Patterns of dental wear in the Lengua Indians of Paraguay

Wear patterns were examined on dental casts of 202 living Lengua Indians from the Chaco area of Paraguay. Consideration was given to the development of the molar helicoidal plane, age-related changes in occlusal attrition, coalescence of dentine exposures, interproximal attrition, and erupted crown height. This study lends support to Osborn's theory of the helicoidal plane development by showing that attrition enhances rather than modifies posteruption molar occlusal planes. The rate of interproximal attrition was found to slow down with the eruption and functional initiation of the third molars. Sinuous and cavo-convex interproximal contact areas that are generated with age, however, appeared to be less abrasion resistant than straight surfaces, hence leading to an increase in interproximal attrition rates with advanced age. Maximum crown height reduction occurred between the ages of 20 and 40 years in central incisors, canines, and first molars. Kruskal-Wallis tests and log linera models failed to demonstrate significant sexually dimorphic or antimeric differences in wear patterns of Lengua teeth.     

The craniofacial pattern of the Lengua Indians of Paraguay

Lateral cephalometric headfilms of 30 male and 30 female Lengua Indians taken in the Chaco area of Paraguay were compared with a sample of 23 male and 25 female South African Caucasoids with excellent occlusion. The most obvious difference noted between the two population groups was the degree of prognathism evident in the Lengua. This was attributed to the generally shorter anterior cranial base in the latter group rather than to the size or forward positioning of their jaws. The significantly larger ANB (Subspinale, Nasion, Supramentale) angle observed in the Lengua was attributed to one or both of two factors, namely, the short anterior cranial base or the clockwise rotation (forward tipping) of the jaws relative to the anterior cranial base. Chinpoint position relative to the anterior cranial base in the Lengua is not much different from that of our Caucasoid sample. The lower incisor teeth in the Lengua, but not the upper ones, are more labially inclined than those of the Caucasoids.     

Fluctuating dental asymmetry as a measure of odontogenic canalization in man

Fluctuating odontometric asymmetry was evaluated in 202 Lengua Indians and in 125 contemporary caucasoids using Euclidean map analyses, rescaled asymmetry values, and Naperian logarithmic transformations. Both populations showed bimodal distributions of canalizing ability, with significantly more Lengua Indians being less well canalized. Student t-tests indicated that significant interpopulation differences in rescaled asymmetry values centered around maxillary mesiodistal dimensions. Analyses of variance failed to show significant levels of sexual dimorphism in the magnitude of asymmetry for both populations. It is concluded that even in a relatively stress-free population, there exist some individuals who are less well canalized than others. When a population is subjected to elevated levels of parasitic and nutritional stress, the number of less-well-canalized individuals increases significantly.     

Canine root development and morphology inMacaca nemestrina

Recently,Yoshikawa andDeguchi (1992) reported an unusually high frequency (40%) of two-rooted maxillary canines inMacaca fuscata females and a complete absence of this trait in males. In the present study, canine root development and morphology was examined using cephalographs taken on 50 male and 50 femaleMacaca nemestrina, and 20 male and 20 femalePapio cynocephalus for comparison with the Japanese macaque. The results showed no double-rooted canines present in either species in the upper or lower canines. This supports the general rule that, among primates, canines possess a single-root. It was further suggested that the two-rooted canines inM. fuscata may be the result of the founder effect, i.e. that the genes for this trait may have been carried by the initial populations when they arrived on the islands sometime during the middle to late Pleistocene.     

Canine genetics comes of age

The dog, as human's favored companion, is unique among animal species in providing new insights into human genetic disease. In this review, we will discuss both the breed and the population structure of dogs and why that makes canines amenable to genetic studies. We will review the current state of the map and discuss the particular disease states in which canines stand to make the greatest contribution to medical genetics.     

Genetic studies in Paraguay: blood group, red cell, and serum genetic patterns of the Guayaki and Ayore Indians, Mennonite settlers, and seven other Indian tribes of the Paraguayan Chaco

Genetic studies of 540 Paraguayan Indians from nine tribal groups and 51 Mennonites are presented for ABO, MNSs, P₁, Rh, Kell, Lewis, Duffy, Diego; for serum immunoglobulins and haptoglobins, G6PD-deficiency, and thalassemia trait. Group O gene frequencies for all Indian groups were 1.00; for r (cde), 0.00. Tapiete, Lengua, Toba, and Sanapana R_z (CDE) frequencies were among the highest ever reported. N frequencies were high for Ache Kwera (Guayaki), Lengua, Cheroti, Guarayu, Tapiete; N and s low for Ayore. MS frequencies were high for Sanapana, Lengua, Ayore; Ns for Tapiete. Diego was notably absent for Toba, Lengua, Guarayu, Tapiete, Ayore. Homogeneous frequencies for Fy^a (1.000) occurred among Guarayu and Tapiete, and for P₁ among Guayaki. Inv(a) frequencies were low for Cheroti, Chulupi, Guayaki. Hp 1 among Guayaki (Ache Kwera 0.15) is lowest ever reported. G6PD deficiency and abnormal hemoglobins were uniformly absent from all groups. Mennonite results were homogeneous and point toward Dutch origins. Differences among groups studied, and between Paraguayan and other Amerinds emphasize importance of genetic drift and founder principle. Abandonment of their tribes by mixed-blood offspring is partly responsible for apparent genetic purity and homogeneity of groups.     

Brief communication: two-rooted lower canines--a European trait and sensitive indicator of admixture across Eurasia

With the exception of Carabelli's trait, the European dentition is better known for the morphological traits that it does not exhibit rather than the ones that it does. One root trait, however, runs counter to the characterization of reduced and simplified European crowns and roots. Although a rare trait in general, two-rooted lower canines are much more common in Europeans than in any other regional grouping and, given adequate sample sizes, can be useful in evaluating gene flow between Europeans and neighboring groups. In European samples, two-rooted lower canines consistently exhibit frequencies of 5-8%. In our sample from northern Spain, the trait attains a frequency of almost 10%. In contrast, in Sub-Saharan Africans the trait is virtually unknown while in Asian and Asian-derived populations, it varies between 0.0 and 1.0%. Here we show that two-rooted canine frequencies for new migrants along the western frontiers of China and Mongolia ranged from 0-4%. These data suggest European-derived populations migrated into western China (Xinjiang Province) and Mongolia (Bayan Olgii Aimag) sometime during the late Bronze age (1000-400 BCE).     

The Impact of Population Demography and Selection on the Genetic Architecture of Complex Traits

Population genetic studies have found evidence for dramatic population growth in recent human history. It is unclear how this recent population growth, combined with the effects of negative natural selection, has affected patterns of deleterious variation, as well as the number, frequency, and effect sizes of mutations that contribute risk to complex traits. Because researchers are performing exome sequencing studies aimed at uncovering the role of low-frequency variants in the risk of complex traits, this topic is of critical importance. Here I use simulations under population genetic models where a proportion of the heritability of the trait is accounted for by mutations in a subset of the exome. I show that recent population growth increases the proportion of nonsynonymous variants segregating in the population, but does not affect the genetic load relative to a population that did not expand. Under a model where a mutation''s effect on a trait is correlated with its effect on fitness, rare variants explain a greater portion of the additive genetic variance of the trait in a population that has recently expanded than in a population that did not recently expand. Further, when using a single-marker test, for a given false-positive rate and sample size, recent population growth decreases the expected number of significant associations with the trait relative to the number detected in a population that did not expand. However, in a model where there is no correlation between a mutation''s effect on fitness and the effect on the trait, common variants account for much of the additive genetic variance, regardless of demography. Moreover, here demography does not affect the number of significant associations detected. These findings suggest recent population history may be an important factor influencing the power of association tests and in accounting for the missing heritability of certain complex traits.     

Directional selection in the evolution of elongated upper canines in clouded leopards and sabre‐toothed cats

Extremely developed or specialized traits such as the elongated upper canines of extinct sabre‐toothed cats are often not analogous to those of any extant species, which limits our understanding of their evolutionary cause. However, an extant species may have undergone directional selection for a similar extreme phenotype. Among living felids, the clouded leopard, Neofelis nebulosa, has exceptionally long upper canines for its body size. We hypothesized that directional selection generated the elongated upper canines of clouded leopards in a manner similar to the process in extinct sabre‐toothed cats. To test this, we developed an approach that compared the effect of directional selection among lineages in a phylogeny using a simulation of trait evolution and approximate Bayesian computation. This approach was applied to analyse the evolution of upper canine length in the Felidae phylogeny. Our analyses consistently showed directional selection favouring longer upper canines in the clouded leopard lineage and a lineage leading to the sabre‐toothed cat with the longest upper canines, Smilodon. Most of our analyses detected an effect of directional selection for longer upper canines in the lineage leading to another sabre‐toothed cat, Homotherium, although this selection may have occurred exclusively in the primitive species. In all the analyses, the clouded leopard and Smilodon lineages showed comparable directional selection. This implies that clouded leopards share a selection advantage with sabre‐toothed cats in having elongated upper canines.     

Variant evolutionary trees under phenotypic variance

Evolutionary branching, which is a coevolutionary phenomenon of the development of two or more distinctive traits from a single trait in a population, is the issue of recent studies on adaptive dynamics. In previous studies, it was revealed that trait variance is a minimum requirement for evolutionary branching, and that it does not play an important role in the formation of an evolutionary pattern of branching. Here we demonstrate that the trait evolution exhibits various evolutionary branching paths starting from an identical initial trait to different evolutional terminus traits as determined by only changing the assumption of trait variance. The key feature of this phenomenon is the topological configuration of equilibria and the initial point in the manifold of dimorphism from which dimorphic branches develop. This suggests that the existing monomorphic or polymorphic set in a population is not an unique inevitable consequence of an identical initial phenotype.     

Control of confounding of genetic associations in stratified populations

To control for hidden population stratification in genetic-association studies, statistical methods that use marker genotype data to infer population structure have been proposed as a possible alternative to family-based designs. In principle, it is possible to infer population structure from associations between marker loci and from associations of markers with the trait, even when no information about the demographic background of the population is available. In a model in which the total population is formed by admixture between two or more subpopulations, confounding can be estimated and controlled. Current implementations of this approach have limitations, the most serious of which is that they do not allow for uncertainty in estimations of individual admixture proportions or for lack of identifiability of subpopulations in the model. We describe methods that overcome these limitations by a combination of Bayesian and classical approaches, and we demonstrate the methods by using data from three admixed populations--African American, African Caribbean, and Hispanic American--in which there is extreme confounding of trait-genotype associations because the trait under study (skin pigmentation) varies with admixture proportions. In these data sets, as many as one-third of marker loci show crude associations with the trait. Control for confounding by population stratification eliminates these associations, except at loci that are linked to candidate genes for the trait. With only 32 markers informative for ancestry, the efficiency of the analysis is 70%. These methods can deal with both confounding and selection bias in genetic-association studies, making family-based designs unnecessary.     

Chromosome polymorphisms and natural selection inLeptysma argentina (Orthoptera): external phenotype affected by a centric fusion predicts adult survival

The relationship between fitness variation associated with a quantitative trait and a Mendelian factor affecting that trait was examined in a natural population of the South American grasshopperLeptysma argentina. Previous studies have shown that a centric fusion between chromosomes 3 and 6 (fusion 3/6) increases adult survival and body size in this grasshopper. Here we examined the possible relationships among fusion 3/6, a size-related trait (prothorax height) and adult survival in a natural population. The study was based on two generations, comparing samples taken at the beginning and at the end of the adult life span. All individuals were karyotyped and scored for prothorax height (PH). A nonparametric regression analysis revealed that adult survival monotonically increased with PH in both generations. Moreover, fusion 3/6 was found to have an additive effect on this trait. Within generations, fusion frequency increased with adult survival in males (but not significantly so), as expected if phenotypic selection on PH influences the fusion polymorphism. Using regression analyses, we show that the correlation between PH and adult survival is not a purely environmental correlation genetically independent from the fusion polymorphism. A simple model is proposed for testing similar hypotheses in studies of selection on a trait influenced by a known genetic polymorphism.     

Brief communication: physiological stress in the Florida Archaic-enamel hypoplasia and patterns of developmental insult in early North American hunter-gatherers

We examined the prevalence and developmental timing of linear enamel hypoplasias (LEHs) in an early Archaic Floridian population from Windover (8,120-6,980 (14)C years B.P. uncorrected). Using digital images, mandibular and maxillary canines were analyzed for defect prevalence and timing of insults. Although overall prevalence was very weakly correlated with earlier defect timing, there were significant differences in defect prevalence that varied by sex and tooth type. The mean LEH count in male mandibular canines was far higher than in male maxillary canines or in female mandibular or maxillary canines. We examined defect timing as a possible predictor of the sex differences in LEH prevalence. There were no significant sex differences in the developmental timing of the earliest defects in either tooth class. Developmental timing is not responsible for the sex differences seen in defect prevalence in mandibular canines.     

Evidence for genetic differentiation in timing of maturation among nine‐spined stickleback populations

Timing of maturation is an important life‐history trait that is likely to be subjected to strong natural selection. Although population differences in timing of maturation have been frequently reported in studies of wild animal populations, little is known about the genetic basis of this differentiation. Here, we investigated population and sex differences in timing of maturation within and between two nine‐spined stickleback (Pungitius pungitius) populations in a laboratory breeding experiment. We found that fish from the high‐predation marine population matured earlier than fish from the low‐predation pond population and males matured earlier than females. Timing of maturation in both reciprocal hybrid crosses between the two populations was similar to that in the marine population, suggesting that early timing of maturation is a dominant trait, whereas delayed timing of maturation in the pond is a recessive trait. Thus, the observed population divergence is suggestive of strong natural selection against early maturation in the piscine‐predator‐free pond population.     

Dental fluctuating asymmetry in the Gullah: tests of hypotheses regarding developmental stability in deciduous vs. permanent and male vs. female teeth

In this investigation, deciduous teeth (canines, c; first molars, m1; second molars, m2) and their permanent successors (canines, C; first premolars, P1; second premolars, P2) were used to test two related hypotheses about fluctuating asymmetry (FA). First, based on the biology of the developing dentition, it was predicted that deciduous teeth would be more developmentally stable and thus exhibit less dimensional FA than their permanent successors. Second, based on sex differences in tooth development, it was predicted that female canines would have greater developmental stability (less FA) than male canines. Bucco-lingual measurements were made on dental casts from a single Gullah population. Using a repeated-measures study design (n = 3 repeated measures), we tested these hypotheses on sample sizes ranging from 63-82 antimeric pairs. Neither hypothesis was supported by our data. In most cases, Gullah deciduous teeth did not exhibit statistically significantly less FA than their permanent successors; indeed, statistically significant differences were found for only 3 of 12 deciduous vs. permanent contrasts, and in two cases, the deciduous tooth had greater FA. Female mandibular canines exhibited statistically significantly greater FA than those of males, while there was no statistically significant sex difference in FA for the maxillary canine. FA in these Gullah samples is high when compared to Archaic and late prehistoric Ohio Valley Native Americans, consistent with historical and archaeological evidence that environmental stress was relatively higher in the Gullah population. We suggest that when environmental stress in a population is high, the impact of differences in tooth formation time spans and developmental buffering upon FA may be minor relative to the effect of developmental noise.     

Collection of pedigree data for genetic analysis in isolate populations

Pedigree data are useful for a wealth of research purposes in human population biology and genetics. The collection of extended pedigrees represents the most powerful sampling design for quantitative genetic and linkage studies of both normal and disease-related quantitative traits. In this paper we outline an approach for collecting pedigree data in stable isolate populations. As an example, the pedigree for the Jirel population, which was obtained using the methods presented, is described. The Jirel pedigree contains 2,000 study participants and more than 62,000 pairwise relationships that are informative for genetic analysis. Once such pedigrees are genetically characterized by a genome scan for a given trait, they become an invaluable resource for future genetic studies of any quantitative trait.     

A brief note on the resemblance between relatives in the presence of population stratification

Population stratification occurs when a study population is comprised of several sub-populations, and can result in increased false positive findings in genomewide-association studies. Recently published work shows that sub-population-specific positive assortative mating at the genotypic level results in population stratification. We show that if the allele frequency of a single nucleotide polymorphism responsible for a trait varies between sub-populations and there is no dominance variance, then the heritability of the trait increases, primarily due to an increase in the additive genetic variance of the trait.     

Moving from QTL experimental results to the utilization of QTL in breeding programmes

Results from quantitative trait loci studies cannot be readily implemented into breeding schemes through marker assisted selection because of uncertainty about whether the quantitative trait loci identified are real and whether the identified quantitative trait loci are segregating in the breeding population. The present paper outlines and discusses strategies to reduce uncertainty in the results from quantitative trait loci studies. One strategy to confirm results from quantitative trait loci studies is to combine P -values from many quantitative trait loci experiments, while another is to establish a confirmation study. The power of a confirmation study must be high to ensure that the postulated quantitative trait loci can be verified. In the calculation of the experimental power, there are many issues that have to be addressed: size of the quantitative trait loci to be detected, significance level required, experimental design and expected heterozygosity for the design. To ensure marker assisted selection can be quickly implemented once quantitative trait loci are confirmed, DNA samples should be retained from daughters, and the sires and dams of elite sires.     

Contemporary changes in phenotypic variation,and the potential consequences for eco-evolutionary dynamics

Most studies assessing rates of phenotypic change focus on population mean trait values, whereas a largely overlooked additional component is changes in population trait variation. Theoretically, eco-evolutionary dynamics mediated by such changes in trait variation could be as important as those mediated by changes in trait means. To date, however, no study has comprehensively summarised how phenotypic variation is changing in contemporary populations. Here, we explore four questions using a large database: How do changes in trait variances compare to changes in trait means? Do different human disturbances have different effects on trait variance? Do different trait types have different effects on changes in trait variance? Do studies that established a genetic basis for trait change show different patterns from those that did not? We find that changes in variation are typically small; yet we also see some very large changes associated with particular disturbances or trait types. We close by interpreting and discussing the implications of our findings in the context of eco-evolutionary studies.     

QTL mapping and the genetic basis of adaptation: recent developments

Quantitative trait loci (QTL) mapping has been used in a number of evolutionary studies to study the genetic basis of adaptation by mapping individual QTL that explain the differences between differentiated populations and also estimating their effects and interaction in the mapping population. This analysis can provide clues about the evolutionary history of populations and causes of the population differentiation. QTL mapping analysis methods and associated computer programs provide us tools for such an inference on the genetic basis and architecture of quantitative trait variation in a mapping population. Current methods have the capability to separate and localize multiple QTL and estimate their effects and interaction on a quantitative trait. More recent methods have been targeted to provide a comprehensive inference on the overall genetic architecture of multiple traits in a number of environments. This development is important for evolutionary studies on the genetic basis of multiple trait variation, genotype by environment interaction, host–parasite interaction, and also microarray gene expression QTL analysis.