Eco-geographic adaptations in the human ribcage throughout a 3D geometric morphometric approach

Eco-geographic and sexual variation of the ribcage in Homo sapiens

Up to now, Allen and Bergmann's rules have been studied in modern humans by analyzing differences in limb length, height, or body mass. However, there are no publications studying the effects of latitude in the 3D configuration of the ribcage. To assess this issue, we digitally reconstructed the ribcages of a balanced sample of 109 adult individuals of global distribution. Shape and size of the ribcage was quantified using geometric morphometrics. Our results show that the ribcage belonging to tropical individuals is smaller and slenderer compared to others living in higher latitudes, which is in line with Allen and Bergmann's rules and suggests an allometric relationship between size and shape. Although sexual dimorphism was observed in the whole sample, significant differences were only found in tropical populations. Our proposal is that, apart from potential sexual selection, avoiding heat loss might be the limiting factor for sexual dimorphism in cold-adapted populations.

How to make a digital reconstruction of the human ribcage

Up to now, there have been no publication standardizing the digital reconstruction of the modern human ribcage from commingled costo-vertebral material. Consequently, we designed a validated protocol based on anatomical features observed in the literature and the CT scanned ribcages of 10 adult European individuals. After quantifying the shape of these ribcages using 3D geometric morphometrics, we split each vertebra and rib within their corresponding (semi)landmarks. Subsequently, individual bones + (semi)landmarks were imported to LhpFusionBox, commingled and 3D reconstructed. To validate the accuracy of the protocol, we first reconstructed a randomly chosen ribcage three times and then compared these reconstructions to the rest of the sample. Since these reconstructions were closer to their original counterpart than to the others, the remaining sample was reconstructed once. Next, we tested the intra-observer error during reconstructing using the Procrustes distances among the original ribcages and the reconstructions. We observed that first each ribcage reconstruction was clustered to its original counterpart and second there was a learning curve showing an improvement in the reconstruction process over time. Subsequently, we explored general size and shape differences among the original and reconstructed ribcages through a study of centroid size and a permutation test on the Procrustes distances (10,000 permutations), respectively. Specific shape differences between both groups were further examined through a principal component analysis in shape space. None of these analyses found statistical differences between the original and reconstructed ribcages (p > 0.05). Eventually, we extracted the mean shapes of the original ribcages and the reconstructions in order to visualize potential deviations caused by the anatomical considerations of the researcher. These results demonstrate that the protocol is accurate enough to be used when reconstructing a disarticulated human ribcage.

Coming to the Caribbean-acclimation of Rhesus macaques (Macaca mulatta) at Cayo Santiago

OBJECTIVES

To investigate whether the Cayo Santiago, Puerto Rico (Latitude: 18.1564°N; temperature range 19°C to 32°C) rhesus macaque population has acclimated to their tropical island conditions since arriving from Lucknow, India (Latitude: 26.8470°N; temperature range 8°C to 41°C) in 1938.

MATERIALS AND METHODS

Using the derived skeletal collection, measurements were taken of long bone lengths, diaphyseal circumference, and body weight using 635 (237 males and 398 females) skeletally mature individuals. Measurements sampled colony members born over a 51-year time span at Cayo Santiago, from 1951 to 2002.

RESULTS

Results demonstrated that body weights and diaphyseal circumferences significantly declined in both males and females. Long bone lengths relative to body weight and diaphyseal circumference also increased in females. Whereas body weight, long bone length and diaphyseal circumference declined at near parallel rates in males.

DISCUSSION

The population has acclimated to homogenous, tropical, conditions of the Caribbean island since their arrival over 80 years ago. Trends in both sexes aligned with Bergmann's rule, though females displayed a greater decline in body weight, as well as greater affinity with Allen's rule, than did males. Buffering effects related to male competition may be responsible for this discrepancy. Overall, the Cayo Santiago populations, as shown over a significant period (1951-2002) of their history, have acclimated to their island conditions by decreasing in size and altering body proportions.

Body proportions and environmental adaptation in gorillas

OBJECTIVES

Limb length and trunk proportions are determined in a large, taxonomically and environmentally diverse sample of gorillas and related to variation in locomotion, climate, altitude, and diet.

MATERIALS AND METHODS

The sample includes 299 gorilla skeletons, 115 of which are infants and juveniles, distributed between western lowland (G. gorilla gorilla), low and high elevation grauer (G. beringei graueri), and Virunga mountain gorillas (G. b. beringei). Limb bone and vertebral column lengths scaled to body mass are compared between subgroups by age group.

RESULTS

All G. beringei have relatively short 3rd metapodials and manual proximal phalanges compared to G. gorilla, and this difference is apparent in infancy. All G. beringei also have shortened total limb lengths relative to either body mass or vertebral column length, although patterns of variation in individual skeletal elements are more complex, and infants do not display the same patterns as adults. Mountain gorillas have relatively long clavicles, present in infancy, and a relatively long thoracic (but not lumbosacral) vertebral column.

DISCUSSION

A variety of environmental factors likely contributed to observed patterns of morphological variation among extant gorillas. We interpret the short hand and foot bones of all G. beringei as genetic adaptations to greater terrestriality in the last common ancestor of G. beringei; variation in other limb lengths to climatic adaptation, both genetic and developmental; and the larger thorax of G. b. beringei to adaptation to reduced oxygen pressure at high altitudes, again as a product of both genetic differences and environmental influences during development.

New data about the 21st Century Identified Skeletal Collection (University of Coimbra, Portugal)

After the publication of the first article in 2014, 21st Century Identified Skeletal Collection, housed in the Laboratory of Forensic Anthropology, Department of Life Sciences at the University of Coimbra, Portugal, has been growing. Currently, the collection is composed of 302 complete adult skeletons of both sexes, which means that in 5 years it has doubled. The collection consists mostly of elderly individuals, with only 12.25% of the individuals aged less than 61 years old. All individuals are Portuguese nationals who died between 1982 and 2012. Ninety individuals exhibit prostheses, other medical devices and signs of surgical procedures. Moreover, a sub-collection of experimentally burned skeletons is under development, and currently includes 56 individuals (18.54% of the collection). The 21st Century Identified Skeletal Collection constitutes a fundamental tool for forensic anthropology research, including the development and validation studies of methods that focus on elderly individuals, as can be ascertained by the numerous scientific publications and academic scholarship that have been produced in previous years.

Late subadult ontogeny and adult aging of the human thorax reveals divergent growth trajectories between sexes

Sexual dimorphism is an important feature of adult thorax morphology, but when and how sex-related differences in the ribcage arise during ontogeny is poorly known. Previous research proposed that sex-related size differences in the nasal region arise during puberty. Therefore, we explore whether ribcage sexual dimorphism also arises at that time and whether this sexual dimorphism is maintained until old age. We measured 526 (semi)landmarks on 80 CT-based human ribcage reconstructions, on individuals ranging from 7 to 65 year-old. The 3D coordinates were submitted to the Procrustes superimposition and analyzed. Our results show that the trajectories of thorax size and shape between sexes diverge at around 12 years of age, and continue slightly diverging until old age. The differential ontogenetic trends cause adult male ribcages to become deeper, shorter, and wider than female. Our results are consistent with the evidence from the cranial respiratory system, with the development of sexual dimorphism probably related to changes in body composition during puberty combined with changes in the reproductive system.

Association between ribs shape and pulmonary function in patients with Osteogenesis Imperfecta

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Chest deformities in Osteogenesis Imperfecta patients affect pulmonary function.

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We present the rib cage deformities related to pulmonary function.

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There are significant relations between ribs shape and spirometric parameters.

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There is no relationship between thoracic spine shape and spirometric parameters.

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Correction of rib cage deformities will serve for better patients’ management.

The aim of the present study was to test the hypothesis that ribs shape changes in patients with OI are more relevant for respiratory function than thoracic spine shape. We used 3D geometric morphometrics to quantify rib cage morphology in OI patients and controls, and to investigate its relationship with forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1), expressed as absolute value and as percentage of predicted value (% pred). Regression analyses on the full sample showed a significant relation between rib shape and FEV1, FVC and FVC % pred whereas thoracic spine shape was not related to any parameter. Subsequent regression analyses on OI patients confirmed significant relations between dynamic lung volumes and rib shape changes. Lower FVC and FEV1 values are identified in OI patients that present more horizontally aligned ribs, a greater antero-posterior depth due to extreme transverse curve at rib angles and a strong spine invagination, greater asymmetry, and a vertically short, thoraco-lumbar spine, which is relatively straight in at levels 1–8 and shows a marked kyphosis in the thoraco-lumbar transition. Our research seems to support that ribs shape is more relevant for ventilator mechanics in OI patients than the spine shape.

Evidences of trauma in adult African enslaved individuals from Valle da Gafaria, Lagos, Portugal (15th-17th centuries)

The aim of this work is to discuss the frequency of traumatic bone injuries in a quite unique skeletal assemblage of enslaved people from Valle da Gafaria, Lagos, Portugal (15th-17th centuries). In all, 30 males, 58 females, and 15 individuals of unknown sex were included in the study. The skeletal remains were macroscopically observed for traumatic lesions. When present, the traumatic bone injuries were classified as having occurred ante or perimortem. The antemortem lesions were also studied through radiological analysis. Traumatic lesions were identified in 11 men (36.7%), 23 women (39.7%) and two individuals of unknown sex (13.3%). From these 36 individuals, 61.1% presented antemortem trauma, 25.0% perimortem trauma and 13.9% exhibited simultaneously ante and perimortem trauma. The mechanism of all traumatic injuries was blunt force trauma. From the 9965 analysed bones, 186 exhibited traumatic lesions (87 antemortem, 97 perimortem, and two with both ante and perimortem lesions). The bone more affected by antemortem trauma was the 5th right intermediate foot phalange (40.0%) and by perimortem trauma was the skull (11.4%), probably related to accidents and interpersonal violence, respectively. When analysed by sex, the only significant differences were found in the skull and the right 5th proximal foot phalanges, men (57.1%) presenting more lesions than women (15.4%). The obtained results are consistent with an arduous life, corroborating historical sources which document labour accidents, physical punishments and hard work in the populations of slaves.

The torso integration hypothesis revisited in Homo sapiens: Contributions to the understanding of hominin body shape evolution

OBJECTIVES

Lower thoracic widths and curvatures track upper pelvic widths and iliac blades curvatures in hominins and other primates (torso integration hypothesis). However, recent studies suggest that sexual dimorphism could challenge this assumption in Homo sapiens. We test the torso integration hypothesis in two modern human populations, both considering and excluding the effect of sexual dimorphism. We further assess covariation patterns between different thoracic and pelvic levels, and we explore the allometric effects on torso shape variation.

MATERIAL AND METHODS

A sex-balanced sample of 50 anatomically connected torsos (25 Mediterraneans, 25 Sub-Saharan Africans) was segmented from computed tomography scans. We compared the maximum medio-lateral width at seventh-ninth rib levels with pelvic bi-iliac breadth in males and females within both populations. We measured 1,030 (semi)landmarks on 3D torso models, and torso shape variation, mean size and shape comparisons, thoraco-pelvic covariation and allometric effects were quantified through 3D geometric morphometrics.

RESULTS

Females show narrow thoraces and wide pelves and males show wide thoraces and narrow pelves, although this trend is more evident in Mediterraneans than in Sub-Saharans. Equal thoracic and pelvic widths, depths and curvatures were found in absence of sexual dimorphism. The highest strength of covariation was found between the lowest rib levels and the ilia, and allometric analyses showed that smaller torsos were wider than larger torsos.

CONCLUSIONS

This is the first study testing statistically the torso integration hypothesis in anatomically connected torsos. We propose a new and more complex torso integration model in H. sapiens with sexual dimorphism leading to different thoracic and pelvic widths and curvatures. These findings have important implications in hominin body shape reconstructions.