Linear enamel hypoplasia as an indicator of physiological stress in Great Apes: reviewing the evidence in light of enamel growth variation

Department of Anthropology, The Ohio State University, Columbus, OH 43210, USA.
American Journal of Physical Anthropology (Impact Factor: 2.38). 06/2012; 148(2):191-204. DOI: 10.1002/ajpa.21619
Source: PubMed


Physiological stress, such as malnutrition or illness, can disrupt normal enamel growth, resulting in linear enamel hypoplasias (LEHs). Although ecological factors may contribute to LEH expression, other factors, such as surface abrasion and enamel growth variables, are also likely to be involved. Attention to these other factors is necessary before we can begin to understand what LEH might signify in terms of ecological sources of physiological stress in non-human primates. This study focuses on assessing the contribution of these other factors to variation in LEH expression within and across great ape taxa. Here, we present LEH data from unabraded crown regions in samples of seven great ape species. We analyze these data with respect to lateral enamel formation time and the angles that striae of Retzius make with the enamel surface, as these variables are expected to affect variation in LEH expression. We find that although the duration of enamel formation is associated with sex differences in LEH expression, it is not clearly related to taxonomic variation in LEH expression, and does not explain the low frequency of LEH in mountain gorillas found in this and a previous study. Our data on striae of Retzius angles suggest that these influence LEH expression along the tooth crown and may contribute to the consistently high frequencies of LEH seen in Pongo in this and previous studies. We suggest that future work aimed at understanding species variation in these angles is crucial to evaluating taxonomic patterns of LEH expression in great apes.

Download full-text


Available from: Debbie Guatelli-Steinberg, Mar 24, 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: We describe a developmental defect that manifests as a mild constricted "waist" in anterior teeth from seven of nine chimpanzee individuals from Taï National Park, Côte D'Ivoire. The sample consists of 21 canine teeth and one incisor, imaged in profile with a digital microscope. Twelve teeth are affected. The waist develops during tooth formation as an external, encircling depression in the contour of the outer enamel surface, more easily seen labially. It is not a thinning of enamel per se, but rather a slight decrement in dentinal crown volume, shown in microCT scans as a change in contour of the enamel-dentin junction, spanning between 3 and 6 years of age, varying among individuals, with maximum expression at about age 4.3 years. The timing and duration of coronal waisting are consistent with descriptions of the weaning process at Taï and other chimpanzee study sites. We propose that coronal waisting records variation in the individual infant chimpanzee's physiological experiences during the process of attaining independence, increased foraging efficiency, and lactational weaning. Am J Phys Anthropol 149:272-282, 2012. © 2012 Wiley Periodicals, Inc.
    American Journal of Physical Anthropology 10/2012; 149(2):272-82. DOI:10.1002/ajpa.22123 · 2.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The goal of this study is to evaluate whether repetitive linear enamel hypoplasia (rLEH) in apes is ecologically informative. LEH, which appears as grooves of thinner enamel often caused by malnutrition and/or disease, is a permanent record of departures from developmental homeostasis in infant and juvenile apes. Orangutans were selected for the study as they are a threatened species, have a remarkably high prevalence of rLEH, and because Sumatra is deemed a better habitat for orangutans than is Borneo, facilitating an ecological comparison. Objectives are to determine: a) whether periodicity of rLEH in orangutans corresponds to monsoon-mediated cycles in precipitation or food; and b) whether patterning of rLEH supports the view that Borneo is an inferior habitat. This study compares the counts of perikymata between adjacent LEH from 9 Sumatran and 26 Bornean orangutans to estimate the periodicity of rLEH. A total of 131 nonredundant inter-LEH perikymata counts were transformed to natural log values to reveal clusters of counts in a multiplicative series. Using a value of 10 days to form one perikyma, rLEH tends to recur semiannually in both populations. However, Sumatran orangutans show significantly fewer semiannual intervals and more annually recurring episodes. Bornean orangutans show mostly semiannual intervals and are more variable in inter-LEH perikymata counts. It is concluded that: a) developmental conditions for infant orangutans in Sumatra protect them somewhat from seasonal and environmental variation; b) temporal patterning of rLEH indicates that Borneo is the poorer habitat for orangutans; and c) the study of rLEH can be ecologically informative. Am J Phys Anthropol, 2014. © 2014 Wiley Periodicals, Inc.
    American Journal of Physical Anthropology 02/2014; 154(1). DOI:10.1002/ajpa.22485 · 2.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Bioarcheology has made tremendous strides since the subdiscipline's inception, subsequent syntheses, the standardization of data collection methods, and analytical advances ranging from molecular analyses through age-estimation and biodistance. Concurrently, health and the adaptive success of past populations have remained primary concerns. However, questions are routinely raised about lesions and whether or not changing frequencies are synonymous with increases or decreases in stress, morbidity, and overall health. These include how and why healed lesions can simultaneously represent stress and survival, demanding that researchers understand how population dynamics influence skeletal sample formation. In this study, methods to analyze age- and sex-specific mortality patterns prior to, and in conjunction with, the analysis of linear enamel hypoplasias are demonstrated. Paleodemographic and paleoepidemiological models are presented for late Pre-Columbian skeletal samples from the Eastern Woodlands. Results of hazard modeling demonstrate that elevated mortality rates were commonplace during the latter half of the Mississippian period (AD 1200–1450) with reproductive-age females experiencing high age-specific risk of death attributed to the development of fortified villages and novel environments for increased pathogen loads. Corollary results are presented for the age-specificity of linear enamel hypoplasias in the central Illinois River valley. The epidemiological models demonstrate that the relationship between adult mortality and early childhood stress varied through space, culture, and time. These findings highlight the need to effectively operationalize measurements related to health and stress in past populations and support the adoption of selective mortality and heterogeneity in frailty as key concepts in bioarcheological research. Am J Phys Anthropol, 2014. © 2014 Wiley Periodicals, Inc.
    American Journal of Physical Anthropology 10/2014; 155(2). DOI:10.1002/ajpa.22601 · 2.38 Impact Factor
Show more