Correlated Selection Responses Research Articles

Examples of overlooking common sense solutions: the domestication gene and selection against mortality.

Today the developments in genetics are exciting. Perhaps this explains why geneticists sometimes seem to overlook common sense solutions. One example of this is the selection experiment done by Bijma et al. (2007a,b). These authors developed a sophisticated statistical method of group selection against mortality in hens randomly placed together. One may safely assume that this mortality is due to cannibalism as a result of severe feather pecking. However, they seemed to overlook the possibility that severe feather pecking is no normal behavior performed by all individuals. As a result their selection seemed not very efficient. It is often assumed that layers selected for production traits show severe feather pecking because more aggressive hens have more opportunities to obtain food. Sufficient food is necessary for a good production. Therefore, aggressive hens are supposed to have a higher fitness during the selection for production traits resulting in an undesirable correlated selection response for this trait. However, aggression does not explain why in other strains selected for production traits severe feather pecking is almost absent. It does also not explain why in species not selected for production traits severe feather pecking occurs frequently under husbandry conditions. For instance, game pheasants, partridges, ostriches and in the wild ancestor of our domestic fowl: the bankiva (Gallus gallus; Van Rooijen, 2010a). Severe feather pecking differs from aggressive pecking in several respects, for instance, aggressive pecks are always aimed at the head, whereas severe feather pecks are aimed at other body parts (Savory, 1995). Unlike aggressive pecking, severe feather pecking is not performed by all individuals but it is a deviant behavior performed by particular individuals (Keeling, 1994). The aim of selection under commercial conditions must be to select against these individuals (Van Rooijen, 2010b). Another example of overlooking a common sense solution is the experiment performed by Rubin et al. (2010). To reveal loci under selection during domestication, these authors resequenced the whole genome of groups of domestic poultry and that of bankiva jungle fowl. These authors found that essentially all individuals of domesticated fowl carry a TSHR allele (the locus for the thyroid stimulating hormone receptor). The TSHR-gene plays a role in the photoperiod control of reproduction, i.e. it explains why domestic hens lay eggs almost the year round. In bankiva zoo populations this allele was only found at intermediate frequency. Therefore, these authors concluded that TSHR may be a domestication locus in chicken. They assumed that the presence of this deviant TSHR-gene in bankiva zoo populations was due to hybridization with domestic chicken. Apparently they overlooked the possibility that this gene could originate from the Ceylon jungle fowl (Gallus lafayetti), otherwise they had incorporated this fowl in their study. There is a good reason to consider this possibility. During the breeding season, to attract females, the male bankiva is less camouflaged than the female. Outside the breeding season the plumage of the bankiva cock is more hen-like (eclipse plumage). The domestic cock does not possess such an eclipse plumage and is able to reproduce the year round. Probably, the TSHR-gene plays also a role in the photoperiod control of the male eclipse plumage, i.e., it probably explains why domestic males have a similar plumage the year round. Also the Ceylon male does not possess an eclipse plumage. The Ceylon male and female seem able to reproduce the year round (this is confirmed by fancy fowl keepers) and, thus, oviposition and male sexual behavior seem hardly controlled by photoperiod. The explanation may be that Ceylon fowl lives on Sri Lanka (formerly Ceylon), where from May to August the Yala monsoon brings rain to the south western half of the island, and from October to January the Maha monsoon to the North and East (Cummings et al., 2006). Therefore the relation between day length and the most suitable period for reproduction is not straightforward for the Ceylon jungle fowl population on Sri Lanka. This suggests that the Ceylon jungle fowl carry the deviant TSHR-locus. Probably, the domestic chicken has a multiple origin (Nishibori et al., 2005). For instance, the gene for the yellow skin descents from the Sonnerats jungle fowl (Gallus sonneratii) (Eriksson et al., 2008. Therefore one may question whether the TSHR-locus does not descend from Ceylon jungle fowl and thus is much older than domestication. The suggestion that the TSHR-locus is a domestication locus seems premature, due to a focus on the genetic method.

Genetic parameters for feather pecking and aggressive behavior in a large F2-cross of laying hens using generalized linear mixed models

Feather pecking and aggressive pecking is a well-known problem in egg production. In the present study, genetic parameters for 4 feather-pecking-related traits were estimated using generalized linear mixed models. The traits were bouts of feather pecking delivered (FPD), bouts of feather pecking received (FPR), bouts of aggressive pecking delivered (APD), and bouts of aggressive pecking received (APR). An F2-design was established from 2 divergent selected founder lines. The lines were selected for low or high feather pecking for 10 generations. The number of F2 hens was 910. They were housed in pens with around 40 birds. Each pen was observed in 21 sessions of 20 min, distributed over 3 consecutive days. An animal model was applied that treated the bouts observed within 20 min as repeated observations. An over-dispersed Poisson distribution was assumed for observed counts and the link function was a log link. The model included a random animal effect, a random permanent environment effect, and a random day-by-hen effect. Residual variance was approximated on the link scale by the delta method. The results showed a heritability around 0.10 on the link scale for FPD and APD and of 0.04 for APR. The heritability of FPR was zero. For all behavior traits, substantial permanent environmental effects were observed. The approximate genetic correlation between FPD and APD (FPD and APR) was 0.81 (0.54). Egg production and feather eating records were collected on the same hens as well and were analyzed with a generalized linear mixed model, assuming a binomial distribution and using a probit link function. The heritability on the link scale for egg production was 0.40 and for feather eating 0.57. The approximate genetic correlation between FPD and egg production was 0.50 and between FPD and feather eating 0.73. Selection might help to reduce feather pecking, but this might result in an unfavorable correlated selection response reducing egg production. Feather eating and feather pecking are genetically correlated and this needs further investigation.

Genetic response to combined family selection for improved mean harvest weight in giant freshwater prawn (Macrobrachium rosenbergii) in Vietnam

We estimated genetic changes in body and carcass weight traits in a giant freshwater prawn (GFP) (Macrobrachium rosenbergii) population selected for increased body weight at harvest in Vietnam. The data set consisted of 18,387 individual body and 1730 carcass weight records, as well as full pedigree information collected over four generations. Average selection response (per generation) in body weight at harvest (transformed to square root) estimated as the difference between the Selection line and the Control group was 7.4% calculated from least squares mean (LSMs), 7.0% from estimated breeding values (EBVs) and 4.4% calculated from EBVs between two consecutive generations. Favorable correlated selection responses (estimated from LSMs) were found for other body traits including: total length, cephalothorax length, abdominal length, cephalothorax width, and abdominal width (12.1%, 14.5%, 10.4%, 15.5% and 13.3% over three selection generations, respectively). Data in the second generation of selection showed positive correlated responses for carcass weight traits including: abdominal weight, exoskeleton-off weight, and telson-off weight of 8.8%, 8.6% and 8.8%, respectively. We conclude that body weight at harvest responded well to the application of combined (between and within) family selection and correlated responses in carcass weight traits were favorable.

Divergent selection for intramuscular fat content in rabbits. II. Correlated responses on carcass and meat quality traits1

Correlated responses on carcass and meat quality characteristics after 3 generations of divergent selection for intramuscular fat (IMF) content were assessed by comparing the high and low lines. Selection was based on the phenotypic value of IMF content of LM, measured in 2 full sibs of the first parity. Traits measured were: BW, HCW, commercial carcass weight (CCW), reference carcass weight (RCW), scapular (SF) and perirenal fat (PF) content, meat-to-bone ratio (M:B) of the hind leg, pH of LM, color (lightness, L*; redness, a*; and yellowness, b*) of the carcass and of a LM section, protein content, and fatty acid (FA) composition of LM. A total of 174 records was used to estimate the correlated selection response. Data were analyzed using Bayesian methodology. We considered one-third of the phenotypic SD of a trait as a relevant value for the difference between lines. Then, the probability of the difference being greater than a relevant value (PR) was calculated. A low PR implies that the lines compared are similar. Carcass weights (PR between 0.24 and 0.31) and M:B of the hind leg (PR = 0.15) were not modified by selection for IMF content. There was a slight negative correlated response for BW, although evidence of its relevance was low (PR = 0.48). Scapular fat content was similar between lines (PR = 0.03). There were differences for PF content, although there was low evidence for showing its relevance (PR = 0.47). Color traits of the carcass were not affected by selection (PR between 0.04 and 0.30). In muscle, L* was also similar between lines (PR = 0.26). There were differences for a* and b*, although there was little evidence of their relevance (PR = 0.35 and 0.40, respectively). There was a positive correlated response on muscle pH and differences could be relevant (PR = 0.77). Protein content of LM was similar between lines (PR = 0.13), whereas FA composition was affected by selection. There were relevant differences between lines for MUFA (PR = 0.99), n-3 (PR = 0.95), and n-6 (PR = 0.98) percentages. For individual FA, differences were relevant for C18:1n-9 (PR = 0.97) and C20:5 n-3 (PR = 0.98). In conclusion, selection for IMF content may modify carcass quality by increasing PF content. Moreover, it led to some modifications in pH and FA composition of LM.

Genetic parameters for growth, reproduction and fitness traits in the South African Dorper sheep breed

Across flock genetic parameter estimates for growth, reproduction and fitness traits were derived using residual maximum likelihood (REML) procedures for the South African Dorper sheep breed. Data were retrieved from the National Small Stock Improvement Scheme (NSIS) data base from breeders that were constantly submitting performance data for a period spanning 30 years (1980–2009). Weaning weight and post-weaning weight were moderately heritable with estimates being 0.21±0.01 and 0.27±0.02 respectively. Maternal effects were significant, although of fairly low magnitude in live weight traits. It was demonstrated that reproductive and fitness traits such as total weaning weight per ewe lambing (TWW/L), number of lambs born per ewe lifetime (NLB/EL), number of lambs weaned per ewe lifetime (NLW/EL), lamb survival to weaning and litter size were lowly heritable with their estimates being 0.12±0.02, 0.10±0.01, 0.09±0.01, 0.07±0.01 and 0.07±0.02 respectively. Selection of Dorper sheep with the objective of improving reproduction and fitness is feasible although relatively low heritability estimates indicate that annual genetic progress may be slow. Low heritabilities for ewe productive life (EPL) and stay ability at two, three and four years of age were estimated to be 0.05±0.01, 0.05±0.02, 0.09±0.03 and 0.11±0.04 respectively. This indicated that these traits are, to some extent, influenced by genetics. Lambing chances per ewe lifetime (LC/EL) and times lambed per ewe lifetime were demonstrated to have a moderate heritability (0.23±0.01 and 0.11±0.04 respectively) and would also result in a correlated selection response in both reproduction and longevity. No genetic basis was found for inter-lambing period (ILP). It was therefore deduced that ILP can be improved through sound management. Live weight traits were positively correlated with reproduction and fitness traits. TWW/L was genetically and environmentally positively correlated with survival, litter size and EPL. It was concluded that despite the low additive genetic variances for reproduction and fitness, genetic improvement is feasible. Therefore, breeders should incorporate these traits in their selection strategies to achieve maximum production.

Dissimilaridade entre famílias e resposta correlacionada à seleção para caracteres de raiz de cenoura cultivada em dois sistemas de produção agroecológicos no Distrito Federal

The objective of this work was to calculate the dissimilarity among families and the correlated selection response in a carrot population grown in two agroecologic production systems. The experiments were conducted in Brasília, in the summer of 2006/2007. A hundred half-sib families of carrot were evaluated in a complete randomized block design with two replications. Twenty plants were harvested individually per plot and were evaluated for root characters. Joint and separated variance analyses for the two systems were performed. The dissimilarity among and between families and the correlated selection response were calculated. It was mainly verified that inside of the population, in both production systems, it is possible to select for more dissimilar families to be used in a next recurrent selection cycle, providing gains with heterosis. In selecting among or within families, for larger root mass, gains superior to 2% per selection cycle could be expected, for longer roots and with larger xylem diameter. Selection for higher levels of carotenoids, mainly in the xylem cannot be made separately from the yield components, length, measures of diameter and average root weight.

Coadapted changes in energy metabolites and body color phenotypes for resistance to starvation and desiccation in latitudinal populations of D. melanogaster

In D. melanogaster, resistance to starvation and desiccation vary in opposite directions across a geographical gradient in India but there is lack of such clinal variation on other continents. However, it is not clear whether these resistance traits or other correlated traits are the target of natural selection. For resistance to starvation or desiccation in D. melanogaster, we tested the hypothesis whether body color phenotypes and energy metabolites show correlated selection response. Our results are interesting in several respects. First, based on within population analysis, assorted darker and lighter flies from a given population showed that darker flies store higher amount of trehalose and confer greater desiccation resistance as compared with lighter flies. By contrast, lighter flies store higher lipids content and confer increased starvation tolerance. Thus, there is a trade-off for energy metabolites as well as body color phenotypes for starvation and desiccation stress. Further, trait associations within populations reflect similar patterns in geographical populations. Second, we found opposite clines for trehalose and body lipids. Third, coadapated phenotypes have evolved under contrasting climatic conditions i.e. drier and colder northern localities select darker flies with higher trehalose as well as desiccation resistance while hot and humid localities favor lighter flies with higher lipids level and greater starvation tolerance. Thus, the evolution of coadapated phenotypes associated with starvation and desiccation resistance might have resulted due to specific ecological conditions i.e. humidity changes on the Indian subcontinent.

Correlated selection responses for female fertility after selection for high protein yield or low mastitis frequency in Norwegian Red cows

Correlated selection responses in female fertility were estimated from a selection experiment with 2 groups of Norwegian Red cows selected for high protein yield (HPY) and low mastitis frequency (LCM), respectively. Genetic trends were calculated for nonreturn rate within 56 d after first insemination (NR56) for heifers, first-lactation cows, and second- and third-lactation cows, calving interval between first and second calving (CIN), and interval from calving to first insemination (CFI) for first-lactation cows and for second- and third-lactation cows. A total of 5,001 cows from the selection experiment had estimated breeding values for fertility, of which 2,806 were HPY and 2,195 were LCM cows. Permutation tests showed significant genetic differences between LCM and HPY for all fertility traits except CFI for second- and third-lactation cows. Observed differences between mean EBV in HPY and in LCM were, with few exceptions, far outside the range of the permutation test (i.e., significantly different from zero). LCM cows were, in general, genetically more fertile than HPY cows, with higher NR56 in heifers and cows, shorter CIN, and shorter CFI in first lactation. Genetic differences between HPY and LCM after 6 cow-generations were 2.5 percentage units NR56 in heifers, 2 percentage units NR56 in cows, and 4 d for CIN. No difference was found for CFI in second and third lactation. This is the first report of genetic change in female fertility as a correlated response after selection against mastitis.

Correlated changes in thermotolerance traits and body color phenotypes in montane populations of Drosophila melanogaster : analysis of within‐ and between‐population variations

Thermotolerance traits vary across geographical gradients but there is a lack of clinal variation in some Drosophila species. Thus, it is not clear whether thermotolerance or other correlated traits are the target of natural selection. In order to test selection responses, we investigated body melanization and thermotolerance traits in six altitudinal populations of Drosophila melanogaster. Based on rearing different geographical populations under uniform growth conditions at 21 °C (common garden experiments), clinal variations for cold resistance are in the direction opposite to heat resistance along an altitudinal gradient, that is darker flies from highland populations evidenced higher levels of cold resistance while lowland populations showed higher heat resistance. Phenotypic plastic responses for body melanization at 17–28 °C showed significant correlations with thermotolerance traits. At 17 °C, regression coefficients as a function of altitude are highly significant and positive for cold resistance but negative for heat knockdown. However, for flies reared at 28 °C, there is no elevational change in melanization as well as thermotolerance traits. Thus, both genetic and plastic changes of body melanization and thermotolerance traits suggest a correlated selection response. Further, within-population analyses of body melanization (based on dark, intermediate and light color phenotypes) showed significant associations with thermotolerance traits. Correlated variations in body melanization and thermal tolerances are associated with climatic thermal variability (Tcv) but not with Tmin. or Tmax. along an altitudinal gradient.

Direct and correlated responses to selection for longevity in Drosophila buzzatii

The possible associations between longevity, early fecundity, and stress-resistance traits were explored using artificial selection on longevity in a laboratory population of Drosophila buzzatii. Three replicated lines were selected for increased lifespan (L lines) and compared with the respective unselected controls (C lines) after the 14th generation of selection. Mean longevity exhibited a significant response to selection. The baseline mortality tended to decrease in the L lines and a negative correlated response to longevity selection was found for early fecundity. Egg-to-adult developmental time increased in L lines. Longevity selection increased stress resistance for both high and low temperatures, as measured by heat knockdown resistance and chill-coma recovery. Starvation resistance also tended to be higher in L than in C lines. The results obtained are consistent with the hypothesis of trade-offs between longevity and early fecundity, and also suggest a trade-off association between adult longevity and developmental time. Correlated selection responses were generally consistent with correlations among the traits previously inferred from altitudinal clines for longevity and stress-resistance phenotypes. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 738–748.

Short Communication: Correlated Selection Responses in Somatic Cell Count from Selection Against Clinical Mastitis

Correlated selection responses in lactation mean somatic cell score (LSCS) were estimated for groups of cows selected for high protein yield and low mastitis frequency, respectively. Selection for increased milk production resulted in an unfavorable correlated response for LSCS, whereas direct selection against clinical mastitis resulted in a favorable correlated selection response. After 6 cow generations, the genetic difference between the high protein yield group and the low mastitis group was 0.3 units LSCS, equivalent to a difference in somatic cell count of approximately 15,000, assuming deviations from a population mean LSCS of 4.1.

Agricultural Fitness of Smooth Bromegrass Populations Selected for Divergent Particle‐Size Reduction Index

Voluntary intake potential of a forage crop is generally considered to be the most important feed characteristic regulating animal performance. Efforts to develop forage crops with reduced neutral detergent fiber (NDF) concentration are associated with reduced plant fitness, prompting the development of alternative approaches to improve intake, such as particle‐size reduction index (PSRI). The objective of this research was to characterize correlated selection responses of four fitness traits following divergent selection for PSRI. Twelve smooth bromegrass (Bromus inermis Leyss.) populations (four base populations and their Cycle‐1 high‐PSRI and Cycle‐1 low‐PSRI progeny) were evaluated for forage yield, ground cover, seed yield, and lodging. Divergent selection for PSRI resulted in a negative change in forage yield, ranging from −0.097 to −0.379 Mg ha−1 cycle−1 across the four base populations. Pleiotropy or very tight linkage between loci controlling forage yield and PSRI accounted for only about half of the variation due to selection. The greater inconsistency of forage yield selection responses across the four populations, the lesser proportion of forage yield sum of squares attributable to divergence (pleiotropy or tight linkage), and the reduced magnitude of linear selection responses for PSRI compared to NDF suggest that PSRI may be a more effective selection criterion for improving intake potential of smooth bromegrass.

Effects of climate change on the degree of protandry in migratory songbirds

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 35:107-114 (2007) - DOI: https://doi.org/10.3354/cr00717 Effects of climate change on the degree of protandry in migratory songbirds Kalle Rainio1, Anders P. Tøttrup2, Esa Lehikoinen1, Timothy Coppack3,* 1Section of Ecology, Department of Biology, University of Turku, 20014 Turku, Finland 2Center for Macroecology, Institute of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen Ø, Denmark 3Institute of Avian Research, An der Vogelwarte 21, 26386 Wilhelmshaven, Germany *-Corresponding author. Email: coppack@vogelwarte-helgoland.de ABSTRACT: Current climate change is affecting the timing of life-history events of birds, such as the timing of spring arrival at the breeding grounds. Interspecific differences in the advancement of spring migration have hitherto been attributed to differences in exposure to climatic variables in winter or on migration, without a more detailed consideration of sex-specific differences in the timing and extent of migration. Since males and females migrate during different times of the season or may segregate into different wintering grounds, we expect climate change to differentially affect the arrival timing of males and females. Furthermore, sexual selection theory predicts that the degree of protandry (i.e. the time difference between male and female arrival) should increase when the forces of natural selection opposing early arrival relax and the earliest males benefit from improved mating opportunities. Here, we explore whether the degree of protandry has changed during a period of climatic warming using long-term phenological data collected at 5 North European bird observatories. We show for 4 sexually dichromatic songbird species that spring migration has generally advanced, but that the degree of protandry has not changed. Moreover, we provide evidence that variation in large-scale weather conditions, as reflected in the North Atlantic Oscillation (NAO) index, have not affected the degree of protandry. We hypothesize that a parallel shift in the timing of male and female migration may be due to similar phenotypic plastic responses of males and females to climatic changes or reflect a correlated selection response in males and females. In addition, we discuss the possibility that the observed variation in protandry could result from seasonal shifts in local environmental conditions under which birds of both sexes ‘fall out’ and are sampled. KEY WORDS: Differential migration · Ficedula hypoleuca · Lanius collurio · Migration timing · Phenology · Phoenicurus phoenicurus · Protandry · Sylvia atricapilla Full text in pdf format PreviousNextCite this article as: Rainio K, Tøttrup AP, Lehikoinen E, Coppack T (2007) Effects of climate change on the degree of protandry in migratory songbirds. Clim Res 35:107-114. https://doi.org/10.3354/cr00717 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 35, No. 1-2. Online publication date: December 31, 2007 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2007 Inter-Research.

Response to selection for harvest body weight of Oreochromis shiranus

Realised and predicted responses to selection were obtained for harvest body weight of Oreochromis shiranus from two generations of selection at the National Aquaculture Centre, Domasi, Malawi. The realised response was estimated from the difference in the least squares means of selected and unselected control populations, while the predicted response was obtained from the difference of the mean breeding values between generations. The realised (13.2%) and predicted (14.4%) responses for harvest body weight over the two generations of selection were not significantly different (P>0.05). The intensity of selection from F1 to F2 (0.66) and from F2 to F3 (0.59) was low due to availability of few selection candidates per family at harvest caused by mortality, tag loss and the need to form broad heterogeneous multi-strain F2 and F3 populations. Within generation, the heritability estimates for the F1 (0.31±0.09), F2 (0.31±0.10) and F3 (0.35±0.11) generations were moderate. Across generation, the heritability estimate was low (0.14±0.27). Within generation, the magnitude of the common full-sib effect was moderate (0.08–0.09) and not significantly different from zero (P>0.05). However, across generations, the common full-sib effect was high (0.27±0.05) and significantly different from zero (P<0.05). A substantial correlated selection response due to selection for increased harvest body weight was observed for both tagging body weight and for survival from tagging to harvest; for tagging body weight 22.8% from F1 to F2 and 15.9% from F2 to F3; for survival 7.2% from F1 to F2 and 13.8% from F2 to F3. The results are discussed in relation to the maximisation of the genetic gain in the future generations while constraining the rate of inbreeding.

A new set of laboratory-selected Drosophila melanogaster lines for the analysis of desiccation resistance: response to selection, physiology and correlated responses

Artificial selection experiments provide insights into the evolutionary factors that can shape adaptive responses and have previously been utilized to examine the physiological adaptations that can improve survival to desiccation in Drosophila melanogaster. While such studies demonstrate that multiple resistance mechanisms may arise via different base populations and selection regimes, water retention emerges as a key mechanism for desiccation survival. Here, we present the physiological, correlated response and life history data for a new set of selection lines designed for the genetic dissection of desiccation resistance. After 26 generations of selection for desiccation resistance, female survival increased twofold. In contrast to previous studies, the altered resistance was associated primarily with enhanced dehydration tolerance and increased mass and less consistently with decreased rates of water loss. Life history tradeoffs and correlated selection responses were examined and overlap with previously published data. We crossed the resistant selected lines to desiccation-sensitive lines from the same control background to examine how each heterozygous resistant chromosome (excluding four) may improve desiccation resistance and observed that most of the resistance was due to genes on the third and first chromosomes, although interaction effects with the second chromosome were also detected. Results are compared to other selection responses and highlight the multiple evolutionary solutions that can arise when organisms are faced with a common selection pressure, although water loss rate remains a common mechanism in all studies.

Genetic and phenotypic parameters for lactation traits in a flock of Saanen goats in Mexico

Heritability, repeatability and genetic and phenotypic correlations of total milk production (TM), cumulated milk production to 120 days (M120) and lactation length (LL), were estimated from the analysis of 1413 records (566 does) obtained from a Saanen goat flock in Querétaro, Mexico, during 1991–1997. Variance components were estimated using a restricted maximum likelihood procedure and applying an animal model. The model included the fixed effects of year–season of kidding, litter size and age of doe, and random effects of animal, permanent environment and residual. For TM, M120 and LL estimates of heritability were 0.22 ± 0.07, 0.12 ± 0.05 and 0.04 ± 0.03, and of repeatability were 0.40, 0.27 and 0.11, respectively. Genetic correlations between TM and M120, TM and LL, and M120 and LL, were 0.98, 0.58 and 0.53, respectively. Phenotypic correlations ranged from 0.30 to 0.83. The correlated selection response for TM from indirect selection on M120 was 71.5% of that expected from direct selection. Efficient selection for TM is possible and M120 could be used as an early indicator of TM, due to the high indirect selection response calculated.

QTL analysis of body composition and metabolic traits in an intercross between chicken lines divergently selected for growth

The high- and low-growth lines of chickens have been developed from a single founder population by divergent selection for body weight at 56 days of age for more than 40 generations. The two lines show a ninefold difference in body weight at selection age and several interesting correlated selection responses such as altered body composition and metabolic differences. We have generated a reciprocal intercross comprising >800 F2 birds. In a previous study, we reported the detection of 13 quantitative trait loci (QTLs) affecting growth. Here we report QTLs for body composition (fat deposition, muscle development), weight of internal organs, and metabolic traits (plasma concentrations of glucose, insulin, cholesterol, glucagon, triglycerides, and IGF-I). Most of the QTLs with convincing statistical support mapped in the vicinity of growth QTLs. One of the most interesting observations was that the type of reciprocal cross had highly significant effects on body weight at hatch and on plasma concentrations of glucose, cholesterol, insulin, and IGF-I, but it had no significant effect on body weight at 56 days of age. The reciprocal cross explained between 15 and 35% of the phenotypic variance for weight at hatch and for plasma concentrations of glucose and insulin. The observed pattern indicated that these effects were caused by maternal effects or by genetic differences in mitochondrial DNA.

Line selection for exploiting durum wheat (T. turgidum L. var. durum) local landraces in modern variety development program

Pure line selection for grain yield applied within four durum wheat local landraces (Triticum turgidum L. var durum) was studied in an effort to determine: (i) the agronomic performance of selected line mixtures (bulks) and their value as potential new cultivars, (ii) the effectiveness of pure line selection for grain yield within local landraces and (iii) the correlated selection response of yield components and kernel quality traits. Four local durum wheat landraces were used. Two of them, Mytilini-1 and Mytilini-2 are still cropped in some rural areas of the island Mytilini whereas the other two, Limnos and Mavragani are maintained in the Greek Gene Bank. Following their preliminary evaluation for agronomic performance under current growing conditions, 100 individual plants from each landrace were randomly selected. Selected plants (pure lines) were field evaluated head to row during 1997–98 and 1998–99 growing seasons. Based on grain yield performance, bidirectional selection, high vs low, was practised within each landrace. Thus the five higher yielding lines and their corresponding lower ones from each landrace were identified. Selected lines, with no further progeny testing, were pooled using a balanced seed composite to form the high yielding five line bulk and its respective low counterpart. The resulting 16 bulks (eight high and eight low) along with their four source landraces and two commercial varieties, Mexicalli and Simmeto, used as checks, entered field testing for agronomic performance in two and one location during 1999–00 and 2000–01 growing seasons respectively. Data for grain yield and yield components (1000 kernel weight, number of kernels, and productive tillers) along with kernel quality data (protein content and vitreous) were recorded. Data for grain yield indicated that the landraces studied seemed to be line mixtures, as expected, since they responded to bidirectional phenotypic pure line selection. The high yielding bulks were of interesting agronomic performance, equivalent to or significantly better than that of the commercial checks and are worth further testing as potential cultivars. Selected high bulks of Mytilini 2 landrace significantly outyielded both the source landrace and the commercial checks maintaining the high protein content of the source landrace, which was significantly higher than checks. This performance provides evidence that the within landraces selection of lines combining high grain yield with high protein content seems to be feasible. In conclusion, evidence is presented that genetic variability seems to be available within the landraces studied which could be worth using in breeding programs. Furthermore the simple pure line selection breeding effort undertaken seemed to be effective in developing line bulks with promising performance and worth further testing as potential cultivars.

Food soiling and diet discrimination of mouse lines divergently selected for response to a nutritional toxicosis

Mouse lines were selected for eight generations for resistance (R) versus susceptibility (S) to growth depression from toxins in endophyte-infected tall fescue seed. To examine a possible correlated response to that selection, three experiments subsequently were conducted to examine food soiling behaviour of the mice. In Experiment 1, the average food soiling score was higher for R mice than S mice; but males had higher scores than females and soiling of the toxin-containing diet (T+) was greater than soiling of the non-toxin-containing diet (T−) only in the R line. When all mice received the T− diet during the first two weeks of Experiment 2, neither line, sex nor their interaction affected food soiling scores. During the second two weeks of Experiment 2, R mice had higher average food soiling scores than S mice on both the T− and the T+ diet; but within the R line, neither sex, diet nor their interaction significantly affected food soiling scores. In Experiment 3, when all mice had simultaneous access to both diets, bowls containing the T− diet were more heavily soiled than bowls containing the T+ diet, lines did not differ in soiling of the two diets, but males expressed greater diet soiling differences than females. In summary, after eight generations of divergent selection for growth depression from ingestion of fungal toxins, resistant and susceptible lines differed in food soiling behaviour, but not consistently across experiments. Differences could be attributable to genetic drift but might also represent correlated selection response in social, nutritional or emotional aspects of eliminative behaviour. Speculations about the biological and behavioural bases for observed differences may lead to testable hypotheses about how toxicosis resistance is inherited and expressed.

Respuesta a la selección para producción láctea de toros Holstein de Estados Unidos en las provincias de Bío-Bío y Malleco, Chile

Correlated selection response of United States Holstein bulls was estimated in the provinces of Bio-Bio and Malleco (Chile). The aim of this research was to ...