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Background: Buoyancy and balance are important parameters for slow-moving, low-metabolic, aquatic organisms. The extant coelacanths have among the lowest metabolic rates of any living vertebrate and can aford little energy to keep station. Previous observations on living coelacanths support the hypothesis that the coelacanth is neutrally buoyant and in close-to-perfect hydrostatic balance. However, precise measurements of buoyancy and balance at diferent depths have never been made. Results: Here we show, using non-invasive imaging, that buoyancy of the coelacanth closely matches its depth distribution. We found that the lipid-flled fatty organ is well suited to support neutral buoyancy, and due to a closeto-perfect hydrostatic balance, simple maneuvers of fns can cause a considerable shift in torque around the pitch axis allowing the coelacanth to assume diferent body orientations with little physical efort. Conclusions: Our results demonstrate a close match between tissue composition, depth range and behavior, and our collection-based approach could be used to predict depth range of less well-studied coelacanth life stages as well as of deep sea fshes in general.

Background: Balance tasks are critical for performance in acrobatic gymnastics, where athletes often train and compete in mixed-age groups with varying maturational stages. To improve individualized training, in this cross-sectional study, the relationship was examined between strength capacity and balance task performance in female gymnasts at two maturational stages based on peak height velocity (PHV). Methods: Circa-PHV (n = 17, 11.92 ± 1.7 years) and post-PHV (n = 17, 16.47 ± 1.8 years) participants performed static balance tasks (standing on blocks, tandem stance, headstand) while center of pressure (CoP) excursion was recorded, and a proactive balance task (time to stabilization after landing, TTS). Strength assessments included isometric mid-thigh pull, handgrip, countermovement jump (CMJ), and push-up tests. Results: Correlational, regression, and inter-group analyses highlighted differences in strength–balance relationships across groups. Maximal isometric strength and CMJ power were the strongest predictors of static standing balance, with greater predictive strength in the circa-PHV group, underscoring the role of maturation in strength–balance interactions. The results also revealed that strength parameters influenced balance differently depending on the task, suggesting that specific balance types (static–proactive) and tasks (standing–inverted) require distinct strength capacities. Conclusions: Strength’s influence on balance varies by maturational stage, emphasizing the need for tailored training programs to enhance balance and optimize performance in young gymnasts.

Behaviors associated with aggression in male-male competition may also be used in courtship. Headstands are performed by male Xiphophorus nezahualcoyotl during male-male interactions and by both males and females during courtship. This behavior consists of a descending vertical tilt of the head until the body is at a 45 ° to 90 ° angle with the substrate. We examined the function of headstands in male-male contests by investigating differences in their use by winners and losers, and correlations between headstands and other behaviors. We also investigated their function in mate choice by determining if females preferred videos of males performing headstands over videos of the same males not performing headstands. There was no correlation between performing the first headstand and biting first, or the total number of headstands and bites used. However, winners performed more headstands than losers in the second half of contests. We suggest that the headstand is an aggressive display providing information about Resource Holding Potential (RHP) in male contests. In addition, females had a significant preference for males performing headstands as compared to males that did not. We discuss the dual role of this behavior in sexual selection in relation to the information it may contain.