Environmental stress increases variability in the expression of dental cusps

Riga, Alessandro; Belcastro, Maria Giovanna; Moggi‐Cecchi, Jacopo

doi:10.1002/ajpa.22438

Cited by 29 publications

(37 citation statements)

References 83 publications

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“…The fact that dental traits are equally or more homoplastic than cranial and postcranial characters in primates and other mammals, and that trees based on dental and skeletal characters are not always consistent with those derived from molecular data has been documented extensively (Kay, 1990;Harris & Disotell, 1998;Ross et al 1998;S anchez-Villagra & Williams, 1998). A recent study by Riga et al (2014) in recent humans also found that environmental stress significantly increases the morphological variability and number of cusps within a tooth. Therefore, we highlight the need of using different lines of evidence for character definition and selection, which ultimately will lead to more reliable phylogenetic reconstructions.…”

Section: Discussionmentioning

confidence: 85%

“…A recent study by Riga et al. () in recent humans also found that environmental stress significantly increases the morphological variability and number of cusps within a tooth. Therefore, we highlight the need of using different lines of evidence for character definition and selection, which ultimately will lead to more reliable phylogenetic reconstructions.…”

Section: Discussionmentioning

confidence: 86%

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Homology, homoplasy and cusp variability at the enamel–dentine junction of hominoid molars

et al. 2017

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Evolutionary studies of mammalian teeth have generally concentrated on the adaptive and functional significance of dental features, whereas the role of development on phenotypic generation and as a source of variation has received comparatively little attention. The present study combines an evolutionary biological framework with state-of-the-art imaging techniques to examine the developmental basis of variation of accessory cusps. Scholars have long used the position and relatedness of cusps to other crown structures as a criterion for differentiating between developmentally homologous and homoplastic features, which can be evaluated with greater accuracy at the enamel-dentine junction (EDJ). Following this approach, we collected digital models of the EDJ and outer enamel surface of more than 1000 hominoid teeth to examine whether cusp 5 of the upper molars (UM C5) and cusps 6 and 7 of the lower molars (LM C6 and LM C7) were associated each with a common developmental origin across species. Results revealed that each of these cusps can develop in a variety of ways, in association with different dental tissues (i.e. oral epithelium, enamel matrix) and dental structures (i.e. from different cusps, crests and cingula). Both within and between species variability in cusp origin was highest in UM C5, followed by LM C7, and finally LM C6. The lack of any species-specific patterns suggests that accessory cusps in hominoids are developmentally homoplastic and that they may not be useful for identifying phylogenetic homology. An important and unanticipated finding of this study was the identification of a new taxonomically informative feature at the EDJ of the upper molars, namely the post-paracone tubercle (PPT). We found that the PPT was nearly ubiquitous in H. neanderthalensis and the small sample of Middle Pleistocene African and European humans (MPAE) examined, differing significantly from the low frequencies observed in all other hominoids, including Pleistocene and recent H. sapiens. We emphasize the utility of the EDJ for human evolutionary studies and demonstrate how features that look similar at the external surface may be the product of different developmental patterns. This study also highlights the importance of incorporating both developmental and morphological data into evolutionary studies in order to gain a better understanding of the evolutionary significance of dental and skeletal features.

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Section: Discussionmentioning

confidence: 85%

Section: Discussionmentioning

confidence: 86%

Homology, homoplasy and cusp variability at the enamel–dentine junction of hominoid molars

et al. 2017

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“…Although permanent molars were not included in their study, results presented here are consistent with their findings. Similarly, Riga, Belcastro, and Moggi‐Checci () documented increased, directional variation in molar cusp number and size in a stressed (vs. nonstressed) sample, indicating that environment can act “nonrandomly” on developmental parameters throughout crown formation. Our results suggest caution is needed in selecting which side to use in dental biodistance analyses.…”

Section: Discussionmentioning

confidence: 93%

Quantitative genetic analyses of postcanine morphological crown variation

Stojanowski

Paul

Seidel

et al. 2019

American J Phys Anthropol

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Objectives: This article presents estimates of narrow-sense heritability and bivariate genetic correlation for 14 tooth crown morphological variants scored on permanent premolars, first molars, and second molars. The objective is to inform data collection and analytical practices in dental biodistance and to provide insights on the development of molar crowns as integrated structures.Materials and Methods: African American dental casts from the Menegaz-Bock collection were recorded for the Arizona State University Dental Anthropology System. Estimates of narrowsense heritability and genetic correlation were generated using SOLAR v.8.1.1, which included assessment of age, sex, and birth year as covariates. Both continuous scale and dichotomized estimates are provided.Results: Heritability estimates were nonsignificant for the majority of variables; however, for variables yielding significant estimates, values were moderate to high in magnitude and comparable to previous studies. Comparing left and right-side heritability estimates suggests directional asymmetry in the expression of environmental variance, something not seen in anterior tooth traits. Genetic correlations were moderate among antimeres and metameres and low for different traits scored on the same tooth crown. Although several negative correlations were noted, few reached statistical significance. Results affirm some of the current data cleaning and analytical practices in dental biodistance, but others are called into question. These include the pooling of males and females and combining left and right-side data into a single dataset.Conclusions: In comparison to anterior tooth crown traits, postcanine heritabilities were more often non-significant; however, those traits with significant heritability also tended to produce higher estimates. Genetic correlations were unremarkable, in part, because they were underpowered. However, M1 results may provide insight into the complex relationship between genes, environment, and development in determining ultimate crown form. K E Y W O R D Sbiodistance, dental morphology, heritability, pleiotropy, quantitative genetics

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“…Modularity is also evident in the dissociations that can occur between dental development, somatic growth, and aspects of life history. Phenotypic plasticity in the dentition is reflected in environmental effects on variation in tooth size (Garn et al, ), dental morphology (Riga et al, ), and dental eruption ages (Garn et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…Garn, Osborne, and McCabe (), however, also showed that prenatal factors could have strong effects on tooth size, establishing that environment can be an important factor. Years later, Riga, Belcastro, and Moggi‐Cecchi () linked developmental stress to variation in crown traits, demonstrating environmental effects on tooth morphology as well.…”

Section: Modern/recent Human Dental Variationmentioning

confidence: 99%

Dental anthropology in the AJPA: Its roots and heights

Guatelli‐Steinberg¹

2018

American J Phys Anthropol

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K E Y W O R D S : dental development, dental morphology, dentition, teethThe roots of dental anthropology in the American Journal of Physical Anthropology (AJPA) go deep. Ale s Hrdlička published his classic comparative study "Shovel-Shaped Teeth" in the AJPA in 1920, just two years after founding the journal.Hrdlička's study on shovel-shaped teeth exemplified his overall vision of physical anthropology, as articulated in the AJPA's inaugural issue. Here, in a 23-page essay, he defined the field of physical anthropology and spelled out its "scope and aims" (Hrdlička, 1918). The field as a whole, he stated, could be defined ". . .in the briefest form as the study of man's variation" (italics his). In multiple places throughout his essay, Hrdlička emphasized that the primary aim of physical anthropology is to understand the "complete" "range of variation" of human anatomy and physiology.Hrdlička was unfortunately a product of his times in thinking about human variation in terms of races and in arranging them along a gradient from primitive to advanced. However, his more fundamental point clearly still stands: physical anthropology greatly enhances our understanding of human biology though its broad perspective on human variation. Hrdlička further explained that to understand the origins of modern human variation, physical anthropologists must trace its evolutionary history. Thus, he explained, a major aim of the field is to uncover that history by studying the living primates, filling in the paleontological record, and analyzing human skeletal remains from the recent past. "Shovel-Shaped Teeth" is a prime example of how Hrdlička employed this broad, comparative approach across space, time, and species, to understand human biological variation. In this paper, Hrdlička documented human variation in the shovel-shaped trait in human skeletal collections (700 teeth), living children of diverse ancestry (2700 of them), non-human primates, and non-primate mammals. This comprehensive comparison allowed Hrdlička to discover that both East Asians and Native Americans shared high frequencies of incisor shoveling, a finding critical to his Asian-origin hypothesis for the peopling of the Americas. From his study of the incisors of non-human primates and other mammals, he gleaned insight into evolution and function. He concluded that "rimmed and hollowed incisors" (Figure 1) had evolved independently in different lineages, likely as a way to strengthen the tooth.Some of Hrdlička conclusions in this paper did not stand the test of time-for example, his idea that incisor shoveling is more prevalent in modern human populations that were late to adopt "advanced" technology. Nevertheless, this landmark paper serves to illustrate how the approach of physical anthropology Hrdlička outlined in 1918 can be used to gain insight into, and formulate hypotheses about, human biology. It also serves to illustrate how the study of teeth, specifically, can be approached to gain such insight. Finally, it helped to shape the form of modern dental ...

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Environmental stress increases variability in the expression of dental cusps

Cited by 29 publications

References 83 publications

Homology, homoplasy and cusp variability at the enamel–dentine junction of hominoid molars

Homology, homoplasy and cusp variability at the enamel–dentine junction of hominoid molars

Quantitative genetic analyses of postcanine morphological crown variation

Dental anthropology in the AJPA: Its roots and heights

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