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1. Gains in relative cortical area during growth and their relationship to nutrition, body size, and physical activity

   https://doi.org/10.1002/ajpa.24805  

   Cowgill, Libby ; Harrington, Lesley ; MacKinnon, Marla ; Kurki, Helen K. ( June 2023 , American Journal of Biological Anthropology)

   In studies of growth in the past, low percentage of cortical area (%CA) is commonly attributed to poor general health, due to factors including poor nutrition, low socioeconomic status, or other physiological stressors. What constitutes low relative cortical dimensions has not been established across a diverse range of human skeletal samples. This study examines %CA in a large immature skeletal sample to establish typical variation in humans with consideration of both body mass and subsistence strategy.

   Percentage of cortical area was calculated at the midshaft of the humerus, femur, and tibia in seven skeletal samples. Age at death was estimated from dental development, and body mass from bone dimensions. Patterns of %CA with age and log‐transformed body mass were examined in the pooled sample and compared among samples using LOESS regression, Welch's ANOVA, and Kruskal‐Wallis tests.

   Across all samples, %CA displays a generally non‐linear pattern, but variation in %CA with age was high, particularly in samples with lower levels of %CA. There was no relationship between %CA and age‐adjusted body mass.

   The lack of a relationship between %CA and body mass suggests that %CA should not be used as an indicator of mechanical loading. The variation present across samples implies that appositional bone growth is affected by physiological stress in varying ways. Without a deeper understanding of what is “typical” for long bone development, it is impossible to draw conclusions about individual or population level health.

    

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2. Low prevalence of anemia among Shuar communities of Amazonian Ecuador

   https://doi.org/10.1002/ajhb.23590  

   DeLouize, Alicia M. ; Liebert, Melissa A. ; Madimenos, Felicia C. ; Urlacher, Samuel S. ; Schrock, Joshua M. ; Cepon‐Robins, Tara J. ; Gildner, Theresa E. ; Blackwell, Aaron D. ; Harrington, Christopher J. ; Amir, Dorsa ; et al ( March 2021 , American Journal of Human Biology)

   Anemia is an important global health challenge. We investigate anemia prevalence among Indigenous Shuar of Ecuador to expand our understanding of population‐level variation, and to test hypotheses about how anemia variation is related to age, sex, and market integration.

   Hemoglobin levels were measured in a total sample of 1650 Shuar participants (ages 6 months to 86 years) from 46 communities between 2008 and 2017 to compare anemia prevalence across regions characterized by different levels of market integration.

   Shuar anemia rates among children under 15 years (12.2%), adult women (10.5%), and adult men (5.3%) were less than half of those previously documented in other neo‐tropical Indigenous populations. Anemia prevalence did not vary between more traditional and market integrated communities (OR = 0.47,p = .52). However, anemia was negatively associated with body mass index (OR = 0.47,p = .002).

   Compared to other South American Indigenous populations, anemia prevalence is relatively low among Shuar of Ecuador and invariant with market integration. Understanding this pattern can provide valuable insights into anemia prevention among at‐risk populations.

    

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3. Evolution of static allometry and constraint on evolutionary allometry in a fossil stickleback

   https://doi.org/10.1111/jeb.13984  

   Voje, Kjetil L ; Bell, Michael A ; Stuart, Yoel E ( March 2022 , Journal of Evolutionary Biology)

   Allometric scaling describes the relationship of trait size to body size within and among taxa. The slope of the population‐level regression of trait size against body size (i.e. static allometry) is typically invariant among closely related populations and species. Such invariance is commonly interpreted to reflect a combination of developmental and selective constraints that delimit a phenotypic space into which evolution could proceed most easily. Thus, understanding how allometric relationships do eventually evolve is important to understanding phenotypic diversification. In a lineage of fossil Threespine Stickleback (Gasterosteus doryssus), we investigated the evolvability of static allometric slopes for nine traits (five armour and four non‐armour) that evolved significant trait differences across 10 samples over 8500 years. The armour traits showed weak static allometric relationships and a mismatch between those slopes and observed evolution. This suggests that observed evolution in these traits was not constrained by relationships with body size, perhaps because prior, repeated adaptation to freshwater habitats by Threespine Stickleback had generated strong selection to break constraint. In contrast, for non‐armour traits, we found stronger allometric relationships. Those allometric slopes did evolve on short time scales. However, those changes were small and fluctuating and the slopes remained strong predictors of the evolutionary trajectory of trait means over time (i.e. evolutionary allometry), supporting the hypothesis of allometry as constraint.

    

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4. Macroscopic differences in adult human femora are linked to body mass index

   https://doi.org/10.1002/ar.25397  

   Sylvester, Adam_D ; Zbijewski, Wojciech ; Shi, Gengxin ; Meckel, Lauren_A ; Chu, Elaine_Y ; Cunningham, Deborah_L ; Wescott, Daniel_J ( January 2024 , The Anatomical Record)

   Bone functional adaptation is routinely invoked to interpret skeletal morphology despite ongoing debate regarding the limits of the bone response to mechanical stimuli. The wide variation in human body mass presents an opportunity to explore the relationship between mechanical load and skeletal response in weight‐bearing elements. Here, we examine variation in femoral macroscopic morphology as a function of body mass index (BMI), which is used as a metric of load history. A sample of 80 femora (40 female; 40 male) from recent modern humans was selected from the Texas State University Donated Skeletal Collection. Femora were imaged using x‐ray computed tomography (voxel size ~0.5 mm), and segmented to produce surface models. Landmark‐based geometric morphometric analyses based on the Coherent Point Drift algorithm were conducted to quantify shape. Principal components analyses were used to summarize shape variation, and component scores were regressed on BMI. Within the male sample, increased BMI was associated with a mediolaterally expanded femoral shaft, as well as increased neck‐shaft angle and decreased femoral neck anteversion angle. No statistically significant relationships between shape and BMI were found in the female sample. While mechanical stimulus has traditionally been applied to changes in long bong diaphyseal shape it appears that bone functional adaptation may also result in fundamental changes in the shape of skeletal elements.

    

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5. Phylogenetically weighted regression: A method for modelling non‐stationarity on evolutionary trees

   https://doi.org/10.1111/geb.12841  

   Davies, T_Jonathan ; Regetz, James ; Wolkovich, Elizabeth_M ; McGill, Brian_J ; Kerkhoff, ed., Andrew ( November 2018 , Global Ecology and Biogeography)

   Closely related species tend to resemble each other in their morphology and ecology because of shared ancestry. When exploring correlations between species traits, therefore, species cannot be treated as statistically independent. Phylogenetic comparative methods (PCMs) attempt to correct statistically for this shared evolutionary history. Almost all such approaches, however, assume that correlations between traits are constant across the tips of the tree, which we refer to as phylogenetic stationarity. We suggest that this assumption of phylogenetic stationarity might be often violated and that relationships between species traits might evolve alongside clades, for example, owing to the effects of unmeasured traits or other latent variables. Specific examples range from shifts in allometric scaling relationships between clades (e.g., basal metabolic rate and body mass in endotherms, and tree diameter and biomass in trees) to the differing relationship between leaf mass per area and shade tolerance in deciduous versus evergreen trees and shrubs.

   Here, we introduce an exploratory modelling framework, phylogenetically weighted regression, which represents an extension of geographically weighted regression (GWR) used in spatial studies, to allow non‐stationarity in model parameters across a phylogenetic tree. We demonstrate our approach using empirical data on flowering time and seed mass from a well‐studied plant community in southeastern Sweden. Our model reveals strong, diverging trends across the phylogeny, including changes in the sign of the relationship between clades.

   By allowing for phylogenetic non‐stationarity, we are able to detect shifting relationships among species traits that would be obscured in traditional PCMs; thus, we suggest that PWR might be an important exploratory tool in the search for key missing variables in comparative analyses.

    

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