Estimates of heritability in a blanched asparagus population

To estimate the heritability values of characters frequently used as selective criteria, 32 half-sib families obtained from selected plants of three populations of the asparagus variety Argenteüil were evaluated in a randomized complete block design. The following characters were measured: days to emergence of the first spear, number and diameter of spears, number of stalks, plant height and average weight. The values of realized heritability were estimated and were compared with those obtained by the parent-offspring regression method. Phenotypic correlation coefficients between the different variables were significant. The values of realized heritability for most of the variables were moderate to high (between 0.18 and 0.68), except for days to emergence; lower values were obtained by the regression method. As there was a high degree of heritability, additive genetic factors contributed significantly to the genetic variance, which would allow the selection of phenotypically superior plants for asparagus improvement projects.     

A meta-analysis of the heritability of developmental stability

The 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.     

Quantitative genetic analysis of larval life history traits in two alpine populations of Rana temporaria

We estimated genetic and maternal variance components of larval life history characters in alpine populations of Rana temporaria (the common frog) using a full-sib/half-sib breeding design. We studied trait plasticity by raising tadpoles at 14 or 20°C in the laboratory. Larval period and metamorphic mass were greater at 14°C. Larval period did not differ between populations, but high elevation metamorphs were larger than low elevation metamorphs. Significant additive variation for larval period was detected in the low altitude population. No significant additive variation was detected for mass at metamorphosis (MM), which instead displayed significant maternal effects. Plasticity in metamorphic mass of froglets was greater in the high altitude population. The plastic response of larval period to temperature did not differ between the populations. Evolution of metamorphic mass is likely constrained by lack of additive genetic variation. In contrast, significant heritability for larval period suggests this trait may evolve in response to environmental change. These results differ from other studies on R. temporaria, suggesting that populations of this broadly distributed species present substantial geographic variation in the genetic architecture and plasticity of tadpole life history traits.     

Heritability estimates from genomewide relatedness matrices in wild populations: Application to a passerine,using a small sample size

Genomic developments have empowered the investigation of heritability in wild populations directly from genomewide relatedness matrices (GRM). Such GRM‐based approaches can in particular be used to improve or substitute approaches based on social pedigree (PED‐social). However, measuring heritability from GRM in the wild has not been widely applied yet, especially using small samples and in nonmodel species. Here, we estimated heritability for four quantitative traits (tarsus length, wing length, bill length and body mass), using PED‐social, a pedigree corrected by genetic data (PED‐corrected) and a GRM from a small sample (n = 494) of blue tits from natural populations in Corsica genotyped at nearly 50,000 filtered SNPs derived from RAD‐seq. We also measured genetic correlations among traits, and we performed chromosome partitioning. Heritability estimates were slightly higher when using GRM compared to PED‐social, and PED‐corrected yielded intermediate values, suggesting a minor underestimation of heritability in PED‐social due to incorrect pedigree links, including extra‐pair paternity, and to lower information content than the GRM. Genetic correlations among traits were similar between PED‐social and GRM but credible intervals were very large in both cases, suggesting a lack of power for this small data set. Although a positive linear relationship was found between the number of genes per chromosome and the chromosome heritability for tarsus length, chromosome partitioning similarly showed a lack of power for the three other traits. We discuss the usefulness and limitations of the quantitative genetic inferences based on genomic data in small samples from wild populations.     

ENVIRONMENT-DEPENDENCE OF QUANTITATIVE GENETIC PARAMETERS IN IMPATIENS PALLIDA

Population response to selection depends on the presence of additive genetic variance for traits under selection. When a population enters an alien environment, environment-induced changes in the expression of genetic variance may occur. These could have large effects on the response to selection. To investigate the environment-dependence of genetic variance, we conducted a reciprocal transplant experiment between two ecotypically differentiated populations of Impatiens pallida using the progeny of a standard mating design. The floodplain site was characterized by high water availability, moderate temperatures, and continuous dense stands of Impatiens. The hillside site was drier, with larger temperature extremes and supported only scattered patches of Impatiens with significantly lower seed production and earlier mortality. Estimates of heritability were low for each of the 13 traits measured in each population and site (range from 0–28%). Additive genetic variance for life-history traits tended to be larger than for morphological traits, but genetic variance in fitness was estimated to be not significantly different from zero in all cases. Significant heritability was detected in both populations for one trait (date of first cleistogamous flower) known to be closely related to fitness on the hillside. In general, heritability was reduced for populations when grown in the hillside site relative to the floodplain site, suggesting that stress acts to reduce the expression of genetic variance and the potential to respond to selection there. Consistent reductions in heritability associated with more stressful environments suggest that populations invading such sites may undergo little adaptive differentiation and be more prone to local extinction.     

Effects of bottlenecks on quantitative genetic variation in the butterfly Bicyclus anynana

The effects of a single population bottleneck of differing severity on heritability and additive genetic variance was investigated experimentally using a butterfly. An outbred laboratory stock was used to found replicate lines with one pair, three pairs and 10 pairs of adults, as well as control lines with approximately 75 effective pairs. Heritability and additive genetic variance of eight wing pattern characters and wing size were estimated using parent-offspring covariances in the base population and in all daughter lines. Individual morphological characters and principal components of the nine characters showed a consistent pattern of treatment effects in which average heritability and additive genetic variance was lower in one pair and three pair lines than in 10 pair and control lines. Observed losses in heritability and additive genetic variance were significantly greater than predicted by the neutral additive model when calculated with coefficients of inbreeding estimated from demographic parameters alone. However, use of molecular markers revealed substantially more inbreeding, generated by increased variance in family size and background selection. Conservative interpretation of a statistical analysis incorporating this previously undetected inbreeding led to the conclusion that the response to inbreeding of the morphological traits studied showed no significant departure from the neutral additive model. This result is consistent with the evidence for minimal directional dominance for these traits. In contrast, egg hatching rate in the same experimental lines showed strong inbreeding depression, increased phenotypic variance and rapid response to selection, highly indicative of an increase in additive genetic variance due to dominance variance conversion.     

HERITABILITY OF CARBON ISOTOPE DISCRIMINATION IN GUTIERREZIA MICROCEPHALA (ASTERACEAE)

The carbon isotope composition (¹³C/¹²C) of C₃ plant tissues provides a long-term, integrated measure of photosynthetic metabolism. Quantitative genetic methods were used to study the inheritance of carbon isotope composition and several morphological characters in Gutierrezia microcephala, a short-lived desert perennial. Open-pollinated seed was collected from a population located near Lee's Ferry, Arizona, in an area that was disturbed approximately 20 years ago. Seeds were germinated and seedlings grown in a common greenhouse environment. Carbon isotope discrimination (Δ) and all morphological characters varied significantly among maternal families. Heritability of Δ was estimated as 81% in the greenhouse and as 92% using the regression of family mean Δ on parent Δ from field samples. Using both field and greenhouse data, we estimated a lower bound for heritability in nature of 54%. Offspring size and biomass both showed significant, positive correlations with Δ. The corresponding genetic correlations were similar in magnitude and direction, but did not differ significantly from zero. These results imply the existence of heritable differences in physiology associated with carbon assimilation and water loss within populations, and the potential for microevolutionary change through natural selection.     

ENVIRONMENTAL AND GENETIC MATERNAL EFFECTS ON SEED CHARACTERS IN NEMOPHILA MENZIESII

Nuclear genetic, maternal genetic and maternal environmental effects on seed characters were estimated in the California native annual plant Nemophila menziesii using two greenhouse crosses. In one cross, according to a nested mating design, the narrow sense heritability of seed weight was small (3.9%). A subset of full-sib progenies produced in this cross was grown singly and in competition with the introduced grass Bromus diandrus. In a second cross, these plants were used as mothers (dams) and were each mated to the same three sires. Seeds produced by mothers competing with B. diandrus showed a significant reduction in weight, increase in time to germination, and increase in the incidence of dormancy, when compared to seeds from mothers grown singly. Significant sire components were found for time to germination and incidence of dormancy. Maternal genetic variation for seed weight was largely expressed as maternal genotype by maternal environment interaction, and showed no significant maternal genetic main effect. Time to germination and dormant fraction showed a relatively large maternal genetic effect. Evolution of seed characters in N. menziesii is more likely to occur via indirect response to selection among maternal plants than among the seeds themselves. Maternal genotype by maternal environment interaction could potentially contribute to the maintenance of maternal genetic variation in seed weight, but this does not appear likely for dormancy.     

INBREEDING DEPRESSION IN FOUR POPULATIONS OF COLLINSIA HETEROPHYLLA NUTT (SCROPHULARIACEAE)

The effects of one and two generations of inbreeding were studied in plants from four natural populations of the annual plant, Collinsia heterophylla, using inbred and outcrossed plants generated by hand pollinations to create expected inbreeding coefficients ranging from 0–0.75. The selfing rates of the populations were estimated using allozyme markers to range from 0.37–0.69. Inbreeding depression was mild, ranging from 5–40%, but significant effects were detected for characters measured at all stages of the life cycle. Fitness components declined significantly with the inbreeding coefficient, and regression of fitness characters on inbreeding coefficients gave no evidence of any strongly synergistic effects attributable to the different genetic factors that contribute to decline in fitness under inbreeding. The magnitude of inbreeding depression did not clearly decrease with the populations' levels of inbreeding. This is not surprising because the selfing rates are similar enough that it is unlikely that the populations have been characterized for long periods of time by these different inbreeding levels.     

The structure of phenotypic variation in gender and floral traits within and among populations of Spergularia marina (Caryophyllaceae)

We sampled four wild populations of the highly autogamous Spergularia marina (Caryophyllaceae) in California to detect and to measure the magnitude of within- and among-population sources of phenotypic variation in gender and floral traits. From flowers and fruits collected from field and greenhouse-raised plants, we measured ovule number, seed number, mean seed mass, pollen production (greenhouse families only), mean pollen grain volume (greenhouse families only), anther number, anther/ovule ratio, pollen/ovule ratio (estimated using different flowers for pollen than for ovules; greenhouse families only), petal number, and petal size. Using greenhouse-raised genotypes, variation among maternal families nested within populations was evaluated for each trait to determine whether populations differ in the degree of maternally transmitted phenotypic variation. For each population, we used 15 greenhouse-raised maternal families to estimate the broad-sense heritability and genetic coefficient of variation of each floral trait. The magnitude and statistical significance of broad-sense heritability estimates were trait- and population-specific. Each population was characterized by a different combination of floral traits that expressed significant maternally transmitted (presumably genetic) variation under greenhouse conditions. Flowers representing two populations expressed low levels of maternally transmitted variation (three or fewer of nine measured traits exhibited significant maternal family effects on phenotype), while flowers representing the other two populations exhibited significant maternal family effects on phenotype for five or more traits. Our ability to detect statistically significant differences among the four populations depended upon the conditions under which plants were grown (field vs. greenhouse) and on the floral trait observed. Field-collected flowers exhibited significant differences among population means for all traits except anther number. Flowers sampled from greenhouse-raised maternal families differed among populations for all traits except ovule number, seed number, and petal size. We detected negligible evidence that genetic correlations constrain selection on floral traits in Spergularia marina.     

Biogeography and population genetics of the Lake Malawi cichlid Melanochromis auratus: habitat transience, philopatry and speciation

Migration rates among nine populations of the endemic Lake Malawi cichlid Melanochromis auratus were estimated along a 42-km stretch of habitat in the southern end of the lake. Allele frequencies were surveyed at four simple sequence repeat (SSR) loci. The data suggest migration rates among populations are quite low. Exact tests indicate that statistically detectable allele frequency differences exist between many adjacent populations in the study. The F_ST value among all populations was estimated to be 0.151 (P < 0.0002). A biogeographic survey suggests that the highest levels of genetic differentiation exist between populations separated by stretches of deep water. Migration is more common between populations separated by shallower water or with shoreline dispersal routes. Reduced allelic diversity was observed at more recently created habitat patches, suggesting that either bottlenecks are associated with the colonization of new habitat patches or that these shallower sites were all founded by genetically depauperate ancestral populations. The extreme philopatry of M. auratus, coupled with the patchy distribution and transient nature of its preferred habitat, provides opportunities for both selection and genetic drift to produce genetic differentiation among populations. Both processes may be important to the evolution of taxonomic diversity in the East African cichlid species flocks.     

GENOTYPE-BY-ENVIRONMENT INTERACTIONS IN THE DETERMINATION OF THE SIZE OF A SECONDARY SEXUAL CHARACTER IN THE COLLARED FLYCATCHER (FICEDULA ALBICOLLIS)

Although genetic variation in characters closely related to fitness is expected to either become depleted by selection or masked by environmental variation, “good gene” models of sexual selection require moderate to high heritabilities of secondary sexual characters to explain the occurrence of costly female mate preferences. In this study, I investigated whether the estimated heritability of a condition-dependent secondary sexual character (i.e., the white forehead badge) in the collared flycatcher varied depending on environmental conditions experienced during offspring growth. The data were collected over a period of 14 years making it possible to exploit natural variation in natal conditions. In addition, natal conditions were experimentally altered through brood size manipulations. During unfavorable conditions caused by generally poor weather or experimentally enlarged brood size, no significant heritability based on father-sons regressions could be demonstrated (0.19 ? h² ? 0.27). In contrast, sons reared during years with favorable weather or in experimentally reduced broods significantly resembled their fathers (0.44 ? h² ? 0.65). In addition, the heritability estimates declined with increasing maternal age. The strong effect of natal environmental condition on the estimated heritability of forehead badge size suggests that the potential genetic benefit from mate choice vary according to environmental conditions (e.g., the benefit is reduced during unfavorable rearing conditions). Because sons reared during poor conditions have probably experienced a natal environment different from that experienced by their fathers, the low heritability estimates obtained under poor conditions seem to be caused by low additive genetic variation expressed in such environments and/or a low genetic correlation between the expression of the trait in the two different environments (i.e., good vs. bad). Both of these explanations imply the presence of genotype-by-environment interactions. If such interactions frequently affect the expression of secondary sexual characters, this may offer an explanation of the high heritabilites sometimes reported for such traits, despite their exposure to long-term directional selection.     

苦瓜主要品质性状的遗传变异、相关和通径分析

对23份苦瓜材料的10个品质性状进行了研究。结果表明,苦瓜维生素C、还原糖、有机酸、果瘤、果色、果刺和苦味遗传变异系数大,遗传力高;水分含量遗传变异系数很小;风味遗传变异系数较小,遗传力低。苦瓜4个内在营养品质之间相关性小,而4个外观品质性状之间关系密切。两个味觉品质与4个内在营养品质之间相关性小,但与4个外观品质之间关系密切。内在营养品质与外观品质之间有一定关系。通径分析提出通过降低果实的苦味和有机酸含量来提高风味品质;通过水分含量和果瘤两性状的直接选择来实现对维生素C的间接选择。     

都市园林植物云南樱花的表型多样性研究

云南樱花(Prunus yunnannensis)为蔷薇科(Rosaceae)多年生落叶乔木,是中国西南地区特有的重要园林观赏植物,其在昆明园林绿化中具有较高的应用价值。以昆明地区的云南樱花为研究对象,研究了6个栽培居群120个单株的16个表型性状的多样性,分析了16个表型性状的相关性和广义遗传力,并对6个栽培居群进行了聚类分析,旨在探明其在资源应用过程中的表型变异程度及变异规律,为今后优良性状选育与种质推广提供科学依据。结果表明:云南樱花在居群间及居群内均存在丰富的表型多样性,除雌蕊长以外,其它15个表型性状在各居群之间均存在显著性差异,其中各性状的平均变异幅度为7.73%~94.04%,在居群内的变异幅度为20.74%~28.22%,各性状居群内的变异明显小于居群间,16个表型性状的广义遗传力介于0.54~0.97之间,其中叶长的广义遗传力最大,而雌蕊长的广义遗传力最小。对云南樱花16个形态指标的相关性分析表明,大部分形态指标之间均存在显著的相关性。利用居群间欧氏距离进行的UPGMA聚类分析结果表明,云南樱花6个栽培居群可以聚为2类。     

Genetic and environmental variations in quantitative characters in fishes: a comparative analysis of monoclonal triploid and bisexual tetraploid spined loaches (<Emphasis Type="Italic">Cobitis</Emphasis>, Cobitidae)

The heritability estimates of 25 external morphometric characters and 23 craniometric indices are obtained by use of variances in monoclonal all-female triploids and bisexual tetraploids of spined loaches (genus Cobitis, Cobitidae) collected from the same breeding biotope. Most of studied traits demonstrate low heritability confirming previous conclusion on the similarity between external morphometric characters and craniological indices in relative effects of genetic and environmental components in their total phenotypic variation. Low heritability estimates in most of external morphological traits correspond to their low diagnostic value in Cobitis species. As a whole, in spite of certain deviations, studies on clonal forms do not refute the concept on higher heritability estimates in diagnostically significant traits in comparison with traits without diagnostic values in the same taxonomic group. Low heritability in most morphometric traits more probably is resulted from their low additive genetic variation caused by strong selection of evolutionary developed specific body shape in spined loaches, because strong selection should reduce the genetic variance in body proportions to minimal size. Sex differences observed in heritability estimates should be interpreted as a result of linkage of several additive genes controlling these traits to sex chromosomes. A few characters demonstrating high heritability estimates up to 0.492–0.580 are of great interest for taxonomic and phylogenetic studies in genus Cobitis and related taxa.     

Genetic variation in a subtropical population of Daphnia

We assayed a subtropical population of Daphnia ambigua for genetic variation using protein electrophoresis (9 loci) and quantitative genetics approaches (life history characters). Our goal was to obtain information about relative levels of variation in a subtropical population, and compare them with extensive previous studies in the temperate and arctic zones. The observed level of allozymic variation (H = 0.11) was consistent with those previously observed in other temperate zone Daphnia populations. However, variation for quantitative traits (heritability) was lower than typically observed in previously-studied temperate populations: estimates were not statistically different from zero. Because allozyme heterozygosity was consistent with previous temperate zone estimates, and the polymorphic allozyme loci did not depart from the expectations of Hardy-Weinberg equilibrium, we concluded that a period of clonal selection was the most likely explanation for the low heritabilities observed. We do not conclude that this study provides evidence to suggest that subtropical populations harbor lower levels of genetic variation because of their location.     

Heritability of Two Morphological Characters within and among Natural Populations of Drosophila melanogaster

Heritabilities of wing length and abdominal bristle number, as well as genetic correlations between these characters, were determined within and among populations of Drosophila melanogaster in nature. Substantial "natural" heritabilities were found when wild-caught flies from one population were compared to their laboratory-reared offspring. Natural heritabilities of bristle number approximated those derived from laboratory-raised parents and offspring, but wing length heritability was significantly lower in nature than in the laboratory. Among-population heritabilities, estimated by regressing population means of wild-caught flies against those of their laboratory-reared descendants, were close to 0.5. The genetic differentiation of populations was clinal with latitude, and was accompanied by significant geographic differences in the norms of reaction to temperature. These clines are similar to those reported on other continents and in other Drosophila species, and are almost certainly caused by natural selection. Genetic regressions between the characters reveal that the cline in bristle number may be a correlated response to geographic selection on wing length, but not vice versa. Our results indicate that there is a sizable genetic component to phenotypic variation within and among populations of D. melanogaster in nature.     

Variability and covariability for plant height,heading date,and seed weight in wheat crosses

Summary Variability, covariability, heritability, and expected genetic gains from selection for heading date, plant height, and kernel weight were estimated in progenies derived from six wheat crosses. The crosses differed in the magnitude of the genetic variabilities of their progenies, but all crosses had significant variabilities for all traits. Heritability estimates were calculated by the variance components method. The estimates of heritability were relatively high for all three traits and averaged 86% for heading date, 77% for plant height, and 70% for kernel weight. The presence of significant genetic variabilities and high heritability estimates indicated that selection would be effective for the three traits.The segregates derived from crosses between medium tall parents showed transgressive segregation that would permit isolation of short-statured types. Transgressive segregation also occurred for heading date and kernel weight.Heading date and plant height were positively and highly significantly correlated in four crosses out of six. But both plant height and heading date had, in general, low negative correlations with kernel weight which would not preclude the development of short wheats with high kernel weight from these crosses. The association between characters was mostly genetic in cause.     

The accuracy of a heritability estimator using molecular information

The heritability of a quantitative trait is a key parameter to quantify the genetic variation present in a population. Although estimates of heritability require accurate information on the genetic relationship among individuals, pedigree data is generally lacking in natural populations. Nowadays, the increasing availability of DNA markers is making possible the estimation of coancestries from neutral molecular information. In 1996, K. Ritland developed an approach to estimate heritability from the regression of the phenotypic similarity on the marker-based coancestry. We carried out simulations to analyze the accuracy of the estimates of heritability obtained by this method using information from a variable number of neutral codominant markers. Because the main application of the estimator is on populations with no family structure, such as natural populations, its accuracy was tested under this scenario. However, the method was also investigated under other scenarios, in order to test the influence of different factors (family structure, assortative mating and phenotypic selection) on the precision. Our results suggest that the main factor causing a directional bias in the estimated heritability is the presence of phenotypic selection, and that very noisy estimates are obtained in the absence of a familiar structure and for small population sizes. The estimated heritabilities from marker-based coancestries showed lower accuracy than the estimated heritabilities from genealogical coancestries. However, a large amount of bias occurred even in the most favourable situation where genealogical coancestries are known. The results also indicate that the molecular markers are more suitable to infer coancestry than inbreeding.     

Realized Sampling Variances of Estimates of Genetic Parameters and the Difference between Genetic and Phenotypic Correlations

A data set of 1572 heritability estimates and 1015 pairs of genetic and phenotypic correlation estimates, constructed from a survey of published beef cattle genetic parameter estimates, provided a rare opportunity to study realized sampling variances of genetic parameter estimates. The distribution of both heritability estimates and genetic correlation estimates, when plotted against estimated accuracy, was consistent with random error variance being some three times the sampling variance predicted from standard formulae. This result was consistent with the observation that the variance of estimates of heritabilities and genetic correlations between populations were about four times the predicted sampling variance, suggesting few real differences in genetic parameters between populations. Except where there was a strong biological or statistical expectation of a difference, there was little evidence for differences between genetic and phenotypic correlations for most trait combinations or for differences in genetic correlations between populations. These results suggest that, even for controlled populations, estimating genetic parameters specific to a given population is less useful than commonly believed. A serendipitous discovery was that, in the standard formula for theoretical standard error of a genetic correlation estimate, the heritabilities refer to the estimated values and not, as seems generally assumed, the true population values.