Journal of Experimental Biology最新文献

Despite the myriad studies examining the diversity and mechanisms of gecko adhesion in the lab, we have a poor understanding of how this translates to locomotion in nature. It has long been assumed that greater adhesive strength should translate to superior performance in nature. Using 13 individuals of Bradfield's Namib day gecko (Rhoptropus bradfieldi) in Namibia, I tested the hypothesis that maximum running performance in nature (speed and acceleration) is driven by maximum frictional adhesive strength. Specifically, those individuals with greater frictional adhesion should escape with faster speed and acceleration because of increased contact with the surface from which to apply propulsive forces. I tested this prediction by quantifying laboratory adhesive performance and then releasing the geckos into the field while simultaneously recording the escape using high-speed videography. Additional measurements included how this species modulates maximum running speed (stride length and/or stride frequency) and how temperature influences field performance. I found that maximum acceleration was significantly correlated with maximum frictional adhesive strength, whereas maximum sprinting speed was only correlated with increases in stride frequency (not stride length) and temperature. Thus, different measures of performance (acceleration and speed) are limited by very different variables. Acceleration is key for rapidly escaping predation and, given their correlation, maximum frictional adhesion likely plays a key role in fitness.

The energetic costs of generating calcium carbonate skeletons and shells in marine organisms remain largely speculative because of the scarcity of empirical data. However, this information is critical for estimating energetic limitations of marine calcifiers that can explain their sensitivity to changes in sea water carbonate chemistry in past, present and future marine systems. Here, the cost of calcification was evaluated using larval stages of the purple sea urchin, Strongylocentrotus purpuratus. We developed a skeleton re-mineralization assay, in which the skeleton was dissolved in live larvae followed by a re-mineralization over a few days. During skeleton re-mineralization, energetic costs were estimated through the measurement of key metabolic parameters including whole-animal metabolic rate, citrate synthase (CS) enzyme activity and mRNA expression as well as mitochondrial density in the calcifying primary mesenchyme cells (PMCs). Minor increases in CS activity and a 10-15% increase in mitochondrial density in PMCs were observed in re-mineralizing larvae as compared with control larvae. Re-mineralization under three different pH conditions (pH 8.1, pH 7.6 and pH 7.1) decreased with decreasing pH, accompanied by pronounced increases in CS expression levels and increased mitochondrial density in PMCs at pH 7.6. Despite a prominent increase in mitochondrial density of primary mesenchyme cells, particularly in the calcifying cohort of this cell type, this work demonstrated a low overall metabolic response to increased mineralization rates at the whole-animal level under both high and low pH conditions. We conclude that calcification in sea urchin larvae is compromised under low pH conditions, associated with low energetic efforts to fuel compensatory processes.

Environmental control systems are important tools for experimental researchers studying animal-environment interactions. Commercial systems for the measurement and regulation of environmental oxygen conditions are relatively expensive and cannot always be adapted to varying experimental applications. Here, I present a low-cost and highly flexible oxygen control system using Arduino microcontrollers in combination with a commercial optical oxygen sensor. Hardware and software examples are provided for three different applications: single-setpoint, sequential and long-term dissolved oxygen (DO) control. All tested control systems created the desired DO conditions with high accuracy and repeatability across trials. The resources provided shown here can be adapted and modified to be used in a variety of experimental contexts.

Small mammals have a higher heart rate and, relative to body mass (Mb), a higher metabolic rate than large mammals. In contrast, heart weight and stroke volume scale linearly with Mb. With mitochondria filling approximately 50% of a shrew cardiomyocyte - space unavailable for myofibrils - it is unclear how small mammals generate enough contractile force to pump blood into circulation. Here, we investigated whether the total number or volume of cardiomyocytes in the left ventricle compensates for allometry-related volume shifts of cardiac mitochondria and myofibrils. Through statistical analysis of data from 25 studies with 19 different mammalian species with Mb spanning seven orders of magnitude (2.2 g to 920 kg), we determined how number, volume density and total volume of cardiomyocytes, mitochondria and myofibrils in the left ventricle depend on Mb. We found that these biological variables follow scaling relationships and are proportional to a power b of Mb. The number [b=1.02 (95% CI: 0.89, 1.14); t-test for b=1: P=0.72] and volume [b=0.95 (95% CI: 0.89, 1.03); t-test for b=1: P=0.18] of cardiomyocytes in the left ventricle increases linearly with increasing Mb. In cardiomyocytes, volume density of mitochondria decreases [b=-0.056 (95% CI: -0.08, -0.04); t-test for b=0: P<0.0001] and that of myofibrils increases [b=0.024 (95%CI: 0.01, 0.04); t-test for b=0: P<0.01] with increasing Mb. Thus, the number or volume of left ventricular cardiomyocytes does not compensate for the higher heart rate and specific metabolic rate of small mammals although a higher mitochondrial and lower myofibrillar volume per cardiomyocyte are present.

Residual force enhancement (rFE) and residual force depression (rFD) are history-dependent properties of muscle which refer to increased and decreased isometric force following a lengthening or shortening contraction, respectively. The history dependence of force is greater in older than in younger human adults when assessed at the joint level. However, it is unclear whether this amplification of the history dependence of force in old age is owing to cellular mechanisms or is a consequence of age-related remodelling of muscle architecture. Single muscle fibres from the psoas major of old and young F344BN rats were dissected and chemically permeabilized. Single muscle fibres were mounted between a force transducer and length controller, then maximally activated (pCa 4.5). To assess rFD, fibres were actively shortened from 3.1 to 2.5 µm at both a slow (0.15 Lo s-1) and fast (0.6 Lo s-1) speed, with a fixed-end isometric reference contraction at 2.5 µm. To assess rFE, fibres were activated and stretched at 0.3 Lo s-1 from a sarcomere length of 2.2 to 2.5 µm, and 2.7 to 3.0 µm, and compared with fixed-end isometric reference contractions at 2.5 and 3.0 µm, respectively. Isometric force (2.5 µm) was ∼19% lower in muscle fibres from old as compared with young rats (P<0.001). Upon normalizing to fibre cross-sectional area, there was no age-related difference in specific force (P>0.05). rFD was ∼33% greater in muscle fibres from old as compared with young rats (P<0.05), while rFE did not differ between groups (P>0.05). rFD is amplified in old age at the cellular level, while rFE appears to be unchanged; thus, previously reported age-related modification of rFE occurs upstream from the cellular level.

Solar radiation is an important environmental variable for terrestrial animals, but its impact on the heat balance of large flying insects has been poorly studied. Desert bees are critical to ecosystem function through their pollination services, and are exposed to high radiant loads. We assessed the role of solar radiation in the heat balance of flying desert Centris pallida bees by calculating heat budgets for individuals in a respirometer in shaded versus sunny conditions from 16 to 37°C air temperatures, comparing the large and small male morphs and females. Solar radiation was responsible for 43 to 54% of mean total heat gain. Bees flying in the sun had thorax temperatures 1.7°C warmer than bees flying in the shade, storing a very small fraction of incident radiation in body tissues. In most cases, flight metabolic rate was not suppressed for bees flying in the sun, but evaporative water loss rates more than doubled. The most dramatic response to solar radiation was an increase in convection, mediated by a more than doubling of convective conductance, allowing thermoregulation while conserving body water. In large morph males and females, the increased convective conductance in the sun was mediated by increased heat transfer from the thorax to abdomen. Because convection is limited as body temperatures approach air temperatures, solar radiation combined with warming air temperatures may cause endothermic flying bees to reach a tipping point at which increases in non-sustainable evaporation are necessary for survival.

Confrontations between predator and prey, driven by the innate survival instincts in both predator and prey, constitute the most significant form of competition in evolution. Yet, understanding how survival skills can benefit from such confrontations remains limited, despite its critical importance for animal survival. We have developed an interactive platform to investigate confrontations between a hungry mouse and an escaping bait. This robotic bait is controlled magnetically through a closed-loop system to continually evade the approaching mouse. Meanwhile, the mouse must capture the escaping bait to receive a food reward. Through analysis of angles, speeds and other kinematic parameters of both the mouse and the bait, we observed that confrontation experiences can notably enhance mice performance. Compared with novice mice, veteran mice enhanced predation efficiency primarily by optimizing the pursuit phase, significantly reducing time costs, mainly by minimizing pauses in movement. Additionally, experience strengthened the navigation strategies used by mice to better track evading bait. Finally, we validated the impact of empirically induced changes in speed distribution and pursuit methods on predation efficiency through modeling of the pursuit phase. In conclusion, this study reveals that confrontation experience could improve pursuit strategy in mice by altering the speed control and pursuit method, providing new insights into these crucial behavioral interactions in nature.

Bacterial infections can substantially impact host metabolic health as a result of the direct and indirect demands of sustaining an immune response and of nutrient piracy by the pathogen itself. Drosophila melanogaster and other insects that survive a sublethal bacterial infection often carry substantial pathogen burdens for the remainder of life. In this study, we asked whether these chronic infections exact metabolic costs for the host, and how these costs scale with the severity of chronic infection. We infected D. melanogaster with four bacterial species (Providencia rettgeri, Serratia marcescens, Enterococcus faecalis and Lactococcus lactis) and assayed metabolic traits in chronically infected survivors. We found that D. melanogaster carrying chronic infections were uniformly more susceptible to starvation than uninfected controls, and that sensitivity to starvation escalated with higher chronic pathogen burden. We observed some evidence for greater depletion of triglyceride and glycogen stores in D. melanogaster carrying chronic bacterial loads, although this varied among bacterial species. Chronically infected flies exhibit sustained upregulation of the immune response, which we hypothesized might contribute to the metabolic costs. Consistent with this prediction, genetic activation of the major innate immune signaling pathways depleted metabolic stores and increased starvation sensitivity even in the absence of infection. These results demonstrate that even sublethal infections can have substantial health and fitness consequences for the hosts, arising in part from pathogen-induced immune activation, and that the consequences scale quantitatively with the severity of infection.

Learning and memory are fundamental processes, influencing animal foraging behaviour and fitness success. Evaluating food nutritional quality, particularly of proteins and essential amino acids, involves complex sensory mechanisms. While olfactory cues have been extensively studied, less is known about proteinaceous chemoreception, especially in invertebrates. Vespula germanica, a globally invasive social wasp species, relies heavily on foraging efficiency and nutritional assessment for colony success. Previous studies have highlighted their associative learning abilities in natural settings, but their cognitive capabilities under laboratory conditions still need to be explored. We investigated the perceptual and learning abilities of V. germanica concerning amino acids using a maxilla-labium extension response (MaLER) conditioning protocol. We aimed to determine whether these wasps can (1) perceive specific amino acids through antennal chemoreception, (2) perform associative learning with amino acids, (3) discriminate between stimuli of varying molecular and nutritional profiles, and (4) generalize among similar stimuli. Our results suggest that V. germanica can detect free amino acids and exhibit associative learning toward them. They can discriminate between amino acids with different profiles and do not generalize among similar compounds. These findings indicate that V. germanica foragers can qualitatively evaluate amino acid solutions, which translates into a natural ability to discern and learn from food sources with varying nutritional qualities. This knowledge could enhance management strategies for this invasive species, which rely on poisoned beef-based baits. Understanding the sensory and cognitive capabilities of V. germanica provides a foundation for developing more effective control methods.