Journal of Experimental Biology - Latest Issue

  • Increases in cortisol production facilitate the transition to exogenous feeding by larval zebrafish

    ABSTRACT
    The transition to exogenous feeding is a critical developmental period that is regulated by corticosteroids in mammals. However, mechanistic evidence linking corticosteroids with feeding transitions in non-mammalian vertebrates remains scarce. Here, we pharmacologically suppressed cortisol production during the period preceding exogenous feeding by larval zebrafish (Danio rerio) and determined how this influenced feeding rates and transcript levels of digestive enzymes. Water-borne metyrapone (an 11β-hydroxylase inhibitor) from 3–5 days post-fertilization (dpf) blocked the 2-fold rise in cortisol levels observed in control larvae during this period. While whole-animal growth and development were unaffected, cortisol synthesis suppression during this period resulted in lower transcript abundance of digestive enzymes and reduced feeding rates at 5 dpf. However, these differences dissipated following a two-day washout period. Together, our results indicate that cortisol influences feeding transitions in zebrafish, highlight the plasticity of these processes following perturbations, and suggest that this mechanism is conserved across vertebrates.

  • Visual place learning by walking bumblebees in virtual reality

    ABSTRACT
    Central-place foragers, such as bumblebees, must navigate complex and ever-changing environments to locate food sources and return to their nests. Visual cues in the vicinity of the target play a crucial role in this process, particularly in distinguishing between otherwise visually similar but nutritionally distinct targets. In this study, we used a virtual reality (VR) trackball system and a free-walk paradigm to investigate how bumblebees utilize visual information for place-learning. We specifically examined how bees resolve conflicts between previously learned and currently available visual cues surrounding a target, how the perceived valence of a target changes through association with rewards or punishments, and how they distinguish between visually identical targets based on differences in surrounding visual features. We found that bumblebees prioritize spatial proximity, probably using motion parallax information over static image matching strategies. Furthermore, bees demonstrated flexibility in associating visual features with rewards or punishments by adapting to reversed valence pairings. However, potential intrinsic preferences for specific colours and patterns influenced learning success. These findings challenge traditional snapshot navigation models and suggest that walking bumblebees employ flexible strategies for solving spatial learning tasks in virtual and real environments.

  • Linking bioenergetics and radiation dose in Chornobyl rodents

    ABSTRACT
    High metabolic rate may provide fitness benefits for individuals. But high metabolic rates incur energetic costs and the need to ingest more food, increasing the risks of ingesting harmful substances from the environment. How organisms respond to elevated ionizing radiation is an important question in the light of pollution from nuclear accidents and waste, and reliance on radiation for medical treatments. Within and around the Chornobyl exclusion zone, we investigated how the bioenergetics of wild rodents inhabiting a gradient of radioactive contamination from ‘clean’ (<15.4 μGy day−1) to contaminated (50–2400 μGy day−1) affects their biological burden of radionuclides. We found that the biological radiation dose negatively correlates with aerobic metabolic scope (high self-maintenance and low aerobic capacity) in adults but positively correlates with metabolic scope (high aerobic capacity) in subadults. These findings suggest that metabolic downregulation may contribute to protection against radionuclide exposure, but that it is constrained by developmental obligations. The results also suggest detrimental effects of radiation on animal physiology. Understanding the physiological mechanisms underlying these relationships will be key for risk assessment of environmental contamination, radiotherapies and space exploration, and may help to rectify discordant opinions concerning the effects of radiation on organismal ecology.