Examining developmental plasticity in the skeletal system through a sensitive developmental windows framework

Abstract

Developmental plasticity facilitates energetically costly but potentially fitnessenhancing adjustments to phenotypic trajectories in response to environmental stressors, and thus may significantly impact patterns of growth, morbidity, and mortality over the life course. Ongoing research into epigenetics and developmental biology indicate that the timing of stress exposures is a key factor when assessing their impact on developmental processes. Specifically, stress experienced within sensitive developmental windows (SDWs), discrete developmental periods characterized by heightened energy requirements and rapid growth, may alter the pace and tempo of growth in ways that significantly influence phenotypic development over both the short and long term. In human skeletal biology, efforts to assess how developmental environments shape health outcomes over the life course could be enhanced by incorporating the SDW concept into existing methodological approaches. The goal of this article is to outline an interpretive framework for identifying and interpreting evidence of developmental stress in the skeletal system using the SDW concept. This framework provides guidance for the identification of elements most likely to capture evidence of stress most relevant to a study's core research questions, the interpretation of developmental stress exhibited by those elements, and the relationship of skeletal indicators of stress to the demographic patterning of morbidity and mortality.

Childhood stress and developmental instability: Comparing microscopic enamel defects and cranial fluctuating asymmetry in a colonial Mexican sample

“…For example, our results suggest that cranial FA partly reflects developmental plasticity as a response to, and perhaps as a buffer against, acute stress that occurs around the time of maximal energetic demands from the brain. The present study therefore refines our understanding of acute stress and cranial FA by incorporating discrete windows of development in which the body is more sensitive to physiological disruption (McPherson, 2021).…”

“…Physiological insults during the first few years of life are hidden by successive development, but those occurring around age 5 result in greater plastic responses as the body trades‐off investment in maintaining cranial asymmetry to protect brain growth. It is possible that the period around 5 years is a window in which a portion of adult cranial FA becomes canalized (McPherson, 2021). Future research may be able to separate how the timing of stress events has differential influences on cranial FA by associating areas of the cranium with specific ages based on their developmental time periods.…”

“…Previous results have often been interpreted to mean that these stress indicators capture unrelated acute and chronic stresses. However, key aspects of the stress experience are not always encapsulated in these studies, such as timing and frequency of stress events, which are critical for a full consideration of developmental plasticity (McPherson, 2021). Because bioarchaeological research on enamel defects usually use macroscopically identified LEH due to methodological or time constraints, many defects are missed (Hassett, 2014), especially in the cervical third of the crown, where perikymata are most closely packed.…”

“…In this study, we test for predictions of DOHaD in an archaeological context by comparing microscopic enamel defects to an index of asymmetry in crania from two colonial Mexican cemeteries. Following previous research (e.g., Gowland, 2015; McPherson, 2021; Reitsema & McIlvaine, 2014; Temple, 2019), we aim to advance our understanding of stress in the archaeological record as a process rooted in early life experiences. Because enamel defects can be tracked to a narrow window of development, exploring their link with cranial asymmetry will provide greater context for the interpretation of these two stress indicators.…”

“…Because enamel defects can be tracked to a narrow window of development, exploring their link with cranial asymmetry will provide greater context for the interpretation of these two stress indicators. Doing so will advance research on developmental plasticity during specific ages and how it trades‐off with later growth and adult health outcomes in the past (McPherson, 2021; Temple, 2019).…”