Effects of reduced mobility on trabecular bone density in captive big cats

Analysis of bone structure in PEROMYSCUS: Effects of burrowing behavior

We compare the effects of burrowing behavior on appendicular bone structure in two Peromyscus (deer mouse) species. P. polionotus creates complex burrows in their territories, while P. eremicus is a non-burrowing nesting mouse. We examined museum specimens' bones of wild-caught mice of the two species and lab-reared P. polionotus not given the opportunity to burrow. Bones were scanned using micro-computed tomography, and cortical and trabecular bone structural properties were quantified. Wild P. polionotus mice had a larger moment of area in the ulnar and tibial cortical bone compared with their lab-reared counterparts, suggesting developmental adaptation to bending resistance. Wild P. polionotus had a larger normalized second moment of area and cross-sectional area in the tibia compared with P. eremicus. Tibial trabecular analysis showed lower trabecular thickness and spacing in wild P. polionotus than in P. eremicus and femoral analysis showed wild P. polionotus had lower thickness than P. eremicus and lower spacing than lab-reared P. polionotus, suggesting adaptation to high loads from digging. Results lay the groundwork for future exploration of the ontogenetic and evolutionary basis of mechanoadaptation in Peromyscus.

Maxillary morphology of chimpanzees: Captive versus wild environments

Morphological studies typically avoid using osteological samples that derive from captive animals because it is assumed that their morphology is not representative of wild populations. Rearing environments indeed differ between wild and captive individuals. For example, mechanical properties of the diets provided to captive animals can be drastically different from the food present in their natural habitats, which could impact cranial morphology and dental health. Here, we examine morphological differences in the maxillae of wild versus captive chimpanzees (Pan troglodytes) given the prominence of this species in comparative samples used in human evolution research and the key role of the maxilla in such studies. Size and shape were analysed using three-dimensional geometric morphometric methods based on computed tomography scans of 94 wild and 30 captive specimens. Captive individuals have on average larger and more asymmetrical maxillae than wild chimpanzees, and significant differences are present in their maxillary shapes. A large proportion of these shape differences are attributable to static allometry, but wild and captive specimens still differ significantly from each other after allometric size adjustment of the shape data. Levels of shape variation are higher in the captive group, while the degree of size variation is likely similar in our two samples. Results are discussed in the context of ontogenetic growth trajectories, changes in dietary texture, an altered social environment, and generational differences. Additionally, sample simulations show that size and shape differences between chimpanzees and bonobos (Pan paniscus) are exaggerated when part of the wild sample is replaced with captive chimpanzees. Overall, this study confirms that maxillae of captive chimpanzees should not be included in morphological or taxonomic analyses when the objective is to characterise the species.

An Anatomical Study Using Computed Tomography, Magnetic Resonance Imaging, and Rhinoscopy of the Nasal Cavity of Domestic Cat (Felis silvestris catus L.) and Big Cats: Lion (Panthera leo leo L.), Leopard (Panthera pardus kotiya L.), and Cheetah (Acinonyx jubatus jubatus S.)

The objective of this work was to study the normal anatomy of the nasal cavity of the three species of big cats (leopard, lion, and cheetah) compared to the domestic cat through the use of computed tomography, magnetic resonance imaging, and rhinoscopy. Computed tomography allowed us to clearly visualize the entire bony and cartilaginous framework that supports the nasal cavity. Magnetic resonance imaging permitted better visualization of the soft tissues of this cavity. On the other hand, rhinoscopy enabled the direct visualization of the mucosa of the vestibule and nasal cavity, which is very useful in the diagnosis of masses or foreign bodies. Furthermore, with this technique, it has been possible to observe several small orifices from the nasolacrimal duct, the pharyngeal auditory tube, and the lateral nasal gland. Computed tomography, magnetic resonance imaging, and rhinoscopy are useful tools in analysis of the anatomical characteristics of the nasal cavity in these species.

The deep trabecular structure of first metacarpals in extant hominids

OBJECTIVES

Recent studies have associated subarticular trabecular bone distribution in the extant hominid first metacarpal (Mc1) with observed thumb use, to infer fossil hominin thumb use. Here, we analyze the entire Mc1 to test for interspecific differences in: (1) the absolute volume of trabecular volume fraction, (2) the distribution of the deeper trabecular network, and (3) the distribution of trabeculae in the medullary cavity, especially beneath the Mc1 disto-radial flange.

MATERIALS AND METHODS

Trabecular bone was imaged using micro-computed tomography in a sample of Homo sapiens (n = 11), Pan paniscus (n = 10), Pan troglodytes (n = 11), Gorilla gorilla (n = 10) and Pongo sp., (n = 7). Using Canonical Holistic Morphometric Analysis (cHMA), we tested for interspecific differences in the trabecular bone volume fraction (BV/TV) and its relative distribution (rBV/TV) throughout the Mc1, including within the head, medullary cavity, and base.

RESULTS

P. paniscus had the highest, and H. sapiens the lowest, BV/TV relative to other species. rBV/TV distribution statistically distinguished the radial concentrations and lack of medullary trabecular bone in the H. sapiens Mc1 from all other hominids. H. sapiens and, to a lesser extent, G. gorilla also had a significantly higher trabecular volume beneath the disto-radial flange relative to other hominids.

DISCUSSION

These results are consistent with differences in observed thumb use in these species and may also reflect systemic differences in bone volume fraction. The trabecular bone extension into the medullary cavity and concentrations beneath the disto-radial flange may represent crucial biomechanical signals that will aid in the inference of fossil hominin thumb use.

Trabecular bone morphology in big cats reflects the complex diversity of limb use but not home range size or daily travel distance

A relationship exists between mechanical loading and bone morphology. Although studies show a relationship between trabecular bone morphology and locomotor strategy in mammals, none of them have studied trabecular bone morphology in felid species occupying disparate and overlapping habitats. We investigate trabecular bone volume fraction (BVF) in the femoral and humeral heads, and distal tibia of four felid species (mountain lions, jaguars, cheetahs, and leopards) to identify whether there is a relationship between BVF and locomotor behavior. This study's goals are to identify whether felid species with high daily travel distance or large home range size have greater BVF compared with those with small daily travel distance or home range size, and whether BVF is correlated among the three elements of the fore and hindlimb studied. We quantified BVF in micro- and peripheral computed tomography images and found no significant differences across species in the femoral and humeral head (p > 0.05). However, in the distal tibia, results showed that leopards, mountain lions, and cheetahs have significantly greater (p < 0.05) BVF than jaguars. Despite differences in home range size and daily travel distance, the proximal elements did not reflect differences in BVF; however, the distal-most element did, suggesting decreased loading among jaguars. These findings suggest that the observed pattern of trabecular bone morphology is potentially due to the diversity in locomotor strategy of the forelimb. Additionally, these results imply that neither home range size nor daily travel distance are clear indicators of activity levels. A cautious approach is warranted in studying how loading influences trabecular morphology.

Physiological differences between wild and captive animals: a century-old dilemma

Laboratory-based research dominates the fields of comparative physiology and biomechanics. The power of lab work has long been recognized by experimental biologists. For example, in 1932, Georgy Gause published an influential paper in Journal of Experimental Biology describing a series of clever lab experiments that provided the first empirical test of competitive exclusion theory, laying the foundation for a field that remains active today. At the time, Gause wrestled with the dilemma of conducting experiments in the lab or the field, ultimately deciding that progress could be best achieved by taking advantage of the high level of control offered by lab experiments. However, physiological experiments often yield different, and even contradictory, results when conducted in lab versus field settings. This is especially concerning in the Anthropocene, as standard laboratory techniques are increasingly relied upon to predict how wild animals will respond to environmental disturbances to inform decisions in conservation and management. In this Commentary, we discuss several hypothesized mechanisms that could explain disparities between experimental biology in the lab and in the field. We propose strategies for understanding why these differences occur and how we can use these results to improve our understanding of the physiology of wild animals. Nearly a century beyond Gause's work, we still know remarkably little about what makes captive animals different from wild ones. Discovering these mechanisms should be an important goal for experimental biologists in the future.

Effects of reduced mobility on trabecular bone density in captive big cats

Bone responds to elevated mechanical loading by increasing in mass and density. Therefore, wild animals should exhibit greater skeletal mass and density than captive conspecifics. This expectation is pertinent to testing bone functional adaptation theories and to comparative studies, which commonly use skeletal remains that combine zoo and wild-caught specimens. Conservationists are also interested in the effects of captivity on bone morphology as it may influence rewilding success. We compared trabecular bone volume fraction (BVF) between wild and captive mountain lions, cheetahs, leopards and jaguars. We found significantly greater BVF in wild than in captive felids. Effects of captivity were more marked in the humerus than in the femur. A ratio of humeral/femoral BVF was also lower in captive animals and showed a positive relationship to home range size in wild animals. Results are consistent with greater forelimb than hindlimb loading during terrestrial travel, and possibly reduced loading of the forelimb associated with lack of predatory behaviour in captive animals. Thus, captivity among felids has general effects on BVF in the postcranial skeleton and location-specific effects related to limb use. Caution should be exercised when identifying skeletal specimens for use in comparative studies and when rearing animals for conservation purposes.