Journal of Experimental Biology最新文献

Procellariforms are the most oceanic among birds, regularly embarking on the longest journeys in the animal kingdom to find food over an apparently featureless sea surface. To minimize energy expenditure, many species harness wind energy through dynamic soaring, extracting kinetic energy from the wind shear. The smallest members of this order, storm petrels, have functional traits that prevent this type of locomotion, and are predicted to rely on flapping flight despite their high motility. However, theoretical predictions have never been validated and their flight strategy and activity budgets are unclear. We hypothesized that, as the benefits of dynamic soaring are out of reach, these birds should rely on gliding to some extent to sustain their long-ranging movements and save energy. To test our hypothesis we used, for the first time, miniaturized Inertial Measurement Units on one of the world's smallest seabirds, the European storm petrel (Hydrobates pelagicus). We demonstrate that these small seafarers spend 78% of the time flying during their foraging trips, with wingbeat frequencies up to 15 Hz. During transiting, they flap wings at high frequency (mean±SD: 8.8±0.8 Hz) for 91% of the time, gliding sporadically and for instants only (mean±SD: 0.11± 0.17 sec). Flight activity was high during night and early morning, while they rest on the sea in the central hours of the day. Overall, our results reveal a peculiar locomotory strategy among procellariforms and raise questions about how they can energetically sustain foraging trips spanning hundreds of kilometres.

Territorial displays include some of the most elaborate behaviours in the animal kingdom. In this study, we investigated the territorial behaviour and vibratory signalling of neonate warty birch caterpillars (Falcaria bilineata Lepidoptera: Drepanidae), which reside solitarily on birch leaves and defend the leaf tip. Upon hatching, these tiny caterpillars - no larger than 2 mm - seek out and establish a small solitary territory (∼1 cm wide) at the leaf tip, where they lay silk mats, feed, and advertise their presence by producing multicomponent vibratory signals - Buzz Scrapes and Drums. When a conspecific neonate (intruder) is introduced to a leaf occupied by a resident, the resident increases its signalling rate up to four times than when undisturbed, and even more - up to 14 times - if the intruder enters the territory. Intruders rarely manage to take over the resident's defended space, with most confrontations (71%) ending in the resident maintaining control. Residents signal significantly more than intruders at all stages of the contest. If physical contact occurs, residents flee by dropping from the leaf by a silk thread. This results in territorial contests that involve no physical aggression, relying entirely on vibratory communication. These vibratory displays most likely function to establish spacing between conspecifics on a tree branch, but these complex signals may also function to exclude other members of the vibratory community by mimicking something dangerous, like a jumping spider.

Maintaining a stable core body temperature is essential for endotherms. Cetaceans live in a highly thermally conductive medium, requiring special adaptations to reduce heat loss and maintain homeothermy. We employed a combination of aerial photogrammetry and existing data sources to estimate heat loss rates in five sympatric cetaceans of varying sizes, inhabiting the sub-arctic waters (∼3.7 °C) of NE-Iceland: harbour porpoises (Phocoena phocoena, 1.0 - 1.6 m, n=50), white-beaked dolphins (Lagenorhynchus albirostris, 1.1 - 2.9 m, n=294), minke whales (Balaenoptera acutorostrata, 4.4 - 8.6 m, n=30), humpback whales (Megaptera novaeangliae, 6.0 - 14.2 m, n=282) and blue whales (Balaenoptera musculus, 13.2 - 24.2 m, n=29). Further, we investigated the effect of body size (length), body shape (surface-area-to-volume ratio, SVR), body temperature, and blubber thermal conductivity and thickness on heat loss for all species. Smaller species had higher volume-specific heat loss compared to larger species due to their higher SVRs, a fundamental consequence of scaling. Apart from body size, blubber thickness had the largest effect on heat loss, followed by thermal conductivity. Smaller cetaceans seem to rely primarily on physiological and morphological adaptations to reduce heat loss, such as increased blubber thickness and lower thermal conductivity, whereas larger species offset heat loss by having larger bodies and lower SVRs. Our findings provide valuable insights into the thermal biology of these species and its implications for habitat use and prey requirements.

Every year, billions of birds migrate to optimize their foraging, shelter and breeding. They use an inclination compass, which, unlike the technical compass, distinguishes between the directions towards the magnetic equator from the magnetic pole based on magnetic inclination angles, which range from ±90 deg at the poles to 0 deg at the equator. During autumn migration, some species cross the magnetic equator, where field lines are horizontal, i.e. the inclination angle is 0 deg. At this point, the avian magnetic compass becomes ambiguous, because the birds can no longer distinguish 'to the pole' from 'to the equator'. Experiments with bobolinks and garden warblers have shown that these birds adaptively change their orientation when exposed to a horizontal magnetic field. We tested this in marsh warblers and spotted flycatchers, but they showed no such response, suggesting they may use other cues. This indicates that different species may rely on varying stimuli, and the current experimental models may not be universally applicable.

Identification of physiological processes setting thermal tolerance limits is essential to describing adaptive response to temperature changes. We used the North American Daphnia pulex complex, which makes a remarkable model for comparative physiology as it is composed of clones differing in heat tolerance and ploidies, and with a wide geographic distribution. The fatty acid composition of 18 diploid and triploid D. pulex clones acclimated to 16°C and 24°C was measured and compared with their tolerance to extreme high and low temperatures (CTmax and CTmin, respectively). Eicosapentaenoic acid (EPA) relative content showed a strong negative relationship with CTmax and a clear association with CTmin. Higher unsaturation and peroxidation indices were associated with better cold tolerance, whereas saturated fatty acids and monounsaturated fatty acids were associated with lower cold tolerance. Triploid D. pulex clones accumulated more EPA and had lower CTmin than diploid clones (better cold tolerance). Triploid clones retained more omega-6 polyunsaturated fatty acids at high temperature. CTmax was positively correlated with CTmin, suggesting the existence of important constraints in temperature tolerance caused by fatty acid composition.

As in plants, photosynthesis also represents a key energy source in photosymbiotic cnidarians bearing microalgae. We observed that the cnidarian sea anemone Anemonia viridis, commonly known as the snakelocks anemone, displayed heliotropism or solar tracking in their natural habitats. When exposed to sunlight, A. viridis point their tentacles towards the sun while remaining sessile, facing east at dawn and west at dusk as they track the sun's relative position through the day. This phenomenon was previously only observed in plants. Solar tracking movements in A. viridis are driven by peak wavelengths that prompt photosynthesis in their endosymbionts. The heliotropic response was absent in both bleached (aposymbiotic) A. viridis and in symbiotic A. viridis with chemically inhibited photosynthesis. We revealed a direct correlation between heliotropism and symbiont oxygen production in A. viridis and showed how photosymbiotic A. viridis utilises this mechanism to modulate exposure to solar irradiation. Our study exemplifies how photosynthetic organisms such as plants and symbiotic sea anemones, display similar behaviour in response to similar environmental pressures.

From a conservation perspective, it is important to identify when sub-lethal temperatures begin to adversely impact an organism. However, it is unclear whether, during acute exposures, sub-lethal cellular thresholds occur at similar temperatures to other physiological or behavioural changes, or at temperatures associated with common physiological endpoints measured in fishes to estimate thermal tolerance. To test this, we estimated temperature preference (15.1±1.1°C, mean±s.d.) using a shuttle box, agitation temperature (22.0±1.4°C), defined as the point where a fish exhibits a behavioural avoidance response, and the upper thermal limit (CTmax, 28.2±0.4°C) for 1 year old brook trout (Salvelinus fontinalis) acclimated to 10°C. We then acutely exposed a different subset of fish to the mean temperatures associated with the pre-determined physiological endpoints and sampled tissues when they reached the target temperature or after 60 min of recovery at 10°C for transcriptomic analysis. We used qPCR to estimate mRNA transcript levels of genes associated with heat shock proteins, oxidative stress, apoptosis and inducible transcription factors. A major shift in the transcriptome response occurred once the agitation temperature was reached, which may identify a possible link between the cellular stress response and the behavioural avoidance response.

The degree of tolerance to adverse conditions ultimately shapes a species' vulnerability to environmental changes. Some studies have reported limited thermal tolerance due to hypoxia in fish employing aquatic respiration. However, there is a lack of information regarding the effects of hypoxia on thermal tolerance in fish exhibiting bimodal respiration. A set of Amazonian fish species has adaptations to breathe air when oxygen in water is not enough to fulfil demand. Additionally, loricariid species within this group possess stomach adaptations for air breathing. The Loricariidae family exhibits varying stomach types and observed morphological differences could influence their ability to obtain oxygen from the air. This ability may, in turn, have consequences for the thermal tolerance of these species. Our objective was to assess the effects of hypoxia on thermal tolerance, along with the physiological (whole-animal metabolic rates and mitochondrial respiration) and behavioural mechanisms involved, in two facultative air-breathing species: Pterygoplichthys pardalis and Ancistrus dolichopterus. These species showcase morphological distinctions in their stomachs, with the former having a higher capacity to obtain oxygen from the air. Thermal tolerance in P. pardalis remained unaffected by dissolved oxygen in the water when air access was available but decreased when access to the water surface was restricted, specifically in hypoxic conditions. Conversely, the thermal tolerance of A. dolichopterus decreased below the critical oxygen partial pressure (Pcrit), even with access to air, highlighting their limited ability to obtain oxygen through their adapted stomach. Our results underscore that air breathing enhances thermal tolerance, but this effect is prominent only in species with a higher capacity for air breathing.

Theoretically, animals with longer hindlimbs are better jumpers, while those with shorter hindlimbs are better maneuverers. Yet, experimental evidence of this relationship in mammals is lacking. We compared jump force and maneuverability in a lab population of Mongolian gerbils (Meriones unguiculatus). We hypothesized that gerbils with long legs (ankle to knee) and thighs (knee to hip) would produce the greatest jump forces, while gerbils with short legs and thighs would be able to run most rapidly around turns. Consistent with these hypotheses, gerbils with longer legs produced greater jump forces after accounting for sex and body mass: a 1 mm greater leg length provided 1 body weight unit greater jump force on average. Furthermore, gerbils with shorter thighs were more maneuverable: a 1 mm greater thigh length reduced turn speed by 5%. Rather than a trade-off, however, there was no significant correlation between jump force and turn speed. There was also no correlation between jump force and total hindlimb length, and a weak positive correlation between corner-turning speed and total hindlimb length. These experiments revealed how distinct hindlimb segments contributed in different ways to each performance measure: legs to jumping and thighs to maneuvering. Understanding how variations in limb morphology contribute to overall gerbil locomotor performance may have important impacts on fitness in natural habitats.

Diversity drives innovation and creativity, directly contributing to scientific excellence. However, achieving equity in academia, including in experimental biology fields such as biomechanics and comparative physiology, remains a significant challenge, with women and other historically marginalized groups underrepresented, especially in more senior roles. When considering gender, the disparity is often linked to difficulties in balancing family responsibilities with demanding careers, along with lower 'academic visibility', as evidenced by fewer professional awards for women scientists. Many successful women who balance career and family keep their family lives private, making these aspects invisible to early career scholars, and thus depriving them of role models. To help close the gender gap, in this Perspective, we propose 10 actionable strategies for scholars at all career stages to promote gender diversity and inclusion through active allyship. Although we focus on gender diversity, these strategies can be broadly applied to harness the benefits of other diversity dimensions (e.g. age or ethnicity). We argue that embracing allyship benefits individual scientists, their research groups, the quality of their research, the broader research community and society at large by enhancing collective scientific output and inspiring the next generation of scientists.