Long‐Period Biorhythm Variation in Enamel Microstructure of Pre‐Columbian South Americans

Abstract

It has been argued that the periodicity (in days) between dental enamel growth lines known as striae of Retzius reflects an autonomic biorhythm regulating metabolism and life history. Therefore, quantifying variation in Retzius periodicity (RP) has been recently used as a tool to provide life history and metabolic information among humans, primates, and other mammals. For example, body size is a major driving factor in life history evolution, and correlates strongly with RP in anthropoid primates but not lemurs.Varying datasets disagree as to whether this particular relationship among anthropoid species extends within species, particularly within modern humans. Moreover, little is known regarding the impact that geography has had on life history evolution among modern human populations. Altitude is one unexamined factor that may have influenced this evolution, as high‐altitude human populations exhibit multiple adaptations to their relatively hypoxic environment, and low oxygen availability has obvious consequences for overall metabolic output. Therefore, this study uses RP variation to compare a coastal (low altitude) and Andean (high altitude) sample of Pre‐Columbian South Americans. We have two major objectives: 1) determine if RP is correlated with body mass within this previously unsampled group, and more importantly; 2) determine if RP differs between coastal and Andean populations, a possible consequence of life history adaptations to altitude.To answer our questions, we gathered teeth from 10 individuals, 5 each from low and high altitude archaeological sites of Peru, all part of the anthropology collection at the American Museum of Natural History. Teeth were cleaned, embedded in acrylic resin, thin‐sectioned, and polished according to standard dental histology protocols. They were imaged in circularly polarized light using a Zeiss Axioskop II microscope. Photomicrographs of dental enamel were used to count the number of 24‐hour growth lines (cross‐striations) between striae of Retzius, indicating the number of days taken to form each successive stria (RP). An average of cross‐striation breadths was also divided into an average of striae of Retzius breadths in the same region of each tooth to verify the counted value. For each individual, orbital height and foramen magnum length were used as proxy variables to assess body size. Individuals were sexed based on standard cranial characteristics.Regressions of RP against body size proxies demonstrate a statistically significant negative correlation in the total combined sample. There is no significant difference in RP variation between the sexes, nor in body size between low and high altitude populations. However, the higher altitude population has significantly longer RP values. In conclusion, our analysis suggests that as predicted, an intraspecific relationship exists for RP and body size among our sample, and that altitude elicits as yet unidentified life history/metabolic differences expressed in RP, warranting further study. The high vs. low altitude pattern appears to be independent of the relationship we find between body size and RP in studies of other human populations.Support or Funding InformationFGCU Professional Development GrantThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.