Search for: All records

Shrews are a morphologically and ecologically diverse group of small-bodied mammals, ranging in body mass from under 2 grams to around 100 grams. Their diversity and size makes them an excellent model for investigating the effects of small body size on the ecomorphology of the skeleton. We want to investigate if there is ecologically informative variation in skeletal morphoogy of these tiny mammals, and if so, does the relationship between shape and ecology vary across body size? Using μCT scans of skeletons from the Field Museum of Natural History, we quantified morphology of the middle lumbar vertebra in 25 species of shrews via 3D geometric morphometrics. Because the lumbar spine is heavily involved in mammalian locomotion, we analyzed the correlation between locomotor mode and vertebral shape, as well as between centroid size and vertebral shape. We found no statistically significant association between centroid size and locomotor group,or between size and shape. However, we found variation in vertebral morphology across locomotor groups, with notable shape differences in centrum aspect ratio, height of the neural arch, and location of the transverse processes. Fossorial and scansorial species diverge the most from the overall mean shape. We also recovered phylogenetic signals associated with shape. Future work will refine the relationship between shape and bone performance under various loading scenarios and enable us to better separate functional from phylogenetic effects. 

The relative contributions of trabecular (spongy) and cortical (compact) bone to bone strength and stiffness are poorly understood across mammalian body size. In mammals, some small species have notably reduced their vertebral trabecular bone structure, resulting in mostly hollow medullary cavities. To assess the importance of trabecular structure to the mechanical properties of small mammalian vertebrae, we conducted finite element analysis on the lumbar vertebrae of 25 species of shrews (Soricidae) weighing 2-100g. We analyzed two sets of models: vertebrae with the trabecular structure intact (full), and vertebrae with all trabeculae excised from the centrum (hollow). All models were scaled to the same ratio of load to surface area. The cranial end of the centrum was immobilized, and a 5N craniocaudally-oriented load was applied to the caudal end of the centrum. We measured mean von Mises stress (MVMS) to capture strength, and total strain energy to capture stiffness. MVMS and total strain energy both decrease as body size increases, and hollow models experience higher stresses and strains than full models. With increasing body size, the difference in total strain energy between full and hollow models decreases, but the difference in MVMS slightly increases. This suggests a difference in the functional advantage conferred by trabeculae among small mammals, as well as a possible selective pressure for different functional emphasis in very small and larger mammalian bones. 

Abstract BackgroundPrevious social determinants of health (SDoH) studies on laryngeal cancer (LC) have assessed individual factors of socioeconomic status and race/ethnicity but seldom investigate a wider breadth of SDoH-factors for their effects in the real-world. This study aims to delineate how a wider array of SDoH-vulnerabilities interactively associates with LC-disparities. MethodsThis retrospective cohort study assessed 74,495 LC-patients between 1975 and 2017 from the Surveillance-Epidemiology-End Results (SEER) database using the Social Vulnerability Index (SVI) from the CDC, total SDoH-vulnerability from 15 SDoH variables across specific vulnerabilities of socioeconomic status, minority-language status, household composition, and infrastructure/housing and transportation, which were measured across US counties. Univariate linear and logistic regressions were performed on length of care/follow-up and survival, staging, and treatment across SVI scores. ResultsSurvival time dropped significantly by 34.37% (from 72.83 to 47.80 months), and surveillance time decreased by 28.09% (from 80.99 to 58.24 months) with increasing overall social vulnerability, alongside advanced staging (OR 1.15; 95%CI 1.13–1.16), increased chemotherapy (OR 1.13; 95%CI 1.11–1.14), decreased surgical resection (OR 0.91; 95%CI 0.90–0.92), and decreased radiotherapy (OR 0.97; 95%CI 0.96–0.99). DiscussionIn this SDoH-study of LCs, detrimental care and prognostic trends were observed with increasing overall SDoH-vulnerability. 

The relative contributions of trabecular (spongy) and cortical (compact) bone to bone strength and stiffness, although investigated in humans, is mostly unclear. As a result, we do not understand how the skeleton of small animals, especially the axial skeleton, has evolved to deal with the particular challenges of life at tiny size. In mammals, some small species have notably reduced their vertebral trabecular bone structure, resulting in mostly hollow medullary cavities. To assess the importance of trabecular structure to the mechanical properties of small mammalian vertebrae, and incorporate the effects of both trabecular and cortical bone structure, we conducted finite element analysis on the lumbar vertebrae of 15 species of shrews (Mammalia: Soricidae). We analyzed two sets of models: vertebrae with the trabecular structure intact, and vertebrae with all trabeculae excised from the centrum. In all models, the cranial end of the centrum was immobilized, and a 5N load was applied to the caudal end of the centrum, parallel to the craniocaudal axis. Results indicate higher peak stresses and larger displacements in models lacking trabeculae. Although smaller body size constrains the number of trabeculae that small mammals develop, we expect that these trabeculae contribute disproportionately to bone strength and stiffness. Ongoing work will validate these analyses with empirical materials testing and assess how bone morphofunctional characteristics change as body size increases. 

Abstract Background, context, and purpose of the studyEnrolling over 60% of all Latinx undergraduate students, Hispanic-serving institutions (HSIs) are poised to play a critical role in diversifying and strengthening Science, Technology, Engineering, and Mathematics (STEM) education and the STEM workforce. However, how HSIs serve STEM students is not well understood. Accordingly, guided by Garcia et al. (Review of Educational Research 89:5–745, 2019) multidimensional servingness framework, we conducted a systematic review of the research on STEM education within the HSI context. By attending to STEM education in conversations around how HSIs may serve Latinx students and their campus communities, our ultimate aim is to improve STEM education particularly at HSIs and advance STEM servingness more broadly. Results, main findingsThrough our systematic review of STEM education research at HSIs, we identified (under)studied components of servingness and gaps within this literature base. Specifically, among the 128 qualifying articles, nearly two-thirds focused on student outcomes but overlooked institutions’ organizational context, raising questions about the effect(iveness) of the studied interventions. Additionally, we identified three thematic gaps in this literature: ghosting the HSI context (i.e., relying on HSIs as research sites without considering the unique HSI context); ghosting Latinx culture (i.e., decentering Latinx students and the Latinx community’s sociocultural aspects and assets), and ghosting people and places (i.e., under-examining certain student populations like Latino men in STEM and places like Hispanic-serving community colleges). Ultimately, our study extends the field’s understanding of servingness by attending to STEM education within the context of HSI institutions. Conclusions, brief summary, and potential implicationsBy systematically reviewing studies on STEM education at HSIs, we identified (under)studied components of servingness and patterned gaps within this literature. In doing so, we highlight opportunities to advance STEM servingness at HSIs through future research, policy, and practice. Collectively, these avenues hold the promise of improving STEM education and diversifying the STEM workforce. 

Abstract Trabecular bone is modelled throughout an animal’s life in response to its mechanical environment, but like other skeletal anatomy, it is also subject to evolutionary influences. Yet the relative strengths of factors that affect trabecular bone architecture are little studied. We investigated these influences across the Philippine endemic murine rodent clade Chrotomyini. These mammals have robustly established phylogenetic relationships, exhibit a range of well-documented substrate-use types, and have a body size range spanning several hundred grammes, making them ideal for a tractable study of extrinsic and intrinsic influences on trabecular bone morphology. We found slight differences in vertebral trabecular bone among different substrate-use categories, with more divergent characteristics in more ecologically specialized taxa. This suggests that the mechanical environment must be relatively extreme to affect trabecular bone morphology in small mammals. We also recovered allometric patterns that imply that selective pressures on bone may differ between small and large mammals. Finally, we found high intrataxonomic variation in trabecular bone morphology, but it is not clearly related to any variable we measured, and may represent a normal degree of variation in these animals rather than a functional trait. Future studies should address how this plasticity affects biomechanical properties and performance of the skeleton. 

Photosynthetic carbon (C) fixation by phytoplankton in the Southern Ocean (SO) plays a critical role in regulating air–sea exchange of carbon dioxide and thus global climate. In the SO, photosynthesis (PS) is often constrained by low iron, low temperatures, and low but highly variable light intensities. Recently, proton-pumping rhodopsins (PPRs) were identified in marine phytoplankton, providing an alternate iron-free, light-driven source of cellular energy. These proteins pump protons across cellular membranes through light absorption by the chromophore retinal, and the resulting pH energy gradient can then be used for active membrane transport or for synthesis of adenosine triphosphate. Here, we show that PPR is pervasive in Antarctic phytoplankton, especially in iron-limited regions. In a model SO diatom, we found that it was localized to the vacuolar membrane, making the vacuole a putative alternative phototrophic organelle for light-driven production of cellular energy. Unlike photosynthetic C fixation, which decreases substantially at colder temperatures, the proton transport activity of PPR was unaffected by decreasing temperature. Cellular PPR levels in cultured SO diatoms increased with decreasing iron concentrations and energy production from PPR photochemistry could substantially augment that of PS, especially under high light intensities, where PS is often photoinhibited. PPR gene expression and high retinal concentrations in phytoplankton in SO waters support its widespread use in polar environments. PPRs are an important adaptation of SO phytoplankton to growth and survival in their cold, iron-limited, and variable light environment. 

Abstract Southern Ocean (SO) diatoms play an important role in global carbon flux, and their influence on carbon export is directly linked to interactions with epiphytic bacteria. Bacterial symbionts that increase diatom growth promote atmospheric carbon uptake, while bacterial degraders divert diatom biomass into the microbial loop where it can then be released as carbon dioxide through respiration. To further explore SO diatom-bacterial associations, a natural model system is needed that is representative of these diverse and important interactions. Here, we use concurrent cultivation to isolate a species of the ecologically-important SO diatom, Pseudo-nitzschia subcurvata, and its co-occurring bacteria. Although vitamin-depleted, axenic Pseudo-nitzschia grew poorly in culture, addition of a co-isolated Roseobacter promoted diatom growth, while addition of a co-isolated Flavobacterium negatively impacted diatom growth. Microscopy revealed both bacterial isolates are physically associated with diatom cells and genome sequencing identified important predicted functions including vitamin synthesis, motility, cell attachment mechanisms, and diverse antimicrobial weapons that could be used for interbacterial competition. These findings revealed the natural coexistence of competing symbiotic strategies of diatom-associated bacteria in the SO, and the utility of this tripartite system, composed of a diatom and two bacterial strains, as a co-culture model to probe ecological-relevant interactions between diatoms and the bacteria that compete for access to the phycosphere.