Journal of Experimental Biology最新文献

Variable thermal environments may have both detrimental and beneficial effects. For example, extreme temperatures may challenge homeostasis and inflict tissue damage, but may also induce acclimation that improves stress resilience. Hormetic models provide a framework to understand dosage-dependent, contrasting beneficial and detrimental effects from physiological and ecological perspectives. We used a hormetic framework and associated quantitative models to investigate how a range of relatively cold, pre-exposure temperatures influence survival and fertility following cold shock at a more extreme cold temperature in the fruit fly Drosophila melanogaster. Cold pre-exposure can induce a protective rapid cold hardening (RCH) response, fail to stimulate a response, or cause direct cold injury. We found a plateau-shaped relationship between pre-exposure temperature and female survival resilience, where survival following a cold shock remained high across a range of temperatures, with sharp transitions at higher and lower temperatures. Bayesian fitting of a bi-logistic model highlights these transitions at temperature thresholds that govern processes mediating both acclimation and cold injury. In contrast to survival, female fertility resilience exhibited a muted response to pre-exposure temperature in the presence and absence of post-stress mating opportunities. Overall, a range of pre-exposure temperatures allowed low but successful reproduction following cold shock. High survival but low fertility resilience is consistent with (1) differential impacts of cold on somatic and reproductive tissues and (2) a growing body of literature suggesting that the thermal sensitivity of fertility may be more limiting than survival for population persistence in variable and changing climates.

Many studies have demonstrated that anthropogenic noise affects animals' auditory perception of salient stimuli. Few have tested whether these effects are different from those experienced in nature. We tested the ability of female field crickets, Teleogryllus oceanicus, to phonotactically locate a speaker playing conspecific male song in four acoustic backgrounds: silence, road noise, river noise and heterospecific song. Crickets approaching conspecific song paused more frequently in river noise and heterospecific song treatments compared with silence or road noise. We also recorded auditory interneuron (AN1 and AN2) activity under the first three acoustic background treatments to construct and compare treatment-specific audiograms and interneuron responses to conspecific song. We found little difference in activity, other than that AN2 thresholds for 6 kHz sounds (the tested frequency closest to male song) were highest in river noise, while heterospecific song increased baseline AN2 activity and reduced AN2 activity to conspecific song onset. Our results suggest road noise is not necessarily a greater disturbance than river noise.

Since the 1950s, muscle contraction has been explained by the sliding filament and cross-bridge theories involving actin and myosin. However, these theories do not account for certain muscle properties, such as residual force enhancement (rFE). The sarcomeric protein titin has been proposed to contribute to active force and rFE, but its role remains unclear. A leading hypothesis suggests that titin binds to actin, thereby shortening its spring-like segment, with calcium regulating this interaction. We investigated the roles of calcium and cross-bridge formation in titin mechanics by measuring the length of titin's PEVK region in sarcomeres during (i) passive stretch, (ii) active stretch with cross-bridge inhibition (via 2,3-butanedione monoxime, BDM) and (iii) active isometric contraction. PEVK lengths were similar for passive and cross-bridge-inhibited conditions but were longer for active contractions. Our results suggest that cross-bridge engagement, not calcium alone, modulates titin extensibility and passive force under physiological conditions.

The expression of sexually selected traits, such as exaggerated weapons and ornaments, often entails trade-offs against life-history traits. While phenotypic trade-offs are well documented, the underlying molecular physiological mechanisms remain largely unexplored. In this study, we investigated the potential role of an insulin-like peptide, ILP2, in mediating the trade-off between sexually selected combat traits and survival traits in the broad-horned flour beetle, Gnatocerus cornutus. RNA interference (RNAi)-mediated knockdown (KD) of ILP2 during larval stages resulted in a reduction in the development of mandibular horns and overall body size. Interestingly, ILP2 KD males had increased lipid storage and enhanced starvation tolerance, indicating a shift in resource allocation from sexually selected traits to survival traits. Behaviorally, ILP2 KD males showed decreased locomotor activity and reduced aggression, leading to lower combat success. These findings suggest that ILP2 functions as a key mediator in the allocation of resources between combat and survival traits, highlighting its pleiotropic effects on morphology, metabolism and behavior. Our study provides novel insights into the molecular physiological mechanisms underlying life-history trade-offs associated with sexually selected traits.

Rapid cyclic movements are generated by antagonistic muscle pairs contracting in an alternating pattern. The highest frequencies can be generated in balanced torque-producing systems with specialized muscle fibers. The system's frequency output is expected to change when it becomes more adapted to functions with conflicting mechanical demand, such as increased static torque production in one direction. This study first conceptualized how distinct factors (fiber type, muscle cross-sectional area, moment arm and inertial properties) could influence this torque-frequency trade-off. Special attention is given to Henneman's principle, as many of these systems contain both slow- and fast-twitch muscle fiber, typically organized in motor units, with the smallest, slow-twitch, fiber-rich motor units being recruited first. Next, we used Hill-type muscle models operating a Java sparrow's mandible as a case study for this framework. Our model showed that muscle fiber type strongly affects the frequency output, with a notable role for Henneman's effect causing the overdeveloped muscle to predominantly recruit slow-twitch muscle fibers. This leads to large muscle torque output overlap, which in turn reduces frequency. Once torque imbalance occurs, altering the other variables only slightly changes the frequency, suggesting a dominant role of muscle contractile properties. This means that the conflicting demands of multifunctional musculoskeletal lever systems such as bird beaks are also tightly linked to fiber type and motor unit roles such as endurance and precision of movement.

We tested whether food availability limits phenotypic plasticity in thermal tolerance in the amphipod Echinogammarus marinus. We shifted specimens from 10°C to an acclimation temperature of 20°C, and kept them there for different durations with and without food before measuring the time to immobilization at 30°C. Our results show that thermal tolerance increases with acclimation duration, but this response was about two times more pronounced in fed than in unfed individuals. We also decomposed the plastic response into a rate component (how fast the trait changes) and a capacity component (by how much it changes). This showed that the overall effect of food treatment on the temporal dynamics of thermal tolerance was primarily driven by the effect on capacity. We conclude that laboratory derived thermal tolerance data from experiments where ecological conditions are otherwise optimal may provide overly optimistic estimates of how well organisms deal with extreme events through phenotypic plasticity.

Metabolic scaling describes the relationship between metabolic rate and body mass and has traditionally been investigated across individuals or species. Scaling of metabolic rate within individuals as they grow through ontogeny has received far less attention. This is presumably because it is temporally and logistically cumbersome to do the longitudinally repeated measurements on the same individuals that are required to quantify direct (within-individual) ontogenetic scaling. Here, we argue for the importance of studying within-individual ontogenetic metabolic scaling to understand energy-allocation trade-offs and variation in metabolic scaling at all biological levels. Using our own data on within-individual ontogenetic metabolic scaling of fish, we explore debated links between metabolic scaling and growth. We outline how covariation between ontogenetic metabolic scaling and growth rate can generate predictable variation in higher-level scaling across individuals. We further demonstrate how timing of sampling during an individual's growth trajectory can introduce variation in metabolic scaling relationships, because growth rate changes through ontogeny and varies among individuals. Thus, variation in metabolic scaling can be driven by often unknown variation in the age composition and growth trajectories among individuals within the species from which they are sampled. We believe that an increased focus on within-individual ontogenetic metabolic scaling and its relationships with other physiological and life-history traits can help clarify the century-long debate about what causes variation in metabolic scaling relationships and the many theories associated with it.

Ultraviolet wing patterns are commonly used for intra- and inter-species communication in butterflies. However, as moths have distinct wing resting positions and crepuscular or nocturnal lifestyles, findings in butterflies might not be generalizable to all Lepidoptera. Here, we investigated the location, size and UV reflectance of wing patterns in both sexes of three species of saturniid moths using UV photography. We also investigated the UV reflection mechanisms at the level of individual scales using microspectrophotometry and focused-ion beam scanning electron microscopy. We found that female wings are more UV reflective than male wings and ventral surfaces are more reflective than dorsal surfaces, which is the opposite of what is generally seen in butterflies. The same trend was observed for UV area with an expansion of size in females and ventral wing surfaces. The mechanisms of UV reflection, however, seem to be conserved between saturniid moths and nymphalid butterflies, but not pierids.

Organisms in the wild constantly encounter fluctuations in temperature and food availability, pathogens and other stressors that disrupt their physiological balance. To counteract these disruptions, organisms initiate stress responses that vary in nature depending on the intensity and duration of the stressor. While severe stress can be harmful or even fatal, moderate stress can activate adaptive mechanisms, a phenomenon known as hormesis. Hormesis enhances resilience to stress and has been associated with improved ageing, immunity and metabolism. Short-term exposures to mild stress, such as heat or oxidative stress, have been shown to extend Drosophila lifespan and promote cross-tolerance to other stressors. Among various environmental stressors, starvation poses a significant and recurring challenge that has driven the evolution of energy-conserving strategies essential for survival. Prior exposure to starvation has been shown to influence longevity, resilience to starvation, physiological status and stress tolerance. However, the mechanisms underlying these hormetic effects remain poorly understood. In this study, we investigated how short-term starvation enhances resistance to prolonged food deprivation in Drosophila. Our findings reveal that metabolic rewiring, including changes in energy utilization, insulin signalling and transcriptomic profiles, underpins this adaptive plasticity. These insights will improve our understanding of the molecular and metabolic mechanisms driving hormesis, with broader implications for stress resilience and organismal health.