Variation in perikymata counts between repetitive episodes of linear enamel hypoplasia among orangutans from Sumatra and Borneo

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.

Developmental defects in the teeth of three wild chimpanzees from theTaï forest

“…Chollet and Teaford (2010) compared hypoplasia frequencies in wild Cebus apella canines from 54 sites in Brazil collected between 1909 and 1976, and found significant differences in hypoplasia frequency among habitat types, as well as between groups with different mean annual temperatures. Similarly, Skinner (2014) recently argued that differences in hypoplasia occurrence between orangutan species reflect ecological differences. Similarly, Skinner (2014) recently argued that differences in hypoplasia occurrence between orangutan species reflect ecological differences.…”

“…Over the last two decades, an increasing number of studies have documented the presence of developmental defects 1 in tooth crowns and roots of fossil hominins (e.g., Skinner, 1996;Guatelli-Steinberg, 2003, 2004Cunha et al, 2004;Guatelli-Steinberg et al, 2004;Lacruz et al, 2005;Smith et al, 2007a;Dean and Smith, 2009;reviewed in Smith, 2013;Hillson, 2014) and nonhuman primates (e.g., Guatelli-Steinberg, 2001;Dirks et al, 2002;Skinner and Hopwood, 2004;Guatelli-Steinberg and Benderlioglu, 2006;Schwartz et al, 2006;Chollet and Teaford, 2010;Dirks et al, 2010;Guatelli-Steinberg et al, 2012;Skinner and Pruetz, 2012;Skinner, 2014). External defects are known as hypoplasias, which may be pit-form, plane-form, or furrow-form disruptions (often termed linear enamel hypoplasias) (reviewed in Suckling, 1989;Goodman and Rose, 1990;Hillson, 1996;Hillson and Bond, 1997;Guatelli-Steinberg, 2001;Witzel et al, 2008;Hillson, 2014).…”

“…Surprisingly they did not find a relationship between hypoplasia frequency and the number of dry months or variation in rainfall amounts. Similarly, Skinner (2014) recently argued that differences in hypoplasia occurrence between orangutan species reflect ecological differences. described gross developmental defects termed "coronal waisting" in the anterior teeth of several Ta€ ı forest (Ivory Coast) chimpanzees, which they suggested are structurally distinct from more spatially discrete linear enamel hypoplasias.…”

“Missing perikymata”—fact or fiction? A study on chimpanzee (Pan troglodytes verus) canines

“…In teeth with a known periodicity of the striae of Retzius (= repeat interval in days as evidenced by the number of prism cross-striations), crown formation times (CFTs) of lateral (imbricational) enamel can be assessed based on perikymata counts. This approach has been widely used to reconstruct life-history traits in extant and fossil hominoids (Reid et al, 2008;Smith, 2008;Dean, 2010;Hillson, 2014) and to determine the timing of developmental stress events in great apes (Skinner and Hopwood, 2004;Guatelli-Steinberg et al, 2012;Skinner and Pruetz, 2012;Skinner, 2014).…”

“…Given these findings, and the conflicting hypothesis of nonemergent striae of Retzius (Skinner and Pruetz, 2012), it is of major importance to clarify whether or not in chimpanzee enamel the number of perikymata on the crown surface matches the number of Retzius increments within the enamel layer. This match is the prerequisite for a reliable reconstruction of the periodicity and duration of stress periods by the inspection of crown surfaces (Skinner and Hopwood, 2004;GuatelliSteinberg et al, 2012;Skinner and Pruetz, 2012;Skinner, 2014).…”