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1. Spatial organization of the kelp microbiome at micron scales

   https://doi.org/10.1186/s40168-022-01235-w  

   Ramírez-Puebla, S. Tabita ; Weigel, Brooke L. ; Jack, Loretha ; Schlundt, Cathleen ; Pfister, Catherine A. ; Mark Welch, Jessica L. ( March 2022 , Microbiome)

   Elucidating the spatial structure of host-associated microbial communities is essential for understanding taxon-taxon interactions within the microbiota and between microbiota and host. Macroalgae are colonized by complex microbial communities, suggesting intimate symbioses that likely play key roles in both macroalgal and bacterial biology, yet little is known about the spatial organization of microbes associated with macroalgae. Canopy-forming kelp are ecologically significant, fixing teragrams of carbon per year in coastal kelp forest ecosystems. We characterized the micron-scale spatial organization of bacterial communities on blades of the kelpNereocystis luetkeanausing fluorescence in situ hybridization and spectral imaging with a probe set combining phylum-, class-, and genus-level probes to localize and identify > 90% of the microbial community.

   We show that kelp blades host a dense microbial biofilm composed of disparate microbial taxa in close contact with one another. The biofilm is spatially differentiated, with clustered cells of the dominant symbiontGranulosicoccussp. (Gammaproteobacteria) close to the kelp surface and filamentousBacteroidetesandAlphaproteobacteriarelatively more abundant near the biofilm-seawater interface. A community rich inBacteroidetescolonized the interior of kelp tissues. Microbial cell density increased markedly along the length of the kelp blade, from sparse microbial colonization of newly produced tissues at the meristematic base of the blade to an abundant microbial biofilm on older tissues at the blade tip. Kelp from a declining population hosted fewer microbial cells compared to kelp from a stable population.

   Imaging revealed close association, at micrometer scales, of different microbial taxa with one another and with the host. This spatial organization creates the conditions necessary for metabolic exchange among microbes and between host and microbiota, such as provisioning of organic carbon to the microbiota and impacts of microbial nitrogen metabolisms on host kelp. The biofilm coating the surface of the kelp blade is well-positioned to mediate interactions between the host and surrounding organisms and to modulate the chemistry of the surrounding water column. The high density of microbial cells on kelp blades (10⁵–10⁷cells/cm²), combined with the immense surface area of kelp forests, indicates that biogeochemical functions of the kelp microbiome may play an important role in coastal ecosystems.

    

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2. Fluid pressurization and tractional forces during TMJ disc loading: A biphasic finite element analysis

   https://doi.org/10.1111/ocr.12147  

   Wu, Y. ; Cisewski, S. E. ; Wei, F. ; She, X. ; Gonzales, T. S. ; Iwasaki, L. R. ; Nickel, J. C. ; Yao, H. ( June 2017 , Orthodontics & Craniofacial Research)

   To investigate the ploughing mechanism associated with tractional force formation on the temporomandibular joint (TMJ) disc surface.

   Ten leftTMJdiscs were harvested from 6‐ to 8‐month‐old male Yorkshire pigs.

   Confined compression tests characterized mechanicalTMJdisc properties, which were incorporated into a biphasic finite element model (FEM). TheFEMwas established to investigate load carriage within the extracellular matrix (ECM) and the ploughing mechanism during tractional force formation by simulating previous in vitro plough experiments.

   Biphasic mechanical properties were determined in fiveTMJdisc regions (average±standard deviation for aggregate modulus: 0.077±0.040MPa; hydraulic permeability: 0.88±0.37×10⁻³mm⁴/Ns).FEsimulation results demonstrated that interstitial fluid pressurization is a dominant loading support mechanism in theTMJdisc. Increased contact load and duration led to increased solidECMstrain and stress within, and increased ploughing force on the surface of the disc.

   Sustained mechanical loading may play a role in load carriage within theECMand ploughing force formation during stress‐field translation at the condyle–disc interface. This study further elucidated the mechanism of ploughing on tractional force formation and provided a baseline for future analysis ofTMJmechanics, cartilage fatigue and earlyTMJdegeneration.

    

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3. Functional trait variability supports the use of mean trait values and identifies resistance trade‐offs for marine macroalgae

   https://doi.org/10.1111/1365-2745.14161  

   Ryznar, E. R. ; Smith, L. L. ; Hà, B. A. ; Grier, S. R. ; Fong, P. ( July 2023 , Journal of Ecology)

   Trait‐based ecology (TBE) has proven useful in the terrestrial realm and beyond for collapsing ecological complexity into traits that can be compared and generalized across species and scales. However, TBE for marine macroalgae is still in its infancy, motivating research to build the foundation of macroalgal TBE by leveraging lessons learned from other systems.

   Our objectives were to evaluate the utility of mean trait values (MTVs) across species, to explore the potential for intraspecific trait variability, and to identify macroalgal ecological strategies by clustering species with similar traits and testing for bivariate relationships between traits. To accomplish this, we measured thallus toughness, a trait associated with resistance to herbivory, and tensile strength, a trait associated with resistance to physical disturbance, in eight tropical macroalgal species across up to seven sites where they were found around Moorea, French Polynesia.

   We found interspecific trait variation generally exceeded intraspecific variation across species. Furthermore, MTV within species varied across sites, suggesting future research should focus on whether these traits are influenced by site‐specific differences in biotic and abiotic drivers. Species grouped into three clusters representing different ecological strategies: species that were defended against herbivores but not strong, species that were strong but not defended and species that were neither. Intraspecific standardized major axis regressions revealed five species exhibited significant or marginally significant positive relationships between these two traits, suggesting trait syndromes within species. Only one species exhibited a significant intraspecific trade‐off, as indicated by a negative regression slope.

   Synthesis. Our results point to three key takeaways that should provide a foundation to rapidly advance development of TBE for macroalgae in the future. First, our evidence supports the use of MTVs for macroalgae. Second, we identified significant spatial variability in macroalgal traits that may indicate an ability to respond to shifting environmental drivers. Third, measuring even a few traits can be a powerful tool to identify different ecological strategies to resist disturbances such as herbivory and removal by wave action. We hope these novel findings motivate future research into a wider suite of macroalgal traits, functions and strategies to further develop trait‐based approaches for marine macroalgae.

    

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4. Xenopus as a model for studies in mechanical stress and cell division

   https://doi.org/10.1002/dvg.23004  

   Stooke‐Vaughan, Georgina A. ; Davidson, Lance A. ; Woolner, Sarah ( January 2017 , genesis)

   We exist in a physical world, and cells within biological tissues must respond appropriately to both environmental forces and forces generated within the tissue to ensure normal development and homeostasis. Cell division is required for normal tissue growth and maintenance, but both the direction and rate of cell division must be tightly controlled to avoid diseases of over‐proliferation such as cancer. Recent studies have shown that mechanical cues can cause mitotic entry and orient the mitotic spindle, suggesting that physical force could play a role in patterning tissue growth. However, to fully understand how mechanics guides cellsin vivo, it is necessary to assess the interaction of mechanical strain and cell division in a whole tissue context. In this mini‐review we first summarise the body of work linking mechanics and cell division, before looking at the advantages that theXenopusembryo can offer as a model organism for understanding: (1) the mechanical environment during embryogenesis, and (2) factors important for cell division. Finally, we introduce a novel method for applying a reproducible strain toXenopusembryonic tissue and assessing subsequent cell divisions.

    

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5. Profiles of Near‐Surface Rock Mass Strength Across Gradients in Burial, Erosion, and Time

   https://doi.org/10.1029/2020JF005694  

   Townsend, Kirk F. ; Clark, Marin K. ; Zekkos, Dimitrios ( April 2021 , Journal of Geophysical Research: Earth Surface)

   Rock mass strength is recognized as an important control on landscape morphology and evolution. However, the controls on rock strength in mountainous topography remain poorly characterized, in part because strength remains challenging to quantify at spatial scales relevant to geomorphology. Here we quantify the mechanical properties of rock masses using subsurface S‐wave velocities, Schmidt hammer hardness values, and Geological Strength Index (GSI) observations. We produce shallow depth profiles of rock mass shear strength using intact rock hardness as measured from a Schmidt hammer, and assessment of the structure and surface conditions of fractures using GSI. We apply these techniques to the Western Transverse Ranges, southern California, USA, where gradients in stratigraphic age and erosion rate allow us to evaluate our methodology. We resolve strength differences of 200 kPa to ∼5 MPa that appear to be related to diagenetic changes associated with the maximum burial depth of young clastic sedimentary rocks. For rocks of the same lithologic type, stratigraphic age, and inferred burial histories, we resolve smaller differences in strength (300 kPa–1.5 MPa) that appear to be positively correlated with mean erosion rates. We suggest that the increase in strength with increasing erosion rate reflects decreased residence time in the weathering zone for ranges experiencing faster fault slip rates. These findings demonstrate up to an order of magnitude variability in strength with respect to burial, erosion, and time for lithologically similar rocks. As such, lithology alone is unlikely to adequately capture the role of rock strength in landscape evolution.

    

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