Dental variation among four prehispanic Mexican populations

In this paper, the dental morphology of prehispanic Mesoamerican populations is described, compared, and examined within the context of New World dental variation. Twenty-eight morphological dental traits were studied and compared in four samples of prehispanic Mexican populations. After eliminating intra- and interobserver error, the dental morphological characteristics observed show evidence of heterogeneity among the populations. In particular, the oldest population, Tlatilco (1300–800 BC ), was significantly different from the other three groups, Cuicuilco (800–100 BC ), Monte Albán (500 BC –700 AD ) and Cholula (550–750 AD ). When the four samples were compared to other Mongoloid populations, either univariately or multivariately, it was observed that the Mexican groups did not follow a strict Sinodont (characteristic of Northeast Asia)/Sundadont (characteristic of Southeast Asia) classification (Turner [1979] Am. J. Phys. Anthropol. 51:619–636). From the traits examined, 27% presented frequencies consistent with Sinodont variation, while 73% of the traits showed similar incidence to Southeast Asian groups. Multivariately, the Mexican populations were found to fit an overall Sundadont classification. These results indicate that there is more dental morphological variation among American Indian populations than previously shown. © 1996 Wiley-Liss, Inc.     

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.     

Bilateral asymmetry in permanent dentition of 13 pre-conquest samples from Argentina (South America)

Bilateral asymmetry is an important field of study in anthropology. The evaluation of bilateral asymmetry of 44 dental non-metric traits of permanent dentition is carried out in this study on 376 adult skulls from different archaeological sites in Argentina (South America). From a total of 44 traits studied, just 12 (27% of the total traits expressed) presented Bilateral Index (BI) values lower than 100% (between 92% and 99%). Results suggest that the expression of all dental traits is probably bilateral. These results show the importance of analysis of bilateral asymmetry for assignment of taxonomic and population value of non-metric dental traits.     

Dietary,Cultural, and Pathogens-Related Selective Pressures Shaped Differential Adaptive Evolution among Native Mexican Populations

Native American genetic ancestry has been remarkably implicated with increased risk of diverse health issues in several Mexican populations, especially in relation to the dramatic changes in environmental, dietary, and cultural settings they have recently undergone. In particular, the effects of these ecological transitions and Westernization of lifestyles have been investigated so far predominantly on Mestizo individuals. Nevertheless, indigenous groups, rather than admixed Mexicans, have plausibly retained the highest proportions of genetic components shaped by natural selection in response to the ancient milieu experienced by Mexican ancestors during their pre-Columbian evolutionary history. These formerly adaptive variants have the potential to represent the genetic determinants of some biological traits that are peculiar to Mexican people, as well as a reservoir of loci with possible biomedical relevance. To test such a hypothesis, we used genome-wide genotype data to infer the unique adaptive evolution of Native Mexican groups selected as reasonable descendants of the main pre-Columbian Mexican civilizations. A combination of haplotype-based and gene-network analyses enabled us to detect genomic signatures ascribable to polygenic adaptive traits plausibly evolved by the main genetic clusters of Mexican indigenous populations to cope with local environmental and/or cultural conditions. Some of these adaptations were found to play a role in modulating the susceptibility/resistance of these groups to certain pathological conditions, thus providing new evidence that diverse selective pressures have contributed to shape the current biological and disease-risk patterns of present-day Native and Mestizo Mexican populations.     

Developmental instability in Brassica campestris (Cruciferae): fluctuating asymmetry of foliar and floral traits

The degree of fluctuating asymmetry of bilateral traits provides a measure of developmental instability, which can be influenced by genetic as well as environmental stress. We studied genetic variation between and within two populations of the mustard Brassica campestris for asymmetry of foliar (cotyledon width) and floral (petal length and width) traits as well as for phenological (germination and flowering) and performance (biomass and flowering) traits. The two populations differed in mean expression of most traits, including asymmetry. However, within-population estimates of genetic variability tended to be lower for asymmetry than other traits. Asymmetry was greater in the population that had lower biomass accumulation and flower production, which supports the idea that population-level asymmetry may be indicative of population-level performance. However, within each population, evidence that performance was negatively correlated with asymmetry was equivocal. Within populations there was little or no concordance among estimates of asymmetry based on different structures, i.e., plants that had highly asymmetrical cotyledons did not tend to have highly asymmetrical petals. The lack of a general buffering capacity at the individual level may be explained by developmental processes (e.g., action of different genes or morphogens) as well as evolutionary processes (e.g., selection on asymmetry of different traits).     

长阳青铜时代与大同北魏朝代人类牙齿的形态变异

本文记述了湖北长阳县深潭湾青铜时代和山西大同市郊北魏朝代两处墓葬遗址出土的人类牙齿形态变异的状况,提供人们对牙齿形态种种变异的认识,探索非测量性牙齿特征在研究种族和人群之间关系中的意义。     

Patterns of morphological variability in reintroduced populations with two beaver subspecies Castor fiber orientoeuropaeus and Castor fiber belorussicus (Castoridae, Rodentia) as an example

Taking as an example two beaver subspecies (Castor fiber orientoeuropaeus and Castor fiber belorussicus) with documented history of population formation, the patterns of morphological variability in translocated groups of mammals are studied. The variability of quantitative and qualitative traits in the formed populations is not characterized by a single direction. The main trend consists in increasing of adaptive norms diversity as related to body size. There observed a slight increase in the level of fluctuating asymmetry, reduction in polymorphism of nonmetric traits, and increase in fraction of rare aberrations. All these may be caused by inbreeding taking place during the period of prapopulations formation. The results of the study allow for considering the intraspecific differentiation as a consequence of adaptive variability (adaptatiogenesis) or subspecies hybridization. As for stochastic processes (genetic drift, founder effect), they seem to not influence the morphological variability significantly. The differences between discrete and dimensional traits are indicative of population groups' peculiarity.     

Leaf morphometric variation in Quercus affinis and Q. laurina (Fagaceae), two hybridizing Mexican red oaks

Leaf variation was examined in two hybridizing Mexican red oaks, Quercus affinis and Q. laurina . Data of nine traits were obtained for ten randomly chosen leaves in each of 512 individuals from 16 populations sampled along a geographical gradient, including the distribution area of both species and a putative area of secondary contact and hybridization. A cluster analysis recognized two main groups of populations, which were congruent with the taxonomic assignment of the predominant morphological type within the populations and were thus labelled ' Q. affinis -like' and ' Q. laurina -like' population groups. A nested analysis of variance revealed that the largest proportion of the total variation was contained within populations, as among-tree variation (28–54%, depending on the trait), and as intra-individual variation (17–56%). However, differences between the two groups of populations (3–27%) and among populations within groups (5–21%) were also significant for the nine traits. A distinct pattern of change across populations was observed for each trait. Variation was particularly pronounced along the geographical gradient for petiole length and leaf-margin teeth number, possibly implying selection on these two traits. Results suggest that phenotypic plasticity, gene flow, hybridization and natural selection have shaped foliar variation in this oak complex. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 427–435.     

Nonmetric tooth crown traits in a Sri Lankan aboriginal Vedda population

This study was conducted to determine the frequencies of non-metric tooth crown traits of Vedda of Sri Lanka and to investigate the affinities of these morphological variations with those of other world populations.Fifty dental plaster casts were observed. The Arizona State University dental anthropology system was adopted for classification of the 16 traits observed. We used 13 traits to compare the Vedda and other world populations. Using the frequencies of 13 traits, Smith Mean Measure of Divergence was calculated to determine inter-population distances. Affinities among the Vedda and other world populations were expressed in two dimensions of the principal coordinate analysis.Cusp number in mandibular second molar and hypocone absence in maxillary second molar had the highest frequency at 95.9% and 93.8%, respectively. Shovelling, double shovelling in the maxillary central incisor and deflecting wrinkle in the mandibular first molar had the lowest frequency at 0%. The principal coordinate analysis showed that Sino American and Western Eurasian populations were separated in negative and positive directions in the first principal coordinate axis. Vedda located with the Western Eurasian population groups. Sahul and Sunda Pacific populations located in the intermediate position between Sino American and Western Eurasian populations.The dental phenotype of Vedda has close affinities with those of early south Asian populations. They are far different from Sino American and Sunda pacific populations. Vedda shows closer affinities to Sahul Pacific and South African (Bantu) populations.     

Phenetic analysis of the Mexican midland pinyon pines, Pinus cembroides and Pinus johannis

This account presents an analysis of allopatric, sympatric and juxtaposed populations of the pinyon pines, Pinus cembroides Zucc. and P. johannis M.-F. Robert, based on phenetic analysis of morphological data, and draws on a comparison and differentiation of P. culminicola Andresen & Beaman. A qualitative and quantitative database for populations has been assembled and used for a cluster and ordination analysis using NTSYS. It was found that individual populations of the taxa were distinguishable. The emergence of morphological intermediate populations between P. cembroides and P. johannis was confirmed. The pattern of variation in P. johannis was found to be discrete, showing three geographical groups. The phenetic similarity between P. johannis from Zacatecas and P. johannis from San Luis Potosi and Queretaro was lower than that of P. johannis from Zacatecas and P. culminicola from Nuevo Leon. The following traits distinguish P. cembroides and the other two species: colour and fertility of seeds; cone shape; colour and width of needles; physiognomy; seed dimensions. This last trait can be used to distinguish three subgroups of pines with white endosperm in the northern, central and southern regions of the Mexican highlands.     

Geographic variation in Mexican jays (Aphelocoma ultramarina): local differentiation,polyphyly or hybridization?

Studies of genetic variation within highly variable taxa can provide valuable insight into the factors influencing biological diversification. We examined six microsatellite loci, a nuclear intron and the mitochondrial control region to determine if the Mexican jay subspecies Aphelocoma ultramarina couchii and A. u. potosina have hybridized with western scrub-jays (A. californica). We suspected hybridization because these Mexican Jay populations resemble scrub-jays in several traits. We sampled six Mexican jay (N = 105) and four scrub-jay (N = 78) populations. Suspected hybrid Mexican Jay populations did not share any mitochondrial types or intron alleles with scrub-jays. All microsatellite alleles found in the suspected hybrid Mexican jay populations are also found in the control Mexican jay populations. Genetic distance-based trees from microsatellites supported reciprocal monophyly of Mexican jays and scrub-jays with bootstrap support > 80%. We randomized genotypes among populations to test scenarios consistent with hybridization. In some areas where Mexican jays and scrub-jays occur in sympatry or geographical proximity, randomization tests yield results expected under hybridization (100% support for seven of nine scenarios). However, these populations were not the primary candidates for hybridization based on phenotype. Even if low-level hybridization did occur, hybridization does not appear to be the main reason some Mexican jay populations resemble scrub-jays more than others. The scrub-jay-like traits in these populations may be due to drift, adaptation or plasticity. Alternatively, ancient hybridization, followed by selection for scrub-jay like traits in some Mexican jay populations, might have given rise to the observed variation.     

The phenetic distances of the living Druze from other human populations suggest a major genetic drift from the Western Eurasian ancestral category

The objectives were to determine the expression frequency and sexual dimorphism of 16 non-metric crown traits on the sample of permanent dentitions of the living Druze population (a Near Eastern genetic isolate) in Jordan, and to assess the biological affinity of this sample to 21 regional groups, and to the living general Jordanian population, based on these traits. Druze schoolchildren (46 males, 40 females; mean age = 16.0, sd = 0.5 years) were studied in 2011. The traits were classified using the Arizona State University dental anthropology system, counted with the individual count method, and dichotomized according to the criteria of Scott and Turner for the purpose of group comparisons. Fisher's exact test for dichotomized scores was used to assess sexual dimorphism in these traits. Smith's mean measure of divergence was used to measure all pairwise distance values among the groups. Sexual dimorphism was found in five traits (i.e., UI2 interruption grooves, 3-cusped UM2, UM1 Carabelli's tubercle/cusp, 4-cusp LM1, and LM2 Y-groove pattern). This study revealed that the dental pattern of living Druze, which is similar to that of the general Jordanian population, is sufficiently distinct from the Western Eurasian pattern and all other known dental patterns to form a distinct dental pattern for the regional group or subcategory to which these two populations belong. Moreover, the relatively large distance values of the living Druze and Jordanians from the other world groups considered, including the Western Eurasian groups, suggest a similar major genetic difference of these two populations from the Western Eurasian ancestry.     

Dental trait expression at the enamel-dentine junction of lower molars in extant and fossil hominoids

Discrete dental traits are used as proxies for biological relatedness among modern human populations and for alpha taxonomy and phylogeny reconstruction within the hominin clade. We present a comparison of the expression of lower molar dental traits (cusp 6, cusp 7, trigonid crest pattern, and protostylid) at the enamel-dentine junction (EDJ) in a variety of extant and fossil hominoid taxa, in order to assess the contribution of the EDJ to the morphology of these traits at the outer enamel surface (OES). Molars (n=44) were imaged nondestructively using high-resolution microCT, and three-dimensional surface models of the EDJ and OES were created to compare trait expression at each surface. Our results indicate that these dental traits originate at the EDJ, and that the EDJ is primarily responsible for their degree of expression at the OES. Importantly, variable trait morphology at the EDJ (often not easily recognizable at the OES) indicates that different developmental processes can produce traits that appear similar at the enamel surface, suggesting caution in intra- and intertaxonomic comparisons. The results also highlight the importance of the EDJ for understanding the morphological development of discrete traits, and for establishing graded scales of variation to compare trait frequency among groups for the purpose of taxonomic and/or phylogenetic analysis. Finally, this study demonstrates that imaging the EDJ of both worn and unworn fossil hominin teeth provides a novel source of information about tooth development and variation in crown morphology.     

Discrete dental traits in four Tlaxcaltecan Mexican populations

Seven hundred dental casts from four Tlaxcaltecan Indian populations of Mexico were analyzed for the incidence of ten discrete dental traits. The populations are of known historical origin, with Cuanalan and Saltillo transplanted from the Valley of Tlaxcala approximately 400 years ago. Given this temporal and geographical separation of these transplanted populations from the parental gene pool, statistically significant morphological divergence was observed. However, varying degrees of admixture with Spanish and possibly African colonists have complicated the interpretation of the results. Shovelling of incisors was shown to be the best discriminator of group differences. Mandibular molar patterns and mandibular incisor extension indicate that Cuanalan is closest to Saltillo while the valley communities, Tlaxcala and San Pablo, are closest to each other.     

Fluctuating dental asymmetry: Variation among skeletal populations

Recent investigations have shown that nongenetic, environmental factors can adversely affect dental growth and produce bilateral asymmetries in tooth size. When asymmetries do not favor either side, i.e., absence of directional asymmetry, the condition is termed fluctuating asymmetry. Fluctuating asymmetry of the mesiodistal and buccolingual dimensions of the total permanent dentition was compared among human skeletal populations which differ socio-economically and nutritionally. Odontometric data were collected from prehistoric hunters (Indian Knoll site), later aboriginal farming groups (Campbell and Larson sites), and a modern cadaver population (Hamann-Todd). The magnitude of asymmetry is expressed by the familiar correlation coefficient, r. The proportion, then, of intra-individual variation due to fluctuating asymmetry is equal to 1-r. With Wilcoxon's signed ranks test on the correlation coefficients no significant sex difference was shown within populations. Among groups, though, Indian Knoll was the most odontometrically asymmetrical; moreover, within Indian Knoll, the taller and ostensibly better nourished individuals had larger, less asymmetrical teeth than the shorter individuals. These results suggest that environmentally mediated growth disturbance may be sensitively reflected by dental asymmetry. A population exhibiting other signs of severe growth disturbance, e.g., enamel hypoplasia and Harris lines, was the most dentally asymmetrical.     

On the meaning of increased fluctuating dental asymmetry: a cross populational study.

Suarez reports a greater magnitude of fluctuating dental asymmetry for Neandertal sample when compared with a sample of modern Ohio whites. He postulates that this greater antimeric variance could be due to a greater degree of inbreeding in the Neandertal populations. In the present investigation, the magnitude of fluctuating dental asymmetry is evaluated for Eskimo and Pueblo populations. These populations were found to exhibit dental variance of equal magnitude to that of the Neandertal population. As these populations are not highly inbred, a stress related mechanism is suggested to explain these observations and the inbreeding hypothesis is rejected. The implications of this mechanism to Brace's Probable Mutation Effect are discussed.     

Evolutionary divergence in the pan-Atlantic mangrove Avicennia germinans

Cuticular hydrocarbon composition was determined for 18 populations of Avicennia germinans (Avicenniaceae) collected from West Africa, Florida, the Pacific coast of Mexico and French Guyana. Variation in covariance structure among the hydrocarbons was evaluated from correlations among the traits for each of the populations and from a hierarchical common principal components analysis. Principal components ordinations of populations based on the 171 z * transformed correlation coefficients, onto which a minimal spanning tree was superimposed, suggested a network in which French Guyanan populations formed a nexus from which African populations differentiated biochemically from Floridan and Mexican groups. Common principal components analysis provided further support for the differentiation in covariance structure among these biochemical traits of African populations. Pacific coast Mexican populations appeared to have diverged less in covariation among traits from Atlantic American sources than did the northern (Floridan) and southern (French Guyanan) Atlantic American populations from one another. The complete isolation of Pacific coast sources after emergence of the Central American isthmus during the Pliocene provides a reference for comparison of levels of differentiation among regions that suggests an underlying pattern of divergence in this species. Partial Mantel matrix tests revealed significant geographic effects, with no significant climatic effects. Our results provide support for recognition of a major differentiation between Old and New World sources within the taxon and indicate the need for a full revision of this species.     

Sexual dimorphism in the Chuvashian population of Russia in two types of dermatoglyphic traits: principal component analysis

With the aim of determining sexual dimorphism in the component structures among the Chuvashian population of Russia, finger and palmar dermatoglyphics of 547 individuals (293 males, 254 females) were analyzed. The sex differences in two categories of dermatoglyphic traits (22 quantitative traits and 38 asymmetry and diversity traits) are reflected differently and contradictory with other ethnic groups. However, a common feature of the factor 1 "digital pattern size factor" (finger ridge counts from the first category of traits) indicate its degree of universality when compared with other populations, which suggests that the variability of finger ridge counts is determined by the same genes that control the pattern types. The factors "intra-individual finger diversity factor", and "bi-lateral asymmetry factor" extracted from the second category of dermatoglyphic traits are also similar in both sexes. However, these components are hardly described in the literature. The nature of variation of these components (from two categories of dermatoglyphic traits) appears with a good similarity between sexes, which suggests their common biological validity of the underlying component structures of the finger and palmar dermatoglyphic characters.     

Developmental stability,sexual selection and speciation

Fluctuating asymmetry occurs when an individual is unable to undergo identical development of an otherwise bilaterally symmetric trait on both sides of its body. Since both sides of a bilaterally symmetric trait are the result of the actions of a single genome, fluctuating asymmetry represents an epigenetic measure of the sensitivity of development to stress. Different morphological traits may show a direct relationship between their functional importance and their degree of developmental canalization. This may explain why some characters show high degrees of fluctuating asymmetry, and why these characters more often become exaggerated secondary sexual ornaments. The degree of fluctuating asymmetry is generally larger in small marginal populations living in novel environments, and this will particularly lead to relatively large degrees of asymmetry in the least developmentally canalized traits. More stringent selection against heterozygotes in marginal populations may further break down developmental stability and linkage groups which would lead to increased genetic variance. Females may prefer to mate with males having large, but relatively symmetric morphological characters, because it is more difficult to make large traits (a good genes argument), a large trait is more easily perceived (a sensory bias preference), and because symmetry signals ability to cope with stress (a good genes argument). The low degree of developmental stability and the large amount of genetic variance in secondary sexual characters in small, marginal populations could set the scene for rapid development of divergence and speciation in marginal populations.     

Geography of fluctuating asymmetry in the greenfinch, Carduelis chloris

Levels of fluctuating asymmetry (FA) in 12 bilateral skeletal traits were estimated from 12 populations of greenfinches (Carduelis chloris) collected along a north‐south gradient across Europe. Average FA of measured traits was positively correlated with latitude indicating that the younger and genetically less diverse northern European populations are developmentally less stable than the older and genetically more diverse southern populations. Levels of FA differed significantly between different traits being lowest for functionally important traits (limb and wing bones) and highest for functionally less important traits such as foramina (apertures through bones)– a pattern that was highly concordant across different populations. Males tended to exhibit higher levels of FA than females, a finding consistent with the suggestions that males are more prone to developmental perturbations than females. Age differences in levels of FA were relatively clear, but inconsistent across traits with different degree of functionality. Individual heterozygosity – as enumerated from variation in allozyme loci – was unrelated to individual FA. No evidence for existence of individual asymmetry parameter (IAP) was found although traits related to locomotion indicated some degree of integration, which was expressed by correlations in the signed asymmetry. Nevertheless, an individual's overall asymmetry was poorly predicted by asymmetry of individual characters. Evidence for existence of population asymmetry parameter (PAP) was clear since all traits exhibited a similar degree of association with latitude. That the latitudinal cline of increasing FA towards north coincided with decreasing levels of genetic variability across the cline could be indicative of break down of developmental stability in the recently established and genetically impoverished populations. To what extent a reduced heterozygosity, the break up of co‐adapted gene complexes and/or environmental differences contributed to this process cannot be distinguished from our data.