Fluctuating asymmetry, a marker of poor growth quality, is associated with adult male metabolic rate

Abstract

Objectives: Life history theory, a branch of evolutionary theory, predicts the existence of trade-offs in energetic allocation between competing physiological functions. The core metabolic cost of self-maintenance, measured by resting metabolic rate (RMR), represents a large component of human daily energy expenditure.Despite strong selective pressures for energetic frugality and high observed interindividual variation in RMR, the link between RMR and energetic allocation to lifehistory traits remains understudied in humans.Materials: In a sample of 105 (m = 57, f = 48), we investigated the relationship between adult RMR and investment in growth quality, as measured by fluctuating asymmetry (FA).Results: Measurement of RMR and FA in university rowers revealed a significant positive correlation amongst males (n = 57, r = 0.344, p = 0.005, 1-tailed; standardized 95% CI, 0.090 to 0.598). Convincing evidence for a correlation among females was not found (n = 48, r = 0.142, p = 0.169, 1-tailed, standardized 95% CI, −0.152 to 0.435). Discussion:The data suggest that low-quality asymmetrical growth is associated with later-life metabolic inefficiencies in males. Energetic investment in processes (likely concerning the stress-response) unrelated to growth during childhood may thereby trade-off against adult metabolic efficiency. We suggest that the presence of a relationship between RMR and FA in males but not females may be explained by the additional metabolic strain associated with larger body size and increased male muscularity, which may amplify the inefficiencies arising from low-quality growth.

Formal models for the study of the relationship between fluctuating asymmetry and fitness in humans

“…The results of this study were compatible with most of the empirical assumptions made for the “good development” hypothesis. In contrast, it is not yet clear whether its theoretical assumptions hold, and to what extent they need to be extended or refined, mainly because despite being formulated in the early 2000s (Wells et al, 2006), only a few studies to date have addressed it directly (Kirchengast, 2019; Longman et al, 2021; Özener & Ertuğrul, 2011). Finally, the present study is less informative about the “growth” hypothesis because the literature is not clear about the theoretical assumptions on the relationship between FA and fitness.…”

“…In contrast, it is not yet clear whether its theoretical assumptions hold, and to what extent they need to be extended or refined, mainly because despite being formulated in the early 2000s (Wells et al, 2006), only a few studies to date have addressed it directly (Kirchengast, 2019;Longman et al, 2021;Özener & Ertu grul, 2011).…”

“…Another secondary empirical estimand derived is the causal effect of adult height on facial FA through developmental noise. Because individuals who developed in suboptimal conditions (i.e., short stature) could not afford symmetric traits (e.g., Longman et al, 2021), a negative relationship between these variables is expected: shorter individuals would have greater facial FA values (e.g., Özener & Ertu grul, 2011).…”

“…The “good development” hypothesis (Figure 1b) relies on the second explanation to propose that FA is a biomarker of developmental plasticity under conditions of energetic stress. Specifically, from a life history perspective, the extra energy requirements associated with, for example, compensatory growth (Wells et al, 2006) or metabolically expensive tissues (Longman et al, 2021) would exert a cost in the development of symmetrical traits. In this case, FA would be indirectly related to fitness through the individual's health status because, similar to the previous hypothesis, only individuals in good conditions could afford a symmetric phenotype in harsh circumstances.…”

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

“…Milne et al (2003) linked FA to adult health outcomes such as higher body mass index and increased number of medical conditions. Studies of FA in humans and animals suggest that FA results from tradeoffs between energy allocated to maintaining homeostasis during physiological disruption and energy allocated toward growth and development (Longman et al, 2021; Møller & Manning, 2003; Rusk et al, 2021).…”