The regionalized vertebral column is a hallmark of mammalian morphology and reflects functional differentiation of the vertebral regions. Mammalian vertebrae are serially homologous and morphologically patterened by Hox expression, but also vary in number and gross morphology across species. The trabecular bone inside vertebral centra is more plastic than gross vertebral bone, and structurally adapts to better withstand forces it experiences during life. However, the functional regionalization of vertebral trabecular bone is poorly examined. Are there trabecular "regions” reflecting the differing functions and in-vivo stress patterns of gross morphological vertebral regions? Or is trabecular morphology homogeneous throughout the spine, suggesting that differences in functional demands are borne exclusively by external characteristics? To address these questions, we collected μCT scans and linear measurements of cervical, thoracic, and lumbar vertebrae in four species of large shrews, including two species of the hero shrew Scutisorex, which has a highly modified vertebral column. We compared linear measurements and trabecular bone characteristics of the cranial and caudal ends of each centrum across species. To detect unique vertebral regions, we executed principal coordinates analysis and segmented regression on three versions of our data set: trabecular bone data only, external measurements only, and the two combined. We found that some regionalization is recovered using only trabecular bone data, but trabecular bone regions do not correspond exactly to gross vertebral regions. This reflects divergence between the functional signals of internal and external vertebral bone morphology, which should be further examined in a kinematic context.
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A Shrewd Inspection of Vertebral Regionalization in Large Shrews (Soricidae: Crocidurinae)
The regionalization of the mammalian spinal column is an important evolutionary, developmental, and functional hallmark of the clade. Vertebral column regions are usually defined using transitions in external bone morphology, such as the presence of transverse foraminae or rib facets, or measurements of vertebral shape. Yet the internal structure of vertebrae, specifically the trabecular (spongy) bone, plays an important role in vertebral function, and is subject to the same variety of selective, functional, and developmental influences as external bone morphology. Here, we investigated regionalization of external and trabecular bone morphology in the vertebral column of a group of shrews (family Soricidae). The primary goals of this study were to: (1) determine if vertebral trabecular bone morphology is regionalized in large shrews, and if so, in what configuration relative to external morphology; (2) assess correlations between trabecular bone regionalization and functional or developmental influences; and (3) determine if external and trabecular bone regionalization patterns provide clues about the function of the highly modified spinal column of the hero shrew Scutisorex. Trabecular bone is regionalized along the soricid vertebral column, but the configuration of trabecular bone regions does not match that of the external vertebral morphology, and is less consistent across individuals and species. The cervical region has the most distinct and consistent trabecular bone morphology, with dense trabeculae indicative of the ability to withstand forces in a variety of directions. Scutisorex exhibits an additional external morphology region compared to unmodified shrews, but this region does not correspond to a change in trabecular architecture. Although trabecular bone architecture is regionalized along the soricid vertebral column, and this regionalization is potentially related to bone functional adaptation, there are likely aspects of vertebral functional regionalization that are not detectable using trabecular bone morphology. For example, the external morphology of the Scutisorex lumbar spine shows signs of an extra functional region that is not apparent in trabecular bone analyses. It is possible that body size and locomotor mode affect the degree to which function is manifest in trabecular bone, and broader study across mammalian size and ecology is warranted to understand the relationship between trabecular bone morphology and other measures of vertebral function such as intervertebral range of motion.
more » « less- NSF-PAR ID:
- 10363743
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Integrative Organismal Biology
- Volume:
- 4
- Issue:
- 1
- ISSN:
- 2517-4843
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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