Skeletal muscle architectural design strongly affects force-generating capacity and excursion range, and its functional importance to animal and human movement is well founded. Traditionally, this 'structure-function relation' has been inferred from architecture measurements with muscles at rest (from anatomical dissections or medical imaging techniques such as ultrasonography or magnetic resonance imaging) and muscle function tested under quasi-steady force conditions (e.g. isometric). A contemporary view recognises that, during active, dynamic contractions, muscles undergo load- and velocity-dependent changes in architecture and three-dimensional shape while remaining near-constant volume. Consequently, whole-muscle length change and velocity can become decoupled from fascicle length change and velocity, such that the whole muscle cannot be treated as a simple linear velocity transmission system but instead as a geared system where the input fascicle length change and velocity differ from the output whole muscle length change and velocity. This phenomenon is described by the concept of 'muscle gearing' and can be quantified as the ratio of the velocities or displacement of the muscle to the fascicle. Gear ratios are not fixed; instead, gear shifts with force and velocity, allowing the whole-muscle output to better match the mechanical demands of the task. Variable gearing is thought to emerge from load-dependent changes in fascicle angle and three-dimensional muscle deformations under volume-preserving and tissue constraints. Variable gearing has important functional implications, as it influences fascicle operating length and shortening velocity for a given task and thereby shifts where fascicles operate along their intrinsic force-length and force-velocity relationships. Through these effects, along with changes in the projection of fascicle force onto the muscle line of action as pennation varies, variable gearing can broaden whole-muscle force and power output across movement conditions. Accordingly, muscle gearing should be considered an integral component of a comprehensive framework for understanding dynamic muscle function in both normal and pathological states. Here, we synthesise evidence from animal and human studies to characterise variation in gearing across muscles, species and contraction conditions, and the factors that may underlie it. We use a previously validated three-dimensional finite-element muscle model to interrogate mechanisms that are difficult to isolate experimentally and, for the first time, demonstrate an effect of muscle activation on gearing. We also consider how ageing, injury and exercise training may alter gearing. Overall, muscle gearing has important functional implications, and our modelling demonstrates that it is an emergent property of the physics of muscle contraction.
ABSTRACT The use of freshwater fish as biological control agents has been widely implemented to manage populations of perceived nuisance species, ranging from disease vectors to aquatic weeds. While these introductions are often intended as a management tool, they can have unintended and severe ecological, economic, and social consequences. This review assesses the risks associated with using non‐native fish for biological control, emphasising the challenges presented by their persistence, adaptability, and interactions with native species and ecosystems. Key case studies illustrate how species such as mosquitofishes ( Gambusia spp.), grass carp ( Ctenopharyngodon idella ), and tilapias (mainly Oreochromis spp.) have inadvertently contributed to biodiversity loss, habitat degradation, trophic disruptions, and disease transmission, while often failing to effectively control the target species. We further explore the limitations of biocontrol strategies, including the context‐dependent nature of species interactions and deferred negative impacts. Given the complexity and unpredictability of biological control interventions, rigorous impact assessments and long‐term monitoring programmes are needed before and after introducing non‐native fish as control agents, embedded within an adaptive management framework that allows for responsive decision‐making based on observed ecological outcomes. Precautionary policies should prioritise habitat restoration and native species‐based solutions over the introduction of non‐native species to support more sustainable and ecologically responsible management decisions.
As anthropogenic activities continue to expand globally, large-scale livestock encroachment into wildlife habitats increasingly threatens ecological balance, particularly by altering species interactions. Millions of wild ungulates now share plant resources with domestic grazers, facing dual pressures from interference competition and nutritional stress due to declining forage quality. Although extensive research has documented potential competition between sympatric wild and domestic ungulates, a comprehensive quantitative synthesis of the magnitude and drivers of these interactions remains lacking. In this study, we conducted a meta-analysis of 57 peer-reviewed studies (329 cases) to evaluate global patterns of dietary niche overlap between wild ungulates and livestock. Our results revealed that both wild ungulate traits and livestock type significantly influenced the effect sizes. Moreover, climate zones, annual precipitation, and interactions with anthropogenic pressures modulated livestock-wildlife dietary niche overlap. Polar regions and large-bodied species exhibited heightened sensitivity to human activities, while areas with higher annual precipitation showed reduced variation in dietary niche overlap intensity. These findings suggest that wildlife-livestock dietary niche overlap is shaped by multiple factors. While additional factors beyond dietary niche overlap should be considered in conservation assessments, our results suggest several potential management strategies including reducing anthropogenic disturbance in polar regions, integrating grazing management with efforts to reduce human disturbance in large ungulate habitats, and adjusting livestock composition and supplementary feeding in moisture-deficient and tropical regions. Future conservation assessments should integrate dietary overlap shifts with other conservation risks for a more comprehensive evaluation.
In 2004, researchers found a population of mitotically active germ stem cells in adult mice capable of differentiating into oocyte-like cells, which, by contradicting the long-existing dogma on the non-existence of postnatal oogenesis, caused a shift in fertility research. Further studies conducted in mice, human and other species have continuously confirmed the existence of these female germline stem cells.Given that these cells represent an extremely small portion of the total ovarian cell population, their isolation has been exceptionally challenging, with some studies being unable to identify these cells. Moreover, studies that identified these stem cells have observed a variety of sizes, morphologies and expression profiles.Thus, there is a lack of consensus on the characteristics of female germline stem cells, including their terminology, as different researchers have called them 'female germline stem cells', 'oogonial stem cells', 'egg precursor cells', 'very small embryonic-like stem cells' or other terms. This review summarises the findings on these stem cells from the ovaries of a range of species, with the aim of proposing a standardised terminology based on their intrinsic characteristics. We hope that this terminology will be unanimously used in future fertility studies.
Ecotoxicologists are using metabolomics increasingly to gain insight into toxicological mechanisms and sublethal effects of chemical exposures. Metabolomics offers a sensitive multi-parameter approach that can detect biochemical responses not obvious using apical and behavioural endpoints. This includes the responses to very low-dose toxicant exposures, variations in the physico-chemical state of experimental media, and even the progression of circadian rhythms. Consequently, repeatability and comparability of metabolomics experiments relies on the control and reporting of these features. In this systematic quantitative literature review, we examine recent ecotoxicology research to determine the rate and quality of reporting of circadian timing and other variables that influence circadian rhythms and the associated metabolome. We found that most circadian variables are underreported and call for further research into the influence of their manipulation on the metabolome.
