Coefficient Of Additive Genetic Variation Research Articles

Lifetime Reproductive Success and Heritability in Nature.

The observation that traits closely related to fitness ("fitness traits") have lower heritabilities than traits more distantly associated with fitness has traditionally been framed in terms of Fisher's fundamental theorem of natural selection-fitness traits are expected to have low levels of additive genetic variance due to rapid fixation of alleles conferring highest fitness. Subsequent treatments have challenged this view by pointing out that high environmental and nonadditive genetic contributions to phenotypic variation may also explain the low heritability of fitness traits. Analysis of a large data set from the collared flycatcher Ficedula albicollis confirmed a previous finding that traits closely associated with fitness tend to have lower heritability. However, analysis of coefficients of additive genetic variation (CVA) revealed that traits closely associated with fitness had higher levels of additive genetic variation (VA) than traits more distantly associated with fitness. Hence, the negative relationship between a trait's association with fitness and its heritability was not due to lower levels of VA in fitness traits but was due to their higher residual variance. However, whether the high residual variance was mainly due to higher levels of environmental variance or due to higher levels of nonadditive genetic variance remains a challenge to be addressed by further studies. Our results are consistent with earlier suggestions that fitness-related traits may have more complex genetic architecture than traits more distantly associated with fitness.

Heritability of fitness in a wild mammal population.

Classical population genetics theory predicts that selection should deplete heritable genetic variance for fitness. We show here that, consistent with this prediction, there was a negative correlation between the heritability of a trait and its association with fitness in a wild population of red deer (Cervus elaphus) and there was no evidence of significant heritability of total fitness. However, the decline in heritability was caused, at least in part, by increased levels of residual variance in longevity and, hence, in total fitness: in this population, longevity is known to be heavily influenced by environmental factors. Other life history traits that were not associated with longevity, such as average annual breeding success, had higher heritabilities. Coefficients of additive genetic variance differed markedly between traits, but highly skewed measures, such as male breeding success, generally had greater coefficients of variance than morphometric traits. Finally, there were significant maternal effects in a range of traits, particularly for females.

Rapid evolution of larval development time during mass‐rearing in the melon fly, Bactrocera cucurbitae

AbstractA quantitative genetic analysis of rapid evolution of a life history trait has been conducted on the first 24 generations of mass‐rearing in the melon fly Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). The phenotypic variance of larval development time in each generation was divided into genetic and residual components. Mean and phenotypic coefficients of variation of larval development time decreased gradually as generations proceeded as a result of artificial selection for shorter larval period in the mass‐rearing procedure. There was a trend that additive genetic coefficients of variation in larval development time decreased with generations. These changes are entirely attributed to genetic responses to laboratory selection under the mass‐rearing environment because the population was maintained at a very large size so as to exclude random genetic drift and inbreeding depression, which would be other factors responsible for the observed genetic changes. The residual coefficients of variation in larval development time did not change with generations. Realized heritability of larval development time was low. The heritabilities for larval development time estimated from parent–offspring regression at generations 60 and 70, when the evolutionary plateau was asymptotically reached, were not significantly larger than 0.

High heritability for heartwood in north Swedish Scots pine

In 44-year-old full-sibs of north Swedish Scots pine (Pinus sylvestris L.), the estimated heritability of heartwood diameter was 0.5 despite the influence of environmental changes (caused by an earlier thinning) which apparently had reduced the heritabilities of height and diameter to around zero. The heritability of bole straightness was estimated to be 0.6. The coefficient of additive genetic variation of heartwood diameter was estimated at 0.2. If a reliable ‘heartwood-meter’ becomes available that allows nondestructive measurements to be rapidly made in the field it should be possible to breed for or against heartwood formation with less effort compared with that required in breeding aimed at improving regular production traits.

Genetic parameters in diallel-crossed Scots pine favor heartwood formation breeding objectives

After 25 years, full-sibs of Scots pine (Pinus sylvestris L.) in a north Swedish progeny test showed an estimated heritability of 0.30 for heartwood diameter at 80 cm above ground. This was equal to the heritability estimate for tree height, although accompanied by a much larger additive genetic coefficient of variation (0.20 compared with 0.06). The heritability estimate for diameter at breast height was about half that for tree height. Strong and positive phenotypic and environmental correlations were assessed between heartwood and the following traits: diameter at breast height, tree height, and branch diameter. The genetic correlation was low and positive at 0.02 between heartwood and diameter at breast height in contrast with 0.27 between heartwood and tree height. The assessed genetic correlations between heartwood and branch diameter and between heartwood and crown length were very weak compared with the phenotypic and, particularly, environmental correlations. This indicates that the association between crown length and heartwood is significant with regard to environmental factors, no matter to what extent they are independently modified by genes. However, crown limit was the trait that showed the strongest genetic correlation with heartwood (0.49). Since no correlations with production traits were unfavorable, we conclude that including heartwood formation capacity in a breeding programmay be done without drawbacks and with good prospects for success.

A meta‐analysis of the heritability of developmental stability

AbstractThe existence of additive genetic variance in developmental stability has important implications for our understanding of morphological variation. The heritability of individual fluctuating asymmetry and other measures of developmental stability have frequently been estimated from parent‐offspring regressions, sib analyses, or from selection experiments. Here we review by meta‐analysis published estimates of the heritability of developmental stability, mainly the degree of individual fluctuating asymmetry in morphological characters. The overall mean effect size of heritabilities of individual fluctuating asymmetry was 0.19 from 34 studies of 17 species differing highly significantly from zero (P < 0.0001). The mean heritability for 14 species was 0.27. This indicates that there is a significant additive genetic component to developmental stability. Effect size was larger for selection experiments than for studies based on parent‐offspring regression or sib analyses, implying that genetic estimates were unbiased by maternal or common environment effects. Additive genetic coefficients of variation for individual fluctuating asymmetry were considerably higher than those for character size per se. Developmental stability may be significantly heritable either because of strong directional selection, or fluctuating selection regimes which prevent populations from achieving a high degree of developmental stability to current environmental and genetic conditions.

On the heritability of developmental stability

Mo*ller and Thornhill (1997) assessed the heritability of developmental stabilityby a meta-analysis of all published (and some unpublished) heritability estimates offluctuating asymmetry in bilateral traits. From a limited number of these studiesthey also calculated the additive genetic coefficient of variation (CVA). Theusefulness of CVA is that it may correct for covariance between phenotypicvariation and trait size (Houle, 1992). In eight out of the thirty-two studies thatthey reported, there was a statistically significant estimate of heritability. Twenty-eight of these studies, representing fifteen species, were entered into a meta-analysis.From this analysis, Mo*ller and Thornhill (1997) concluded that there was asignificant additive genetic component to development stability, but this componentwas relatively small. They also found that the CVA is approximately eight timeslarger for developmental stability than for trait size. In this manuscript I wish tohighlight some of the benefits and limitations of this analysis, its implications andto suggest alternative approaches to the study of heritability of developmentalstability that may prove useful.

Emergency Decisions, Cultural-Selection Mechanics, and Group Selection [and Comments and Reply

Emergency behaviors of nonliterate groups are taken as a useful starting point for demonstrating that decisions can be integrated more directly into cultural analysis and that the explanatory pay-offs can be far-reaching. The methodological feasibility of studying group decisions directly is explored through three exceptional tribal ethnographies with a focus on emergency adaptive problem solving and its implications for both cultural- and gene-selection theory. Urgently discussed decision alternatives become apprehensible to fieldworkers through open group debate, while the reproductive effects of decisions are readily assessed whenever groups act in unison. Implications for the development of a more effective theory of cultural microselection and a truly processual definition of culture in its guided phase are suggested. With respect to long-term genetic evolution, the implications of emergency decision making are extended to foragers, exploring special possibilities that enable genetic group selection to become robust when groups are egalitarian and engage in consensual problem solving. Prehistorically, the verdict is that group-selection effects were amplified at the same time that individual effects were suppressed. On this basis it is hypothesized that the genetic evolution of human cooperative and altruistic tendencies can be explained in part by selection at the level of groups rather than inclusive fitness

Sexual selection in seaweed flies: genetic variation in male size and its reliability as an indicator in natural populations

Characters that are evolving in response to indirect sexual selection operating through the production either of attractive sons (the Fisher process) or of progeny with high viability (good genes), are expected to exhibit high levels of additive genetic variation. In seaweed flies ( Coelopa frigida ) male size is subject to both direct and indirect sexual selection, whereas female size has probably evolved in response to direct selection alone. Coefficients of additive genetic variance ( CV A 9s) in adult size were shown to be larger in males than females. Virtually all the genetic variation is attributable to the αβ chromosomal inversion which is known to be associated with larval survival. Sexual selection appears to have led to differential expression of relevant loci in the two sexes, and in the focussing of this variation into a single region of the genome. Samples from 25 natural populations provided estimates of CV A 9s in male size. Although the CV A values suggest male size is, on average, a reliable indicator of offspring fitness, both spatial and temporal differences in CV A ’s were observed. We suggest that indirect sexual selection is a very inconstant force of evolution.

Artificial selection for a courtship signal inDrosophila melanogaster

The mean inter-pulse interval of the song of maleDrosophila melanogasteris a courtship signal which shows relatively little variability in natural populations and is important to male mating success. Artificial selection was carried out on this trait for six generations, producing a line of flies that had a mean inter-pulse interval outside the normal range for the species. The stock used was derived from isofemale lines taken from a natural population in which other studies had suggested heritability for this trait was low. The response to selection was asymmetric, with a greater response for longer inter-pulse interval. Analysis of other changes between the lines suggests that the genes selected for act fairly specifically on inter-pulse interval, reducing both the mean inter-pulse interval and the number of pulses produced. Analysis of F2and back-cross generations suggested a polygenic additive architecture without a significant non-additive component or disproportionate role of sex-linked genes on mean inter-pulse interval. Contrary to expectations, variance was greater in the F1than in F2or back-cross generations, and the realized heritability was much greater than the evolvability (coefficient of additive genetic variation). The results suggest that behavioural traits with low variability still retain the potential for rapid evolution, perhaps because environmental sources of variation counteract fixation.

THE EVOLUTIONARY GENETICS OF MALE LIFE-HISTORY CHARACTERS IN DROSOPHILA MELANOGASTER.

Alternative models of the maintenance of genetic variability, theories of life-history evolution, and theories of sexual selection and mate choice can be tested by measuring additive and nonadditive genetic variances of components of fitness. A quantitative genetic breeding design was used to produce estimates of genetic variances for male life-history traits in Drosophila melanogaster. Additive genetic covariances and correlations between traits were also estimated. Flies from a large, outbred, laboratory population were assayed for age-specific competitive mating ability, age-specific survivorship, body mass, and fertility. Variance-component analysis then allowed the decomposition of phenotypic variation into components associated with additive genetic, nonadditive genetic, and environmental variability. A comparison of dominance and additive components of genetic variation provides little support for an important role for balancing selection in maintaining genetic variance in this suite of traits. The results provide support for the mutation-accumulation theory, but not the antagonistic-pleiotropy theory of senescence. No evidence is found for the positive genetic correlations between mating success and offspring quality or quantity that are predicted by "good genes" models of sexual selection. Additive genetic coefficients of variation for life-history characters are larger than those for body weight. Finally, this set of male life-history characters exhibits a very low correspondence between estimates of genetic and phenotypic correlations.

Heritabilities and additive genetic coefficients of variation in forest trees

Estimates of individual-tree narrow-sense heritability and additive genetic coefficient of variation of seven traits of forest trees were compiled from 67 published papers. Distributions of the values for each trait were characterized and compared by calculating medians and running Kolmogorov–Smirnov and Wilcoxon signed-rank tests. Generalizations are possible about at least some of the traits examined. Heritability of wood specific gravity was almost always above 0.3 (median 0.48). Heritabilities for other traits tended to be low: medians ranged from 0.185 to 0.26, and individual values generally ranged from 0.1 to 0.4. Evidence that heritabilities of form traits tend to be higher than those of growth traits was weak. The analysis of additive genetic coefficients of variation suggested that specific gravity tends to have lower values than other traits (median 5.1%), while height and diameter (medians 8.5 and 8.6%, respectively) had lower values than straightness (median 11.65%). Individual-tree volume showed the highest levels of additive genetic coefficient of variation (median 20.3%). The levels of additive genetic variation and heritabilities suggest that reasonable levels of genetic gain can be achieved by screening relatively low numbers of trees.

Heritability and ‘evolvability’ of fitness components in Callosobruchus maculatus

Heritabilities of traits closely related to fitness (e.g. life-history traits) tend to be lower than those of morphological traits in natural populations. It is unclear, however, whether this pattern reflects relatively low additive-genetic variation, relatively high residual variation (i.e. non-additive and environmental effects) or both. A standard, half-sib breeding design was used to estimate narrow-sense heritabilities and coefficients of additive-genetic variation (CVA) for a life-history trait (total fecundity), a morphological trait (wing length) and a behavioural trait (allocation of eggs among available resources) in two outbred populations of the seed beetle Callosobruchus maculatus. Heritabilities of fecundity and wing length were high in both populations whereas the heritability of egg-laying behaviour was low but non-zero. In contrast, estimates of ‘evolvability’, which depend on CVA, were highest for fecundity, intermediate for egg-laying behaviour and lowest for wing length. These results resemble those from a recent survey of Drosophila studies and suggest that the typically low heritabilities of behavioural or life-history traits are better explained by high residual variation than by low additive-genetic variation. Phenotypic and genetic correlations were generally not significant except for a positive relationship between wing length and fecundity. No evidence was obtained of a trade-off or underlying functional relationship between the number of eggs laid and the pattern of egg dispersion among available resources.

Comparing evolvability and variability of quantitative traits.

There are two distinct reasons for making comparisons of genetic variation for quantitative characters. The first is to compare evolvabilities, or ability to respond to selection, and the second is to make inferences about the forces that maintain genetic variability. Measures of variation that are standardized by the trait mean, such as the additive genetic coefficient of variation, are appropriate for both purposes. Variation has usually been compared as narrow sense heritabilities, but this is almost always an inappropriate comparative measure of evolvability and variability. Coefficients of variation were calculated from 842 estimates of trait means, variances and heritabilities in the literature. Traits closely related to fitness have higher additive genetic and nongenetic variability by the coefficient of variation criterion than characters under weak selection. This is the reverse of the accepted conclusion based on comparisons of heritability. The low heritability of fitness components is best explained by their high residual variation. The high additive genetic and residual variability of fitness traits might be explained by the great number of genetic and environmental events they are affected by, or by a lack of stabilizing selection to reduce their phenotypic variance. Over one-third of the quantitative genetics papers reviewed did not report trait means or variances. Researchers should always report these statistics, so that measures of variation appropriate to a variety of situations may be calculated.

Genetic Relationships and Additive Genetic Variation of Productive and Reproductive Traits in Guernsey Dairy Cattle ,

Data were first lactation production and reproduction records initiated from 1958 to 1981 in two experiment station Guernsey herds. Heritability estimates using paternal half sib groups were .24±.12 for milk yield, .27±.12 for fat yield, and .77±.15 for fat percentage. Heritability estimates for reproductive traits ranged from .01 to .04 for number of services, service period, conception rate, and days open, but were higher for days in milk at first breeding (.12) and age at first calving (.13). Except for age at first calving, coefficients of additive genetic variation were larger for reproductive traits than for productive traits. Genetic correlations between measures of production and reproduction were moderate to large and antagonistic, except that the relationship between production and age at first calving was favorable. Breeding value estimates for milk yield and reproduction were negatively correlated for sires with above average breeding values for milk yield. Huge phenotypic variances for reproductive traits masked substantial additive genetic variation for these traits. When all things are considered it seems unwise to ignore reproductive performance in selection programs for dairy cattle.

Quantitative Inheritance and Correlations of Agronomic and Grain Quality Traits of Sorghum1

Two S2 or S1‐derived families from each of 118 S0 plants from Purdue random‐mated population (PP18) of Sorghum bicolor (L.) Moench, were evaluated in a randomized complete‐block design over 1 or 2 years. Genetic parameters were estimated for days to bloom, plant height, lodging, panicle compactness, panicle weight, kernel weight, weathering, hardness, and vitreosity to assess breeding potential of the population. Additive variances were estimated using a weighted least‐squares procedure. Additive variances were significant for all traits. The additive genetic coefficients of variation ranged from 2.9% for days to bloom to 25.5% for lodging. Narrow‐sense heritabilities ranged from 0.349 to 0.734 for S0‐derived family selection (unit equals mean of S2 progeny of two S1/S0 plants in two replicatio/ts in either 1 or 2 years). Heritabilities ranged from 0.359 to 0.842 for S1‐derived family selection (unit equals mean of S2 progeny of a single S1/S0 plant in two replications in either 1 or 2 years). Additive genetic (−0.737 to 0.839) and phenotypic (−0.649 to 0.710) correlations were high among agronomic traits and among quality traits, and low between agronomic and quality traits. Kernel hardness had strong correlations with weathering (negative) and vitreosity (positive). Direct selection responses (percentage of mean) ranged from 3.70 to 28.58% and from 5.10 to 37.10% for S0‐ and S1‐derived family selection, respectively, Correlated responses were lower than direct responses for most traits. However, for some pairs of traits the difference between the two responses was not large. The results suggested good potential for conventional breeding methods and early generation selection for all traits tested. More improvement would be expected from S1‐derived than from S0‐derived family selection.