Quantitative genetics of skeletal nonmetric traits in the rhesus macaques on Cayo Santiago. I. Single trait heritabilities

The use of skeletal nonmetric traits in studies of biological relationships often involves the assumption that variation in these traits is genetic. Studies of nonmetric traits in human groups and in inbred strains of mice and rabbits have indicated a genetic component to nonmetric trait variation. Skeletons of animals with known matrilineage membership were obtained from the Cayo Santiago skeletal collection in order to obtain a direct estimate of the heritabilities of several nonmetric traits in the free-ranging population of rhesus macaques on Cayo Santiago. Falconer's (1965) method was used to calculate heritability. Heritability estimates range from zero to one, and half of them are greater than 0.5. This indicates that there is a considerable amount of genetic variation for these traits among the Cayo macaques. There is a significant tendency for traits scoring the number of foramina to have lower heritabilities than those scoring hyperstotic or hypostotic traits.     

Maximum-likelihood variance components analysis of heritabilities of cranial nonmetric traits

Nonmetric traits of the cranium are often used to support hypotheses of the history and divergence of human populations. These studies rely on the assumption that nonmetric traits are heritable, yet few skeletal series exist with associated pedigree information that allow for the calculation of additive genetic variance, or heritability. In addition, traits for which heritabilities have been published represent dichotomous present/absent forms instead of the range of expression that can be observed for many nonmetric characters. In the present study I use a maximum-likelihood variance components analysis to calculate univariate narrow-sense heritability estimates on the skeletal series from Hallstatt, Austria, for 9 sutural bones, 27 multilevel traits, and dichotomized present/absent forms for 19 of these multilevel characters. Most of the trait heritabilities do not differ significantly from a model of h2 = 0, and they have large standard errors. In a heuristic comparison of multilevel versus dichotomous trait forms, most of the nonmetric characters showed no differences in heritability between the two methods used for parsing the phenotypic variation, although where differences were noted, the presence-absence version had higher heritabilities. These results have implications not only for the use of particular nonmetric traits in population studies but also for the practice of character dichotomization in data collection.     

Quantitative genetics of cranial nonmetric traits in randombred mice: heritability and etiology

Cheverud and Buikstra (1981) demonstrated a tendency for nonmetric traits representing the number of foramina to have lower heritabilities than those representing hyperstotic or hypostotic traits in a sample of rhesus macaques. Based on this observation, Cheverud and Buikstra hypothesize that differences in the heritability of the two sets of traits may be due to differences in trait etiology. This study addresses the proposed relationship between trait heritability and etiology. Heritability values are calculated for 35 cranial nonmetric traits in a sample of 320 randombred mice using analysis of variance. The results are minimally consistent with the etiological hypothesis, but only 4 of the 35 traits showed statistically significant heritability values. These results are discussed with reference to the assumption that nonmetric traits have a strong genetic component. It is concluded that the developmental pathways that genetic variation traverses before being expressed in the form of nonmetric traits must be understood before variation in nonmetric traits can be used to its fullest potential.     

The relationship between cranial metric and nonmetric traits in the rhesus macaques from Cayo Santiago

This study addresses the relationship between cranial metric variables and nonmetric traits using the skeletal sample of rhesus macaques from Cayo Santiago. Discriminant function analysis is used to study the metric differences between macaque crania grouped according to the presence or absence of nine nonmetric traits. The computation of total structure coefficients from the discriminant function analyses provides information regarding how closely each metric variable is related to the discriminant functions derived. Total structure coefficients have not been used previously in the study of the relationship between metric and nonmetric traits. The results of the analysis are interpreted using an explicit approach to cranial morphogenesis-functional cranial analysis. It is concluded that the relationship between cranial metric and nonmetric traits is explicable in terms of a common developmental pathway shared by the two types of traits. Identification of the specific etiology of nonmetric traits depends on future anatomical studies or organisms throughout the period of nonmetric trait development.     

Genetic correlations between sides and heritability of asymmetry for nonmetric traits in rhesus macaques on Cayo Santiago

The use of nonmetric traits for estimation of biological distance is a long-standing practice in biological anthropology. Nonmetric traits can be scored using either the individual or the side of the individual as the unit of measure. If sides of the individual are genetically correlated the use of sides would produce redundant genetic information. For this reason, Korey (Am. J. Phys. Anthropol. 53:19-23, 1980) argues for the use of individuals as the unit of measure for nonmetric traits. Ossenberg (Am. J. Phys, Anthropol. 54:471-479, 1981), however, argues that bilateral occurrence of nonmetric traits indicates greater genetic liability for the trait and that therefore the sides are the more biologically correct unit of measure. Genetic correlations for 13 cranial nonmetric traits are estimated for a sample of rhesus macaque skeletons from Cayo Santiago. In addition, heritability of asymmetry is estimated for these 13 traits as a test of Ossenberg's contention that asymmetry is genetically influenced. Significant genetic correlations between sides support Korey's contention that nonmetric traits should be scored by individual. Only two asymmetry heritabilities were significantly different from zero, providing no significant support for Ossenberg's contention that asymmetry is genetically determined. Our results support the theory that asymmetry represents a measure of the ability of an organism to buffer stresses. Therefore, a measure of the heritability of asymmetry is a measure of the heritability of the ability to buffer stresses. This ability does not appear to be heritable in this sample.     

Quantitative genetics of skeletal nonmetric traits in the rhesus macaques on Cayo Santiago. II. Phenotypic,genetic, and environmental correlations between traits

The general lack of phenotypic correlation among skeletal nonmetric traits has been interpreted as indicating a lack of genetic correlation among these traits. Nonmetric traits scored on animals in the skeletal collection of rhesus macaques from Cayo Santiago are used to calculate phenotypic, genetic, and environmental correlations between traits. The results show that even when phenotypic correlations are low, there may be large, significant genetic correlations among these traits. The genetic correlation pattern suggests that genes which affect nonmetric trait variation act primarily at a local level in the cranium, even though there are genes with pleiotropic effects on skeletal nonmetric traits throughout the cranium. Environmental and phenotypic correlations do not show this neighborhood pattern of correlation.     

The incidence of bilateral nonmetric skeletal traits: A reanalysis of sampling procedures

For reporting the incidence of bilateral skeletal traits, the choice between sampling statistics depends upon more than their relative efficiencies. Of overreaching importance are the fundamentally different assumptions about the genetic significance of bilateral asymmetry represented by the two principal sampling approaches. Sampling by side is consistent with the premise that trait expression on each side reflects an additive component of genetic variation. Implicit in sampling by individual, by contrast, is the proposition that asymmetries of expression result chiefly from developmental noise. The pattern of age-regression indicated for many of these traits, suggesting a transient developmental role for unilateral expression, supports both this latter view and the thesis of stress asymmetry. Given this pattern, furthermore, incorporating unadjusted trait frequencies into divergence statistics would seem injudicious.     

Relationships between non-metric skeletal traits and cranial size and shape.

A long-standing controversy exists about the comparative utility of metric and non-metric traits as biological indicators in population studies. We hypothesize that the underlying scale which determines the presence or absence of a cranial non-metric trait is an expression of general and/or local size variation in the cranium. Therefore metric and non-metric traits will share a common developmental determination. The hypothesis implies that the underlying scale of a non-metric trait will be correlated with measures of cranial size and shape. Forty-eight cranial metric and twenty-five cranial non-metric traits were scored on the left side of adult male crania from four North American Indian populations. New threshold traits were generated for each non-metric trait by dichotomizing discriminant scores produced by discriminant function analysis. The discriminant analysis was performed using metric traits to discriminate between groups formed by non-metric trait presence or absence. Every non-metric trait tested was significantly correlated with its threshold trait in at least one population. The correlations were of moderate to high levels depending on the trait and population sample studied. This implies that metric and non-metric traits share a moderate to high degree of developmental determination. The cause of these correlations may lie in the common effects that growth and development of the soft tissue and functional spaces of the cranium exert on both metric and non-metric traits.     

An argument for the use of total side frequencies of bilateral nonmetric skeletal traits in population distance analysis: The regression of symmetry on incidence

In population studies based on frequencies of bilateral nonmetric skeletal traits, the choice between sampling by individuals or by sides should depend less on the exigencies imposed by fragmentary remains than on fundamental assumptions about the biological meaning of symmetry/asymmetry. Though the latter has been interpreted in various ways, little attention has focused on the possibility that bilateral correlation is meaningful in quantifying genetic liability for a trait. Analysis of two independent mandibular features, mylohyoid bridge and suppressed third molar, in Indian and Eskimo population samples (total N ? 1,200) reveals a statistically significant pattern of increasing bilateral occurrence with increasing population incidence. This pattern is consistent with the theory that liability for a “quasi-continuous” variant is normally distributed with constant increment between thresholds on an underlying scale. According to theory, phenotypes with more pronounced expression (bilateral occurrence) have greater genetic potential than those with less pronounced expression (unilateral occurrence). Therefore, scoring traits in total left and right sides, by giving greater weight to bilaterally affected individuals, may provide a better estimate of the liability for the trait in the population. Viewed in a theoretical context broader than that of the sampling debate, this pattern of positive regression of symmetry on incidence means that prevalence of unilateral occurrence probably cannot be used to assess the relative strength of genetic versus nongenetic control of threshold variants.     

The use of nonmetric variation in estimating human population admixture: a test case with Brazilian blacks, whites, and mulattos

Measurements in populations which serve as valid indicators of biological relationship should be proportional to genetic distance. In order to test the utility of discrete cranial traits for estimating genetic distances among populations, estimates of admixture are obtained for gene frequency data and nonmetric cranial data in São Paulo mulattos (M). The gene frequency data serve as a control that the three populations are related as stated: estimates of admixture are obtained by using São Paulo whites (W) and blacks (B) as parental populations and by estimating the parameter of admixture, m, in the model p_M = (1 ? m) p_W + mp_B (Elston, 1971) where the p's are either gene frequencies or nonmetric trait frequencies. A test of goodness of fit of the model provides a means of ascertaining whether or not the data fit this linear model. While the gene frequency data indicate distances among the three populations which are highly compatible with the linear model of admixture, the nonmetric data show significant deviations from the model. This implies that the frequencies of the nonmetric traits in the populations used in this analysis are not a linear function of genetic distance. This discourages the use of nonmetric traits in making quantitative conclusions about genetic relationships. It also suggests the need for investigation of the use of other skeletal characters for estimating genetic distance, as well as approaches for such investigations through the study of hybrid individuals.     

An examination of the meaning of cranial discrete traits for human skeletal biological studies

Discrete traits are of increasing interest in comparative skeletal biological research. Characteristics justifying their use have been investigated primarily in mice, however. Using 72 discrete variants, 321 human skulls from the Terry Collection of known race, sex and age have been studied. Significant sex and age differences were detected. Inter-trait correlation was found to be at a low but significant overall level. Multivariate comparison with conventional craniometric analysis was undertaken on subdivisions of the sample, and distance based on metric and nonmetric data were concordant. It is concluded, on the basis of these findings and the discontinuous variant frequency distributions, that discrete traits in isolation are not of paramount value to skeletal genetic studies, but may be vital in comparison and conjunction with other types of data in analyzing the population genetics of extinct groups.     

Selection in a cycling population: differential response among skeletal traits

Abstract Population density cycles influence phenotypic evolution through both density‐dependent selection during periods of high density and through enhanced genetic drift during periods of low density. We investigated the response of different phenotypic traits to the same density cycles in a population of the yellow‐necked mouse, Apodemus flavicollis, from Bia?owieza National Park in Poland. We examined nonmetric skull traits, skull and mandible size, skull and mandible shape, and transferrin allele frequencies. We found that all of the traits changed significantly over the seven‐year study period. The greatest changes in nonmetric traits and mandible size occurred during periods of increasing density, and the magnitude of changes in skull and mandible shape was correlated with the magnitude of density changes. Frequencies of transferrin alleles changed the most when population density was in decline. Changes among the five phenotypic traits were generally uncorrelated with one another, except for skull and mandible shape. Nonmetric traits were selectively neutral when assessed with Q_ST/F_ST analysis, whereas mandible size, mandible shape, and skull shape showed evidence of fairly strong selection. Selection on skull size was weak or nonexistent. We discuss how different assumptions about the genetic components of variance affect Q_ST estimates when phenotypic variances are substituted for genetic ones. We also found that change in mandible size, mandible shape, skull size, and skull shape were greater than expected under a neutral model given reasonable assumptions about heritability and effective population size.     

The interaction between nonmetric and metric cranial variation.

Cranial discrete or 'epigenetic" traits have been analyzed for interrelationships with measurements of the skull in a sample of American Negro males. Univariate t and multivariate T2 tests are used. It has been the previous consensus view that nonmetric and metric characters are unrelated. Statistically significant associations between the total of 50 discrete and 23 metrical characters, however, are much more frequent than would be expected through random distribution. Multivariate analysis supplements simpler statistics by synthesizing patterns of variation within regions of the skull, identifying many interrelations of skull size and shape with discrete traits. A low but observable general influence is exerted upon nonmetric morphology by metrical variation of the human skull (or vice versa).     

Dental anthropology of Central-Southern,Iron Age Italy: The evidence of metric versus nonmetric traits

Discrete and metric dental traits are used to assess biological similarities and differences among 13 bioarchaeological populations located on each side of the Apennine mountains in central-southern Italy and dated to the first millennium BC . An initial hypothesis, that the mountain chain might provide a significant geographical barrier for population movement (resulting in greater biological affinities among those groups on the same side), is not supported. Instead, the samples appear to cluster more on the basis of time than geography. Archaeological evidence, however, supports an association between populations on opposite sides of the mountains and thus is in accord with the dental data. As anticipated, discrete dental traits appear to be more useful than metric dental traits in assessing such population affinities. This research represents a beginning to a better comprehension of the complexity of the biological and cultural dynamics of Italian populations during recent millennia. Am J Phys Anthropol 107:371–386, 1998. © 1998 Wiley-Liss, Inc.     

The influence of artificial cranial vault deformation on the expression of cranial nonmetric traits: its importance in the study of evolutionary relationships

Nonmetric cranial traits have been commonly used in evolutionary relationship studies. They develop during the growth and development of an individual, and for this reason its expression presents different sources of genetic and nongenetic variation. However, the use of these features in evolutionary relationship studies carries the implicit assumption that much of the nonmetric trait variation is essentially genetic. Among the nonheritable factors, cranial vault deformation has been the most studied in human populations. Because of the widespread distribution and elevated rate of artificial cranial vault deformation found in America, and the importance of nonmetric traits in evolutionary relationship studies in this area, the objectives of this paper are as follows: (a) to study the influence of artificial cranial vault deformation on the presence of nonmetric traits within samples of human craniofacial remains; and (b) to establish artificial cranial vault deformation influence on evolutionary relationships between local populations on a regional scale. Our results indicate that artificial cranial vault deformations alter the variation and covariation of metric and nonmetric traits in some samples. Wormian bones, placed in cranial vault sutures, are the most influenced by this factor. However, our results suggest that when all nonmetric traits were used the artificial cranial vault deformation did not influence the basic pattern of variation among samples. The exclusion or inclusion of wormians bones in evolutionary relationships analysis did not modify the results, but using only wormians bones lead to inconsistent results indicating that these traits have little value on these kind of studies.     

Comparison of the stability of morphometric and nonmetric skeletal characteristics of inbred mice with regard to environmental exposure in prenatal development

The influence of some environmental factors on size and shape of mandible in BALB/cJLacSto inbred mice was studied during prenatal development by multivariate morphometric methods. The factors under study were: introduction of methylthiouracil into the diet of pregnant females; injections of pregnant females with adrenocorticotropic or parathyroid hormones; keeping the females at low temperatures (two regimes). It was established that the changes of mandible shape caused by the changes of conditions of prenatal development did not achieve the level of differences between strains, and mouse strain identification was possible under various conditions of animal's keeping. It has been shown by comparison of these results with preceding data that the nonmetric skeletal traits were more stable to the influence of the same factors than morphometric ones. This gives us the foundations to consider the method of evaluation of phenetic distances between natural groups of animals for the set of non-metric threshold skeletal traits more suitable for detection of genetical differentiation of wild populations.     

Heritability estimates for carcass traits of cattle: a review

We present estimates of heritability for carcass traits of cattle published in the scientific literature. Seventy-two papers published from 1962 to 2004, which reported estimates of heritability for carcass traits, were reviewed. The unweighted means of estimates of heritability for 14 carcass traits by slaughter end point (age, weight, and fat depth) were calculated. Among the three end points, carcass weight, backfat thickness, longissimus muscle area, and marbling score were the carcass traits with the most estimates of heritability (56 相似文献   

A critical review of the mean measure of divergence and Mahalanobis distances using artificial data and new approaches to the estimation of biodistances employing nonmetric traits

This article reviews the two most common distance measures employed for the calculation of biodistances based on nonmetric traits, the mean measure of divergence (MMD) and the tetrachoric Mahalanobis D² distance (TMD). In addition, two new approaches for the estimation of biodistances from nonmetric traits are proposed and assessed. The first (OMD) is based on the direct application of the Mahalanobis distance to ordinally recorded data before their transformation to binary dichotomies. The second (RMD) approximates the covariances of the Mahalanobis distance by the Pearson correlation coefficients calculated in the binary dataset. The application of all four methods to artificial datasets demonstrates that they overall provide a satisfactory estimation of the biodistance among samples especially when the number of statistically non significant distances is very limited. However, the best performance is observed by the OMD, whereas special attention should be paid to the TMD since its values might come out of an ill‐conditioned system. The influence of the number of traits, the effect of missing values, as well as the validity of the test statistics used to assess biodistance significance are also examined and discussed. Am J Phys Anthropol 157:284–294, 2015. © 2015 Wiley Periodicals, Inc.     

Accuracy of marker-assisted selection with auxiliary traits

Genetic information on molecular markers is increasingly being used in plant and animal improvement programmes particularly as indirect means to improve a metric trait by selection either on an individual basis or on the basis of an index incorporating such information. This paper examines the utility of an index of selection that not only combines phenotypic and molecular information on the trait under improvement but also combines similar information on one or more auxiliary traits. The accuracy of such a selection procedure has been theoretically studied for sufficiently large populations so that the effects of detected quantitative trait loci can be perfectly estimated. The theory is illustrated numerically by considering one auxiliary trait. It is shown that the use of an auxiliary trait improves the selection accuracy; and, hence, the relative efficiency of index selection compared to individual selection which is based on the same intensity of selection. This is particularly so for higher magnitudes of residual genetic correlation and environmental correlation having opposite signs, lower values of the proportion of genetic variation in the main trait associated with the markers, negligible proportion of genetic variation in the auxiliary trait associated with the markers, and lower values of the heritability of the main trait but higher values of the heritability of the auxiliary trait.