Trade-Offs in Relative Limb Length among Peruvian Children: Extending the Thrifty Phenotype Hypothesis to Limb Proportions

Abstract

Background and MethodsBoth the concept of ‘brain-sparing’ growth and associations between relative lower limb length, childhood environment and adult disease risk are well established. Furthermore, tibia length is suggested to be particularly plastic under conditions of environmental stress. The mechanisms responsible are uncertain, but three hypotheses may be relevant. The ‘thrifty phenotype’ assumes that some components of growth are selectively sacrificed to preserve more critical outcomes, like the brain. The ‘distal blood flow’ hypothesis assumes that blood nutrients decline with distance from the heart, and hence may affect limbs in relation to basic body geometry. Temperature adaptation predicts a gradient of decreased size along the limbs reflecting decreasing tissue temperature/blood flow. We examined these questions by comparing the size of body segments among Peruvian children born and raised in differentially stressful environments. In a cross-sectional sample of children aged 6 months to 14 years (n = 447) we measured head circumference, head-trunk height, total upper and lower limb lengths, and zeugopod (ulna and tibia) and autopod (hand and foot) lengths.ResultsHighland children (exposed to greater stress) had significantly shorter limbs and zeugopod and autopod elements than lowland children, while differences in head-trunk height were smaller. Zeugopod elements appeared most sensitive to environmental conditions, as they were relatively shorter among highland children than their respective autopod elements.DiscussionThe results suggest that functional traits (hand, foot, and head) may be partially protected at the expense of the tibia and ulna. The results do not fit the predictions of the distal blood flow and temperature adaptation models as explanations for relative limb segment growth under stress conditions. Rather, our data support the extension of the thrifty phenotype hypothesis to limb growth, and suggest that certain elements of limb growth may be sacrificed under tough conditions to buffer more functional traits.

Genetic and Phenotypic Differentiation of an Andean Intermediate Altitude Population

“…The tibia is more susceptible to periods of poorer health than the femur (Bogin and Varela-Silva 2008), thus also reduced oxygen supply is likely to impact bone growth at a critical time during development (Bailey and Hu 2001). Reduced tibia length was also observed among Tibetan and Peruvian children at HA (Stinson and Frisancho 1978;Bailey and Hu 2001;Pomeroy et al 2012), the latter also showing reduction of forearm length. This suggests hypoxia's effect on distal limb segments, though other climatic factors cannot be excluded.…”

The Skeletal Phenotype of “Negritos” from the Andaman Islands and Philippines Relative to Global Variation among Hunter-Gatherers

“…However, the results also identify phenotypic variation among the negritos, particularly in the form of narrower pelves among the Andaman Islanders compared with the Aeta, but also higher brachial indices. Differences in the Andaman Islander and Aeta lower limbs were reflected in the length of the femur, the proximal limb segment, rather than the more "plastic" distal limb segment (tibia), which appears to be more sensitive to environmental stress (Pomeroy et al 2012). In general, the characteristics of narrow bi-iliac breadths and short crural indices are shared with Southern African hunter-gatherers and not other Asian populations.…”

Skull and limb morphology differentially track population history and environmental factors in the transition to agriculture in Europe

“…In this case, an initial shift towards smaller body size could correspond with climatic warming associated with the onset of the Holocene. Recent research has suggested that limb segment lengths may be influenced by 'thrifty' phenotypic mechanisms and exposure to environmental stress [64]. In this context, a decrease in body size associated with the transition to agriculture could be a plastic response to dietary stress.…”