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.     

Fluctuating asymmetry and genetic variability in the roe deer (Capreolus capreolus): a test of the developmental stability hypothesis in mammals using neutral molecular markers

Fluctuating asymmetry (FA), used as an indicator of developmental stability, has long been hypothesized to be negatively correlated with genetic variability as a consequence of more variable organisms being better suited to buffer developmental pathways against environmental stress. However, it is still a matter of debate if this is due to metabolic properties of enzymes encoded by certain key loci or rather to overall genomic heterozygosity. Previous analyses suggest that there might be a general difference between homeo- and poikilotherms in that only the latter tend to exhibit the negative correlation predicted by theory. In the present study, we addressed these questions by analysing roe deer (Capreolus capreolus) from five German populations with regard to FA in metric and non-metric skull and mandible traits as well as variability at eight microsatellite loci. Genetic variability was quantified by heterozygosity and mean d2 parameters, and although the latter did not show any relationship with FA, we found for the first time a statistically significant negative correlation of microsatellite heterozygosity and non-metric FA among populations. Because microsatellites are non-coding markers, this may be interpreted as evidence for the role of overall genomic heterozygosity in determining developmental stability. To test if the threshold character of non-metric traits is responsible for the metric vs non-metric difference we also carried out calculations where we treated our metric traits as threshold values. This, however, did not yield significant correlations between FA and genetic variability either.     

A comparative study of metric and non-metric traits in a series of modern crania

The purpose of this study is to question the utility of non-metric traits as predictors of age, race, and sex by comparing a group of non-metric variables with a group of metric variables. Twelve metric variables and 15 nonmetric variables were scored on 317 crania from the Terry Collection at the U. S. National Museum, and later statistically evaluated with a number of multivariate analysis programs and a stepwise discriminant program. The metric variables were found to be significant sex and race discriminators, where-as the non-metric variables were non-significant. The non-metric variables were found to be better age discriminators than the metric variables, even though neither could be classified as highly significant. It was concluded that non-metric traits by themselves have very little discriminatory value and should be used instead to supplement other osteological measurements and observations.     

Cranial variation in the terminal Late Archaic of Ohio

Cranial and mandibular discrete traits and cranial metric traits were collected from 99-125 individuals in eight terminal Late Archaic sites. The analysis of ten metric traits in six samples showed that the samples shared the same generalized variance and that sexual dimorphism in the means of the metric traits was greater than inter-site differences. Since these samples share the same size and shape expression of a complex set of polygenic traits, we hypothesize a historical relationship among these samples. Discrete trait analysis showed a pattern of differentiation among the eight samples. This pattern of differentiation is related directly to the geographical separation between samples, and, as with metric traits, cultural differences do not contribute to the pattern of biological differences. The overall pattern of osteological variation in these samples can be summarized parsimoniously by paraphrasing the first law of geography: All of the terminal Late Archaic populations of Ohio were related to each other, but closer ones were more related than distant ones.     

现代中国人群形成与分化的形态证据——中国与非洲和欧洲人群头骨非测量特征分析

现代人群形成与分化导致生活在世界不同地区的人类形成了具有明显体质特征差别的人群(或种族)。对更新世末期及全新世以来不同地理区域近代和现代人群体质特征差别、相互亲缘关系的分析是现代人群形成与分化研究的重要组成部分。本文通过对21项头骨非测量特征在近代和现代中国人群, 以及现代非洲和欧洲人群共330例标本的出现率和表现特点的观察和数据分析, 发现绝大多数特征的出现率或表现特点在三个人群间都具有不同程度的差异, 有些特征在人群间的差异甚至非常明显。与非洲及欧洲人群相比, 现代中国人头骨总体显得纤细, 眉弓、角圆枕、颧三角、颧结节等反映头骨粗壮程度的特征在现代中国人群的发育明显弱于非洲和欧洲人群。此外, 现代中国人群还具有一些明显不同于非洲和欧洲人群的头骨非测量特征, 包括锐利的眶外下缘、相对平坦的眉间鼻根点、较圆隆的颅侧壁、平坦的顶孔人字区、深弧形的上颌颧突下缘, 梯形和左右不一的鼻额-额颌缝走向等。采用判别分析可以将67.0%—79.5%的标本正确地判别归入其原来所属的组群。其中对中国人群的正确判别率分别达到70.4%和82.9%。个体标本分布显示非洲人群表现较大的分散性, 而中国和欧洲人群样本的分布明显密集集中, 提示中国和欧洲人群似乎具有更多的衍生性特征。本研究还发现多数在人群间差别显著的头骨非测量特征与头骨粗壮程度有关, 作者对相关的问题进行了分析探讨。     

Morphologic variation in the cranium and mandible of the white-tailed deer (Odocoileus virginianus): A comparative study of geographical and four biological distances

Several biological distances based on cranial and mandibular variation among breeding groups of white-tailed deer were calculated and compared with geographic distances among the groups. Distances based on epigenetic variation among ten groups were calculated using 16 non-metric variants of the cranium and mandible. Penrose's size and shape distances and Mahalanobis' D² distance were calculated for 11 groups; the calculations were based on seven skeletal and seven dental metric variables of the mandible. The biological distances were correlated with geographic distance as follows: the epigenetic distance, 0.74; Penrose's shape distance, 0.71; Penrose's size distance, 0.45; and Mahalanobis' distance, 0.37. All correlations were significant at the 0.01 level. The epigenetic and Penrose shape correlations were significantly higher than the Mahalanobis correlation. Because of the conditions under which the breeding groups were selected, it was assumed that genetic affinites among the groups would be a function of geographic distance. The results suggest that the epigenetic distance and Penrose's shape distance reflect genetic affinities among groups better than do the Penrose size and Mahalanobis distances.     

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.     

Sexual dimorphism in human cranial trait scores: Effects of population,age, and body size

Sex estimation from the skull is commonly performed by physical and forensic anthropologists using a five‐trait scoring system developed by Walker. Despite the popularity of this method, validation studies evaluating its accuracy across a variety of samples are lacking. Furthermore, it remains unclear what other intrinsic or extrinsic variables are related to the expression of these traits. In this study, cranial trait scores and postcranial measurements were collected from four diverse population groups (U.S. Whites, U.S. Blacks, medieval Nubians, and Arikara Native Americans) following Walker's protocols (total n = 499). Univariate and multivariate analyses were utilized to evaluate the accuracy of these traits in sex estimation, and to test for the effects of population, age, and body size on trait expressions. Results revealed significant effects of population on all trait scores. Sample‐specific correct sex classification rates ranged from 74% to 94%, with an overall accuracy of 85% for the pooled sample. Classification performance varied among the traits (best for glabella and mastoid scores and worst for nuchal scores). Furthermore, correlations between traits were weak or nonsignificant, suggesting that different factors may influence individual traits. Some traits displayed correlations with age and/or postcranial size that were significant but weak, and within‐population analyses did not reveal any consistent relationships between these traits across all groups. These results indicate that neither age nor body size plays a large role in trait expression, and thus does not need to be incorporated into sex estimation methods. Am J Phys Anthropol 154:259–269, 2014. © 2014 Wiley Periodicals, Inc.     

Cranial metric and discrete trait variation and biological differentiation in the terminal Late Archaic of Ohio: the Duff site cemetery

Cranial metric and discrete traits were collected from adult individuals of the terminal Late Archaic Duff site cemetery (33 LO 111). Comparisons of cranial metric traits among eight terminal Late Archaic samples including the Duff site sample showed that all samples shared the same generalized variance and by inference the same pattern of shape variation. Some significant size differences were found but these were interpreted as reflecting only minor differences in the underlying polygenic system or differences in environmental interactions. The overall similarity in cranial metrics among the terminal Late Archaic samples strongly suggests that they represent populations that, at least, shared a recent common ancestor. Analysis of discrete trait variation in all the terminal Late Archaic samples showed that the biological distances between samples are associated significantly with the between-sample geographical distances. This association accounts for approximately 25% of the variation in discrete trait frequencies. These results along with the results of the analysis of cranial metrics indicate that all of the terminal Late Archaic samples considered here are related, but geographically nearer samples are more closely related than distant ones.     

甘肃泾川化石人类头骨性别鉴定

1984年刘玉林等报道了在甘肃泾川发现的一具晚期智人头骨化石,判定该头骨代表一个女性青年个体。本文检查了顶矢状脊、乳突、耳孔上脊、枕外脊、枕外隆凸、枕骨上项线、枕骨圆枕和肌脊8项非测量性状,及星点间宽、星点至人字点距离、颅宽、耳上颅高、顶矢状弦、颞骨鼓板长和宽7项测量性状,并就7项测量性状与武山头骨进行了对比,认为它更有可能属于男性。     

Individual‐level leaf trait variation and correlation across biological and spatial scales

Even with increasing interest in the ecological importance of intraspecific trait variation (ITV) for better understanding ecological processes, few studies have quantified ITV in seedlings and assessed constraints imposed by trade‐offs and correlations among individual‐level leaf traits. Estimating the amount and role of ITV in seedlings is important to understand tree recruitment and long‐term forest dynamics. We measured ten different size, economics, and whole leaf traits (lamina and petiole) for more than 2,800 seedlings (height ≥ 10 cm and diameter at breast height < 1 cm) in 283 seedling plots and then quantified the amount of ITV and trait correlations across two biological (intraspecific and interspecific) and spatial (within and among plots) scales. Finally, we explored the effects of trait variance and sample size on the strength of trait correlations. We found about 40% (6%–63%) variation in leaf‐level traits was explained by ITV across all traits. Lamina and petiole traits were correlated across biological and spatial scales, whereas leaf size traits (e.g., lamina area) were weakly correlated with economics traits (e.g., specific lamina area); lamina mass ratio was strongly related to the petiole length. Trait correlations varied among species, plots, and different scales but there was no evidence that the strength of trait relationships was stronger at broader than finer biological and spatial scales. While larger trait variance increased the strength of correlations, the sample size was the most important factor that was negatively related to the strength of trait correlations. Our results showed that a large amount of trait variation was explained by ITV, which highlighted the importance of considering ITV when using trait‐based approaches in seedling ecology. In addition, sample size was an important factor that influenced the strength of trait correlations, which suggests that comparing trait correlations across studies should consider the differences in sample size.     

Migration costs drive convergence of threshold traits for migratory tactics

Partial migration of some, but not all, members of a population is a common form of migration. We evaluated how migration costs influence which members migrate in 10 populations of two salmonid species. The migratory patterns of both species were evaluated based on the size at maturity for resident males, which is the threshold trait that determines the migratory tactics used within a population. In both species, this size was smaller in males located further from the sea, where migration costs are presumably higher. Moreover, the threshold sizes at maturity in males were correlated between both species. Our results suggest that migration costs are a significant convergent selective force on migratory tactics and life-history traits in nature.     

Natural selection and non-metric traits in skeletal populations

The hypothesis of this article is that the frequency of non-metric traits varies at different reproductive periods because of differential mortality associated with non-metric traits. 450 male and 203 female crania were examined. Mortality in the reproduction period is connected with the elimination of individuals with certain variants of non-metric traits. It seems that key genes which perform the stimulating function in the appearance of traits in a given category of formation are under selective pressure. It is assumed that natural selection acts both on the morphology of organisms and on developmental process through environmental conditions. Selection not only optimises the fitness of morphological features but also the processes leading to the formation of features during ontogeny. Both these mechanisms influence the interpopulational variability of non-metric traits.     

Constraint and developmental dissociation of phenotypic integration in a genetically accommodated trait

SUMMARY The genetic accommodation of novel adaptive traits may be accompanied by the evolution of correlated traits that constrain adaptive evolution. Very little is known about the removal of maladaptive correlated traits. In the present study, body size was found to have evolved as a correlated trait during the artificial selection for a polyphenism and a monophenism, and the developmental basis underlying this correlated trait was investigated. The body size and coloration were found to be developmentally integrated by titers of the insect developmental hormone, juvenile hormone (JH). Attempts to uncouple the two traits resulted in the evolution of one of the body size determinants—the critical weight—but not the delay period whose evolution is constrained by JH titers. Thus, maladaptive correlated traits can be removed when multiple developmental modules exist, and the evolution of one or more of these modules is not constrained.     

Developmental stress and cranial hypostosis by epigenetic trait occurrence and distribution: an exploratory study on the Italian Neandertals

The occurrence and distribution of 35 cranial epigenetic traits in the Italian Neandertals (Saccopastore 1 and 2, Guattari 1) were examined according to morpho-functional cranial regions and with respect to a distinction between hypostosis (i.e., weak osseous development, arrested morphogenesis, retention of infantile features) and hyperostosis (i.e. excess of ossification, not reaching the pathological condition). The results, expressed ashypostotic scores, showed higher levels of hypostosis in these Neandertal specimens than in recent European samples. The highest expressions of hypostotis were observed in those regions of the Neandertal cranium where disequilibrium between skeletal and cerebral growth factors was expected. These results—interpreted as expression of developmental stress—are consistent with a heterochronic interpretation of the development of the Neandertal cranium; namely, a faster ossification of the cranial vault relative to brain growth rates.     

The statistical treatment of correlated bilateral traits in the analysis of cranial material.

At present there is no standardized method to derive frequencies from bilateral non-metric traits. In this paper the commonly used methods are evaluated in light of statistical considerations and degree of sample preservation. In particular, we explore the question of dependence between sides for the bilateral traits. Several workers have tested for bilateral trait correlation in incorrect ways, confusing tests for differences in side frequencies with tests for independence. An easy method to test for independence, using the chi-squared test, is recommended. This test is used on 16 bilateral traits in a large sample of prehistoric carnia from Central California and significant dependence is found for all 16 of these traits. We suggest the traditional method of deriving frequencies be used. Both sides of the cranium should be considered, dividing the number of times the trait occurs by the number of sides available for observation. This method can be used even in poorly preserved samples. Side to side correlation may be compensated for by modifying the constants subtracted in the mean measure of divergence and in the expression for the approximate variance of the mean measure of divergence when the samples are drawn from identical populations.     

Expression of a dispersal trait in a guild of mites colonizing transient habitats

Summary Dispersal as a means of escape from deteriorating habitats is of particular ecological relevance for organisms such as certain astigmatic mites that colonize habitats which vary unpredictably in space and time. The mites meet these ecological challenges by a facultative dispersal morph, the heteromorphic deutonymph, also called hypopus. The appearance or absence of hypopodes in natural populations is attributable to two fundamentally different, albeit interacting, causes. Genetic polymorphism for the propensity to induce a hypopus provides for heritable variation within the population and allows selection to favor or eliminate certain genotypes. The genotypic composition of a population reflects selection forces previously acting on the population. But it holds no predictive power. Rather, it adapts the population to cope with unpredictably varying living conditions because it ensures instantaneous fit of certain genotypes of the population (those displaying hypopus-free development) to favorable (moist) environmental conditions, and others (those expressing a hypopus) to detrimental (dry) conditions. In contrast, environmentally cued inducibility allows mites to anticipate food quality inasmuch as it allows each genotype of the population to adjust its development rapidly to impending adversity or benefit. Inducibility occurs by means of a developmental switching mechanism and leads either to a developmental pathway with a hypopus or else one without. The expression of a hypopus depends on interacting genetic and environmental (trophic) factors. High levels of additive genetic variation combine with considerable genetic-trophical interaction (comprising a threshold for phenotypic expression of the trait) to control hypopus induction. The results are consistent with a variable threshold whose level depends on diet quality. Different trophic conditions set the threshold at different points along the genetic scale resulting in different proportions of hypopus-forming and directly developing individuals within the population. The threshold, therefore, converts the concealed continuous genetic variation underlying the trait into a discontinuous response of the mite.     

Within and between population variation in inbreeding depression in the locally threatened perennial Scabiosa columbaria

Inbreeding depression plays a central role within the conservation genetics paradigm. Until now inbreeding depression is incorporated into models of population viability as a mean value (e.g. number of lethal equivalents) for all traits in a population. In this study of the locally threatened perennial plant species Scabiosa columbaria we investigated both the mean and the variance among families of inbreeding depression in eight life history traits for five natural populations varying in size from 300 to more than 120,000 individuals. Significant inbreeding depression was found in all populations and all traits. The mean inbreeding depression value per trait was never correlated to population size. Within each population, highly significant variation in inbreeding depression between families (VIFLID) was found. Per trait, families with inbreeding depression next to families with outbreeding depression were often found within the same population. Inbreeding depression at the family level was in many cases not correlated among traits and independent of correlations between traits themselves. VIFLID was negatively correlated with population size: in two traits these correlations were significant. The results underline that inbreeding depression is a complex, highly dynamic phenomenon. Models of viability should incorporate inbreeding depression distributions, with a trait specific mean and variance. Moreover, models of metapopulation dynamics should incorporate genotype quality as factor in colonization success.     

Predictors of Species Sensitivity to Fragmentation

We reviewed empirical data and hypotheses derived from demographic, optimal foraging, life-history, community, and biogeographic theory for predicting the sensitivity of species to habitat fragmentation. We found 12 traits or trait groups that have been suggested as predictors of species sensitivity: population size; population fluctuation and storage effect; dispersal power; reproductive potential; annual survival; sociality; body size; trophic position; ecological specialisation, microhabitat and matrix use; disturbance and competition sensitive traits; rarity; and biogeographic position. For each trait we discuss the theoretical justification for its sensitivity to fragmentation and empirical evidence for and against the suitability of the trait as a predictor of fragmentation sensitivity. Where relevant, we also discuss experimental design problems for testing the underlying hypotheses. There is good empirical support for 6 of the 12 traits as sensitivity predictors: population size; population fluctuation and storage effects; traits associated with competitive ability and disturbance sensitivity in plants; microhabitat specialisation and matrix use; rarity in the form of low abundance within a habitat; and relative biogeographic position. Few clear patterns emerge for the remaining traits from empirical studies if examined in isolation. Consequently, interactions of species traits and environmental conditions must be considered if we want to be able to predict species sensitivity to fragmentation. We develop a classification of fragmentation sensitivity based on specific trait combinations and discuss the implications of the results for ecological theory.     

Distinct genetic architectures for male and female inflorescence traits of maize

We compared the genetic architecture of thirteen maize morphological traits in a large population of recombinant inbred lines. Four traits from the male inflorescence (tassel) and three traits from the female inflorescence (ear) were measured and studied using linkage and genome-wide association analyses and compared to three flowering and three leaf traits previously studied in the same population. Inflorescence loci have larger effects than flowering and leaf loci, and ear effects are larger than tassel effects. Ear trait models also have lower predictive ability than tassel, flowering, or leaf trait models. Pleiotropic loci were identified that control elongation of ear and tassel, consistent with their common developmental origin. For these pleiotropic loci, the ear effects are larger than tassel effects even though the same causal polymorphisms are likely involved. This implies that the observed differences in genetic architecture are not due to distinct features of the underlying polymorphisms. Our results support the hypothesis that genetic architecture is a function of trait stability over evolutionary time, since the traits that changed most during the relatively recent domestication of maize have the largest effects.