Heterosis among lines of mice selected for body weight

Summary To examine the effect of selection on levels of heterosis, crosses were made between three groups of six lines of mice, one group unselected (controls) and the other two selected for high (large lines) and low (small lines) 6-week body weight, respectively. The coefficient of inbreeding of each line was about 0.60. Each line was crossed reciprocally to one line from each of the parental groups, as well as producing purebred progeny. Heterosis for 3-week weight, 6-week weight and 3–6 week gain averaged 0.0%, 2.4% and 4.2%, respectively, and was higher for males than for females. Heterosis was more extensive in crosses involving large or control lines than in crosses with small lines. There was no detectable heterosis in several measures of developmental rate, such as age at vaginal opening. Food conversion efficiency and carcass composition were measured on a sample of the animals. Food consumption, gonadal fat pad weight, and hindquarters weight, each expressed as a proportion of body weight, exhibited –4.0%, 5.6%, and 2.3% heterosis, respectively.     

Assessment of genomic variability through DNA fingerprinting within and between chicken lines divergently selected for residual food consumption

DNA fingerprints obtained by multi-locus probes have been shown to be convenient tools to assess genetic variability and genetic distances in animal populations. This method has been applied in the present study to two Rhode Island Red lines of chickens divergently selected for residual food consumption (RFC) for 16 generations (R-: low RFC; R+: high RFC). Within each line, individuals were sampled from each tail of the phenotypic distribution of RFC for males and for females. The three probes used were two minisatellite probes, R18-1 and 33-6, and the endogenous avian retroviral element probe. Altogether, 101 bands were scored. Band-sharing levels obtained from analysis of pooled DNA were extremely high within-Line (> 0.9) and still high between the lines (0.82 to 0.86). When band frequencies were compared, correlation coefficients were lower between lines than between extreme groups within lines regardless of the performance level. Although the selected lines differed widely in the selected trait RFC and a few correlated traits, it was concluded that they are probably different by only a low proportion of their genome.     

Energy expenditure and locomotor activity in mice selected for food intake adjusted for body weight

Summary The aim of this study was to examine the differences in physical activity and their contribution to differences in energy utilization in mice, selected either high or low for food intake, adjusted for body weight, which show correlated responses in lean content and metabolic rate. Simultaneous measurements of fasting metabolic rate and activity were made in lines of mice selected at either: a young age, 4-to 6-week food intake corrected for 4-week body weight; or an older age, 8- to 10-week food intake corrected for mean weight at 8 and 10 weeks of age. Correlated response in metabolic rate was found to have been accompanied by changes in locomotor activity near the ages at selection in both sets of lines. Activity, however, accounted for only a small proportion of variation in fasting heat production, generally less than 5%, although a highly positive correlation (r=0.63) between the two traits was found. It was concluded that selection for food intake adjusted for body weight has led to correlated response in physical activity. In consequence, mice selected in the upward direction expend some of the excess energy intake rather than assimilating it as body mass and are, therefore, slightly leaner than their counterparts selected in the downward direction.     

A comparison of two methods for prediction of response and rates of inbreeding in selected populations with the results obtained in two selection experiments

Selection programmes are mainly concerned with increasing genetic gain. However, short-term progress should not be obtained at the expense of the within-population genetic variability. Different prediction models for the evolution within a small population of the genetic mean of a selected trait, its genetic variance and its inbreeding have been developed but have mainly been validated through Monte Carlo simulation studies. The purpose of this study was to compare theoretical predictions to experimental results. Two deterministic methods were considered, both grounded on a polygenic additive model. Differences between theoretical predictions and experimental results arise from differences between the true and the assumed genetic model, and from mathematical simplifications applied in the prediction methods. Two sets of experimental lines of chickens were used in this study: the Dutch lines undergoing true truncation mass selection, the other lines (French) undergoing mass selection with a restriction on the representation of the different families. This study confirmed, on an experimental basis, that modelling is an efficient approach to make useful predictions of the evolution of selected populations although the basic assumptions considered in the models (polygenic additive model, normality of the distribution, base population at the equilibrium, etc.) are not met in reality. The two deterministic methods compared yielded results that were close to those observed in real data, especially when the selection scheme followed the rules of strict mass selection: for instance, both predictions overestimated the genetic gain in the French experiment, whereas both predictions were close to the observed values in the Dutch experiment.     

Influence of early pregnancy on reproductive rate in lines of mice selected for litter size

Summary The influence of male-induced early puberty on female reproductive rate was determined in three lines of mice differing in litter size and body weight. The lines originated from a single base population and had undergone 20 generations of selection for the following criteria: large litter size at birth (L⁺), large litter size and small 6-week body weight (L⁺W^–), or small litter size and large 6-week body weight (L^–W⁺). Females were paired with a mature intact male of the same line at 3, 5 or 7 weeks of age. Mean mating age, averaged over lines, was 26.5 ± .3, 38.3 ± .3 and 52.7 ± .3 days. Exposure to a mature male accelerated female sexual maturation in each line. When contrasted with their sibs mated at a later age, early-pregnant females from each line exhibited a decline in one or more component of reproductive performance, suggesting that the physiological state of the very young female was not optimum for normal pregnancy. In comparisons of early and later mating ages, all three lines showed a decreased littering rate at first mating, number born alive, and individual birth weight of progeny adjusted for litter size; L⁺ and L⁺W^– mice showed an increased perinatal mortality rate; L⁺ and L^–W⁺ had a reduction in litter size at birth. When the L⁺, L⁺W^– and L^–W⁺ lines were compared with an unselected strain and a line selected for high postweaning gain in similar experiments, a genotype by environment interaction was apparent since all lines did not respond in a similar manner to early mating. The line ranking for litter size at birth for each age at male-exposure was L⁺>L⁺W^–>L^–W⁺, despite the significant line by age interaction. When litter size was adjusted by covariance for body weight at mating, the significant effects of age at male-exposure and line by age interaction were eliminated. All fertile females were remated after they had weaned their first litter to obtain information on litter size in parity two. Line differences in litter size at birth and number born alive were uniform across parities. An age by parity interaction was evident since the decreased fecundity at younger ages of male exposure in the L⁺ and L^–W⁺ litters of parity one was not evident in parity two. Litter feed efficiency during first parity gestation was defined as litter birth weight divided by either cumulative feed intake of the dam from mating to parturition (GEI) or cumulative feed intake from weaning to parturition (GEII). The ranking of lines for GEI and GEH was L⁺> L⁺W^–>L^–W⁺, but when feed efficiency was adjusted for littering rate, L⁺W^– and L^–W⁺ were not significantly different. With regard to age at mating, the ranking for GEI (7 wk > 5 wk > 3 wk) was reversed from GEII (3 wk >5 wk > 7 wk) and these significant differences were maintained after adjustment for littering rate.Paper No. 6302 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the products named, nor criticism of similar ones not mentionedOn leave at the Institute of Animal Genetics, West Mains Road, Edinburgh EH9 3JN, Scotland. Supported, in part, by an Underwood Fund Fellowship, Agricultural Research Council, and an Edinburgh University Biological Fellowship in the Department of Genetics     

Sperm competition does not influence sperm hook morphology in selection lines of house mice

Sperm show a remarkable degree of variation in size, shape and complexity. Murine rodents exhibit a sperm head morphology that differs greatly from the ovoid shape that is characteristic of most mammals. These rodents have sperm that bear one or more apical hooks, the function of which is currently surrounded by much controversy. It has been suggested that the hook serves to facilitate the formation of sperm groups, which in some species exhibit relatively faster velocities than single cells and thus, may provide an advantage when ejaculates are competing for fertilisations. In support of this hypothesis, a comparative study reported a positive association between the strength of sperm competition (estimated from testes size) and the curvature of the sperm hook amongst 37 murine species. Here, we assessed whether sperm competition influences sperm hookedness at the intra-specific level. Following 16 generations of selection, we used geometric morphometry (GM) to describe sperm head morphology in selection lines of house mice evolving with (polygamous) and without (monogamous) sperm competition. Although the GM analysis returned two relative warps that described variation in the curvature of the sperm hook, we found no evidence of divergence between the selection lines. Thus, we can conclude that sperm competition does not influence the degree of sperm hookedness in house mice.     

Optimization of a crossing system using mate selection

A simple model based on one single identified quantitative trait locus (QTL) in a two-way crossing system was used to demonstrate the power of mate selection algorithms as a natural means of opportunistic line development for optimization of crossbreeding programs over multiple generations. Mate selection automatically invokes divergent selection in two parental lines for an over-dominant QTL and increased frequency of the favorable allele toward fixation in the sire-line for a fully-dominant QTL. It was concluded that an optimal strategy of line development could be found by mate selection algorithms for a given set of parameters such as genetic model of QTL, breeding objective and initial frequency of the favorable allele in the base populations, etc. The same framework could be used in other scenarios, such as programs involving crossing to exploit breed effects and heterosis. In contrast to classical index selection, this approach to mate selection can optimize long-term responses.     

性能测定规模对父系猪短期选择效果的影响

利用Monte Carlo模拟,研究了群体大小、公母比例和每窝测定猪头数对父系猪的近交系数、选择反应及其变异系数的影响。设定基础群母猪规模大小为100头到500头共5个规模,公母猪比例为1：10和1：20,每窝测定猪头数为2头和4头,公母猪各半。选择的性状为一般父系猪的选择性状,即断奶后生长速度和达100kg体重时的活体背膘厚,利用多性状BLUP估计性状的育种值,选择指数中后一性状的经济加权系数是前一个的2．5倍,选择共进行了5个世代。结果表明,随着选择群母猪头数的增加,第五世代累积选择反应提高,近交系数上升速度变慢,第五世代累积选择反应的变异系数下降。随每窝测定仔猪头数的增加和公母比例的升高,累积选择反应加快,近交系数上升速度提高,第五世代累积选择反应的变异系数上升。保持公母猪比例不变和每窝测定仔猪头数不变,基础群母猪头数从100头增加到300头,累积选择反应有显著增加,近交系数上升速度显著减慢。母猪头数300头和400头以上的相比,第五世代的累积选择反应增加有限,近交系数下降速度减低。综合评价,对于父系猪的短期选育来说,基础群需要400头母猪以上,每窝测定4头仔猪,公母比例以1：20较好。     

Longevity differences among lines artificially selected for developmental time and wing length in Drosophila buzzatii

We assessed the indirect response of longevity in lines selected for wing length (WL) and developmental time (DT). Longevity in selection lines was compared to laboratory control lines and the offspring of recently collected females. Wild flies (W lines), flies from lines selected for fast development (F lines), and for fast development and large wing length (L lines) outlived control laboratory lines (C lines) and lines selected for fast development and short wing (S lines). The decline in longevity in S lines is in line with the idea that body size and longevity are correlated and may be the result of the fixation of alleles at loci affecting pleiotropically the two traits under selection and longevity. In addition, inbreeding and artificial selection affected the correlation between wing length and longevity that occurs in natural populations of Drosophila buzzatii, suggesting that correlations between traits are not a perdurable feature in a population.     

The immunoregulatory effects of edeine analogues in mice

The edeines analogs were tested in several in vitro and in vivo assays using the mouse model, with edeine B (peptide W1) and cyclosporine A as reference compounds. The peptides displayed moderate, stimulatory effects on concanavalin A-induced (ConA-induced) splenocyte proliferation, whereas their effects on pokeweed mitogen-induced (PWM-induced) splenocyte proliferation were inhibitory. The peptides inhibited lipopolysacharide-induced (LPS-induced) tumor necrosis factor alpha production but had little effect on interleukin 6 production. In the model of the humoral immune response in vitro to sheep red blood cells, peptide 1 was distinctly stimulatory in the investigated concentrations (1-100 μg/ml), whereas peptides 3 and 4 only stimulated the number of antibody-forming cells at the highest concentration (100 μg/ml). In the model of the delayed type hypersensitivity in vivo to ovalbumin, the peptides were moderately suppressive (3 being the most active). The reference peptide W1 stimulated ConA-induced cell proliferation at 1–10 μg/ml but was inhibitory at 100 μg/ml. It also inhibited PWM-induced cell proliferation in a dose-dependent manner. This peptide had no effect on the humoral immune response in vitro or on cytokine production, but inhibited DTH reaction in vivo. The relationship between structure and activity, and a possible mode of action of the peptides, is discussed in this paper.     

Aggressive and non-aggressive personalities differ in oxidative status in selected lines of mice (Mus musculus)

Mice selected for aggression and coping (long attack latency (LAL), reactive coping strategy; short attack latency (SAL), pro-active coping strategy) are a useful model for studying the physiological background of animal personalities. These mice also show a differential stress responsiveness, especially in terms of hypothalamic-pituitary-adrenal axis reactivity, to various challenges. Since the stress response can increase the production of reactive oxygen species, we predicted that the basic oxidative status of the lines could differ. We found that LAL showed higher serum antioxidant capacity (OXY) than SAL, while no differences emerged for reactive oxygen metabolites (ROMs) or the balance between ROMs and OXY, reflecting oxidative stress. Moreover, the lines showed inverse relationships between ROMs or OXY and body mass corrected for age. The results indicate that variation in oxidative status is heritable and linked to personality. This suggests that different animal personalities may be accompanied by differences in oxidative status, which may predict differences in longevity.     

Reduced Mating Vigor in Selection Lines of the Butterfly Bicyclus anynana

Despite its acknowledged value for testing evolutionary theory, artificial selection is vulnerable to artifacts that are difficult to control. Here, we show that lines of the butterfly Bicyclus anynana, being artificially selected for differences in egg size, show considerably reduced mating vigor and male mating success than control lines, which is attributed to presumed differences in the levels of inbreeding. Besides selection line, neither forewing length, body dry mass or fat content of males had a detectable impact on male mating performance. Because artificial selection may (e.g. due to inbreeding) yield inadvertent effects even on traits that seem not to be related to the target trait, their results should be interpreted with caution.     

Growth,feed efficiency and lifetime performance of crosses between lines selected for nursing ability and/or adult weight in mice

Summary Two populations of randombred of different origin (P and Q) containing eight lines (M_P, W_P, B_P, C_P, M_Q, W_Q, B_Q and C_Q) were used to evaluate the growth, feed efficiency and lifetime performance of females from eight pure lines and 16 F₁ crosses. Line comparisons within populations (P or Q) revealed that the heaviest line at days 21, 42 and 63 was W, followed by lines B, M and C in both populations, while the highest in feed efficiency between days 21 and 63 was line W, followed by lines B, M and C in population P, and was line B followed by lines W, M and C in population Q. Generally, average body weights and feed efficiencies of crosses within and between populations were similar to those of mid-parents. Selection produced line W superior to the line M in additive direct genetic effects on body weight and feed efficiency in each population, and line W_P superior to line W_Q in additive maternal genetic effects on body weights at days 21, 42 and 63. In lifetime performance tests, total 20-day weight of litters produced by a dam during 200 days averaged from 442.7 g (W_P) to 739.1 g (M_P) for the eight lines. Lines M and W of populations P and Q generally did not differ in additive direct and maternal genetic effects on lifetime performance. Crosses excelled lines in the number of litters raised to weaning (5.44 vs. 5.25) and total 20-day litter weight per dam during 200 days (648.5 vs. 589.3 g). For lifetime 20-day litter weight per group, crosses from unselected lines (C) exceeded crosses from lines selected for nursing ability (M), adult weight (W) and both traits (B). Crosses of lines from different populations showed a higher heterosis in lifetime performance than crosses of lines within populations. Heterosis in the number of litters raised to weaning, and total 20-day litter weight per dam was significant in crosses between lines C_P and C_Q, between lines W_P and w_Q, and between lines W_P and m_Q. Crosses C_PC_Q and C_QC_P had a highly persistent production during lifetime tests.Animal Research Institute Publication 860USDA SEA-AR, Purdue University, West Lafayette, In. 47906 (USA)     

Feed efficiency and body composition of selected and unselected mice

Summary An examination was carried out of the feed intake, feed efficiency and body composition of selected and unselected mice. It was demonstrated that selected mice utilised food more economically, and, in total, produced more protein than the control animals. However, selection had a negative influence on the percentage content of protein and ash. Also, selection caused greater adiposity of selected females and a greater water content in the bodies of selected males (in %).This work was partly supported by grant No. FG-Po-348 (JB-13), Project No. PL-ARS-68.     

Heterosis among lines of mice selected for body weight

Summary After treatment of one strain of A. bitorquis and 12 strains of A. bisporus in modified monokaryotization solution, three types of mycelia were received: one is the original di- or heterokaryon, the other two were proven to be neohaplonts in A. bitorquis and two strains of A. bisporus. In neohaplonts of good fruiting strains, homokaryotic fruiting was observed.     

Accumulation of lethals in highly selected lines of Drosophila melanogaster

Summary Four synthetic lines of D. melanogaster selected for low sternopleural bristle number for 50 generations were screened for lethals on chromosome III when their mean score equalled 2.5. Each line originated from a cross between line M (previously selected for the same trait during 130 generations) and a different unselected cage population. Line M was already known to carry a recessive lethal on chromosome III affecting the selected trait, such that the bristle score of the lethal heterozygote was lower than that of the viable homozygote. Tests revealed 18 lethals, 15 of these present in at least two lines. Each line carried from 10 to 16 lethals. All lines carried groups of lethals present on the same chromosome, and at least six lethals in each line were included in such an association with a frequency of 0.18 or higher. It appears that the lethal affecting bristle score in line M has protected a segment of chromosome III from natural selection and that the remaining 14 lethals have accumulated later in that line.     

Analysis of lethals in selected lines of Drosophila melanogaster

Summary Five lines of Drosophila melanogaster that reached an extreme phenotype after long-term selection for increased dorsocentral bristle number, were analysed for the presence of lethals. Seven chromosome II and three chromosome III lethal types were detected in four of the lines, at frequencies ranging from between 6% and 36%. No lethal had any demonstrable effect over the selected trait. In one line, where almost every chromosome II was a lethal carrier, it was shown that the main lethal (at a frequency of 36%) was associated with the transmission ratio distortion in males. The processes which could lead to the accumulation of this lethal and others linked in disequilibrium to it is discussed. Some results suggest similar mechanisms for the accumulation of lethals in the other lines. These findings show that causes other than the direct effect of artificial selection must be taken into account when trying to explain the accumulation of lethals in selected lines.     

Mating schemes for optimum contribution selection with constrained rates of inbreeding

The effect of non-random mating on genetic response was compared for populations with discrete generations. Mating followed a selection step where the average coancestry of selected animals was constrained, while genetic response was maximised. Minimum coancestry (MC), Minimum coancestry with a maximum of one offspring per mating pair (MC1) and Minimum variance of the relationships of offspring (MVRO) mating schemes resulted in a delay in inbreeding of about two generations compared with Random, Random factorial and Compensatory mating. In these breeding schemes where selection constrains the rate of inbreeding, ΔF, the improved family structure due to non-random mating increased genetic response. For schemes with ΔF constrained to 1.0% and 100 selection candidates, genetic response was 22% higher for the MC1 and MVRO schemes compared with Random mating schemes. For schemes with a less stringent constraint on ΔF or more selection candidates, the superiority of the MC1 and MVRO schemes was smaller (5–6%). In general, MC1 seemed to be the preferred mating method, since it almost always yielded the highest genetic response. MC1 mainly achieved these high genetic responses by avoiding extreme relationships among the offspring, i.e. fullsib offspring are avoided, and by making the contributions of ancestors to offspring more equal by mating least related animals.     

Chiasma frequency in strains of mice selected for litter size and for high body weight

Summary Chiasma frequency was measured in male mice of three outbred lines: FZt:DU (control); DU:6, selected for increased body weight; and DU:C, selected for high fertility. Chiasma frequency was seen to increase in the high body weight line, but decrease in the high fertility line. In both selected lines the intragroup variance in chiasma frequency increased while in DU:C the intracell variance was lower than in the control.     

Kin selection may inhibit the evolution of reciprocation

Kin selection and reciprocal cooperation provide two candidate explanations for the evolution of cooperation. Models of the evolution of cooperation have typically focussed on one or the other mechanism, despite claims that kin selection could pave the way for the evolution of reciprocal cooperation. We describe a computer simulation model that explicitly supports both kin selection and reciprocal cooperation. The model simulates a viscous population of discrete individuals with social interaction taking the form of the Prisoner's Dilemma and selection acting on performance in these interactions. We recount how the analytical and empirical study of this model led to the conclusion that kin selection may actually inhibit the evolution of effective strategies for establishing reciprocal cooperation.