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1. Damage-Fitness Model: Evaluation and synthesis

   https://doi.org/10.1093/icb/icz060  

   Wada, Haruka; Heidinger, Britt (June 2019, Integrative and Comparative Biology)

   Abstract Decades of research into stress responses have highlighted large variation among individuals, populations, and species, and the sources of this variation have been a center of research across disciplines. The most common measure of the vertebrate stress response is glucocorticoids. However, the predictive power of glucocorticoid responses to fitness is surprisingly low. This is partly because the hormone levels rapidly change in response to stressor exposure and elevated levels at one time point can indicate either that glucocorticoids are helping the organism cope with the stressor or that dysregulation of hormone release is harming the organism. Meaning, the fitness consequences of the stressor depends on how efficient the stress responses are at negating the harmful impacts of stressors to cells and tissues. To encompass the idea of the efficiency of stress responses and to integrate cellular and organismal stress responses, a new theoretical model called the Damage-Fitness Model was developed. The model focuses on the downstream effects of stress responses and predicts that the accumulation of damage in cells and tissues (e.g., persistent damage to proteins, lipids, and DNA) negatively impacts fitness components. In this mini-review, we examine evidence supporting the Damage-Fitness Model and explore new directions forward. 

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2. Manipulating the Patterns of Mechanical Forces That Shape Multicellular Tissues

   https://doi.org/10.1152/physiol.00018.2019  

   Herrera-Perez, R. Marisol; Kasza, Karen E. (November 2019, Physiology)

   During embryonic development, spatial and temporal patterns of mechanical forces help to transform unstructured groups of cells into complex, functional tissue architectures. Here, we review emerging approaches to manipulate these patterns of forces to investigate the mechanical mechanisms that shape multicellular tissues, with a focus on recent experimental studies of epithelial tissue sheets in the embryo of the model organism Drosophila melanogaster. 

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3. Engineered Tissue Models to Decode Host–Microbiota Interactions

   https://doi.org/10.1002/advs.202417687  

   Adelfio, Miryam; Callen, Grace E; He, Xuesong; Paster, Bruce J; Hasturk, Hatice; Ghezzi, Chiara E (May 2025, Advanced Science)

   Abstract A mutualistic co‐evolution exists between the host and its associated microbiota in the human body. Bacteria establish ecological niches in various tissues of the body, locally influencing their physiology and functions, but also contributing to the well‐being of the whole organism through systemic communication with other distant niches (axis). Emerging evidence indicates that when the composition of the microbiota inhabiting the niche changes toward a pathogenic state (dysbiosis) and interactions with the host become unbalanced, diseases may present. In addition, imbalances within a single niche can cause dysbiosis in distant organs. Current research efforts are focused on elucidating the mechanisms leading to dysbiosis, with the goal of restoring tissue homeostasis. In vitro models can provide critical experimental platforms to address this need, by reproducing the niche cyto‐architecture and physiology with high fidelity. This review surveys current in in vitro host–microbiota research strategies and provides a roadmap that can guide the field in further developing physiologically relevant in vitro models of ecological niches, thus enabling investigation of the role of the microbiota in human health and diseases. Lastly, given the Food and Drug Administration Modernization Act 2.0, this review highlights emerging in vitro strategies to support the development and validation of new therapies on the market. 

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4. Hair, there and everywhere: A comparison of bat wing sensory hair distribution

   https://doi.org/10.1002/ar.25176  

   Rummel, Andrea_D; Sierra, Melissa_M; Quinn, Brooke_L; Swartz, Sharon_M (February 2023, The Anatomical Record)

   Abstract Bat wing membranes are composed of specialized skin that is covered with small sensory hairs which are likely mechanosensory and have been suggested to help bats sense airflow during flight. These sensory hairs have to date been studied in only a few of the more than 1,400 bat species around the world. Little is known about the diversity of the sensory hair network across the bat phylogeny. In this study, we use high‐resolution photomicrographs of preserved bat wings from 17 species in 12 families to characterize the distribution of sensory hairs along the wing and among species. We identify general patterns of sensory hair distribution across species, including the apparent relationships of sensory hairs to intramembranous wing muscles, the network of connective tissues in the wing membrane, and the bones of the forelimb. We also describe distinctive clustering of these sensory structures in some species. We also quantified sensory hair density in several regions of interest in the propatagium, plagiopatagium, and dactylopagatia, finding that sensory hair density was higher proximally than distally. This examination of the anatomical organization of the sensory hair network in a comparative context provides a framework for existing research on sensory hair function and highlights avenues for further research. 

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5. When Defenses Fail: Atelopus zeteki Skin Secretions Increase Growth of the Pathogen Batrachochytrium dendrobatidis

   https://doi.org/10.1093/icb/icac060  

   Gass, Jordan; Voyles, Jamie (May 2022, Integrative and Comparative Biology)

   Abstract To combat the threat of emerging infectious diseases in wildlife, ecoimmunologists seek to understand the complex interactions among pathogens, their hosts, and their shared environments. The cutaneous fungal pathogen Batrachochytrium dendrobatidis (Bd), has led to the decline of innumerable amphibian species, including the Panamanian golden frog (Atelopus zeteki). Given that Bd can evade or dampen the acquired immune responses of some amphibians, nonspecific immune defenses are thought to be especially important for amphibian defenses against Bd. In particular, skin secretions constitute a vital component of amphibian innate immunity against skin infections, but their role in protecting A. zeteki from Bd is unknown. We investigated the importance of this innate immune component by reducing the skin secretions from A. zeteki and evaluating their effectiveness against Bd in vitro and in vivo. Following exposure to Bd in a controlled inoculation experiment, we compared key disease characteristics (e.g., changes in body condition, prevalence, pathogen loads, and survival) among groups of frogs that had their skin secretions reduced and control frogs that maintained their skin secretions. Surprisingly, we found that the skin secretions collected from A. zeteki increased Bd growth in vitro. This finding was further supported by infection and survival patterns in the in vivo experiment where frogs with reduced skin secretions tended to have lower pathogen loads and survive longer compared to frogs that maintained their secretions. These results suggest that the skin secretions of A. zeteki are not only ineffective at inhibiting Bd but may enhance Bd growth, possibly leading to greater severity of disease and higher mortality in this highly vulnerable species. These results differ from those of previous studies in other amphibian host species that suggest that skin secretions are a key defense in protecting amphibians from developing severe chytridiomycosis. Therefore, we suggest that the importance of immune components cannot be generalized across all amphibian species or over time. Moreover, the finding that skin secretions may be enhancing Bd growth emphasizes the importance of investigating these immune components in detail, especially for species that are a conservation priority. 

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