Birth is but our death begun: A bioarchaeological assessment of skeletal emaciation in immature human skeletons in the context of environmental,social, and subsistence transition

The second millennium BC was a period of significant social and environmental changes in prehistoric India. After the disintegration of the Indus civilization, in a phase known as the Early Jorwe (1400–1000 BC), hundreds of agrarian villages flourished in the Deccan region of west-central India. Environmental degradation, combined with unsustainable agricultural practices, contributed to the abandonment of many communities around 1000 BC. Inamgaon was one of a handful of villages to persist into the Late Jorwe phase (1000–700 BC), wherein reliance on dry-plough agricultural production declined. Previous research demonstrated a significant decline in body size (stature and body mass index) through time, which is often used to infer increased levels of biocultural stress in bioarchaeology. This article assesses evidence for growth disruption in the immature human skeletal remains from Inamgaon by correlating measures of whole bone morphology with midshaft femur compact bone geometry and histology. Growth derangement is observable in immature archaeological femora as an alteration in the expected amount and distribution of bone mass and porosity in the midshaft cross-section. Cross-section shape matched expectations for older infants with the acquisition of bipedal locomotion. These results support the hypothesis that small body size was related to disruptions in homeostasis and high levels of biocultural stress in the Late Jorwe at Inamgaon. Further, the combined use of geometric properties and histological details provides a method for teasing apart the complex interactions among activity and “health,” demonstrating how biocultural stressors affect the acquisition and quality of bone mass. Am J Phys Anthropol 155:243–259, 2014. © 2014 Wiley Periodicals, Inc.     

Mechanical and electrical interactions in bone remodeling

The natural remodeling and adaptation of skeletal tissues in response to mechanical loading is a classic example of physical regulation in biology. It is largely because it involves forces that do not seem to fit into the familiar schemes of biochemical controls that bone adaptation mechanisms have intrigued us for at least a century. The effect of electromagnetic fields on organisms is another example of this, and the two have become linked in an attempt to explain bone remodeling (“Yasuda's hypothesis”). This paper re-examines the roles of endogenous and exogenous electromagnetic fields in the response of bone to mechanical forces. A series of experiments is reviewed in which mechanical and electrical stimuli were applied to implants in the medullary canal of rabbit long bones. The results suggest that endogenously generated electrical currents are not required to initiate mechanically stimulated bone formation, but that direct mechanical effects on bone cells is the more likely scenario. Based on this and other evidence from the literature, it is suggested that when exogenous electromagnetic stimuli are applied, bone cells respond by modulating the activity of more primary activators such as hormones, growth factors, cytokines, and mechanical forces. Bioelectromagnetics 18:193–202, 1997. © 1997 Wiley-Liss, Inc.     

Sex differences in humeral bilateral asymmetry in two hunter‐gatherer populations: California Amerinds and British Columbian Amerinds

This study uses two prehistoric Amerindian populations of hunter‐gatherer subsistence patterns to determine whether levels of sexual dimorphism in humeral bilateral cross‐sectional asymmetry are related to sex‐specific differences in activities among these populations. Results confirmed that males of the California Amerind population who engaged in the more unimanual activities of spear hunting and warfare were more asymmetrical than were their female counterparts who engaged in the more bimanual activities of grinding acorns. California Amerind males were also more asymmetrical than British Columbian Amerind males who rowed (using both arms) extensively. Sex differences within British Columbian Amerinds were not statistically significant, nor were female differences between populations. In general, levels of humeral asymmetry appear to be more dependent on sex and population‐specific behaviors rather than broad subsistence patterns. Am J Phys Anthropol 2009. © 2009 Wiley‐Liss, Inc.     

Cross-talk between FGF and other cytokine signalling pathways during endochondral bone development

FGF (fibroblast growth factor)/FGFR (FGF receptor) signalling plays an essential role in both endochondral and intramembranous bone development. FGF signalling pathways are important for the earliest stages of limb development and throughout skeletal development. The activity and the outcome of this signalling pathway during bone development are also influenced by many other intracellular and extracellular signals. In this review, we focus on the interplay between FGF signalling and other pathways, which is tightly regulated both spatially and temporally during endochondral skeletal development.     

Hibernation does not reduce cortical bone density,area or second moments of inertia in woodchucks (Marmota monax)

Long periods of inactivity in most mammals result in bone loss that may not be completely recoverable during an individual's lifetime regardless of future activity. Prolonged inactivity is normal during hibernation, but it remains uncertain whether hibernating mammals suffer decreased bone properties after hibernation that affects survival. We test the hypothesis that relative cortical area (C_A), apparent density, bone area fraction (B.Ar/T.Ar), and moments of inertia do not differ between museum samples of woodchucks (Marmota monax) collected before and after hibernation. We used peripheral quantitative computed tomography to examine bone geometry in the femur, tibia, humerus and mandible. We see little evidence for changes in bone measures with hibernation supporting our hypothesis. In fact, when including subadults to increase sample sizes and controlling age statistically, we observed a trend toward increased bone properties following hibernation. Diaphyses were significantly denser in the humerus, femur, and tibia after hibernation, and relative mandibular cortical area was significantly larger. Similarly, relative mechanical indices were significantly larger in the mandible after hibernation. Although tests of individual measures in many cases were not significantly different prehibernation versus posthibernation, the overall pattern of average increase posthibernation was significant for relative C_A and densities as well as relative diaphyseal mechanical indices when examining outcomes collectively. The exception to this pattern was a reduction in metaphyseal trabecular bone following hibernation. Individually, only humeral B.Ar/T.Ar was significantly reduced, but the average reduction in trabecular measures post‐hibernation was significant when examined collectively. Because the sample included subadults, we suggest that much of the increased bone relates to their continued growth during hibernation. Our results indicate that woodchucks are more similar to large hibernators that maintain skeletal integrity compared to smaller‐bodied hibernators that may lose bone. This result suggests a potential size‐related trend in bone response to hibernation across mammals. J. Morphol., 2012. © 2012Wiley Periodicals, Inc.     

A method for immunohistochemical detection of osteogenic markers in undecalcified bone sections

To evaluate the osteogenic potential of novel implant materials, it is important to examine their effect on osteoblastic differentiation. Characterizing the tissue response at the bone-biomaterial interface in vivo at a molecular level would contribute significantly to enhancing our understanding of tissue integration of endosseous implant materials. We describe here a new technique that overcomes difficulties commonly associated with performing immunohistochemistry on undecalcified sawed sections of bone. Sheep mandible specimens were fixed in an ethanol based fixative to maintain adequate antigenicity of the tissue. As a result, it was possible to omit antigen retrieval at high temperature for recovery of antigenicity, and detachment of sections from the slides was avoided. Following dehydration and infiltration, the specimens were embedded in a resin composed of polymethylmethacrylate and polybutylmethacrylate. Polymerization was achieved by adding benzoylperoxide and N,N-dimethyl-toluidine. This resin was selected because it maintained the antigenicity of the tissue, provided adequate properties for cutting 50 µm thick sections, and it facilitated deacrylizing the sawed sections. Acid-resistant acrylic slides were glued to the blocks using an epoxy resin based two-component adhesive to avoid detachment of the slides during the deacrylation procedure. Samples were stained for alkaline phosphatase, type I collagen, osteonectin, osteopontin, osteocalcin and bone sialoprotein. The EnVision + ™ dextran polymer conjugate two-step visualization system was applied for immunohistochemical detection of these bone matrix proteins. This procedure yielded positive staining for the osteogenic markers in cells and matrix components. The protocol described here facilitates the use of immunohistochemistry on resin embedded sawed sections of bone and provides a convenient and reliable method that can be used routinely for immunohistochemical analysis of hard tissue specimens containing implant materials.     

The growth of children in relation to the timing of obesity development

Objective: To examine whether there is an association between the timing of the development of obesity and children's growth. Research Methods and Procedures: This study investigated 141 prepubertal obese children (76 girls) and 72 healthy non‐obese children (39 girls). The target height standard deviation score (SDS), the percentage weight for height, and the height SDS (H‐SDS) at presentation and at the age of 2 years were calculated. Patients were classified, according to whether obesity developed before or after the age of 3 years, as presenting with early‐onset or late‐onset obesity, respectively. Results: Mean age (±SD) at presentation was 9.4 (2.1) years. At the age of 2 years, the H‐SDS of the children with early‐onset obesity was 1.3 (1.0) vs. 0.9 (1.3) for the late‐onset obese (p > 0.5) and 0.4 (1.0) for controls (p < 0.001), and the children with late‐onset obesity were also significantly taller than controls (p < 0.005). At presentation, children with early‐onset obesity were significantly taller than children with late‐onset obesity [1.1 (0.8) vs. 0.6 (1.0); p < 0.001] and controls [0.2 (0.8); p < 0.001]. There was no increase in H‐SDS after the age of 2 years in the late‐onset obese children (p > 0.05). H‐SDS values were below average in 21% of the children with late‐onset obesity and in only 4% of the children with early‐onset obesity. Discussion: These findings indicate that late development of obesity is not associated with increased stature in prepubertal children; however, it may be preceded by growth acceleration in the early years of life. Growth acceleration in early life may be a predictor for future obesity.     

Effects of developmental stress on animal phenotype and performance: a quantitative review

Developmental stressors are increasingly recognised for their pervasive influence on the ecology and evolution of animals. In particular, many studies have focused on how developmental stress can give rise to variation in adult behaviour, physiology, and performance. However, there remains a poor understanding of whether general patterns exist in the effects and magnitude of phenotypic responses across taxonomic groups. Furthermore, given the extensive phenotypic variation that arises from developmental stressors, it remains important to ascertain how multiple processes may explain these responses. We compiled data from 111 studies to examine and quantify the effect of developmental stress on animal phenotype and performance from juveniles to adulthood, including studies from birds, reptiles, fish, mammals, insects, arachnids, and amphibians. Using meta‐analytic approaches, we show that across all studies there is, on average, a moderate to large negative effect of developmental stress exposure (posterior mean effect: |d| = ?0.51) on animal phenotype or performance. Additionally, we demonstrate that interactive effects of timing of stressor onset and the duration of exposure to stressors best explained variation in developmental stress responses. Animals exposed to stressors earlier in development had more‐positive responses than those with later onset, whereas longer duration of exposure to a stressor caused responses to be stronger in magnitude. However, the high amount of heterogeneity in our results, and the low degree of variance explained by fixed effects in both the meta‐analysis (R² = 0.034) and top‐ranked meta‐regression model (R² = 0.02), indicate that phenotypic responses to developmental stressors are likely highly idiosyncratic in nature and difficult to predict. Despite this, our analyses address a critical knowledge gap in understanding what effect developmental stress has on phenotypic variation in animals. Additionally, our results highlight important environmental and proximate factors that may influence phenotypic responses to developmental stressors.     

Mechanical loading: biphasic osteocyte survival and targeting of osteoclasts for bone destruction in rat cortical bone

Bone isremoved or replaced in defined locations by targeting osteoclasts andosteoblasts in response to its local history of mechanical loading.There is increasing evidence that osteocytes modulate this targeting bytheir apoptosis, which is associated with locally increasedbone resorption. To investigate the role of osteocytes in the controlof loading-related modeling or remodeling, we studied the effects onosteocyte viability of short periods of mechanical loading applied tothe ulnae of rats. Loading, which produced peak compressive strains of0.003 or 0.004, was associated with a 78% reduction in theresorption surface at the midshaft. The same loading regimen resultedin a 40% relative reduction in osteocyte apoptosis at the samesite 3 days after loading compared with the contralateral side(P = 0.01). The proportion of osteocytes that wereapoptotic was inversely related to the estimated local strain(P < 0.02). In contrast, a single short period ofloading resulting in strains of 0.008 engendered both tissuemicrodamage and subsequent bone remodeling and was associated with aneightfold increase in the proportion of apoptotic osteocytes(P = 0.02) at 7 days. This increase in osteocyteapoptosis was transient and preceded both intracorticalremodeling and death of half of the osteocytes (P < 0.01). The data suggest that osteocytes might use their U-shapedsurvival response to strain as a mechanism to influence boneremodeling. We hypothesize that this relationship reflects a causalmechanism by which osteocyte apoptosis regulates bone'sstructural architecture.

     

Divergence in skeletal mass and bone morphology in antarctic notothenioid fishes

Although notothenioid fishes lack swim bladders, some species live temporarily or permanently in the water column. Given its relatively high density, skeletal mass is a key determinant of buoyancy. Notothenioids have reduced skeletal ossification, but there is little quantitative data on the phylogenetic distribution of this trait. We obtained dry skeletal masses for 54 specimens representing 20 species from six notothenioid families. Although comparative data are sparse, notothenioid skeletons comprise a smaller percentage of body mass, <3.5%, than those of three non‐notothenioid perciforms. With relatively high skeletal mass, the non‐Antarctic Bovichtus diacanthus is similar in skeletal mass to some non‐notothenioids. Eleginops maclovinus, the non‐Antarctic sister group of the Antarctic clade, has a relatively light skeleton (<2% of body mass) similar to many species in the Antarctic clade. Low skeletal mass is therefore a synapomorphy shared by Eleginops plus the Antarctic clade. We provide gross, histological, and micro‐CT documentation of the structure and location of bone and cartilage in skulls, pectoral girdles, and vertebrae, with emphasis on the bovichtid B. diacanthus, the eleginopsid E. maclovinus, and the channichthyid Chaenodraco wilsoni. In Eleginops and the Antarctic clade, most bone is spongy and most species have persisting cartilage in the skull and appendicular skeleton. We also measured the relative size of the notochordal canal in adult vertebral centra of 38 species representing all eight families. There is considerable interspecific variation in this pedomorphic trait and all species show an ontogenetic reduction in the relative size of the canal. However, large persisting canals are present in adults of the Antarctic clade, especially in the nototheniids Pleuragramma and Aethotaxis and in a number of bathydraconid and channichthyid genera. J. Morphol. 275:841–861, 2014. © 2014 Wiley Periodicals, Inc.     

In vivo bone strain and bone functional adaptation

Mechanistic interpretations of bone cross-sectional shapes are based on the paradigm of shape optimization such that bone offers maximum mechanical resistance with a minimum of material. Recent in vivo strain studies (Demes et al., Am J Phys Anthropol 106 (1998) 87-100, Am J Phys Anthropol 116 (2001) 257-265; Lieberman et al., Am J Phys Anthropol 123 (2004) 156-171) have questioned these interpretations by demonstrating that long bones diaphyses are not necessarily bent in planes in which they offer maximum resistance to bending. Potential limitations of these in vivo studies have been pointed out by Ruff et al. (Am J Phys Anthropol 129 (2006) 484-498). It is demonstrated here that two loading scenarios, asymmetric bending and buckling, would indeed not lead to correct predictions of loads from strain. It is also shown that buckling is of limited relevance for many primate long bones. This challenges a widely held view that circular bone cross sections make loading directions unpredictable for bones which is based on a buckling load model. Asymmetric bending is a potentially confounding factor for bones with directional differences in principal area moments (I(max) > I(min)). Mathematical corrections are available and should be applied to determine the bending axis in such cases. It is concluded that loads can be reliably extrapolated from strains. More strain studies are needed to improve our understanding of the relationships between activities, bone loading regimes associated with them, and the cross-sectional geometry of bones.     

Simulation of creep in non-homogenous samples of human cortical bone

Characterising the mechanisms causing viscoelastic mechanical properties of human cortical bone, as well as understanding sources of variation, is important in predicting response of the bone to creep and fatigue loads. Any better understanding, when incorporated into simulations including finite element analysis, would assist bioengineers, clinicians and biomedical scientists. In this study, we used an empirically verified model of creep strain accumulation, in a simulation of 10 non-homogeneous samples, which were created from micro-CT scans of human cortical bone of the femur midshaft obtained from a 74-year-old female cadaver. These non-homogeneous samples incorporate the presence of Haversian canals and resorption cavities. The influence of inhomogeneity on the response and variation in the samples in both creep and stress relaxation tests are examined. The relationship between steady-state creep rate, applied loads (stress relaxation and creep tests) and microstructure, that is bone apparent porosity, is obtained. These relations may provide insight into damage accumulation of whole human bones and be relevant to studies on osteoporosis.     

Effect of oscillating fluid shear on solute transport in cortical bone

The consequences of an oscillatory fluid shear mechanism on nutrient transport in bone during physical activity and ultrasonic therapy are discussed. During movement, periodic stress on bone creates transient pressure gradients that circulate interstitial fluid through calcified bone. A transport model derived from oscillatory Taylor-Aris dispersion phenomena was used to predict a ratio of effective-to-molecular diffusivity, K/D, for solutes of varying sizes up to 50 nm in diameter, in pores filled with interstitial fluid and pericellular matrix. The magnitude of the estimated transport enhancement depended on the molecular size, pore dimension, applied frequency and the displacement of the fluid during pressurization. For oscillation frequencies and amplitudes corresponding to those experienced during normal human activity, transport enhancements of up to 100 fold are expected for molecules larger than 5 nm in diameter. Enhancements of up to one order of magnitude, due to ultrasound stimulations in the MHz frequency range, are also expected for 7-nm-sized solutes. No effects are anticipated for ions, whose molecular diffusion time is too fast relative to the oscillation frequency. This model is expected to be useful for understanding differences in bone growth as a function of type of movement or to develop new physical therapies.     

Contribution, development and morphology of microcracking in cortical bone during crack propagation

A fracture mechanics study of cortical bone is presented to investigate the contribution, development morphology of microcracking in cortical bone during crack propagation. Post-hoc analyses of microcrack orientation, crack propagation velocity and fracture surface roughness were conducted on previously tested human and bovine bone compact tension specimens. It was found that, consistent with its higher toughness, bovine bone formed significantly more longitudinal, transverse and inclined microcracks than human bone. However, in human bone more of the microcracks that formed were longitudinal than transverse or inclined, a feature that would optimise bone's toughness. Crack propagation velocity in human and bovine bone displayed the same characteristic pattern with crack extension, where an increase in velocity is followed by a consequent decrease and vice versa. On the basis of this pattern, a model or crack propagation has been proposed. It provides a detailed account of mocrocrack formation and contribution towards the propagation of a fracture crack. Analyses of fracture surfaces indicated that, consistent with its higher toughness, bovine bone displays a rougher surface than human bone but they both have the same basic fractured element, i.e. a mineralised collagen fibril.     

Morphology, testes development and behaviour of unusual triploid males in microchromosome-carrying clones of Poecilia formosa

In a microchromosome-carrying laboratory stock of the normally all-female Amazon molly Poecilia formosa triploid individuals were obtained, all of which spontaneously developed into males. A comparison of morphology of the external and internal insemination apparatus and the gonads, sperm ploidy and behaviour, to laboratory-bred F(1) hybrids revealed that the triploid P. formosa males, though producing mostly aneuploid sperm, are partly functional males that differ mainly in sperm maturation and sexual motivation from gonochoristic P. formosa males.     

Heritability of resting metabolic rate in a wild population of blue tits

We report the first study with the aim to estimate heritability in a wild population, a nest box breeding population of blue tits. We estimated heritability as well as genetic and phenotypic correlations of resting metabolic rate (RMR), body mass and tarsus length with an animal model based on data from a split cross‐fostering experiment with brood size manipulations. RMR and body mass, but not tarsus length, showed significant levels of explained variation but for different underlying reasons. In body mass, the contribution to the explained variation is mainly because of a strong brood effect, while in RMR it is mainly because of a high heritability. The additive variance in RMR was significant and the heritability was estimated to 0.59. The estimates of heritability of body mass (0.08) and tarsus length (0.00) were both low and based on nonsignificant additive variances. Thus, given the low heritability (and additive variances) in body mass and tarsus length the potential for direct selection on RMR independent of the two traits is high in this population. However, the strong phenotypic correlation between RMR and mass (0.643 ± 0.079) was partly accounted for by a potentially strong, although highly uncertain, genetic correlation (1.178 ± 0.456) between the two traits. This indicates that the additive variance of body mass, although low, might still somewhat constrain the independent evolvability of RMR.