Genetic and environmental factors in the longitudinal growth of rats: I. Body weight and overall craniofacial size

By means of roentgenographic cephalometry and quantitative genetic analysis, the relative contribution of the genetic and environmental components to total variance of body weight and overall craniofacial size was shown to vary with age. The genetic component of variance significantly increased until 80 days of age. Inversely, the maternal component of variance showed a high value during the early stage of postnatal growth and gradually decreased thereafter to a very small amount by day 80. Thus it appeared that the genetic effect became larger with age of the rat and the maternal effects diminished. The environmental component of variance did not change much over the course of the experiment. We thus conclude that genetic effect contributed the change of ontogenetic variation of craniofacial complex through all experimental periods and that maternal effect contributed to it at early growth stage of the craniofacial complex.     

Genetic and environmental factors in the longitudinal growth of rats: III. Craniofacial shape change

This investigation expresses the similarity of the craniofacial shape of rats in terms of a single parameter and determines to what extent the shape variation of the craniofacial complex is genetically determined. To quantify the similarity of the craniofacial shape between any two individuals, diagrams plotted from their lateral cephalograms are so oriented that the distance from the points on the one to the corresponding points on the other is minimized. The data consist of measurements from within-strain, between-strain, maternal half-sibs and paternal half-sibs groups. The average dissimilarity is computed in each group and compared. The results indicate that this method can be used to estimate the similarity of the craniofacial shape. The dissimilarity of within-strain pairs shows the smallest Dh value, whereas between-strain pairs have the largest Dh value. Those of maternal and paternal half-sib pairs show the intermediate Dh value. The value of dissimilarity for these four pairs tends to decrease gradually with age and a considerable genetic effect acts on the change of the craniofacial shape during growth, while the maternal effect does not act significantly on the change of the craniofacial shape during growth.     

A Genetic Analysis of Targeted Growth in Mice

Effects of normal growth regulation on components of phenotypic variance and covariance of body weight were examined in a cross-fostering study of growth between 2 and 10 wk of age in ICR randombred mice. Different early growth rates caused genetic, postnatal maternal and residual environmental variances to increase, but these variances were subsequently reduced by negative autocorrelation between early and later growth. Postnatal maternal variance continued to increase for about 1 wk after weaning but then decreased substantially. Genetic variance caused by preweaning growth followed a pattern of increase and decrease very similar to that of postnatal maternal variance, but this pattern was masked by new genetic variance. Normal growth regulation affects the magnitudes of genetic variances and serial autocorrelations. The timing of these changes suggests that regulation of cell numbers reduces variance near the end of exponential growth, but this may be obscured by subsequent increase in cell size. In contrast with earlier studies, we find that targeted growth reduces both genetically and environmentally determined differences among early growth trajectories. Final size may be determined by an antagonistic balance between early growth rate and age at initiation of puberty.     

Ontogeny of additive and maternal genetic effects: lessons from domestic mammals

Evolution of size and growth depends on heritable variation arising from additive and maternal genetic effects. Levels of heritable (and nonheritable) variation might change over ontogeny, increasing through "variance compounding" or decreasing through "compensatory growth." We test for these processes using a meta-analysis of age-specific weight traits in domestic ungulates. Generally, mean standardized variance components decrease with age, consistent with compensatory growth. Phenotypic convergence among adult sheep occurs through decreasing environmental and maternal genetic variation. Maternal variation similarly declines in cattle. Maternal genetic effects are thus reduced with age (both in absolute and relative terms). Significant trends in heritability (decreasing in cattle, increasing in sheep) result from declining maternal and environmental components rather than from changing additive variation. There was no evidence for increasing standardized variance components. Any compounding must therefore be masked by more important compensatory processes. While extrapolation of these patterns to processes in natural population is difficult, our results highlight the inadequacy of assuming constancy in genetic parameters over ontogeny. Negative covariance between direct and maternal genetic effects was common. Negative correlations with additive and maternal genetic variances indicate that antagonistic pleiotropy (between additive and maternal genetic effects) may maintain genetic variance and limit responses to selection.     

Genetic parameters of body weight in sheep estimated via random regression and multi-trait animal models

Variance components for five consecutive measurements of body weight in Polish sheep were estimated using random regression and multi-trait animal models. The data included between 7856 and 31694 body weight records at 5 age classes from birth to 150 days of age. The random additive genetic, maternal environmental and individual permanent environmental effects were fitted. All variance components were increasing over time (not at equal rates), which reflects increasing phenotypic mean and variance with age. Direct heritability tended to increase with age, whereas the effect of dam was reduced for older ages, and the proportion of permanent environmental component was relatively stable. Generally, similar tendencies were registered for estimates obtained via multi-trait animal model. The results confirm that there is a scope for genetic improvement in growth pattern in Polish sheep.     

Genetic study of dentinal growth in mandibular first molars of mice

The dentinal growth of mandibular molars of mice could be determined by genetic and environmental factors as are other quantitative characters, such as crown size and craniofacial size. To study the relative contribution of genetic and environmental factors to dentinal growth, a partial diallel cross was carried out by the mating of one pair from each of six strains of mice. In each F1 offspring, the total amount of dentinal formation in the first molar of the right mandible was quantified as a volume by the time-marking method, using nitrilotri-acetate lead with the computerized image scanning system, and then analyzed by a quantitative genetic method. The result obtained was as follows: In either sex, both additive genetic and nonadditive genetic variance components of the accumulative volume of dentinal formation in the first molar were relatively large throughout the experimental period, while the environmental variance component was much smaller. Thus it could be concluded that the genetic factor contributed more to the whole process of dentinal growth in the first molar rather than the environmental one in this F1 population.     

PARENTAL EFFECTS ON SEED DEVELOPMENT AND SEED YIELD IN RAPHANUS RAPHANISTRUM: IMPLICATIONS FOR NATURAL AND SEXUAL SELECTION

The possibility that sexual selection operates in angiosperms to effect evolutionary change in polygenic traits affecting male reproductive success requires that there is additive genetic variance for these traits. I applied a half-sib breeding design to individuals of the annual, hermaphroditic angiosperm, wild radish (Raphanus raphanistrum: Brassicaceae), to estimate paternal genetic effects on, or, when possible, the narrow-sense heritability of several quantitative traits influencing male reproductive success. In spite of significant differences among pollen donors with respect to in vitro pollen tube growth rates, I detected no significant additive genetic variance in male performance with respect to the proportion of ovules fertilized, early ovule growth, the number of seeds per fruit, or mean individual seed weight per fruit. In all cases, differences among maternal plants in these traits far exceeded differences among pollen donors. Abortion rates of pollinated flowers and fertilized ovules also differed more among individuals as maternal plants than as pollen donors, suggesting strong maternal control over these processes. Significant maternal phenotypic effects in the absence of paternal genetic or phenotypic effects on reproductive traits may be due to maternal environmental effects, to non-nuclear or non-additive maternal genetic effects, or to additive genetic variance in maternal control over offspring development, independent of offspring genotype. While I could not distinguish among these alternatives, it is clear that, in wild radish, the opportunity for natural or sexual selection to effect change in seed weight or seed number per fruit appears to be greater through differences in female performance than through differences in male performance.     

Ontogenetic patterns in heritable variation for body size: using random regression models in a wild ungulate population

Body size is an important determinant of fitness in many organisms. While size will typically change over the lifetime of an individual, heritable components of phenotypic variance may also show ontogenetic variation. We estimated genetic (additive and maternal) and environmental covariance structures for a size trait (June weight) measured over the first 5 years of life in a natural population of bighorn sheep Ovis canadensis. We also assessed the utility of random regression models for estimating these structures. Additive genetic variance was found for June weight, with heritability increasing over ontogeny because of declining environmental variance. This pattern, mirrored at the phenotypic level, likely reflects viability selection acting on early size traits. Maternal genetic effects were significant at ages 0 and 1, having important evolutionary implications for early weight, but declined with age being negligible by age 2. Strong positive genetic correlations between age-specific traits suggest that selection on June weight at any age will likely induce positively correlated responses across ontogeny. Random regression modeling yielded similar results to traditional methods. However, by facilitating more efficient data use where phenotypic sampling is incomplete, random regression should allow better estimation of genetic (co)variances for size and growth traits in natural populations.     

Parental effects on embryonic viability and growth in Arctic charr Salvelinus alpinus at two incubation temperatures

The parental influences on three progeny traits (survival to eyed‐embryo stage, post‐hatching body length and yolk‐sac volume) of Arctic charr Salvelinus alpinus were studied under two thermal conditions (2 and 7° C) using a factorial mating design. The higher temperature resulted in elevated mortality rates and less advanced development at hatching. Survival was mostly attributable to maternal effects at both temperatures, but the variation among families was dependent on egg size only at the low temperature. No additive genetic variation (or pure sire effect) could be observed, whereas the non‐additive genetic effects (parental combination) contributed to offspring viability at 2° C. In contrast, any observable genetic variance in survival was lost at 7° C, most likely due to the increased environmental variance. Irrespective of temperature, dam and sire–dam interaction contributed significantly to the phenotypic variation in both larval length and yolk size. A significant proportion of the variation in larval length was also due to the sire effect at 2° C. Maternal effects were mediated partly through egg size, but as a whole, they decreased in importance at the high temperature, enabling a concomitant increase in non‐additive genetic effects. For larval length, however, the additive component, like maternal effects, decreased at 7° C. The present results suggest that an exposure to thermal stress during incubation can modify the genetic architecture of early developmental traits in S. alpinus and presumably constrain their short‐term adaptive potential and evolvability by increasing the amount of environmentally induced variation.     

Estimates of (co)variance components due to direct and maternal effects for body weights in Jamunapari goats

Estimates of (co)variance components were obtained for weights at birth, weaning and at 6, 9 and 12 months of age in Jamunapari goats maintained at the Central Institute for Research on Goats, Makhdoom, Mathura, India, over a period of 23 years (1982 to 2004). Records of 4301 kids descended from 204 sires and 1233 does were used in the study. Analyses were carried out by restricted maximum likelihood (REML), fitting an animal model and ignoring or including maternal genetic or permanent environmental effects. Six different animal models were fitted for all traits. The best model was chosen after testing the improvement of the log-likelihood values. Direct heritability estimates were inflated substantially for all traits when maternal effects were ignored. Heritability estimates for weights at birth, weaning and at 6, 9 and 12 months of age were 0.12, 0.18, 0.13, 0.17 and 0.21, respectively. Maternal heritability of body weight declined from 0.19 at birth to 0.08 at weaning and was near zero and not significant thereafter. Estimates of the fraction of variance due to maternal permanent environmental effects were 0.09, 0.13 and 0.10 for body weights at weaning, 6 months and 9 months of age, respectively. Results suggest that maternal additive effects were important only in the early stages of growth, whereas a permanent environmental maternal effect existed from weaning to 9 months of age. These results indicate that modest rates of genetic progress appear possible for all weights.     

Where do all the maternal effects go? Variation in offspring body size through ontogeny in the live-bearing fish Poecilia parae

Maternal effects are an important source of adaptive variation, but little is known about how they vary throughout ontogeny. We estimate the contribution of maternal effects, sire genetic and environmental variation to offspring body size from birth until 1 year of age in the live-bearing fish Poecilia parae. In both the sexes, maternal effects on body size were initially high in juveniles, and then declined to zero at sexual maturity. In sons, this was accompanied by a sharp rise in sire genetic variance, consistent with the expression of Y-linked loci affecting male size. In daughters, all variance components decreased with time, consistent with compensatory growth. There were significant negative among-dam correlations between early body size and the timing of sexual maturity in both sons and daughters. However, there was no relationship between early life maternal effects and adult longevity, suggesting that maternal effects, although important early in life, may not always influence late life-history traits.     

Contribution of maternal effect QTL to genetic architecture of early growth in mice

Existing approaches to characterizing quantitative trait loci (QTL) utilize a paradigm explicitly focused on the direct effects of genes, where phenotypic variation among individuals is mapped onto genetic variation of those individuals. For many characters, however, the genotype of the mother via its maternal effect accounts for a considerable portion of the genetically based variation in progeny phenotypes. Thus the focus on direct effect QTL may result in an insufficient or misleading characterization of genetic architecture due to the omission of the potentially important source of genetic variance contributed by maternal effects. We analyze the relative contribution of direct and maternal effect (ME) QTL to early growth in mice using a three-generation intercross of the Small (SM/J) and Large (LG/J) inbred mouse lineages. Using interval mapping and composite interval mapping, direct effect (DE) QTL for early growth (change in body mass during the interval from week 1 to 2) were detected in the F(2) generation of the intercross (n = 510), where no maternal genetic effect variance is present (all individuals are progeny of genetically identical F(1) mothers). ME QTL were detected by treating the phenotypes of cross-fostered F(3) pups as a characteristic of their nurse-dam (n = 168 dams with cross-fostered progeny). Five DE QTL, significant at a chromosome wide level (alpha = 0.05), were detected, with two significant at a genome wide level. FourME QTL significant at the chromosome wide level were detected, with three significant at the genome wide level. A model containing only DE QTL accounted for 11.8% of phenotypic variance, while a model containing only ME QTL accounted for 31.5% of the among litter variance in growth. There was no evidence for pleiotropy of DE and ME loci since there was no overlap between loci detected in these two analyses. Epistasis between all pairs of loci was analyzed for both DEs and MEs. Ten pairs of loci showed significant epistasis for MEs (alpha = 0.05 corrected for multiple comparisons) while four pairs showed significant epistasis for DEs on early growth.     

Age-specific genetic and maternal effects in fecundity of preindustrial Finnish women

A population's potential for evolutionary change depends on the amount of genetic variability expressed in traits under selection. Studies attempting to measure this variability typically do so over the life span of individuals, but theory suggests that the amount of additive genetic variance can change during the course of individuals' lives. Here we use pedigree data from historical Finns and a quantitative genetic framework to investigate how female fecundity, throughout an individual's reproductive life, is influenced by "maternal" versus additive genetic effects. We show that although maternal effects explain variation in female fecundity early in life, these effects wane with female age. Moreover, this decline in maternal effects is associated with a concomitant increase in additive genetic variance with age. Our results thus highlight that single over-lifetime estimates of trait heritability may give a misleading view of a trait's potential to respond to changing selection pressures.     

Genetic study of the craniofacial growth in male rats by factor scores.

The craniofacial growth of F1 male offspring produced by a complete diallel cross of five strains of rats was observed with the use of cephalometry. Factor analysis was applied to several dimensions of dorsoventral and lateral cephalograms to assess the integration of the craniofacial complex with growth. The first three factors were chosen in each cephalogram, resulting in an explanation of 50.7% and 59.3% of the variation in the dorsoventral and lateral cephalograms, respectively, on an average throughout the period of the experiment, and disclosing that Factor I was associated most closely with the change in the craniofacial growth of rats. A further genetic analysis of the factor scores of each offspring lead to the conclusion that the growth changes of craniofacial width and length were more strongly influenced by the genetic effects; while those of upper jaw, nasal cavity, and pharyngeal part were more strongly influenced by the environmental effects.     

Random regression analyses using B-spline functions to model growth of Nellore cattle

The objective of this study was to estimate (co)variance components using random regression on B-spline functions to weight records obtained from birth to adulthood. A total of 82 064 weight records of 8145 females obtained from the data bank of the Nellore Breeding Program (PMGRN/Nellore Brazil) which started in 1987, were used. The models included direct additive and maternal genetic effects and animal and maternal permanent environmental effects as random. Contemporary group and dam age at calving (linear and quadratic effect) were included as fixed effects, and orthogonal Legendre polynomials of age (cubic regression) were considered as random covariate. The random effects were modeled using B-spline functions considering linear, quadratic and cubic polynomials for each individual segment. Residual variances were grouped in five age classes. Direct additive genetic and animal permanent environmental effects were modeled using up to seven knots (six segments). A single segment with two knots at the end points of the curve was used for the estimation of maternal genetic and maternal permanent environmental effects. A total of 15 models were studied, with the number of parameters ranging from 17 to 81. The models that used B-splines were compared with multi-trait analyses with nine weight traits and to a random regression model that used orthogonal Legendre polynomials. A model fitting quadratic B-splines, with four knots or three segments for direct additive genetic effect and animal permanent environmental effect and two knots for maternal additive genetic effect and maternal permanent environmental effect, was the most appropriate and parsimonious model to describe the covariance structure of the data. Selection for higher weight, such as at young ages, should be performed taking into account an increase in mature cow weight. Particularly, this is important in most of Nellore beef cattle production systems, where the cow herd is maintained on range conditions. There is limited modification of the growth curve of Nellore cattle with respect to the aim of selecting them for rapid growth at young ages while maintaining constant adult weight.     

Genetic parameters for growth traits of a Brazilian Bos taurus x Bos indicus beef composite

The genetic analysis of composite data is very complicated, mainly because it is necessary to adjust data to the effects of heterosis and breed complementarity, and because there is usually considerable confounding of these data with several other effects, such as contemporary group effects, breed composition of the animal and maternal breed composition, among others. Data on birth weight (n = 151,083), weaning weight adjusted to 205 days (n = 137,257), yearling weight adjusted to 390 days (n = 61,410), weight gain from weaning to yearling (n = 56,653), and scrotum circumference (n = 23,323) and muscle score (n = 54,770), both adjusted to 390 days, from Bos taurus x Bos indicus composite beef calves born from 1994 to 2003 were analyzed to estimate (co)variance components and genetic parameters of growth traits. The animals belonged to the Montana Tropical program. Estimation was made by three models that approach adjustment to heterozygosis in order to suggest the best model. The RM model included contemporary groups, class of age of dam, outcrossing percentages for direct and maternal effects, and direct and maternal additive genetic breed effects as covariates; the R model was the same as RM, but without additive maternal breed effects, and H was the same as RM, but not considering any additive breed effect. Both R2 values and consistency of genetic parameters indicate that the more complex model (RM), which considers maternal and individual additive genetic breed effect, produces the best estimates when compared to other models. The R model seems to overestimate (co)variance components. The magnitudes of direct and maternal heritability estimates, obtained in this study, would permit genetic improvement for weight and growth traits, as much by selection of direct genetic effects for weight and growth as for the improvement of maternal performance, but in different lineages. Therefore, the correlations between these effects were unfavorable.     

Common genetic and environmental factors among craniofacial traits in Belgian nuclear families: Comparing skeletal and soft-tissue related phenotypes

The major objective of this study was to determine the possible effects of common genetic and environmental factors among 18 craniofacial anthropometric traits, with special attention to the differences between skeletal and soft-tissue related phenotypes. The studied sample consisted of 122 nuclear families living in Brussels and included 251 males and 258 females aged from 13 to 72 years. Univariate and bivariate quantitative genetic analyses were performed using a variance components procedure implemented in SOLAR software.All phenotypes were significantly influenced by additive genetic factors with heritability estimates ranging from 0.46 (nose height) to 0.72 (external biocular breadth). Sex, age and their interactions explained 7-46% of the total phenotypic variance of the traits. Bivariate analysis revealed that several traits share a common genetic and/or environmental basis while other traits show genetic and environmental independence from one another. More and greater genetic and environmental correlations were observed among skeletal phenotypes, than among soft-tissue traits and between both categories. Apart from the tissue composition, other characteristics of the craniofacial morphology such as the orientation (e.g. heights, breadths) have shown to be important factors in determining pleiotropy and common environmental effects between some pairs of traits. In conclusion, the results confirm that overall head configuration is largely determined by additive genetic effects, and that common genetic and environmental factors affecting craniofacial size and shape are stronger for the skeletal traits than for the soft-tissue traits.     

Genetic conservation and management of the California endemic,Torrey pine (Pinus torreyana Parry): Implications of genetic rescue in a genetically depauperate species

Rare species present a challenge under changing environmental conditions as the genetic consequences of rarity may limit species ability to adapt to environmental change. To evaluate the evolutionary potential of a rare species, we assessed variation in traits important to plant fitness using multigenerational common garden experiments. Torrey pine, Pinus torreyana Parry, is one of the rarest pines in the world, restricted to one mainland and one island population. Morphological differentiation between island and mainland populations suggests adaptation to local environments may have contributed to trait variation. The distribution of phenotypic variances within the common garden suggests distinct population‐specific growth trajectories underlay genetic differences, with the island population exhibiting substantially reduced genetic variance for growth relative to the mainland population. Furthermore, F1 hybrids, representing a cross between mainland and island trees, exhibit increased height accumulation and fecundity relative to mainland and island parents. This may indicate genetic rescue via intraspecific hybridization could provide the necessary genetic variation to persist in environments modified as a result of climate change. Long‐term common garden experiments, such as these, provide invaluable resources to assess the distribution of genetic variance that may inform conservation strategies to preserve evolutionary potential of rare species, including genetic rescue.     

Age differences in craniofacial dimensions among adults from Indian Knoll,Kentucky

Adult craniofacial expansion with aging has recently been documented in a living US white population sample (Israel, '73a, '77). The present study extends these findings to a prehistoric Amerindian skeletal sample from the Indian Knoll, Kentucky site. Sixteen craniofacial dimensions available for 136 adult males were compared in younger (20–34 years) and older (35–50 years) age groups. Of these, six dimensions showed a significant difference between age groups; all significantly different dimensions were larger in the older adult age group. The multivariate (T²) difference between age groups was highly significant. Comparison of results before and after a size standardization indicated that the majority of differences between age groups were associated with an overall size increase, or expansion with aging, and did not represent merely remodeling, or “shape” changes. The pattern of craniofacial change with age appeared generally similar to that observed in the modern US white sample; however, some differences were noted. It is shown that the age trends observed at Indian Knoll are most likely to reflect true craniofacial growth in size among the adult male inhabitants of the site, rather than secular trends or other artifacts of the sampling procedure. The causes for continuing adult craniofacial expansion are unknown, and probably involve a complex interaction of many factors. However, this pattern of change with age among adults does appear to be characteristic of population samples of widely differing genetic and environmental backgrounds.     

Age-related variation in genetic control of height growth in Douglas-fir

Summary The development of genetic variances in height growth of Douglas-fir over a 53-year period is analyzed and found to fall into three periods. In the juvenile period, variances in environmental error increase logarithmically, genetic variance within populations exists at moderate levels, and variance among populations is low but increasing. In the early reproductive period, the response to environmental sources of error variance is restricted, genetic variance within populations disappears, and populational differences strongly emerge but do not increase as expected. In the later period, environmental error again increases rapidly, but genetic variance within populations does not reappear and population differences are maintained at about the same level as established in the early reproductive period. The change between the juvenile and early reproductive periods is perhaps associated with the onset of ecological dominance and significant allocations of energy to reproduction.This paper is published with the approval of the Director of Research, North Carolina Agricultural Experiment Station, as No. 3361 of the Journal Series. The computing services in this project were supported by NIH Grant GM-11 546, held by the Institute of Statistics, North Carolina State University at Raleigh.