Journal of Experimental Biology最新文献

Most orb-weaving spiders use static webs that deform only after flying prey hit the webs. However, ray spiders (Theridiosoma gemmosum) pull orb webs into cones that are loaded with enough elastic energy to snap back like slingshots at accelerations of up to 504 m s-2 once released. We test the hypothesis that ray spiders sense vibrations from flying insects to release their webs and capture prey in mid-flight. We show that spiders release webs in response to live tethered mosquitoes that are not touching silk. Web release is most likely when mosquitoes are in front of the web and within the 'capture cone' where the capture spiral moves directly into the insects' flight. In summary, ray spiders use airborne stimuli to determine both the direction and distance of flying prey. Perception of airborne cues from flying insects may be an under-appreciated source of information for other web-building spider species about the approach, size and/or behaviors of insects prior to contact with webs.

Polar marine invertebrates serve as bellwethers for species vulnerabilities in the face of changing climate at high latitudes of the Earth. Ocean acidification, warming/heatwaves, freshening, sea ice retreat and productivity change are challenges for polar species. Adaptations to life in cold water with intensely seasonal productivity has shaped species traits at both poles. Polar species have life histories often characterised as K-strategist or K-selected (e.g. slow growth and development, larval hypometabolism) that make them sensitive to climate stress and altered seasonal productivity. Moderate warming results in faster development and can have positive effects on development, up to a limit. However, ocean acidification can retard development, impair skeletogenesis and result in smaller larvae. Given the fast pace of warming, data on the thermal tolerance of larvae from diverse species is urgently needed, as well as knowledge of adaptive responses to ocean acidification and changes to sea ice and productivity. Predicted productivity increase would benefit energy-limited reproduction and development, while sea ice loss negatively impacts species with reproduction that directly or indirectly depend on this habitat. It is critical to understand the interactive effects between warming, acidification and other stressors. Polar specialists cannot migrate, making them susceptible to competition and extinction from range-extending subpolar species. The borealisation and australisation of Arctic and Antarctic ecosystems, respectively, is underway as these regions become more hospitable for the larval and adult life-history stages of lower-latitude species. Differences in biogeography and pace of change point to different prospects for Arctic and Antarctic communities. In this Commentary, we hypothesise outcomes for polar species based on life history traits and sensitivity to climate change and suggest research avenues to test our predictions.

Energy governs species' life histories and pace of living, requiring individuals to make trade-offs. However, measuring energetic parameters in the wild is challenging, often resulting in data collected from heterogeneous sources. This complicates comprehensive analysis and hampers transferability within and across case studies. We present a novel framework, combining information obtained from eco-physiology and biologging techniques, to estimate both energy expenditure and intake in 48 Adélie penguins (Pygoscelis adeliae) during the chick-rearing stage. We employed the machine learning algorithm random forest (RF) to predict accelerometry-derived metrics for feeding behaviour using depth data (our proxy for energy acquisition). We also built a time-activity model calibrated with doubly labelled water data to estimate energy expenditure. Using depth-derived time spent diving and amount of vertical movement in the sub-surface phase, we accurately predicted energy expenditure. Movement metrics derived from the RF algorithm deployed on depth data were able to accurately detect the same feeding behaviour predicted from accelerometry. The RF predicted accelerometry-estimated time spent feeding more accurately compared with historical proxies such as number of undulations or dive bottom duration. The proposed framework is accurate, reliable and simple to implement on data from biologging technology widely used on marine species. It enables coupling energy intake and expenditure, which is crucial to further assess individual trade-offs. Our work allows us to revisit historical data, to study how long-term environmental changes affect animal energetics.

The interaction of widespread stressors such as nitrate pollution and increasing temperatures associated with climate change is likely to affect aquatic ectotherms such as amphibians. The metamorphic and physiological traits of amphibian larvae during the critical onset of metamorphosis are particularly susceptible to these stressors. We used a crossed experimental design subjecting Rana temporaria larvae to four constant rearing temperatures (18, 22, 26, 28°C) crossed with three environmentally relevant nitrate concentrations (0, 50, 100 mg l-1) to investigate the interactive and individual effects of these stressors on metamorphic (i.e. growth and development) and physiological traits (i.e. metabolism and heat tolerance) at the onset of metamorphosis. Larvae exposed to elevated nitrate concentrations and thermal stress displayed increased metabolic rates but decreased developmental rate, highlighting interactive effects of these stressors. However, nitrate pollution alone had no effect on either metamorphic or physiological traits, suggesting that detoxification processes were sufficient to maintain homeostasis but not in combination with increased rearing temperatures. Furthermore, larvae exposed to nitrate displayed diminished abilities to exhibit temperature-induced plasticity in metamorphosis timing and heat tolerance, as well as reduced acclimation capacity in heat tolerance and an increased thermal sensitivity of metabolic rate to higher temperatures. These results highlight the importance of considering the exposure to multiple stressors when investigating how natural populations respond to global change.

While the impressive singing abilities of birds are made possible by the syrinx, the upper vocal system (i.e. trachea, larynx and beak) could also play a role in sound filtration. Yet, we still lack a clear understanding of the range of elongation this system can undertake, especially along the trachea. Here, we used biplanar cineradiography and X-ray reconstruction of moving morphology (XROMM) to record 15 species of cadaveric birds from 9 different orders while an operator moved the birds' heads in different directions. In all studied species, we found elongation of the trachea to be correlated with neck extension, and significantly greater (ranging from 18 to 48% for the whole motion; and from 1.4 to 15.7% for the singing positions) than previously reported on a live singing bird (3%). This elongation or compression was not always homogeneous along its entire length. Some specimens showed increased lengthening in the rostral part and others in both the rostral and caudal parts of the vocal tract. The diversity of elongation patterns shows that trachea elongation is more complex than previously thought. Since tracheal lengthening affects sound frequencies, our results contribute to our understanding of the mechanisms involved in complex communication signals, one of the amazing traits we share with birds.

Most predators rely on capturing prey for survival, yet failure is common. Failure is often attributed to prey evasion, but predator miscalculation and/or inaccuracy may also drive an unsuccessful event. We addressed the latter using threespine stickleback as predators and bloodworms (non-evasive) as prey. High-speed videography of the entire attack allowed us to determine the strike tactics leading to successful or missed strikes. We analyzed movements and morphological traits from 57 individuals. Our results reveal that kinematics drive the strike outcome and that failed strikes primarily arise from incorrect timing of mouth opening, often beginning too far from the prey for suction to be effective. This likely stems from the lack of integration between locomotion and feeding systems. Our study begins to unravel the important link between behavior and success in fish feeding.

Disease may be both a cause and a consequence of stress, and physiological responses to infectious disease may involve stress coping mechanisms that have important fitness consequences. For example, glucocorticoid and glycemic responses may affect host fitness by altering resource allocation and use in hosts, and these responses may be affected by competing stressors. To better understand the factors that affect host responses to infection, we challenged the immune system of field-acclimatized pygmy rattlesnakes, Sistrurus miliarius, with a sterile antigen, lipopolysaccharide (LPS), and measured the glucocorticoid and glycemic response in healthy non-reproductive snakes, snakes afflicted with an emerging mycosis (ophidiomycosis) and pregnant snakes. We hypothesized that LPS challenge would result in a glucocorticoid and glycemic response typical of the vertebrate acute phase response (APR), and therefore predicted that LPS challenge would result in an acute increase in plasma corticosterone (CORT) and a decline in plasma glucose in all individuals. Additionally, we hypothesized that the APR would be attenuated in individuals simultaneously coping with additional challenges to homeostasis (i.e. disease or reproduction). As predicted, the immune challenge elicited an acute increase in plasma CORT and a decrease in plasma glucose. Snakes coping with ophidiomycosis and pregnant snakes were able to mount a robust glucocorticoid and hypoglycemic response to LPS challenge, which was contrary to our hypothesis. Our findings clarify directions of causality linking infection, glucocorticoids and glucose, and emphasize the importance of future research examining the fitness consequences of interactions between stress and disease in wildlife threatened by emerging pathogens.

Insects use walking behavior in a large number of contexts, such as exploration, foraging, escape and pursuit, or migration. A lot is known about how nervous systems produce this behavior in general and also how certain parameters vary with regard to walking direction or speed, for instance. An aspect that has not received much attention is whether and how walking behavior varies across individuals of a particular species. To address this, we created a large corpus of kinematic walking data of many individuals of the fruit fly Drosophila. We only selected instances of straight walking in a narrow range of walking speeds to minimize the influence of high-level parameters, such as turning and walking speed, aiming to uncover more subtle aspects of variability. Using high-speed videography and automated annotation, we captured the positions of the six leg tips for thousands of steps and used principal components analysis to characterize the postural space individuals used during walking. Our analysis shows that the largest part of walking kinematics can be described by five principal components (PCs). Separation of these five PCs into a 2D and a 3D subspace divided the description of walking behavior into invariant features shared across individuals and features that relate to the specifics of individuals; the latter features can be regarded as idiosyncrasies. We also demonstrate that this approach can detect the effects of experimental interventions in an unbiased manner and that general aspects of individuality, such as the individual walking posture, can be described.

Animals initiate physiological mechanisms to re-establish homeostasis following environmental stress. To understand how bird physiology responds to abiotic stress, we quantified changes in haematological markers of chronic stress response and body condition of male zebra finches (Taeniopygia guttata) acclimated for 18 weeks to hot and cool temperatures (daytime temperature: 40°C and 23°C) with water available ad libitum or restricted during half of the active phase. Ambient temperature induced greater chronic stress than restricted water availability. While cool compared with hot temperatures induced higher numbers of heterophils and heterophil to lymphocyte (H:L) ratios and reduced total leucocyte count, water restriction decreased the number of lymphocytes compared with water ad libitum. Body condition correlated with haematological parameters showing that birds with better condition had greater capacity to face environmental stress. Therefore, prolonged exposure to cool periods may result in chronic stress in zebra finches, especially if body condition is weakened.

A diversity of organisms live within underground environments. However, visualizing subterranean behavior is challenging because of the opacity of most substrates. We demonstrate that laser speckle imaging, a non-invasive technique resolving nanometer-scale movements, facilitates quantifying biological activity in a granular medium. We monitored fire ants (Solenopsis invicta) at different developmental stages, burial depths (1-5 cm) and moisture fractions (0 and 0.1 by volume) in a container of 0.7 mm glass particles. Although the speckle pattern from the backscattered light precludes direct imaging of animal kinematics, analysis of integrated image differences revealed that spiking during ant movement increased with the developmental phase. Greater burial depth and saturation resulted in fewer and lower magnitude spikes. We verified that spiking correlated with movement via quasi-2D experiments. This straightforward method, involving a laser and digital camera, can be applied to laboratory and potentially field situations to gain insight into subterranean organism activities.