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1. Foretelling the flex—vertebral shape predicts behavior and ecology of fishes

   https://doi.org/10.1093/icb/icab110  

   Donatelli, Cassandra M ; Roberts, Alexus S ; Scott, Eric ; DeSmith, Kylene ; Summers, Dexter ; Abu-Bader, Layanne ; Baxter, Dana ; Standen, Emily M ; Porter, Marianne E ; Summers, Adam P ; et al ( May 2021 , Integrative and Comparative Biology)

   null (Ed.)

   Abstract One key evolutionary innovation that separates vertebrates from invertebrates is the notochord, a central element that provides the stiffness needed for powerful movements. Later, the notochord was further stiffened by the vertebrae, cartilaginous and bony elements, surrounding the notochord. The ancestral notochord is retained in modern vertebrates as intervertebral material, but we know little about its mechanical interactions with surrounding vertebrae. In this study, the internal shape of the vertebrae—where this material is found—was quantified in sixteen species of fishes with various body shapes, swimming modes, and habitats. We used micro-computed tomography to measure the internal shape. We then created and mechanically tested physical models of intervertebral joints. We also mechanically tested actual vertebrae of five species. Material testing shows that internal morphology of the centrum significantly affects bending and torsional stiffness. Finally, we performed swimming trials to gather kinematic data. Combining these data, we created a model that uses internal vertebral morphology to make predictions about swimming kinematics and mechanics. We used linear discriminant analysis (LDA) to assess the relationship between vertebral shape and our categorical traits. The analysis revealed that internal vertebral morphology is sufficient to predict habitat, body shape, and swimming mode in our fishes. This model can also be used to make predictions about swimming in fishes not easily studied in the lab, such as deep sea and extinct species, allowing the development of hypotheses about their natural behavior. 

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2. Internal vertebral morphology of bony fishes matches the mechanical demands of different environments

   https://doi.org/10.1002/ece3.9499  

   Baxter, Dana ; Cohen, Karly E. ; Donatelli, Cassandra M. ; Tytell, Eric D. ( November 2022 , Ecology and Evolution)

   Fishes have repeatedly evolved characteristic body shapes depending on how close they live to the substrate. Pelagic fishes live in open water and typically have narrow, streamlined body shapes; benthic and demersal fishes live close to the substrate; and demersal fishes often have deeper bodies. These shape differences are often associated with behavioral differences: pelagic fishes swim nearly constantly, demersal fishes tend to maneuver near the substrate, and benthic fishes often lie in wait on the substrate. We hypothesized that these morphological and behavioral differences would be reflected in the mechanical properties of the body, and specifically in vertebral column stiffness, because it is an attachment point for the locomotor musculature and a central axis for body bending. The vertebrae of bony fishes are composed of two cones connected by a foramen, which is filled by the notochord. Since the notochord is more flexible than bony vertebral centra, we predicted that pelagic fishes would have narrower foramina or shallower cones, leading to less notochordal material and a stiffer vertebral column which might support continuous swimming. In contrast, we predicted that benthic and demersal fishes would have more notochordal material, making the vertebral column more flexible for diverse behaviors in these species. We therefore examined vertebral morphology in 79 species using micro‐computed tomography scans. Six vertebral features were measured including notochordal foramen diameter, centrum body length, and the cone angles and diameters for the anterior and posterior vertebral cones, along with body fineness. Using phylogenetic generalized least squares analyses, we found that benthic and pelagic species differed significantly, with larger foramina, shorter centra, and larger cones in benthic species. Thus, morphological differences in the internal shape of the vertebrae of fishes are consistent with a stiffer vertebral column in pelagic fishes and with a more flexible vertebral column in benthic species.

    

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3. A Tail of Four Fishes: An analysis of kinematics and material properties of elongate fishes

   https://doi.org/10.1093/icb/icab060  

   Naughton, Lydia F ; Kruppert, Sebastian ; Jackson, Beverly ; Porter, Marianne E ; Donatelli, Cassandra M ( May 2021 , Integrative and Comparative Biology)

   null (Ed.)

   Abstract The elongate body plan is present in many groups of fishes, and this morphology dictates functional consequences seen in swimming behavior. Previous work has shown that increasing the number of vertebrae, or decreasing the intervertebral joint length, in a fixed length artificial system increases stiffness. Tails with increased stiffness can generate more power from tail beats, resulting in an increased mean swimming speed. This demonstrates the impacts of morphology on both material properties and kinematics, establishing mechanisms for form contributing to function. Here, we wanted to investigate relationships between form and ecological function, such as differences in dietary strategies and habitat preferences among fish species. This study aims to characterize and compare the kinematics, material properties, and vertebral morphology of four species of elongate fishes: Anoplarchus insignis, Anoplarchus purpurescens, Xiphister atropurpureus, and Xiphister mucosus. We hypothesized that these properties would differ among the four species due to their differential ecological niches. To calculate kinematic variables, we filmed these fishes swimming volitionally. We also measured body stiffness by bending the abdominal and tail regions of sacrificed individuals in different stages of dissection (whole body, removed skin, removed muscle). Finally, we counted the number of vertebrae from CT scans of each species to quantify vertebral morphology. Principal component and linear discriminant analyses suggested that the elongate fish species can be distinguished from one another by their material properties, morphology, and swimming kinematics. With this information combined, we can draw connections between the physical properties of the fishes and their ecological niches. 

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4. A Shrewd Inspection of Vertebral Regionalization in Large Shrews (Soricidae: Crocidurinae)

   https://doi.org/10.1093/iob/obac006  

   Smith, Stephanie M. ; Angielczyk, Kenneth D. ( February 2022 , Integrative Organismal Biology)

   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.

    

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5. Vertebral pneumaticity is correlated with serial variation in vertebral shape in storks

   https://doi.org/10.1111/joa.13322  

   Moore, Andrew J. ( September 2020 , Journal of Anatomy)

   Birds and their ornithodiran ancestors are unique among vertebrates in exhibiting air‐filled sinuses in their postcranial bones, a phenomenon called postcranial skeletal pneumaticity. The factors that account for serial and interspecific variation in postcranial skeletal pneumaticity are poorly understood, although body size, ecology, and bone biomechanics have all been implicated as influencing the extent to which pneumatizing epithelia invade the skeleton and induce bone resorption. Here, I use high‐resolution computed‐tomography to holistically quantify vertebral pneumaticity in members of the neognath family Ciconiidae (storks), with pneumaticity measured as the relative volume of internal air space. These data are used to describe serial variation in extent of pneumaticity and to assess whether and how pneumaticity varies with the size and shape of a vertebra. Pneumaticity increases dramatically from the middle of the neck onwards, contrary to previous predictions that cervical pneumaticity should decrease toward the thorax to maintain structural integrity as the mass and bending moments of the neck increase. Although the largest vertebrae sampled are also the most pneumatic, vertebral size cannot on its own account for serial or interspecific variation in extent of pneumaticity. Vertebral shape, as quantified by three‐dimensional geometric morphometrics, is found to be significantly correlated with extent of pneumaticity, with elongate vertebrae being less pneumatic than craniocaudally short and dorsoventrally tall vertebrae. Considered together, the results of this study are consistent with the hypothesis that shape‐ and position‐specific biomechanics influence the amount of bone loss that can be safely tolerated. These results have potentially important implications for the evolution of vertebral morphology in birds and their extinct relatives.

    

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