Journal of Experimental Biology最新文献

Nectar-feeding bats exhibit a range of specialized adaptations that allow them to extract nectar from flowers efficiently. These adaptations include tongue morphological traits and feeding strategies that reflect varying degrees of specialization to nectarivory. While some aspects of the drinking mechanics of highly specialized nectar bats have been studied, little is known about the feeding behaviors of non-specialized species such as Phyllostomus discolor. This study compares the nectar extraction behaviors of P. discolor and the specialized Anoura geoffroyi, examining morphological and biomechanical adaptations that affect feeding efficiency and foraging strategies. We used electron microscopy to study the lingual surface, and high-speed videography to analyze tongue kinematics and feeding efficiency. Both bat species possess hair-like papillae that form a brush-like tongue surface, and both extract nectar using a lapping mechanism; however, they exhibited notable behavioral and biomechanical differences resulting in variation in feeding efficiency. Phyllostomus discolor has a shorter, less flexible tongue than A. geoffroyi, but exhibits similar licking frequencies. Unlike A. geoffroyi, which performs brief hover-feeding bouts, P. discolor perches on the inflorescences, drinks for longer, and extracts more nectar per visit. However, P. discolor exhibited lower feeding efficiency, likely due to its reduced tongue protrusion distance and shorter, less abundant papillae. These findings reveal convergence in general feeding mechanism, i.e. brush-tongue lapping, but highlight divergence in morphological and behavioral traits that affect feeding kinematics and efficiency. Our study illuminates how foraging strategy and tongue morphology affect drinking efficiency, pointing to evolutionary pathways that promote niche differentiation within nectar-feeding bat communities.

Understanding oxidative stress in ecological and evolutionary contexts requires reliable biomarker quantification across taxa, tissues and experimental setups. However, storage conditions such as temperature and duration may bias these measurements. Here, we evaluated the stability of oxidative stress biomarkers, including three antioxidant enzymes (superoxide dismutase, glutathione reductase, glutathione peroxidase) and a lipid peroxidation marker (malondialdehyde) in amphibian, mammal, bird and insect samples stored under various temperature conditions (-80, -20, 4°C) from a few hours to 8 months. Storage significantly affected biomarker values depending on the marker, tissue and taxon. Notably, even long-term storage at -80°C altered some markers. In insect samples, lipid peroxidation was also influenced by triglyceride levels, indicating a potential confounding factor. Our results highlight the need to consider storage effects in oxidative stress studies. We also provide practical recommendations, aiming to improve data reliability across field and laboratory eco-evolutionary studies, as well as biomedical contexts.

The energetic costs of carrying loads can significantly impact animal fitness but appear to vary dramatically among animals. For some, they equal the cost of carrying an equivalent amount of extra body mass, while others carry loads more economically. Locomotor systems can plastically respond to acute and chronic loading, but how such responses impact the energetics of locomotion is unclear. We asked how loading affects the energetics of an immature hemimetabolous insect, the cockroach Blaberus discoidalis, at rest and during locomotion at various speeds, and whether energetics change as animals adjust to chronic loading. Cockroaches carried loads economically as early as 2 h after load addition, with no change in energetic costs during a 10 day period. We discuss the implications of these findings and potential mechanisms underlying economical load carrying in arthropods.

Muscle-tendon units (MTUs) tend to exploit their elastic elements to meet a range of energy-absorption and power input demands, but the extent of this may depend on how the muscle produces force. Muscle pre-activation is a habitual strategy observed in vivo during energy-absorbing demands, but it remains a question whether pre-activation alters the power input demands among elastic elements and muscle fascicles. To determine the effect of pre-activation on peak power input demands, we conducted in situ experiments using sonomicrometry and a linear actuator to simulate a pre-activation strategy in the lateral gastrocnemius MTU of wild turkeys (n=6). Onset timing of muscle activation was manipulated to start (1) simultaneously with or (2) before an active MTU stretch (i.e. no pre-activation versus with pre-activation). During MTU stretch, we quantified a peak power input decoupling ratio to determine the relative power input between muscle fascicles and elastic elements. We found that muscle pre-activation decreased the decoupling ratio (mean±s.d., 0.68±0.09 versus 0.56±0.11; P=0.015; Cohen's d=1.49), signifying that muscle fascicles absorbed a greater percentage of total MTU peak power input. We also found that the MTU generated greater force with pre-activation by relying more on active fascicle lengthening during the late phase of MTU stretch, which allowed for greater peak power input capacity of the MTU. These findings highlight how a simple shift in muscle activation timing can prime the MTU to deal with greater peak power input during energy-absorbing activities.

Skeletogenesis is a tightly regulated process that is highly sensitive to abiotic factors and environmental change. Any skeletal abnormalities arising in early life can have lifelong consequences. Freshwater fish must cope with increased temperatures and declining pH, as well as with pollutants released into the environment by human activities. Our study aims to determine whether warming modulates the impacts of low pH and the environmental pollutant cadmium on zebrafish skeletal development. Zebrafish larvae were exposed to warming (31.5°C), acidification (pH 4.5) and cadmium (nominal concentration of 0.3 µmol l-1) in E3 medium from 0 till 7 days post fertilisation. Whole-body calcium content and mineralisation of craniofacial structures were reduced by low pH, cadmium, and a combination of both. Warming accelerates all physiological processes, including calcification, and was shown to partly mitigate the disruption of mineralisation induced by acidification. This attenuating effect of warming was found even after accounting for the thermal effects on development by comparing fish at the same developmental stage. In contrast, cadmium-induced disruption was not attenuated by warming. By comparing larval locomotor behaviour, it was shown that the effects of cadmium and acidification on swimming behaviour are dependent on environmental temperature, and occur mainly during the night. However, the combined effects of low pH and cadmium on swimming distance were not modulated by warming. In summary, we found that multiple stressors influence each other and impact calcium metabolism, bone development and swimming behaviour of zebrafish larvae. We found evidence for a mitigation of stressor effects in a warming context.

The outcome of male-male contests is a major determinant of reproductive success in many species. Because of this, traits that are associated with winning fights are often more pronounced in winner males than in loser males. Here, we examined a variety of morphological, physiological and performance traits that may predict the outcome of contests between male fall field crickets (Gryllus pennsylvanicus). We staged contests between size-matched male crickets and also collected data on jumping performance, standard and maximum metabolic rate, and head and hindlimb morphological traits. Though some of these traits have been examined previously, others have not been examined in the context of male-male competition and the full set of traits have not been measured on the same individuals. Our results indicate that winners, as compared with losers, had significantly greater head size, maxilla size, jump performance (distance, takeoff velocity, total kinetic energy and mass-specific power) and marginally greater hindlimb muscle mass. We found no differences between winners and losers for standard or maximum metabolic rate or factorial metabolic scope. This integrative dataset contributes to a broader understanding of sexual selection in this species.

The University of Washington's marine field station, the Friday Harbor Laboratories (FHL), has been a center for diverse biological research for over 100 years. The facility is a complete mini-campus with housing and dining facilities. Experimental biologists visit from all over the world to focus intensively on their research efforts, an endeavor that is made possible by state-of-the-art equipment and biologically diverse local habitats. FHL also offers courses and short workshops that use local marine organisms and common-use equipment to train the next generation of scientists in fields as diverse as natural history to evolutionary development of invertebrates to biomechanics of fishes. Particularly strong areas of focus over the long history of FHL include comparative biomechanics (of everything from seaweed to sharks), developmental biology, neurophysiology and other physiology, genomics and marine ecology. Recent interactions of FHL researchers with other specialists ranging from engineers to restoration practitioners keep FHL on the cutting edge of research.

Seasonal acclimatisation is a mechanism enabling individuals to advantageously adjust one or more physiological parameters in response to changing environmental conditions. The ability to adjust metabolic rates and thermal physiology in response to seasonal changes is known to be central to the physiological ecology of some reptiles, but few studies have examined the ability of reptiles to exhibit seasonal flexibility in rates of evaporative water loss (EWL). We measured acclimatisation to seasonal changes for both temperature and water-related traits in six species of geckos in the genus Gehyra from the highly seasonal tropics of northern Australia. Four species from a mesic, more thermally stable site did not have seasonal differences in thermal preference (Tpref), but Tpref was significantly lower during the cooler dry season in three species from a semi-arid, more thermally variable site. EWL was lower (34-76% reduction) during the dry season compared with the wet season, representing a significant reduction for all gecko species. EWL decreased rapidly from wet to early dry season, then either remained low or continued to decrease to a minimum in the late dry season. These results indicate acclimatisation in EWL, resulting in the conservation of water during the dry season. A growing body of evidence suggests that seasonal acclimatisation of EWL broadly occurs in lizards in the wet-dry tropics of Australia, but less is known about seasonal acclimatisation of EWL in other geographic regions.

As anthropogenic climate change and urbanization continue to elevate global temperatures, understanding how ectotherms respond physiologically to temperature is of increasing importance. Squamates (lizards and snakes) have a history of serving as models for studies in thermal biology. Comparisons of physiological responses among different species or populations of the same species could provide insight into the capacity of these organisms to adapt to changing thermal environments. However, we rarely document the physiological phenotype of voucher specimens, and current research lacks clear methodological standardization, which potentially creates biases when making direct comparisons and performing analyses. To address this problem, we propose the 'physiotype' as a standardized, comprehensive framework for documenting the thermal physiology of squamates. We envisage the physiotype as an integrated suite of physiological traits that can function as a comparative tool, much like a morphological phenotype. Here, we recommend a standardized methodology for defining the physiotype, including an array of established measurements taken at ecologically relevant temperatures. Implementing this approach will enable robust comparative analyses, allowing for a more holistic understanding of how squamate physiology influences and is influenced by ecology and behavior. To maximize the utility of this approach, we also advocate for the creation of accessible repositories for physiotypes, which could facilitate large-scale data synthesis. This proposed methodological framework will enhance our ability to predict species' vulnerabilities and forecast their capacity for thermal adaptation, and will inform future conservation strategies across a thermally dynamic landscape.

Male mayflies (Ephemeroptera) engage in oscillating nuptial flight patterns in which they climb vertically before passively parachuting downward. Males hold station above an area often in large numbers, intercepting adult females passing overhead. We reconstructed the flight behaviour of common mayfly (Ephemera vulgata) aggregations in 3D, while they were performing their nuptial dance and chasing artificial targets. Male mayflies chased any object that travelled horizontally above them and attempted to mate with it. Despite this indiscriminative chasing, we observed that male mayflies infrequently caught each other by mistake. We suggest that the flight pattern of male mayflies helps them avoid each other whilst keeping the flight-motor system active. By flying vertically, males rarely fly horizontally overhead of each other, the key signature used to identify potential mates. Male mayflies stop their pursuit if the target drops beneath the horizon. Therefore, we suggest that male mayflies engage in a downward parachute as an effective evasion strategy against other males that may aim to intercept them. During target interception, mayfly flight behaviour resembles the guidance law of proportional navigation. We found that mayflies selectively change speed, fanning their long posterior filaments and spreading their hindwings to decelerate before turning. Mayflies are more manoeuvrable at low speeds, and thus this deceleration prior to turns reduces overshooting and increases steering performance. Through simulation, we demonstrate that a speed-changing, mayfly-inspired proportional navigation controller is more effective than constant-speed models at staying below and colliding with manoeuvring targets.