Environmental Sources Of Variation Research Articles

Apparent Heritability of Parental Care in Savannah Sparrows

Parental effort measures the total amount of time and energy allocated toward care of offspring, and it is often an obvious and variable component of an animal's life history (Winkler and Wilkinson 1988, Clutton-Brock 1991). Among birds, intraspecific variation in parental effort is more quantitative than qualitative. Individual adults differ in feeding rate (Yasukawa et al. 1990, Wright and Cuthill 1992), intensity of offspring defense (Winkler 1992), and tendency to engage in prolonged associations with young (Weatherhead and McRae 1990). Like all quantitative traits, intraspecific variation in parental effort can be attributed to genetic and environmental causes. However, recent work has focused mostly on environmental sources of variation (Ketterson and Nolan 1994, Gowaty 1996a), and individual birds often are viewed as decision-making machines that respond adaptively to changes in their physical or social environments (Winkler and Wilkinson 1988). Indeed, birds modify parental effort in response to numerous proximate factors, including genetic parentage (Lifjeld et al. 1998), brood size (Ruusila and P6ysa 1998), and offspring age and condition (Whittingham and Robertson 1993). In no case have environmental factors accounted completely for differences among individuals in the intensity of parental care, however, and some role for genetic or cultural determination seems likely. For quantitative traits, genetic and environmental effects can be distinguished by examining the phenotypic resemblance of relatives. In cases of high narrow-sense heritability (h2), additive genetic effects contribute substantially to overall phenotypic variation, and relatives strongly covary (Falconer and Mackay 1996). Among vertebrates, estimates of heritability are lacking for measures of parental effort and for most quantitative behaviors in the field (Hailman 1986, Boag and van Noordwijk 1987, Mousseau and Roff 1987; but see Waser and Jones 1989). In general, heritabilities for behavioral traits are low (Lemon 1993, Berthold and Pulido 1994), suggesting that quantitative differences among individuals are largely driven by the environment. Here, we examine the degree to which male and female feeding rates are heritable in an insular population of Savannah Sparrows (Passerculus sandwichensis). We show that quantitative differences in feeding rates among males can be attributed to the be-

Genetic and environmental sources of variation in leaf morphology of Sphagnum fallax and Sphagnum isoviitae (Bryopsida): comparison of experiments conducted in the field and laboratory

Gametophores from mixtures of the closely related Sphagnum fallax (H. Klinggr.) H. Klinggr. and Sphagnum isoviitae Flatberg, from two localities were clonally propagated in axenic culture and back transplanted from laboratory to field conditions, as well as reciprocally transplanted between the same localities. Genetic and environmental effects on leaf morphology were estimated to assess the taxonomic merit of these characters. Differences between populations exceeded between-taxon differences and could not be taken as evidence of two separate species. Plastic responses were apparent in the reciprocal transplant experiment, and a species-specific norm of reaction could be discerned in one character. Compared with the field experiments the species- and population-level genetic variances increased in the laboratory. This indicates that increased differences between species and populations were an artefact of experimental conditions, rather than caused by environmental effects opposing genetic effects on morphology in the field. Among-clone variances remained relatively stable across all experiments, as did residual variances indicating that the clonal propagation process did not elevate developmental noise. Contrasting responses between clonally propagated and field collected gametophores provide indirect evidence of changing levels of genetic and plastic variation throughout ontogeny.Key words: cultivation experiment, phenotypic plasticity, phenetics, Sphagnum, morphology.

Genetic and environmental sources of variation in leaf morphology of <i>Sphagnum fallax</i> and <i>Sphagnum isoviitae </i>(<i>Bryopsida</i>): comparison of experiments conducted in the field and laboratory

Genetic and environmental sources of variation in leaf morphology of <i>Sphagnum fallax</i> and <i>Sphagnum isoviitae </i>(<i>Bryopsida</i>): comparison of experiments conducted in the field and laboratory

Quantitative trait loci for fluctuating asymmetry of discrete skeletal characters in mice.

Levels of fluctuating asymmetry (FA) are often taken as indicators of the degree to which genotypes differ in their ability to buffer genetic and environmental sources of variation. Interval mapping techniques were used to search for quantitative trait loci (QTLs) affecting directional asymmetry (DA) and fluctuating asymmetry (FA) in six bilateral discrete skeletal traits in house mice. These six characters as well as 76 microsatellite markers were scored in over 500 mice that resulted from crosses of F1 mice originally produced from matings of the Large (LG/J) and Small (SM/J) inbred strains. The number of QTLs affecting DA in each of the characters was no more than expected by chance alone so it was concluded that there was little evidence for individual genes affecting DA. There appeared to be a genetical basis for FA in these characters, however, because the number of QTLs significantly affecting FA (10 at the 5% level, three at the 1% level) was greater than expected by chance alone. The 10 QTLs significantly affecting FA in any given character were located on eight different chromosomes, mostly at locations for QTLs affecting other characters or DA in other characters. Their cumulative contribution to the total phenotypic variance was small, averaging only 3.9% per locus. Dominance genotypic values for these QTLs were more extreme than additive genotypic values, suggesting that heterozygotes at many loci are better buffered than homozygotes and that allelic interactions (dominance) may play an important role in the production of FA.

Quantitative trait loci for fluctuating asymmetry of discrete skeletal charactersin mice

Levels of fluctuating asymmetry (FA) are often taken as indicators of the degree to which genotypes differ in their ability to buffer genetic and environmental sources of variation. Interval mapping techniques were used to search for quantitative trait loci (QTLs) affecting directional asymmetry (DA) and fluctuating asymmetry (FA) in six bilateral discrete skeletal traits in house mice. These six characters as well as 76 microsatellite markers were scored in over 500 mice that resulted from crosses of F1 mice originally produced from matings of the Large (LG/J) and Small (SM/J) inbred strains. The number of QTLs affecting DA in each of the characters was no more than expected by chance alone so it was concluded that there was little evidence for individual genes affecting DA. There appeared to be a genetical basis for FA in these characters, however, because the number of QTLs significantly affecting FA (10 at the 5% level, three at the 1% level) was greater than expected by chance alone. The 10 QTLs significantly affecting FA in any given character were located on eight different chromosomes, mostly at locations for QTLs affecting other characters or DA in other characters. Their cumulative contribution to the total phenotypic variance was small, averaging only 3.9% per locus. Dominance genotypic values for these QTLs were more extreme than additive genotypic values, suggesting that heterozygotes at many loci are better buffered than homozygotes and that allelic interactions (dominance) may play an important role in the production of FA.

Evolutionary consequences of indirect genetic effects

Indirect genetic effects (IGEs) are environmental influences on the phenotype of one individual that are due to the expression of genes in a different, conspecific, individual. Historically, work has focused on the influence of parents on offspring but recent advances have extended this perspective to interactions among other relatives and even unrelated individuals. IGEs lead to complicated pathways of inheritance, where environmental sources of variation can be transmitted across generations and therefore contribute to evolutionary change. The existence of IGEs alters the genotype-phenotype relationship, changing the evolutionary process in some dramatic and non-intuitive ways.

Variance Component Analysis and Heritability of Antler Traits in White-Tailed Deer

Information on genetic and environmental sources of variation that control antler development in white-tailed deer (Odocoileus virginianus) is needed to develop harvest management programs. We estimated genetic and environmental components of variance for antler development traits collected from deer born from 1977 to 1993 in a captive population. Antler traits were incidence of spikes versus forks, number of points, maximum inside spread, total mass, main beam circumference, and main beam length. In 1.5-year-old males, the degree of additive genetic determination, or heritability (h 2 ), was low (range = 0.00-0.13) for incidence of spikes versus forks, number of points, maximum inside spread, total mass, and main beam length, and was moderate for main beam circumference (h 2 = 0.25). The relatively large carryover influence of the dam as a source of variation was more important than heritability. In 2.5-year-old males, antler-trait heritabilities were low to moderate (0.08-0.39), whereas heritability ranged from 0.03 to 0.43 in mature males (3.5-7.5 years old) with repeated antler-trait records. Permanent and residual effects caused by nonadditive genetic and environmental factors accounted for most of the variation in antler traits expressed by mature males. Our results do not support the use of yearling antler records as criteria for selective breeding management or harvest schemes to alter the genetic quality of a white-tailed deer population.

Sources and implications of variability in sensitivity to chemicals for ecotoxicological risk assessment.

Variability among individuals in their responses to toxic chemicals arises from several sources, the most important of which are genetic differences, environmental influences (including maternal effects and historical factors) and measurement error. Effective risk assessment requires that estimates of toxicant response (e.g., LD50, EC50, LOEC, NOEC) are precise--that is, have narrow confidence limits-, repeatable--that is, different laboratories must obtain the same or very similar result-, and accurate--that is, they must provide a reasonable approximation of the effects of toxicants on real ecological systems. Determining which of the above-mentioned sources of variability has the greatest influence on toxicant response has implications for both the design and interpretation of ecotoxicological tests. If, for example, genetic influences are of overriding importance, controlling genotype (by using clones or inbred strains) can lead to greater precision but at the expense of accuracy when the objective is to estimate toxicant response for the species as a whole. Likewise, if environmental influences are of primary importance in controlling the response to toxicants, performing experiments under a standard temperature, light, and food regime may provide highly repeatable test results that have little relevance to the responses of populations in nature. Although there is little doubt that the development of standard ecotoxicological test guidelines (e.g., by the OECD), that control genetic and environmental sources of variability, has led to improvements in the practice of risk assessment, further advances will require a more sophisticated approach for dealing with these sources of uncertainty. There is a need for more systematic approaches for quantifying the sources of variability in toxicant response and for formally combining the error associated with each source in key risk assessment endpoints.

No evidence for effects of family environment on asthma. A retrospective study of Norwegian twins.

The risk of developing asthma contingent upon the co-twins' history of asthma was analyzed in a population-based study of 5,864 Norwegian twins. A primary aim was to assess the significance of shared environment for the development of asthma from infancy through age 25. Retrospective reports were collected when the twins were 18 to 25 yr of age. The risk of developing asthma, contingent upon the co-twin's history of asthma, was estimated using survival analyses, and genetic and environmental sources of variation in liability for asthma were analyzed with structural equation models. The cumulative incidence of asthma was 6% for males and 5.4% for females. The relative risk of developing asthma among twins whose co-twin had a positive history of asthma compared with those whose co-twin had no history of asthma was 17.9 (95% CI, 10.3 to 31.0) for identical, and 2.3 (95% CI, 1.2 to 4.4) for fraternal twins. Although shared environment encompasses many of the exposures that are putative risk factors for asthma in this age range, there is no evidence of shared environmental influences for asthma. Rather, 75% of the variation in liability for asthma was explained by genetic effects and the remaining variation was due to nonshared environmental influences. These results suggest that the familial risk for asthma is primarily, genetic.

Tel-Aviv-Heidelberg Three Generation Offspring Study: Genetic and environmental sources of variation and covariation among plasma lipids, lipoproteins, and apoliproteins.

Multivariate genetic analysis, implemented in the statistical package for pedigree analysis, FISHER, was carried out on a large sample of Israeli pedigrees to evaluate heritability and genetic correlations among an array of plasma lipids: total cholesterol (TCHL), triglycerides (TRIG), HDL-C and HDL2-C, HDL3-C, LDL-C and HDL-C%, apolipoproteins A and B (APO-A1 and APO-B), lipoprotein LP(a) and fibrinogen (FIBR). Multiple regression analysis showed that although sex, age, smoking and other study environmental factors, have a significant contribution to the variation of each plasma lipid, they exert little effect on covariation in lipids. Genes, however, are important factors of the variation and covariation in lipids. Thus, variance component analysis showed that the genetic component of the study variables, adjusted on age, sex and environmental factors, ranged between 31% for logarithm-transformed TRIG and 77% for plasma concentrations of LP(a). Coefficients of multiple genetic determination of the genetic variation of each variable attributable to all of the other variables, ranged from low values (<30%) for TRIG, LP(a) and FIBR, to moderate (64%) for HDL2-C. The genetic variation of each of the remaining variables was completely explained by variation in other lipids. The results of a factor analyses of phenotypic, genetic and environmental correlation matrices were similar and clearly identified several clusters of variables. The first included APO-A1, HDL-C, HDL2-C and HDL3-C, and the second-APO-B, LDL-C and THCL. Further analysis showed that it was probable the genetic component of variation of HDL3-C plasma concentration that fully depended on APO-A1, while those of LDL-C and TCHL fully depended on APO-B. The degree of correlation between TRIG, LP(a), FIBR and other variables, if any, was considerably lower. Am. J. Hum. Biol. 9:357-370, 1997. © 1997 Wiley-Liss, Inc.

Analysis of Transmissible and Nontransmissible Components of Variation in Human Physique

The paper is aimed at decomposition the continuously varying phenotype into components due to transmissible and nontransmissible factors. The linear causal model (path analysis) was applied to incorporate the contribution of environmental sources of variation (described in terms of indices of socioeconomic status) to familial resemblance on physique (height and weight) in 342 nuclear families. Parameters of the causal model were estimated according to the TAU transmission model of Rice, Cloninger, Reich [1978] and linear constraints placed upon the parameters were tested. The proportion of total phenotypic variance accounted for by genetic and environmental transmissible factors was estimated to be 62% for height and 38% for weight.

Inheritance of physical fitness in 10-yr-old twins and their parents.

This study focuses on the quantification of genetic and environmental sources of variation in physical fitness components in 105 10-yr-old twin pairs and their parents. Nine motor tests and six skinfold measures were administered. Motor tests can be divided into those that are performance-related: static strength, explosive strength, running speed, speed of limb movement, and balance; and those that are health-related: trunk strength, functional strength, maximum oxygen uptake, and flexibility. The significance and contribution of genetic and environmental factors to variation in physical fitness were tested with model fitting. Performance-related fitness characteristics were moderately to highly heritable. The heritability estimates were slightly higher for health-related fitness characteristics. For most variables a simple model including genetic and specific environmental factors fitted the observed phenotypic variance well. Common environmental factors explained a significant part of the variation in speed components and flexibility. Assortative mating was significant and positive for speed components, balance, trunk strength, and cardiorespiratory fitness, but negative for adiposity. Static strength, explosive strength, functional strength, and cardiorespiratory fitness showed evidence for reduced genetic transmission or dominance. The hypothesis that performance-related fitness characteristics are more determined by genetic factors than health-related fitness was not supported. At this prepubertal age, genetic factors have the predominant effect on fitness.

Genetics and behavioral medicine.

Genetics has substantial relevance to behavioral medicine. A rapidly growing body of evidence indicates the influence of genetics on health and disease and on the behavioral factors related to them. The model of quantitative genetics provides a general interpretational scheme for this burgeoning field. The model focuses on variability, and a major research objective is the decomposition of observed individual differences into portions attributable to various types of genetic and environmental sources of variability. This approach emphasizes the coaction of genes and environments and stands in sharp contrast to the archaic view that places nature and nurture in opposition. Some relevant examples are given in this first article to illustrate the general analytic process. A detailed application to cardiovascular health and disease is provided in the second article, and some policy implications are briefly considered in the third article.

Optimum Plot Size in Field Experiments with Strawberries

Abstract Optimum plot size is a function of costs and precision. As plot size increases, up to a limit, there is a gradual improvement in precision expressed in terms of a plot variance while higher costs are entailed. The common measure linking all the sources of environmental variability in field trials is Smith'S index of soil heterogeneity b. In the present study two methods of evaluation of bhave been applied. Koch and Rigney'S formula enables the calculation of bfrom replicated experiments using estimates of variances associated with different plot sizes (the size of a block, main plot or sub-plot). Lin and Binns' proposal bases bon an adjusted Smith'S formula (with a “correction factor” for the number of plots in a block) and the coefficient of intraclass correlation (estimated from variance components). Slightly higher values of bderived in the present study from Lin and Binns' method in comparison with that of Koch and Rigney were probably due to including the “correction factor.” In our strawber...

Intrapopulation Variability in Sublethal Response to Heavy Metal Stress in Sexual and Asexual Gastropod Populations

Asexual species have been described by some to be more broadly tolerant of environmental stresses (i.e. to have general purpose genotypes) and by others to be more responsive to environmental stresses (i.e. to exhibit narrower tolerance distributions to environmental perturbations) in comparison to their sexual relatives. We examined the sublethal response of asexual and sexual gastropod populations of the family Hydrobiidae to cadmium exposure to determine: whether populations rank consistently in mean and variance of growth rate when reared in different environments; whether the variance in growth rate within populations alters in response to stress; and whether growth rates within genetically uniform clones are less variable than growth rates within sexually outcrossed populations. We found that, in addition to reducing mean growth rate in all populations, exposure to cadmium increased the variability in growth rate within populations and altered the ranking of both means and variances among populations. The average intraclonal variability in growth in the parthenogenetic species Potamopyrgus antipodarum was comparable to the average intrapopulation variability in growth within the closely related but sexually reproducing Hydrobia species. Our results indicate that environmental toxicants, such as cadmium, can alter the relative performance of these potentially competing species. Our results are of broad relevance to the examination of phenotype variance and its partitioning between genetic and environmental sources of variation. Non-genetic variation was the most important component of the total phenotypic variance in growth rate within these gastropod populations. In addition, the assumption frequently applied in the development of toxicity test protocols, that uniformity in phenotypic traits (i.e. response to toxicant exposure) is tightly coupled to genotypic uniformity, is not supported by our results.

Heredity and environment in phoneme articulation: hereditary and environmental contributions to articulation proficiency.

Large twin samples and recent applications of multiple regression techniques to behavioral genetics methodology makes possible evaluation of genetic and environmental contributions to the articulation proficiency of individual phonemes. Factor analysis of the articulation scores from 256 MZ and DZ twins and 124 of their non-twin siblings (all children ranged from 2; 11 to 9; 8 years) were conducted to reduce a 50-item articulation test to a more manageable set of five articulation factors. The twins' factor scores were then analyzed using multiple regression procedures to determine the extent to which the individual factors resulted from genetic and/or environmental influences. The /r/ and /[symbol: see text], t[symbol: see text], d[symbol: see text]/ factors were found to have strong genetic components, while the /l, j, w/ factor was found to be strongly influenced by environmental sources of variation.

Variation between Merino ewes in pasture intake 1. Between flock differences and some environmental sources of variation

Pasture intake of Merino breeding ewes was measured by marker dilution using chromium sesquioxide. Measurements were made on approx. 300 ewes in four seasons associated with stages of the annual reproductive cycle in each of 2 years. The ewes represented 15 separate randomly-bred bloodlines (flocks) in an experiment to determine the extent of environmental and genetic sources of variation. Mean digestible organic matter intakes (DOMI) were 623, 734, 1123 and 779 g/day in autumn (early pregnancy), winter (late pregnancy), spring (mid-lactation) and summer (post-weaning), respectively. The repeatability of daily estimates of DOMI within measurement periods varied from 0.32 to 0.47 across seasons, while the repeatability across periods was lower (0.09 to 0.27). Flock differences in DOMI were significant in all seasons except spring. In all seasons DOMI was positively related to liveweight and was negatively associated with ultrasonic fat depth. After adjusting for liveweight and fat differences, between-flock variation in DOMI was small relative to that of wool growth and liveweight. L'ingestion au pâturage des brebis mérinos a été mesurée par dilution du sesquioxide de chrome utilisé comme marqueur. Les mesures ont été effectuées sur environ 300 brebis de 15 lignées génétiques distinctes pendant 2 années consécutives englobant quatre saisons correspondant aux différents stades du cycle annuel de reproduction. Ce troupeau faisait partie d'une étude dont le but était l'estimation des sources de variation génétiques et environnementales de caractères de production. Les quantités de matière organique digestible ingérées (DOMI) ont été de 632, 736, 1196 et 791 g/jour respectivement, en automne (début de gestation), en hiver (fin de gestation), au printemps (mi-lactation) et en été (après sevrage), La répétabilité de la DOMI ingérée par jour a varié de 0.32 à 0.47 suivant les saisons, alors qu'elle n'a varié que de 0.09 à 0.27 suivant les périodes de mesure. Les différences de DOMI entre lignées ont été significatives pour toutes les saisons sauf au printemps. La DOMI est en corrétlation positive avec le poids vif et en corrélation négative avec l'épaisseur de gras quelle que soit la saison. Après correction pour les différences de poids vif et d'épaisseur de gras, la variation de DOMI entre-lignée a été plus faible que celle du poids vif et de la production de laine. Die Weidefutteraufnahme von Merino-Müttern wurde mittels einer Markerlösung unter Verwendung von Chromsesquioxid festgestellt. Etwa 300 Müttern wurden in 4 Saisonabschnitten mit entsprechendem jährlichen Reproduktionszyklus in insgesamt 2 Jahren untersucht. Die Mütter gehören zu 15 getrennten zufällig gezüchteten Blutlinien (Herden) in einem Experiment, um das Ausmaβ von genetischen und umweltbedingten Einflüssen auf die Variation festzustellen. Die mittlere Aufnahme an verdaulicher organischer Substanz (DOMI) betrug 623, 734, 1123 und 779 g/Tag im Herbst (frühe Trächtigkeit), Winter (späte Trächtigkeit), Frühling (mittlere Laktation) und Sommer (nach dem Absetzen). Die Wiederholbarkeit der täglichen Schätzwerte der DOMI innerhalb der Meβperioden variiert von 0,32 bis 0,47 über die Saisonperioden, während sie über die Perioden niedriger war (0,09 bis 0,27). Herdendifferenzen im DOMI waren in allen Saisons mit Ausnahme des Frühlings signifikant. In allen Saisons war DOMI positiv korreliert mit dem Lebendgewicht, aber negativ mit der Fettdicke (Ultraschall). Nach einer Korrektur auf Lebendgewicht und Fettdicke war die Zwischen-Herden-Variation der DOMI nur gering im Vergleich zum Wollwachstum und zum Lebendgewicht.

The effects of social and physical environment on social behaviour in farm animals

The restricted conditions under which many farm animals are kept do not permit the animals to show many aspects of social behaviour. These conditions also limit what the animals can learn and hence modify their future sexual and other social behaviour. Management methods are also important sources of environmental variation which can affect social behaviour. For example, many animals have difficulties in adapting to groups whose composition is often changed. Physical conditions, such as temperature, humidity and floor conditions, can also have an effect on the occurrence and frequency of certain social interactions. Animals vary in their behavioural strategies in social situations. So it is wrong to assume that all individuals in a group will be equally affected by any imposed condition. This variation may concern the proportions of affiliative or friendly behaviour and of aggressive behaviour. Most domestic animals spend far longer showing social behaviour in which aggression plays no part than in competitive behaviour. There is also variation in the extent to which individuals become involved in social interactions or avoid them and this is affected by their previous experience as well as by their basic physiology. One theory about variation in the impact on an animal of its social world is that animals can be differentiated on the basis of how free they are to move around and to utilise resources. It seems to be correct that there is a scale ranging from very free to very much restricted by social pressures. Another theory about variation in the behaviour shown in difficult situations, including social situations, is that animals can be divided into active and passive copers or into active copers and depressed non-copers. Although both of these theories are helpful in explaining some situations, it is clear from a variety of studies that neither is correct in all situations.

Natural variation in the temporal patterning of calling song structure in the field cricket Gryllus pennsylvanicus: effects of temperature, age, mass, time of day, and nearest neighbour

Genetic and environmental sources of variation in the temporal patterning of song structure may be important variables influencing male field cricket reproductive success. Song structure in both field and laboratory populations of Gryllus pennsylvanicus was examined to assess possible sources of variation. Factors examined included temperature, male age, body mass, time of day, and male spacing patterns. Temperature was positively correlated with pulse rate and negatively correlated with interchirp interval for both field and laboratory populations. Temperature was negatively correlated with chirp duration only in the field population. Calling song structure did not vary with male age or mass. Time of day had a significant effect on the song parameters examined, even when data were corrected for temperature differences. Males calling in the morning had faster pulse rates and shorter chirp durations than males recorded at night time. Male spacing patterns also influenced calling; isolated males had longer intervals between consecutive chirps than clumped males. Data are discussed in terms of acoustical competition between males and female choice.

Production performance of prolific Javanese ewes

Production performance of Javanese ewes (483 ewes with 1263 records) in West Java, Indonesia, was evaluated. The focus was on the effect of prolificacy and environmental sources of variation on lamb survival (S) as a ewe trait and on lambing and weaning outputs. Non-carriers (FecJ +FecJ +), carriers (FecJ FFecJ +) and homozygotes (FecJ FFecJ F) for a gene affecting prolificacy, averaged 1.24, 1.95 and 2.59 lambs born, respectively. Prolificacy-year (PY) effects were significant, with FecJ FFecJ F animals being more sensitive to fluctuations. Repeatability for litter size was 0.51 and heritability 0.62. PY, gestation ewe weight gain (EGG) and parity significantly affected S. Singles, twins, triplets and quadruplets averaged 87, 69, 47, and 35% S, respectively, with fewer lambs surviving in these litter size categories in poor years. Repeatability of S was 0.19. Litter weaning weights (TWW) were influenced significantly by PY, parity and EGG. EGG contributed less than litter birth weight to the determination of S and TWW in all litters, although its contribution to TWW was proportionally higher than that to S. Repeatability of TWW was 0.20. Higher prolificacy led to a diminution of the ewe's body resources as indicated by EGG, therefore reducing the ewe's ability to support satisfactory birth weights of lambs and lactation, particularly under poor nutrition. With higher EGGs and survival rates under improved nutrition, a single copy of the FecJ F gene increased the productivity of ewes (TWW) by at least 18%; while under suboptimum nutrition, it had a negative effect. There is a need to investigate the nutritional management of animals having the FecJ F gene since the gene is widely distributed in most Indonesian sheep populations.