, but neither the single coefficients of identity nor the coefficient of dominance can be estimated. More than two alleles are required for a full estimation as illustrated with the triallelic situation.

Uncovering QTL for resistance and survival time to Philasterides dicentrarchi in turbot (Scophthalmus maximus)

Disease resistance-related traits have received increasing importance in aquaculture breeding programs worldwide. Currently, genomic information offers new possibilities in breeding to address the improvement of this kind of traits. The turbot is one of the most promising European aquaculture species, and Philasterides dicentrarchi is a scuticociliate parasite causing fatal disease in farmed turbot. An appealing approach to fight against disease is to achieve a more robust broodstock, which could prevent or diminish the devastating effects of scuticociliatosis on farmed individuals. In the present study, a genome scan for quantitative trait loci (QTL) affecting resistance and survival time to P. dicentrarchi in four turbot families was carried out. The objectives were to identify QTL using different statistical approaches [linear regression (LR) and maximum likelihood (ML)] and to locate significantly associated markers for their application in genetic breeding strategies. Several genomic regions controlling resistance and survival time to P. dicentrarchi were detected. When analyzing each family separately, significant QTL for resistance were identified by the LR method in two linkage groups (LG1 and LG9) and for survival time in LG1, while the ML methodology identified QTL for resistance in LG9 and LG23 and for survival time in LG6 and LG23. The analysis of the total data set identified an additional significant QTL for resistance and survival time in LG3 with the LR method. Significant association between disease resistance-related traits and genotypes was detected for several markers, a single one explaining up to 22% of the phenotypic variance. Obtained results will be essential to identify candidate genes for resistance and to apply them in marker-assisted selection programs to improve turbot production.

Restricting inbreeding while maintaining selection response for weight gain in Mus musculus

An experiment with mice was designed to test the relative efficiency of three selection methods that help to minimize the rate of inbreeding during selection. A common house mice (Mus musculus) population was selected for 17 generations to increase the weight gain between 21 and 42 days. The population was split at random into three lines A, B and C where three selection methods were applied: individual selection and random mating, weighted selection with random mating and individual selection with minimum coancestry mating, respectively. There were three replicates for each line. Cumulated selection response was similar in the three lines, but there were differences in the level of inbreeding attained (in percentage): 31.24 (method A), 24.72 (method B) and 27.88 (method C). As consequence, lines B and C (weighted selection and minimum coancestry) showed a lower value of deterioration of fitness traits (the intrauterine mortality and the mortality at birth) than line A (random mating).

Accuracy of genome-wide evaluation for disease resistance in aquaculture breeding programs

Current aquaculture breeding programs aimed at improving resistance to diseases are based on challenge tests, where performance is recorded on sibs of candidates to selection, and on selection between families. Genome-wide evaluation (GWE) of breeding values offers new opportunities for using variation within families when dealing with such traits. However, up-to-date studies on GWE in aquaculture programs have only considered continuous traits. The objectives of this study were to extend GWE methodology, in particular the Bayes B method, to analyze dichotomous traits such as resistance to disease, and to quantify, through computer simulation, the accuracy of GWE for disease resistance in aquaculture sib-based programs, using the methodology developed. Two heritabilities (0.1 and 0.3) and 2 disease prevalences (0.1 and 0.5) were assumed in the simulations. We followed the threshold liability model, which assumes that there is an underlying variable (liability) with a continuous distribution and assumed a BayesB model for the liabilities. It was shown that the threshold liability model used fits very well with the BayesB model of GWE. The advantage of using the threshold model was clear when dealing with disease resistance dichotomous phenotypes, particularly under the conditions where linear models are less appropriate (low heritability and disease prevalence). In the testing set (where individuals are genotyped but not measured), the increase in accuracy for the simulated schemes when using the threshold model ranged from 4 (for heritability equal to 0.3 and prevalence equal to 0.5) to 16% (for heritability and prevalence equal to 0.1) when compared with the linear model.

Objectives, criteria and methods for using molecular genetic data in priority setting for conservation of animal genetic resources

The genetic diversity of the world's livestock populations is decreasing, both within and across breeds. A wide variety of factors has contributed to the loss, replacement or genetic dilution of many local breeds. Genetic variability within the more common commercial breeds has been greatly decreased by selectively intense breeding programmes. Conservation of livestock genetic variability is thus important, especially when considering possible future changes in production environments. The world has more than 7500 livestock breeds and conservation of all of them is not feasible. Therefore, prioritization is needed. The objective of this article is to review the state of the art in approaches for prioritization of breeds for conservation, particularly those approaches that consider molecular genetic information, and to identify any shortcomings that may restrict their application. The Weitzman method was among the first and most well-known approaches for utilization of molecular genetic information in conservation prioritization. This approach balances diversity and extinction probability to yield an objective measure of conservation potential. However, this approach was designed for decision making across species and measures diversity as distinctiveness. For livestock, prioritization will most commonly be performed among breeds within species, so alternatives that measure diversity as co-ancestry (i.e. also within-breed variability) have been proposed. Although these methods are technically sound, their application has generally been limited to research studies; most existing conservation programmes have effectively primarily based decisions on extinction risk. The development of user-friendly software incorporating these approaches may increase their rate of utilization.

Genetic diversity in farm animals--a review

Domestication of livestock species and a long history of migrations, selection and adaptation have created an enormous variety of breeds. Conservation of these genetic resources relies on demographic characterization, recording of production environments and effective data management. In addition, molecular genetic studies allow a comparison of genetic diversity within and across breeds and a reconstruction of the history of breeds and ancestral populations. This has been summarized for cattle, yak, water buffalo, sheep, goats, camelids, pigs, horses, and chickens. Further progress is expected to benefit from advances in molecular technology.

A quantitative trait locus genome scan for porcine muscle fiber traits reveals overdominance and epistasis

Muscle histochemical characteristics are decisive determinants of meat quality. The relative percentage and diameters of the different muscular fiber types influence crucial aspects of meat such as color, tenderness, and ultimate pH. Despite its relevance, however, the information on muscle fiber genetic architecture is scant, because histochemical muscle characterization is a laborious task. Here we report a complete QTL scan of muscle fiber traits in 160 animals from a F(2) cross between Iberian and Landrace pigs using 139 markers. We identified 20 genome regions distributed along 15 porcine chromosomes (SSC1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and X) with direct and(or) epistatic effects. Epistasis was frequent and some interactions were highly significant. Chromosomes 10 and 11 seemed to behave as hubs; they harbored 2 individual QTL, but also 6 epistatic regions. Numerous individual QTL effects had cryptic alleles, with opposite effects to phenotypic pure breed differences. Many of the QTL identified here coincided with previous reports for these traits in the literature, and there was overlapping with potential candidate genes and previously reported meat quality QTL.

A new method to estimate relatedness from molecular markers

Four major problems can affect the efficiency of methods developed to estimate relatedness between individuals from information of molecular markers: (i) some of them are dependent on the knowledge of the true allelic frequencies in the base population; (ii) they assume that all loci are unlinked and in Hardy-Weinberg and linkage equilibrium; (iii) pairwise methods can lead to incongruous assignations because they take into account only two individuals at a time; (iv) most are usually constructed for particular structured populations (only consider a few relationship classes, e.g. full-sibs vs. unrelated). We have developed a new approach to estimate relatedness that is free from the above limitations. The method uses a 'blind search algorithm' (actually simulated annealing) to find the genealogy that yield a co-ancestry matrix with the highest correlation with the molecular co-ancestry matrix calculated using the markers. Thus (i and ii) it makes no direct assumptions about allelic frequencies or Hardy-Weinberg and linkage equilibrium; (iii) it always provide congruent relationships, as it considers all individuals at a time; (iv) degrees of relatedness can be as complex as desired just increasing the 'depth' (i.e. number of generations) of the proposed genealogies. Computer simulations have shown that the accuracy and robustness against genotyping errors of this new approach is comparable to that of other proposed methods in those particular situations they were developed for, but it is more flexible and can cope with more complex situations.

Sex ratio variation in Iberian pigs

Within the area of sex allocation, one of the topics that has attracted a lot of attention is the sex ratio problem. Fisher (1930) proposed that equal numbers of males and females have been promoted by natural selection and it has an adaptive significance. But the empirical success of Fisher's theory remains doubtful because a sex ratio of 0.50 is also expected from the chromosomal mechanism of sex determination. Another way of approaching the subject is to consider that Fisher's argument relies on the underlying assumption that offspring inherit their parent's tendency in biased sex ratio and therefore that genetic variance for this trait exists. Here, we analyzed sex ratio data of 56,807 piglets coming from 550 boars and 1893 dams. In addition to classical analysis of heterogeneity we performed analyses fitting linear and threshold animal models in a Bayesian framework using Gibbs sampling techniques. The marginal posterior mean of heritability was 2.63 x 10(-4) under the sire linear model and 9.17 x 10(-4) under the sire threshold model. The probability of the hypothesis p(h(2) = 0) fitting the last model was 0.996. Also, we did not detect any trend in sex ratio related to maternal age. From an evolutionary point of view, the chromosomal sex determination acts as a constraint that precludes control of offspring sex ratio in vertebrates and it should be included in the general theory of sex allocation. From a practical view that means that the sex ratio in domestic species is hardly susceptible to modification by artificial selection.

Benefits from marker-assisted selection under an additive polygenic genetic model1

This study investigated, through stochastic computer simulation, the extra gains expected from marker-assisted selection (MAS) in an infinitesimal model with linkage. The trait under selection was assumed to be controlled by 2,000 loci of additive small effect and evenly distributed in c chromosomes of one Morgan each (and c = 5, 10, 20, or 30). This approach differs from previous studies on the benefits of MAS that have considered mixed inheritance models. Marker information was used together with pedigree information to compute the relationship matrix used in BLUP genetic evaluations. The MAS schemes were compared with schemes where genetic evaluations were performed using standard BLUP (i.e., the relationship matrix is obtained using pedigree information only). When the number of markers was large enough (approximately one marker every 10 cM), there were increases in the accuracy of selection with MAS, and this led to extra gains compared with standard BLUP for all genome sizes considered. The benefit from MAS increased over generations. At the last generation of selection (Generation 10), the response from MAS was 11, 9, 7, and 5% greater than with standard BLUP for genomes with 5, 10, 20, and 30 chromosomes, respectively. Thus, although small, gains from MAS were nonetheless detectable for genome sizes typical of livestock populations.

Inferences on the role of insertion in a mutation accumulation experiment with Drosophila melanogaster using RAPDs

The genetic variability for RAPDs band pattern was studied in a set of 157 mutation accumulation (MA) lines of Drosophila melanogaster. These MA lines were derived from the same isogenic base population and subsequently maintained by full-sib mating during 132 generations. The ancestral pattern of the original isogenic base can be unambiguously established as the consensus pattern of the MA lines and, because these lines are expected to be homozygous, dominance for band pattern is not a concern. Only repeatable changes in band pattern were considered. The number of ancestral bands detected implies that nine-nucleotide targets are enough for repeatable PCR amplification. Compared with the ancestral pattern, one MA line lost one band and two MA lines gained a new one. These results can be accounted for by the insertion of transposable elements occurring at a rate 0.07 < i < 0.21 per whole haploid genome and generation. This range is typical for Drosophila and consistent with the previously observed mobility for the roo family, supporting the generality of previous estimates of spontaneous mutation rates for morphological and fitness traits based on these MA lines. The sequence of one of the new bands suggests that the Idefix family is also active in the lines.

[Activity index in Crohn's disease]

The gold standard to quantify Crohn's disease activity is still not defined and a world consensus to unify criteria is necessary. Criticism has been directed towards every existing indexes. We summarize some of the currently used criteria for the assessment of disease activity, point out the controversies and issues that will need further investigations, and discuss their usefulness based on our experience.

Fixed contributions designs vs. minimization of global coancestry to control inbreeding in small populations

Populations with small census sizes are at risk because of the loss of genetic variability and the increase of inbreeding and its harmful consequences. For situations with different numbers of males and females, several hierarchical designs have been proposed to control inbreeding through the fixation of individuals' contributions. An alternative method, based on the minimization of global coancestry, has been proposed to determine contributions as to yield of the lowest levels of inbreeding in the population. We use computer simulations to assess the relative efficiency of the different methods. The results show that minimizing the global coancestry leads to equal or lower levels of inbreeding in the short and medium term, although one of the hierarchical designs provides lower asymptotic inbreeding rates and, thus, less net inbreeding in the long term. We also investigate the performance of the alternative methods against departures from the ideal conditions, such as inbred or differentially related base individuals and random failures in the expected contributions. The method of minimization of global coancestry turns out to be more flexible and robust under these realistic situations.

Analysis of genetic diversity and conservation priorities in Iberian pigs based on microsatellite markers

The Iberian breed is the most important pig population of the Mediterranean type. The genetic structure of two strains (Torbiscal and Guadyerbas) and three varieties (Retinto, Entrepelado and Lampiño) of this breed was studied using 173 pigs genotyped for 36 microsatellites. In addition, 40 pigs of the related Duroc breed were also analysed. In the 1960s, the Iberian breed's numbers were severely reduced by disease, due to economic change and to crossbreeding. Varieties are in danger of disappearance or blending. A new conservation strategy is required. An analysis was performed that allows us to ascertain the loss or gain of genetic diversity if one or several subpopulations are removed. The results are compared with those using the Weitzman method. The two methodologies produce conservation priorities that are completely different, the reason being that the Weitzman method does not take into account the within-population genetic diversity. We apply optimal contribution theory and a new procedure for cluster analysis, and discuss their value in the general framework of the problems of setting of priorities and tactics for the conservation of genetic resources.

Assessment of heterogeneity of residual variances using changepoint techniques

Several studies using test-day models show clear heterogeneity of residual variance along lactation. A changepoint technique to account for this heterogeneity is proposed. The data set included 100 744 test-day records of 10 869 Holstein-Friesian cows from northern Spain. A three-stage hierarchical model using the Wood lactation function was employed. Two unknown changepoints at times T₁ and T₂, (0 <T₁ <T₂ <t_max), with continuity of residual variance at these points, were assumed. Also, a nonlinear relationship between residual variance and the number of days of milking t was postulated. The residual variance at a time t() in the lactation phase i was modeled as: for (i = 1, 2, 3), where λ_ι is a phase-specific parameter. A Bayesian analysis using Gibbs sampling and the Metropolis-Hastings algorithm for marginalization was implemented. After a burn-in of 20 000 iterations, 40 000 samples were drawn to estimate posterior features. The posterior modes of T₁, T₂, λ₁, λ₂, λ₃, , , were 53.2 and 248.2 days; 0.575, -0.406, 0.797 and 0.702, 34.63 and 0.0455 kg², respectively. The residual variance predicted using these point estimates were 2.64, 6.88, 3.59 and 4.35 kg² at days of milking 10, 53, 248 and 305, respectively. This technique requires less restrictive assumptions and the model has fewer parameters than other methods proposed to account for the heterogeneity of residual variance during lactation.

Estimation of genetic variability of the founder population in a conservation scheme using microsatellites

In a conservation programme with genealogical records it is possible to estimate the amount of variability of the founder population from a measure of the similarity among the individuals in the current population based on microsatellite markers. Here we compare three available methods and we shown that the one based on the molecular coancestry coefficient should be preferred.

Quantitative trait locus mapping for meat quality traits in an Iberian x Landrace F2 pig population

An experimental F2 cross between Iberian and Landrace pig strains was performed to map quantitative trait loci (QTL) for diverse productive traits. Here we report results for meat quality traits from 369 F2 animals with records for pH 24 h postmortem (pH 24 h), muscle color Minolta measurements L* (lightness), a* (redness), and b* (yellowness), H* (hue angle), C* (chroma), intramuscular fat (IMF) and haematin pigment content measured in the longissimus thoracis. Pigs were genotyped for 92 markers covering the 18 porcine autosomes (SSC). Results of the genome scan show evidence for QTL for IMF (SSC6; F = 27.16), pH 24 h (SSC3; F = 7.73), haematin pigments (SSC4 and SSC7; F = 8.68 and 9.47 respectively) and Minolta color measurements L* (SSC4 and SSC7; F =16.42 and 7.17 respectively), and a* (SSC4 and SSC8; F = 8.05 and 7.36 respectively). No QTL were observed for the color measurements b*, H*, and C*. Alternative models fitting epistasis between QTL were also tested, but detected epistatic interactions were not significant at a genome-wise level. In this work we identify genomic regions related with meat quality traits. Improvement by traditional selection methods is complicated, and finer mapping would be required for their application in introgression programs.

QTL mapping for growth and carcass traits in an Iberian by Landrace pig intercross: additive, dominant and epistatic effects

Results from a QTL experiment on growth and carcass traits in an experimental F2 cross between Iberian and Landrace pigs are reported. Phenotypic data for growth, length of carcass and muscle mass, fat deposition and carcass composition traits from 321 individuals corresponding to 58 families were recorded. Animals were genotyped for 92 markers covering the 18 porcine autosomes (SSC). The results from the genomic scan show genomewide significant QTL in SSC2 (longissimus muscle area and backfat thickness), SSC4 (length of carcass, backfat thickness, loin, shoulder and belly bacon weights) and SSC6 (longissimus muscle area, backfat thickness, loin, shoulder and belly bacon weights). Suggestive QTL were also found on SSC1, SSC5, SSC7, SSC8, SSC9, SSC13, SCC14, SSC16 and SSC17. A bidimensional genomic scan every 10 cM was performed to detect interaction between QTL. The joint action of two suggestive QTL in SSC2 and SSC17 led to a genome-wide significant effect in live weight. The results of the bidimensional genomic scan showed that the genetic architecture was mainly additive or the experimental set-up did not have enough power to detect epistatic interactions.

Inbreeding effects on the parameters of the growth function in three strains of Iberian pigs

The growth performance of inbred pigs coming from full-sib matings was compared to that of contemporary animals coming from the same sires mated to control dams. The animals belong to three strains of Iberian pigs with different histories of previous inbreeding. The data consisted of 1,615 weight records between 50 and 250 d of age from 229 pigs. The statistical model assumed the two parameters that describe the linear growth function (a = intercept, b = slope) as different traits (weight at 120 d and daily gain) and the analysis was carried out in a Bayesian framework via Gibbs sampling. The means of the posterior distribution of heritabilities, common litter environmental coefficients, and genetic correlation were 0.328 (h(2)a), 0.332 (h2b), 0.084 (c(2)a), 0.060 (c(2)b) and 0.973 (rhoG). Inbreeding depression, expressed as the performance decrease relative to the mean, per 10% increase of the inbreeding coefficient, was -3.18, -2.31 and -5.37% for weight at 120 d (a), and -3.16, -2.08 and -6.49% for daily gain (b) in each of the three strains. The results indicate that the inbreeding effects are dependent on the level of previous inbreeding, the more previous inbreeding, the less inbreeding depression.

Bayesian analysis of lactation curves of Holstein-Friesian cattle using a nonlinear model

A Bayesian procedure was developed for fitting Wood's incomplete Gamma function to test-day milk records of Spanish Holstein Friesian cattle. Each parameter of Wood's function was considered as a dependent variable in a submodel that accounted for systematic effects and genetic relationships among animals. Marginal posterior distributions of model parameters were obtained using Gibbs sampling. Variables of economic interest, such as 305-d yield, persistency, peak yield, and days in milk at peak day were predicted as functions of Wood's function curve parameters. Heritability estimates were 0.26, 0.32, and 0.19 for parameters of Wood's function and 0.26, 0.14, 0.26, and 0.05 for 305-d yield, persistency, peak yield, and days in milk at peak yield. These estimates indicate that it is possible to modify the shape of the lactation curve through genetic selection. Genetic correlations between parameters of Wood's curve and the aforementioned functions of these parameters suggest that selection for 305-d milk yield would result in higher and later peak yield, but only a slight improvement in persistency is expected.

Inter- and intraspecific sexual discrimination in the flour beetles Tribolium castaneum and Tribolium confusum

In Tribolium castaneum (CS) and T. confusum (CF), intra- and interspecific rates of homosexual mounting have been measured. The intraspecific results are compatible with the hypothesis of both species being sexually indiscriminate. However, the CF intraspecific rates were very high (35%-53% of mountings were homosexual), suggesting a lower sexual attractiveness, or a stronger rejection to being mounted, of CF females relative to conspecific males. CS males discriminate between species but, in interspecific contacts, preferentially mounted CF males rather than CF females. CF males do not discriminate between species, but the loss of sexual attractiveness of CF females, or their rejection to being mounted, may act as a precopulatory isolation mechanism.

Epistasis and the conversion of non-additive to additive genetic variance at population bottlenecks

The effect of population bottlenecks on the mean and the additive variance generated by two neutral independent epistatic loci has been studied theoretically. Six epistatic models, used in the analysis of binary disease traits, were considered. Ancestral values in an infinitely large panmictic population were compared with their expectations at equilibrium, after t consecutive bottlenecks of equal size N (derived values). An increase in the additive variance after bottlenecks (inversely related to N and t) will occur only if the frequencies of the negative allele at each locus are: (1) low, invariably associated to strong inbreeding depression; (2) high, always accompanied by an enhancement of the mean with inbreeding. The latter is an undesirable property, making the pertinent models unsuitable for the genetic analysis of disease. For the epistatic models considered, it is unlikely that the rate of evolution may be accelerated after population bottlenecks, in spite of occasional increments of the derived additive variance over its ancestral value.

Interrelations between effective population size and other pedigree tools for the management of conserved populations

Genetic parameters widely used to monitor genetic variation in conservation programmes, such as effective number of founders, founder genome equivalents and effective population size, are interrelated in terms of coancestries and variances of contributions from ancestors to descendants. A new parameter, the effective number of non-founders, is introduced to describe the relation between effective number of founders and founder genome equivalents. Practical recommendations for the maintenance of genetic variation in small captive populations are discussed. To maintain genetic diversity, minimum coancestry among individuals should be sought. This minimizes the variances of contributions from ancestors to descendants in all previous generations. The method of choice of parents and the system of mating should be independent of each other because a clear-cut recommendation cannot be given on the latter.

Robust QTL effect estimation using the minimum distance method

Robustness has received little attention in QTL studies. We compare Maximum Likelihood (ML) and the Minimum Distance (MD) methods when there exists data contamination caused by outliers. A backcross population of size (N) 200 and 500 and 0, 5 or 25 outliers was simulated. The mean and standard deviation of the first QTL genotype were set to 1. Four cases were considered: (i) micro2=1, sigma2=1; (ii)micro2=1, sigma2=1.25; (iii) micro2=1.252, sigma2=1; (iv) micro2=1.282, sigma2=1.25, where micro2 and sigma2 are the mean and standard deviation of the second genotype. Either full or selective genotyping was considered. A Monte Carlo MD method is proposed to deal with missing genotypes. MD estimates were much more robust than ML estimates, especially with respect to scale parameter estimates, and with selective genotyping.

Improving the efficiency of artificial selection: more selection pressure with less inbreeding

The use of population genetic variability in present-day selection schemes can be improved to reduce inbreeding rate and inbreeding depression without impairing genetic progress. We performed an experiment with Drosophila melanogaster to test mate selection, an optimizing method that uses linear programming to maximize the selection differential applied while at the same time respecting a restriction on the increase in inbreeding expected in the next generation. Previous studies about mate selection used computer simulation on simple additive genetic models, and no experiment with a real character in a real population had been carried out. After six selection generations, the optimized lines showed an increase in cumulated phenotypic selection differential of 10.76%, and at the same time, a reduction of 19.91 and 60.47% in inbreeding coefficient mean and variance, respectively. The increased selection pressure would bring greater selection response, and in fact, the observed change in the selected trait was on average 31.03% greater in the optimized lines. These improvements in the selection scheme were not made at the expense of the long-term expectations of genetic variability in the population, as these expectations were very similar for both mate selection and conventionally selected lines in our experiment.

Spontaneous mutation for life-history traits in Drosophila melanogaster

Spontaneous mutations accumulated during 80 generations in 94 lines derived from a completely homozygous population of Drosophila melanogaster, all of them maintained by a single brother-sister mating per generation. Three traits were evaluated: early productivity, late productivity, and longevity. Mutational heritabilities were similar for all traits: 3.18 x 10(-3), 3.52 x 10(-3), and 3.38 x 10(-3), respectively. Nine lines were examined, their means being in the upper or lower tails of the distribution of line's means for at least two traits. Reciprocal crosses were made between each line and the control population to estimate line effects. The results can be summarised as follows: all lines carried putative mutations affecting fitness traits; five lines affect the three traits scored; one affects exclusively early productivity; and three affect exclusively late life-history traits (late productivity and longevity). Most mutations were deleterious and recessive, except one that favourably affected early-productivity and was dominant. Additional fitness traits were evaluated, indicating pleiotropy. We have not found mutations with antagonistic effects early and late in life; moreover, positive mutational correlation seems to be the rule.

Conceptual Capacity to Categorize and the Evolution of Altruism

The conceptual capacity to categorize and consequently the ability to approve or reprove the one's and other's behavior allows the appearance of individuals with a new type of cooperative behavior that we have called "Assessor". The Assessor individual, if the partner behaves in a selfish way, reproves and penalizes this behavior changing his initial cooperation into defect. The reprobation permits that Assessor individuals, through simple observation, inhibit their altruistic behavior towards individuals whose selfish behavior has already been reproved, without having to interact with them. The evolutionary properties of Assessor behavior are analysed using the model of the iterated prisoner's dilemma where Assessor individuals compete with "always defect" individuals. The results are compared with those obtained, in the same circumstances, by other cooperative behaviors such as "always cooperate", "Tit-for-Tat" and "Observer-Tit-For-Tat". It is shown that in all situations Assessor is evolutionarily stronger than Tit-for-Tat when both face ALL D. It is also advantageous with respect to Observer-Tit-For-Tat in those situations that favor the evolution of reciprocal altruism "Tit-for Tat".Copyright 1998 Academic Press Limited

[Lipoxygenase and trypsin inhibitor inactivation in soymilk processing by direct milling and ultra high temperature (DM-UHT)]

Soymilk production by a new process based on Direct Milling of soy grits and Ultra High Temperature (DM-UHT) has been studied at laboratory scale in order to evaluate solids and protein extraction, lipoxygenases (LO) and Trypsin Inhibitors (TI) inactivation during milling and heat-treatment steps. For TI measurements in soy extracts and soymilk a modification of the classical Kakade method (17) was used. Highest extraction yields were accomplished at 70 degrees C and 2 minutes milling of soy grits. LO was appreciably inactivated when using, as dispersing medium for milling, 0.01M sodium carbonate (Residual Activity 14%) instead of water (Residual Activity 46%), so in this way lower levels of undesired substances can be generated. LO destruction in the resulting suspension was finished by a short heating (30 seconds) from 70 degrees C to boiling temperature (96 degrees C). On the other hand, TI were not fully inactivated in milling nor even in the steaming step at 96 degrees C for many minutes. The TI were inactivated to the accepted levels for soymilk in the final UHT step at 135 degrees C and 2 minutes, being possible at the same time to carry out the simultaneous microorganisms destruction.

The distribution of spontaneous mutations on quantitative traits and fitness in Drosophila melanogaster

Starting from a completely homozygous population of Drosophila melanogaster, two groups of 100 inbred lines each were established and maintained for 46 generations, by a single brother-sister mating and two double first cousin matings, respectively. Sternopleural bristle number, wing length and wing width were simultaneously scored in all lines every 4-5 generations. The means of four lines in each group departed significantly from the overall mean and, in each case, this was attributed to a single mutation of relatively large effect on at least one trait (0.3-1.4 environmental standard deviations in absolute value). Further analyses revealed widespread pleiotropy, similar gene action of a given mutation for all traits affected, and predominant additive action. No apparent association was found between the magnitudes of mutational effects on the traits and fitness. However, all recessive mutations were deleterious. The distribution of mutant effects was asymmetrical (positive for bristles and negative for wing measurements). Moreover, these distributions had a high variance and may be leptokurtic, due to the presence of major genes. Estimates of the ratio of new mutational variance to environmental variance ranged within (0.7-3.4) x 10(-3), those for wing measurements being generally larger. In agreement with theory, the rate of between-line differentiation was independent of population size.

The genetic properties of homosexual copulation behavior in Tribolium castaneum: diallel analysis

The rate of homosexual copulation has been defined as the ratio between the number of homosexual mountings and the total number of mountings (homo and heterosexual) performed by a Tribolium castaneum male during a period of 30 min. In a laboratory population, the average rate when a number of males (m) and females (k x m) are tested together has been estimated in each of the six situations defined by m = 2 and 10 and k = 0.5, 1, and 2, k being the sex ratio among scored individuals. Good agreement was found between the observed rates of homosexual copulation and those expected assuming random contacts between pairs of individuals totally indiscriminate with respect to sex. The genetic properties of the trait have been investigated by means of a diallel analysis of six highly inbred lines derived from the same population and their F1 crosses. Significant general and specific combining ability effects were detected. When noninbred females were used for testing, the rate of homosexual copulation is expected to be higher for inbred than for noninbred males. This prediction, implying the existence of inbreeding depression for the trait, also was confirmed by the data.

The response to artificial selection from new mutations in Drosophila melanogaster

Twenty generations of divergent selection for abdominal bristle number were carried out starting from a completely homozygous population of Drosophila melanogaster. All lines were selected with the same proportion (20%) but at two different numbers of selected parents of each sex (5 or 25). A significant response to selection was detected in eight lines (out of 40) and, in most cases, it could be wholly attributed to a single mutation of relatively large effect (0.5-2 phenotypic standard deviations). The ratio of new mutational variance to environmental variance was estimated to be (0.33 +/- 0.11) X 10(-3). The distribution of mutant effects was asymmetrical, both with respect to bristle number (85% of it was negative) and to fitness (most detected bristle mutations were lethal or semilethal). Moreover, this distribution was leptokurtic, due to the presence of major genes. Gene action on bristles ranged from additive to completely recessive, no epistatic interactions being found. In agreement with theory, larger responses in each direction were achieved by those lines selected at greater effective population sizes. Furthermore, the observed divergence between lines selected in opposite directions was proportional to their effective size, as predicted for mutations of large effect.

Individual and group selection for productivity in Tribolium castaneum

The usefulness of a non-random group selection method in the improvement of a character influenced by interactions among individuals has been experimentally tested in a population of Tribolium castaneum. The selected trait -number of adults produced in a fixed period of time -showed a clear increase after 11 generations of selection. This increase is related to a reduction in developmental time, and it was specific for the population structure in which selection was applied, vanishing when this structure was altered.

Competition and genotypic variability in Drosophila melanogaster

It has been claimed that in competitive conditions larval viabilities of Drosophila melanogaster depend on the similarity of genotypes coexisting. Two types of experimental populations were established: homogeneous (low genotypic variability) and heterogeneous (high genotypic variability). Under conditions of moderate larval competition productivity was similar, in each although the developmental time was shorter in the heterogeneous series. Under conditions of high larval competition the productivity of heterogeneous populations exceeded that of the homogeneous and attained the adult stage in shorter period of time.

A simple method for increasing the response to artificial selection

Selection theory usually assumes an equally probable contribution of each selected individual to a large ‘gene pool’ from which the individuals to be measured in the next generation are sampled. With unequal contributions it is possible to find several sets of values for N (the number of selected individuals) and fi (probability of contribution of the ith individual) such that the same selection intensity is attained. It is suggested that the set of values producing minimum genetic drift should be chosen in order to increase the long-term response without any reduction in the short-term advance.