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Abstract Reversible phenotypic flexibility allows organisms to better match phenotypes to prevailing environmental conditions and may produce fitness benefits. Costs and constraints of phenotypic flexibility may limit the capacity for flexible responses but are not well understood nor documented. Costs could include expenses associated with maintaining the flexible system or with generating the flexible response. One potential cost of maintaining a flexible system is an energetic cost reflected in the basal metabolic rate (BMR), with elevated BMR in individuals with more flexible metabolic responses. We accessed data from thermal acclimation studies of birds where BMR and/or Msum(maximum cold-induced metabolic rate) were measured before and after acclimation, as a measure of metabolic flexibility, to test the hypothesis that flexibility in BMR (ΔBMR), Msum(ΔMsum), or metabolic scope (Msum − BMR; ΔScope) is positively correlated with BMR. When temperature treatments lasted at least three weeks, three of six species showed significant positive correlations between ΔBMR and BMR, one species showed a significant negative correlation, and two species showed no significant correlation. ΔMsumand BMR were not significantly correlated for any species and ΔScope and BMR were significantly positively correlated for only one species. These data suggest that support costs exist for maintaining high BMR flexibility for some bird species, but high flexibility in Msumor metabolic scope does not generally incur elevated maintenance costs.
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Metabolic demands and sexual dimorphism in human nasal morphology: A test of the respiratory‐energetics hypothesis
Abstract ObjectivesAlthough ecogeographic variation in human nasal morphology is commonly attributed to climatic adaptation, recent research into the “respiratory‐energetics hypothesis” has suggested that metabolic demands for oxygen intake may influence overall nasal size. Here, we further test the respiratory‐energetics hypothesis and investigate potential interactions between metabolic and climatic pressures on human nasal morphology. Materials and MethodsThis study employed computed tomography (CT) scans of 79 mixed‐sex crania derived from an extreme cold‐dry locale (Point Hope, Alaska). In conjunction with basal metabolic rate (BMR, kcal/day) estimates derived from associated femoral head diameter measurements, 41 cranial three‐dimensional (3D) coordinate landmarks and 17 linear measurements were employed in multivariate analyses to test for associations between metabolic demands and nasal/facial morphology across and within the sexes. ResultsOverall nasal size was found to be significantly correlated with BMR both across and within the sexes, with higher metabolic demands predictably associated with larger noses. However, associations between BMR and overall nasal size were found to be predominantly driven by nasal passage height and length dimensions, with the Arctic sample exhibiting minimal (non‐dimorphic) variation in nasal passage breadths. Accordingly, significant correlations between BMR and 3D nasal shape were also identified. DiscussionOur study provides additional support for the respiratory‐energetics hypothesis, while providing insights into potential metabolic and climatic constraints on specific nasal dimensions. In particular, our results suggest that climatic pressures on nasal passage breadths for heat/moisture transfers may necessitate compensatory changes in passage heights (and developmentally‐linked lengths) to maintain sufficient air intake to meet metabolic requirements.
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- Award ID(s):
- 2050253
- PAR ID:
- 10397218
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Biological Anthropology
- Volume:
- 180
- Issue:
- 3
- ISSN:
- 2692-7691
- Format(s):
- Medium: X Size: p. 453-471
- Size(s):
- p. 453-471
- Sponsoring Org:
- National Science Foundation
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