Trabecular Bone mass and Daily Travel Distance in Mammals
This abstract is from the Experimental Biology 2016 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
The novel energetics of bipedalism affords humans the ability to walk and run for long distances; for instance, humans in traditional societies are known to walk up to 11km a day. Compared to their close relatives, humans appear unique in their ability to travel long distances, and it has been posited that this ability conferred human ancestors an advantage in exploiting large home ranges, tracking down prey, avoiding predation and scavenging for meat and marrow, and was related to changes in body shape in some members of early Homo. To better understand the anatomical adaptations that offered advantages to members of our genus, it is useful to employ comparative models of living mammals that bear adaptations for long distance travel and running. Cursorial mammals, in comparison to non-cursorial ones, display external structural adaptations that minimize mass, such as having thin, distally-tapering limbs to reduce the energetic costs of moving the distal limb; however, it is unclear how internal anatomical structures vary. Specifically, it is not clear how trabecular bone mass varies in related taxa with differing daily travel distances. It is plausible that taxa with long daily travel distances have adapted to greater energetic demands with decreased trabecular bone mass in limbs relative to those with short daily travel distances, as a means of minimizing energetic costs associated with moving and maintaining greater mass.
To test this hypothesis, we measured trabecular bone mass (TBM) in fore- and hindlimb articulations of canids (Crocuta crocuta, Canis mesomelas, Lycaon pictus, Vulpes vulpes, Canis lupus), felids (Panthera onca, Panthera pardus, Acinonyx jubatus, Puma concolor), and cercopithecines (Chlorocebus aethiops, Erythrocebus patas, Theropithecus gelada, Papio anubis)—taxa underlined represent those with long daily travel distances (>10km/day). We accounted for body size differences by dividing TBM by body mass. TBM was measured using peripheral Quantitative Computed Tomography scans taken through epiphyseal regions. The sample sizes per species ranged from N=5 to N=20.
Our overall results show that, instead of minimizing mass as a way of reducing energetic expenditure, mammals with longer daily travel distances display higher TBM, which is consistent with observations of greater bone mass resulting from greater physical activity in experimental and exercise science studies. These results are not only consistent with the conventional understanding of bone functional adaptation, but also support the idea that recently documented variation in trabecular bone structure among hominins was not specifically related to a suite of adaptations for long-distance travel and running in early Homo, but were more influenced by changes in physical activity levels.
Support or Funding Information
This study was supported by the Peter Buck Postdoctoral Fellowship at the National Museum of Natural History, Smithsonian Institution.