Journal of Experimental Biology - Latest Issue

  • Welcoming Emily Baird and Philipp Lehmann to the JEB editorial team

  • Evidence for size-dependent cardiac oxygen supply in a fish

    ABSTRACT
    Gill oxygen uptake and cardiac oxygen supply have been proposed as key parameters governing size-dependent environmental resilience in fish. We investigated the allometry of arterial (PaO2) and venous (PvO2) oxygen partial pressures in rainbow trout (Oncorhynchus mykiss) across a large body mass range (282–3834 g, n=40) during acute warming (18–25°C), with or without hyperoxia (150% air saturation), and following exhaustive exercise. PaO2 scaling exponents (b) were not significantly negative during warming, indicating no size-dependent limitation in gill oxygen uptake of resting fish. However, following exhaustive exercise at 25°C, PaO2 declined significantly with body mass (b=−0.21), suggesting oxygen uptake may become limiting in larger individuals under combined thermal and physical stress. PvO2 exhibited significant negative scaling with body mass at both 18°C and 25°C (b=−0.34 and −0.37), suggesting lower cardiac oxygen availability in larger fish. Hyperoxia mitigated the mass effect on PvO2 – disproportionately benefiting larger fish – but loss of equilibrium occurred in several fish following exhaustive exercise regardless of oxygen treatment. The negative scaling of venous oxygenation with size highlights a novel mechanism that may constrain oxygen transport in large fish. Our results emphasize the need to account for size-dependent physiological vulnerability in conservation planning under climate change.

  • Warmer waters may pose problems for bigger trout

  • Bumblebees learn to use antennal and tarsal taste to predict the presence of nectar rewards in flowers

    ABSTRACT
    Learning cues such as tastes associated with palatable food is an important mechanism animals have for foraging optimally. Insects can use gustatory receptor neurons (GRNs) in their mouthparts to detect nutrients and toxins, but they also taste compounds using sensilla on other organs such as their antennae and tarsi. Bees are adept at learning to associate floral traits with the presence of nectar rewards, but few studies have examined how they incorporate gustatory information from their antennae or tarsi detected on flower surfaces. Here, we characterize the ability of bumblebees (Bombus terrestris) to taste sugar, salt and bitter compounds using their antennae and then tested whether they could use this sensory information to associate it with rewarding artificial floral displays. We show that bumblebees have antennal GRNs sensitive to sugars, salts and bitter compounds and can use surface chemistry differences detected by their antennae and/or tarsi to learn about the presence or absence of flower rewards in a free-flight assay. Naïve bumblebees showed no detected spontaneous preferences toward or against any surface chemistry tested. Bumblebees performed best when sucrose surface cues were associated with rewards, but they could learn to associate any cue with the presence or absence of sucrose solution. Interestingly, the bees found it more difficult to associate quinine surface chemistry with the presence of reward than its absence. These results indicate that bees have the potential to learn to associate another floral trait – chemicals on the surfaces of petals – with the quality of floral rewards.

  • Using physiology to unravel the implications of heatwaves for big brown bats ( Eptesicus fuscus )

    ABSTRACT
    Nocturnal endotherms are vulnerable to high ambient temperatures (Ta) during the day when sequestered in retreat sites. Artificial roost design must therefore account for the thermal sensitivity of target species and the potential roost temperatures during heatwave conditions at installation sites. We recorded physiological responses of big brown bats (Eptesicus fuscus) under naturally observed roost temperatures using flow-through respirometry. We used the resulting data to parameterise a biophysical model with which we calculated the evaporative cooling requirements as percent body mass during the hottest day of 2023 and a heatwave during 2021. Our data revealed that the evaporative cooling requirements of bats roosting in certain artificial roosts would have exceeded the lethal dehydration threshold for both females and males during the 2021 heatwave (>22.1% body mass). Regardless of the availability of freestanding water in the environment, bats roosting in artificial roosts prone to overheating are at risk of lethal dehydration during heatwaves, even in high latitude habitats. Therefore, conservation management of small nocturnal endotherms should incorporate both physiological data and roost microclimate data when designing and deploying artificial roosts.