Effect Of Long-term Selection Research Articles

Assessment of a long-term selective breeding program for giant freshwater prawn Macrobrachium rosenbergii since 2007

Effects of long term selection for improved growth on traits of commercial interest are generally not well documented in aquaculture species, specifically in giant freshwater prawn (GFP) Macrobrachium rosenbergii. The present study analysed a total of 106,756 data records collected from a pedigreed GFP population over nine years (2007–2015) or nine generations (including base population) to evaluate genetic progress achieved for body weight and to examine correlated genetic changes in measurements of body dimensions (carapace length, abdominal length, carapace width and abdominal width), as well as fitness related traits (early maturity, EM and small blue claw male, SM). Linear mixed model fitting the random effects of individual prawn and common full-sib groups and the fixed effects of generation, line, pond by generation subclass, morphotypes for each sex and a linear covariate of grow-out day was used to analyse growth-related traits, whereas threshold logistic animal model was applied to binary data (EM and SM). The heritabilities were moderate for body weight and measurements of body dimensions (10 to 60%), but the estimates for EM and SM were low (0.13 ± 0.06 and 0.08 ± 0.01, respectively). The proportion of variance explained by the common full-sib effects was only 5–7% for measurements of body traits (weight and body dimensions). Genetic correlations among body traits were high and positive (0.93–0.97). These body traits however showed negative (i.e. favourable) genetic correlations with both EM and SM. Direct genetic gain for body weight and correlated changes in measurements of body dimensions and fitness related traits (EM and SM) were measured as differences in estimated breeding values (EBVs) between the selection line and control group within the same generation. The accumulative genetic gain in body weight after eight generations was 56%, averaging 7% per generation. Selection for high growth, however, did not have detrimental effects on measures of body dimensions and fitness related traits (i.e. EM and SM). In comparison to one of the founder stocks collected from Mekong river, the selection line had 50% greater body weight under the same testing environment in the latest generation 2015. Our findings provide information to refine the current breeding program to simultaneously improve traits of commercial interest in this important aquaculture species M. rosenbergii.

Effects of Long-Term Selection in the Border Collie Dog Breed: Inbreeding Purge of Canine Hip and Elbow Dysplasia.

Simple SummaryFor dog breeders, health is one of the main criteria when choosing a breeding animal; thus, selection for good anatomy is the key to reduce orthopedic disorders. In many dog breeds, radiographic screening for canine hip and elbow dysplasia is a compulsory test for breeding; however, these multifactorial traits are determined by genetic and environmental factors. Therefore, it is extremely difficult to eliminate these disorders from the population. In natural selection, such traits can be “purged” out of the population with inbreeding. The study aimed to examine the inbreeding-purge of canine hip and elbow dysplasia in the border collie breed. The main conclusion was that over-representation of homozygous individuals may have a positive effect on hip and elbow conformation.Pedigree data of 13,339 border collie dog was collected along with canine hip dysplasia (CHD) and canine elbow dysplasia (CED) records (1352 CHD and 524 CED), and an inbreeding–purging (IP) model was created. Ancestral inbreeding coefficients were calculated by using a gene dropping simulation method with GRain 2.2 software. Cumulative logit models (CLM) for CHD and CED were fitted using a logit-link Poisson distribution and the classical (F_W), and ancestral inbreeding (F_BAL, F_KAL, and F_KAL_NEW) coefficients as linear regression coefficients. The effective population size was calculated from F_W and decreased in the examined period along with an increase of F_W; however, slight differences were found as a consequence of breeding dog imports. CHD values were lowered by the expansion of F_BAL, as the alleles had been inbred in the past. For CHD, signs of purging were obtained. There was a positive trend regarding the breeding activity (both sire and dam of the future litters should be screened and certified free from CHD and CED), as years of selection increased the frequency of alleles with favorable hip and elbow conformation. Division of the ancestral inbreeding coefficient showed that alleles that had been identical by descent (IBD) for the first time (F_KAL_NEW) had a negative effect on both traits, while F_KAL has shown favorable results for alleles IBD in past generations. Some authors had proven this phenomenon in captive populations or experimental conditions; however, no evidence of inbreeding purge has ever been described in dog populations. Despite the various breeding practices, it seems that alleles of these polygenic disorders could be successfully purged out of the population with long-term selection.

Quantitative genetic changes in reproductive performance of giant freshwater prawn after 10 years of selection for increased growth rate.

Effect of long-term selection for improved growth on reproductive performance of giant freshwater prawn (GFP) Macrobrachium rosenbergii has not been reported in the literature. The present study aimed to measure correlated responses in reproductive traits and to estimate genetic parameters for these characters in a GFP population selected for high growth over ten generations from 2007 to 2016. A total of 959 breeding females (offspring of 515 sires and 810 dams) had measurements for seven reproductive traits (weight before spawn WBS; weight after spawn WAS; Fecundity FEC or number of larvae per female at hatching; first age to reach post-larvae PLAGE; zoea (e) weight ZOEAWT; larval survival during hatchery phase SURV1 and survival from PL to tagging SURV2. The restricted maximum likelihood (REML) and mixed model analysis were used to estimate genetic parameters and evaluate selection responses for the seven traits studied. Our REML analysis showed that heritability for these traits ranged from 0.04 to 0.42 (SE: 0.19-0.28). Female body weight either before or after spawning had strong positive phenotypic correlations with fecundity (0.52-0.98). By contrast, the phenotypic correlations of WBS/WAS with larval and fry survivals were not significant (-0.08-0.05). Genetic correlations among fecundity-related traits studied were not different from zero due to their high standard errors. Correlated responses in reproductive traits were measured by comparing least squares means of the selection line and control group. Females of the selected line for high growth had significantly greater weight before or after spawning than that of the control group. There were, however, no statistical differences between the two lines in the other traits. It is concluded that selection for high growth did not have detrimental impact on reproductive performance of breeding females in the present population of GFP.

Genome-Wide Characterization of Selection Signatures and Runs of Homozygosity in Ugandan Goat Breeds.

Both natural and artificial selection are among the main driving forces shaping genetic variation across the genome of livestock species. Selection typically leaves signatures in the genome, which are often characterized by high genetic differentiation across breeds and/or a strong reduction in genetic diversity in regions associated with traits under intense selection pressure. In this study, we evaluated selection signatures and genomic inbreeding coefficients, FROH, based on runs of homozygosity (ROH), in six Ugandan goat breeds: Boer (n = 13), and the indigenous breeds Karamojong (n = 15), Kigezi (n = 29), Mubende (n = 29), Small East African (n = 29), and Sebei (n = 29). After genotyping quality control, 45,294 autosomal single nucleotide polymorphisms (SNPs) remained for further analyses. A total of 394 and 6 breed-specific putative selection signatures were identified across all breeds, based on marker-specific fixation index (FST-values) and haplotype differentiation (hapFLK), respectively. These regions were enriched with genes involved in signaling pathways associated directly or indirectly with environmental adaptation, such as immune response (e.g., IL10RB and IL23A), growth and fatty acid composition (e.g., FGF9 and IGF1), and thermo-tolerance (e.g., MTOR and MAPK3). The study revealed little overlap between breeds in genomic regions under selection and generally did not display the typical classic selection signatures as expected due to the complex nature of the traits. In the Boer breed, candidate genes associated with production traits, such as body size and growth (e.g., GJB2 and GJA3) were also identified. Furthermore, analysis of ROH in indigenous goat breeds showed very low levels of genomic inbreeding (with the mean FROH per breed ranging from 0.8% to 2.4%), as compared to higher inbreeding in Boer (mean FROH = 13.8%). Short ROH were more frequent than long ROH, except in Karamojong, providing insight in the developmental history of these goat breeds. This study provides insights into the effects of long-term selection in Boer and indigenous Ugandan goat breeds, which are relevant for implementation of breeding programs and conservation of genetic resources, as well as their sustainable use and management.

Effect of long-term selection on primary trait (5 week body weight) in synthetic coloured broiler male line: Direct and correlated responses

Synthetic coloured broiler male line (PB-1) has been under continuous mass selection for 5week body weight for 15 generations with a target to increase the 6 week body weight of the terminal commercial cross (Krishibro) to 1.6Kg. The effect of long term selection on economic traits was studied. Direct responses for primary traits (5 week body weight) were calculated as a regression of generation mean on generation number (Phenotypic response) and regression of control deviated mean on generation number (Genetic response). Similarly, correlated phenotypic and genetic responses were calculated in secondary traits. Direct response of 5wk body weight was 5.01±3.31g on phenotypic scale and 15.54±6.84g on genetic scale. Correlated response for 20wk body weight was-28.32±10.08g on phenotypic scale 1.05±10.43g on genetic scale. For 40wk body weight this was-26.24±11.88g on phenotypic scale and-1.97±9.70g on genetic scale. For 5wk shank length response was-0.48±0.19mm on phenotypic scale and-0.15±0.25 on genetic scale. Phenotypic response in breast angle was-0.70±0.26 degrees and genetic response was 0.07±0.31 degrees. Phenotypic response in 32wk egg weight was-0.066±0.04g and genetic response was 0.005±0.08g. For 40wk egg weight response was-0.035±0.07g on phenotypic scale and 0.03±0.121g on genetic scale. Phenotypic response in ASM was 0.81±0.44days and genetic response was-0.41±0.48days. For 40wk egg production response was-0.43±0.23eggs on phenotypic scale and 0.20±0.18 eggs on genetic scale. Phenotypic responses were mostly negative for primary and correlated traits except the ASM. Majority of genetic responses were positive for these traits indicating the improvement of the primary trait over the generations.

Effect of long term selection for juvenile body weight and egg production on semen quality in broiler breeder dam line

Effect of long term selection for juvenile body weight and egg production on semen quality in broiler breeder dam line

Divergent selection for shape of the growth curve in Japanese quail. 8. Effect of long-term selection on embryonic development and growth

1. Changes in embryonic development and growth were analysed in relation to direct changes in postnatal growth and correlated responses in egg parameters using Japanese quail lines selected for more than 30 generations for high (HG) and low (LG) relative gain of body weight (BW) between 11 and 28 d of age, and constant BW at 49 d of age.2. During the first 42 h as well as at the end of incubation, LG embryos were developmentally accelerated in comparison with their HG counterparts. An expected increase of line divergence across generations was observed only in traits analysed at the end of incubation.3. In contrast to early generations, LG embryos continuously exhibited a higher BW than HG embryos and this difference temporarily disappeared only around incubation d 8. Analogous to early generations, the HG compared with LG embryos showed two periods of transient growth retardation compensated subsequently by a higher growth rate (incubation d 3–8 and 8–16).4. More pronounced growth retardation of HG versus LG embryos in late versus early generations corresponded to more distinct decrease of HG versus LG growth rate during the first post-hatch days. Likewise, a disappearance of line BW differences on incubation d 8 characterising the late generations corresponded to the elimination of line differences in adult BW.5. Alterations of growth pattern were associated with changes of egg size. While HG quail maintained a relatively constant adult BW and egg size across generations, the gradually increasing incidence of large eggs in the LG line allowed selection of birds with higher growth potential, which in turn amplified the line differences in the embryonic BW and eliminated the line differences in adult BW. Line differences in egg composition (larger albumen with lower density in LG compared with HG eggs) apparently contributed to the strengthening of line developmental divergence during incubation.6. Transient lack of nutrient supply to HG embryos due to their developmental delay is probably responsible for a higher HG versus LG embryo mortality.

Protein aggregation in E. coli : short term and long term effects of nutrient density.

During exponential growth some cells of E. coli undergo senescence mediated by asymmetric segregation of damaged components, particularly protein aggregates. We showed previously that functional cell division asymmetry in E. coli was responsive to the nutritional environment. Short term exposure as well as long term selection in low calorie environments led to greater cell division symmetry and decreased frequency of senescent cells as compared to high calorie environments. We show here that long term selection in low nutrient environment decreased protein aggregation as revealed by fluorescence microscopy and proportion of insoluble proteins. Across selection lines protein aggregation was correlated significantly positively with the RNA content, presumably indicating metabolic rate. This suggests that the effects of caloric restriction on cell division symmetry and aging in E. coli may work via altered protein handling mechanisms. The demonstrable effects of long term selection on protein aggregation suggest that protein aggregation is an evolvable phenomenon rather than being a passive inevitable process. The aggregated proteins progressively disappeared on facing starvation indicating degradation and recycling demonstrating that protein aggregation is a reversible process in E. coli.

Individual animal model estimates of genetic parameters for performance test traits of male and female landrace pigs tested in a commercial nucleus herd

AbstractEstimates of heritabilities, common litter of birth effects and additive maternal genetic effects were produced for ultrasonic backfat depth, average daily food intake, average daily gain and food conversion ratio of Landrace boars and gilts. Boars and gilts were performance tested under different regimes. A bivariate derivative-free restricted maximum likelihood procedure was used to estimate genetic correlations between the performance test traits as recorded in the two sexes.Heritability estimates from the analysis including the common litter of birth effect tended to be towards the low end of the range of recently published estimates. This may reflect either population specific effects, such as effects of long-term selection, or the use of an individual animal model.Estimates of the common litter of birth effect were around 0·05, and generally had a significant effect upon the fit of the model, while additive maternal genetic effect estimates were negligible. Therefore, it is expected that omission of maternal effects from models for evaluation by best linear unbiased prediction will not hinder genetic progress. Inclusion of common litter of birth effects would be recommended, although this result may not hold for populations given food ad libitum.The estimates of genetic correlations between performance test traits of boars and gilts indicate that the levels of genotype-environment interaction (G × E) and genotype-sex interaction were low across most traits and data sets, with all genetic correlation estimates lying between 0·8 and 1·0. The lowest estimates of the genetic correlations, which were observed in data sets where the environments appeared to differ most, indicate that G × E interactions may be a problem in populations where males and females are subject to test regimes with greater differences than those seen here.

Maximizing the response of selection with a predefined rate of inbreeding.

A method was derived that maximizes the genetic level of selected animals while constraining their average coancestry to a predefined value. The average coancestry of the selected parents equals the inbreeding level in the next generation, so that rates of inbreeding were controlled. When this method was applied for several generations of selection, stable rates of genetic gain were attained, which indicates that the method could control the short- and long-term effects of selection on inbreeding. At equal rates of inbreeding, genetic gains were 21 to 60% greater than that with selection for BLUP-EBV, because of increased selection differentials. The difference was larger when the desirable rate of inbreeding was smallest. Selection with a constraint on inbreeding required only EBV of, and relationships between, the selection candidates and is therefore easy to apply in practice. The optimal solution is expressed in genetic contributions of selection candidates to the next generation, which is equivalent to numbers of offspring per candidate. These optimal numbers of offspring may be difficult to attain because of female reproductive limitations. The optimal method could be adapted to situations with additional reproductive constraints. The method can also be used to constrain the variance of response by restricting the average prediction error variance of the selected animals.

Effect of long term selection on genetic parameters of economic traits in white leghorn

Effect of long term selection on genetic parameters of economic traits in white leghorn

Genetic changes occurring over 500 generations in lines of Drosophila melanogaster selected divergently for geotaxis.

Populations of Drosophila melanogaster selected divergently and intermittently over 600 generations for geotaxis were analyzed genetically by assaying individual chromosomes and their interactions. Effects were found for each of the three major chromosomes from both the negatively and the positively geotactic lines, as were interactions among chromosomes from the latter. This situation differs from an assay performed about 500 generations earlier (Erlenmeyer-Kimling, L.,Dissert. Abstr. 22:1262–1263, 1961) in which (a) significant effects were reported for only two of the three chromosomes from each line and (b) no significant interactions among chromosomes were found. The amount of evolutionary change in each line may well be even greater than reported here because the chromosomal assay cannot detect all effects. However, the comparison indicates a large magnitude of genetic change due to the effects of long-term selection.

Effect of Long-Term Selection for Litter Size in Mice on Lifetime Reproduction Rate

Effect of Long-Term Selection for Litter Size in Mice on Lifetime Reproduction Rate

An experimental check on quantitative genetical theory II. The long-term effects of selection

1. The results of continued selection for abdominal bristles in a large population ofDrosophila melanogaster are presented and discussed. 2. Response had slowed down considerably in many lines after twenty generations, although in some it continued until the 30th generation. In many of the lines, the cessation of response was abrupt and lack of response did not mean exhaustion of genetic variability. 3. In three of the high lines, the high variability was apparently due to continued selection of heterozygotes for a lethal gene. In two high lines, such genes were present on both 2nd and 3rd chromosomes. 4. In the low lines, a striking phenomenon was a sudden increase of variation in females followed by a rapid response in that sex. This appeared in all lines with different times of onset. The ratio of male to female score in all low lines was greater than unity, compared to 0.8 in the initial population. 5. Genetic variation was maintained in many of the low lines after response had ceased. The situation appeared to be complex in that lethal genes, infertility of extreme females, and heterozygosity for inversions all played some part. 6. In such situations, the classical heritability approach appeared to break down completely. In some cases, the reason for the breakdown could be given in terms of the other phenomena observed, but in some of the low lines the full explanation was not clear. 7. The relevance of these results to practical problems of animal breeding is discussed.