Journal of Experimental Biology最新文献

For gap-crossing agility, arboreal animals require the ability to stabilize dynamic landings on branches. Despite lacking a prehensile grip, squirrels achieve stable landings using a palmar grasp. We investigated the landing dynamics of free-ranging fox squirrels (Sciurus niger) to uncover strategies for stable, above-branch landings. Using high-speed video and force-torque measurements in the sagittal plane, we quantified landing kinetics across gap distances. Squirrels rapidly managed >80% of the landing energy with their forelimbs. With larger gaps, peak leg force and foot torque increased. Alignment between forelimbs, velocity, and force increased, likely reducing joint moments. We tested control hypotheses based on an extensible pendulum model used in the physical, hopping robot named Salto. Squirrels stabilized off-target landings by modulating leg force and foot torque. To correct for undershooting, squirrels generated pull up torques and reduced leg force. For overshooting, squirrels generated braking torques and increased leg force. Embodying control principles in leg and foot design can enable stable landings in sparse environments for animals and robots alike, even those lacking prehensile grasps.

Gill regeneration in fish varies inter and intra-specifically. The latter may be associated with myriad factors including capacity of energy metabolism. This study investigated whether mitochondrial respiration capacity influences the degree of gill regeneration, and features of mitochondria in regenerated tissue by feeding fish an experimental diet aimed at modulating mitochondrial efficiency. Fish reared on control and experimental diet were subjected to 50% filament resection on a subset of filaments on the ventral and dorsal regions of the first gill arch. Mitochondrial respiration and citrate synthase activity (CSA) were measured in the resected tips of filaments (week-0) and then in the regenerated tissue at week-20 post-resection. The degree of filament regeneration was measured at week-20 post-resection (week-20). The experimental diet reduced CSA and respiratory control ratio (RCR), and increased proton leak at week-0 which was associated with a 30% reduction in tissue regeneration compared to fish on standard diet. While CSA increased in the regenerated tissue at week-20, there was a decline in state 3 respiration, proton leak, complex IV activity, and RCR as compared to week-0 irrespective of diet. Overall, mitochondrial respiration efficiency at week-0 was positively correlated with the degree of subsequent gill tissue regeneration. Additionally, state 3 respiration and proton leak at week-20 were positively correlated with tissue regeneration, whereas CSA exhibited a negative relationship. Our results indicate that capacity of mitochondrial respiration may at least partially explain the inter-individual variations in tissue regeneration, but mitochondrial function in the regenerating tissue may be limited.

Basal metabolic rate (BMR) is the most commonly measured energetic variable in endothermic animals. Identifying the underlying factors driving interspecific variation in BMR remains a major question in the field of energetics. While body size (M) and taxonomic affiliation are the intrinsic factors that account for most of the interspecific variation in BMR, haploid genome size (C-value) is hypothesized to directly influence cell size and indirectly, the specific metabolic rate. Climatic variables, mostly ambient temperature, have also been proposed as predictors of mass-independent BMR for endotherms. Therefore, in this study, we aimed to investigate the relative importance of intrinsic (C-value: CV) and extrinsic (climatic variables) factors as predictors of BMR in 67 rodent species in a phylogenetic context. The best ordinary least square (OLS) and phylogenetic generalized linear (PGLS) models explaining interspecific variation in BMR included the variables log M, log CV, maximum temperature of the warmest month (Tmax), minimum temperature of the coldest month (Tmin) and net primary productivity (NPP). Log M is the main determinant of log BMR variation in the rodents analyzed. Part of the remaining variation is attributed to a negative effect of genome size explaining 14% of the BMR variance, when Tmin is included in the model. As expected, one or two climatic variables were involved in explaining the remaining BMR variation (Tmin, Tmax and NPP). Our study highlights the importance of a denser sampling within vertebrate clades and the use of a phylogenetic context to elucidate the factors that contribute to explain BMR variation.

All ionoregulating marine fishes examined to date utilize seawater-type ionocytes expressing the apical Cl- channel, cystic fibrosis transmembrane conductance regulator (Cftr) to secrete Cl-. We performed transcriptomic, molecular, and functional studies to identify Cl- transporters in the seawater-type ionocytes of sea lamprey (Petromyzon marinus). Gill cftr expression was minimal or undetectable in larvae and post-metamorphic juveniles. We identified other Cl- transporters highly expressed in the gills and/or upregulated following metamorphosis and further investigated two candidates that stood out in our analysis, a Ca2+-activated Cl- channel, anoctamin 1 (ano1), and the Clc chloride channel family member 2 (clcn2). Of these, ano1 was expressed 10-100 times more than clcn2 in the gills; moreover, ano1 was upregulated during seawater acclimation, while clcn2 was not. Using an antibody raised against sea lamprey Ano1, we did not detect Ano1 in the gills of larvae, found elevated levels in juveniles and observed a 4-fold increase in juveniles after seawater acclimation. Ano1 was localized to seawater-type branchial ionocytes but, surprisingly, was localized to the basolateral membrane. In vivo pharmacological inhibition experiments demonstrated that a DIDS-sensitive mechanism was critical to the maintenance of osmoregulatory homeostasis in seawater- but not freshwater-acclimated sea lamprey. Taken together, our results provide evidence of a Cftr-independent mechanism for branchial Cl- secretion in sea lamprey that leverages Ano1-expressing ionocytes. Once further characterized, the Cftr-independent, Ano1-rich ionocytes of sea lamprey could reveal novel strategies for branchial Cl- secretion, whether by Ano1 or some other Cl- transporter, not previously known in ionoregulating marine organisms.

Salps are marine pelagic tunicates with a complex life cycle including a solitary and colonial stage. Salp colonies are composed of asexually budded individuals that coordinate their swimming by multi-jet propulsion. Colonies develop into species-specific architectures with distinct zooid orientations. These distinct colonial architectures vary in how frontal area scales with the number of zooids in the colony. Here, we address how differences in frontal area drive differences in swimming speed and the relationship between swimming speed and cost of transport in salps. We (1) compare swimming speed across salp species and architectures, (2) evaluate how swimming speed scales with the number of zooids across colony in architectures, and (3) compare the metabolic cost of transport across species and how it scales with swimming speed. To measure swimming speeds, we recorded swimming salp colonies using in situ videography while SCUBA diving in the open ocean. To estimate the cost of transport, we measured the respiration rates of swimming and anesthetized salps collected in situ using jars equipped with non-invasive oxygen sensors. We found that linear colonies swim faster, which supports idea that their differential advantage in frontal area scales with an increasing number of zooids. We also found that higher swimming speeds predict lower costs of transport in salps. These findings underscore the importance of considering propeller arrangement to optimize speed and energy efficiency in bioinspired underwater vehicle design, leveraging lessons learned from the diverse natural laboratory provided by salp diversity.

There are increasing concerns from scientists and policymakers regarding the potential effects of sound on aquatic life. While mobile species can move away from sound sources, slow moving or sessile organisms are unable to escape. Many species of elasmobranchs are oviparous and deposit egg cases that remain in a fixed position on or near the seabed with development times ranging from months to over a year. The auditory sensitivity of elasmobranchs has been relatively understudied compared to marine mammals and teleost fish, with little known about the effect of sound on adults and almost nothing reported on how sound may impact developing embryos. Therefore, the effect of sound on the behavior of late stage embryonic little skates (Leucoraja erinacea) and chain dogfish (Scyliorhinus rotifer) in their egg case, was monitored. Both species reacted to sound prior to hatching. Little skates interrupted tail movements in response to 300 and 400 Hz pure tones as well as playbacks of boat sound, while sharks ceased respiratory movements during boat sound playbacks. Thus, late-stage embryos can detect and are affected by sound and fisheries managers may need to account for the impact of anthropogenic sound near oviparous elasmobranch breeding grounds.

In birds, the sound generated in the syrinx is modified by upper vocal tract filter properties prior to being emitted. Filtering of upper harmonics, for example, allows birds to produce tonal sounds. The main dynamic filter component is the oropharyngeal-esophageal cavity (OEC), whose volume can be adjusted to track the fundamental frequency of modulated sounds. It is less well understood, how birds, which use harmonically rich sounds, such as the zebra finch (Taeniopygia guttata), engage upper vocal tract structures to produce the complex spectral composition of their vocalizations. Furthermore, it is not known whether birds use instantaneous auditory feedback to adjust filter properties of the upper vocal tract structures. To fill these gaps, we developed a sensor system for tracking expansion of the OEC and recorded these movements together with subsyringeal air sac pressure and vocal behavior in intact zebra finches and after denervation of the right syringeal muscles. To go beyond correlations between OEC expansion and acoustic features, we prevented OEC expansion. The results illustrate the stereotyped dynamics of OEC expansion and confirm that relationships between OEC volume and acoustic features are complex. Significant shifts in sound frequency after denervation did not induce changes in the stereotyped OEC expansion patterns. Preventing OEC expansion caused predicted and unpredicted changes in the spectral composition of song syllables. Together these results illustrate that the complex spectral composition of zebra finch song syllables arises from dynamic adjustments of OEC volume, but resonance features are determined by an interaction of all upper vocal tract structures.

Mitochondria generate up to 90% of cellular ATP, making it critical to understand how abiotic factors affect mitochondrial function under varying conditions. Using clones of the rotifer Lecane inermis with known thermal preferences, we investigated mitochondrial bioenergetic responses to four thermal regimes: standard temperature, optimal temperature, low suboptimal temperature, and high suboptimal temperature. The study aimed to determine how mitochondrial parameters in intact organisms vary with temperature shifts and whether these responses differ across experimental populations. We assessed key bioenergetic parameters: routine respiration (representing overall metabolic rate), electron transport system (ETS) capacity (indicative of oxidative phosphorylation potential), and proton leak rates (reflecting the energetic costs of maintaining mitochondrial membrane potential). Our results showed that populations with different thermal preferences displayed distinct mitochondrial responses to temperature changes, particularly at suboptimal temperatures. In contrast, responses were more uniform under standard and optimal conditions. Our findings demonstrated that metabolic plasticity in changing environments often involves trade-offs between mitochondrial efficiency and maintenance. By studying mitochondrial respiration at the whole-organism level, we revealed the complex temperature dependence of bioenergetic traits, providing insights beyond isolated mitochondria studies. This research highlights how a cascade of plastic responses spanning from mitochondrial responses to overall growth patterns is triggered by temperature changes, offering a valuable perspective in the context of global warming and organismal adaptation.

1. Energy can be limiting, especially for small animals with high metabolisms, particularly if they rely on ephemeral resources. Some energy-saving strategies, such as torpor, can impair physiological processes. Alternatively, group living can reduce energetic costs through social thermoregulation. This may allow individuals to maintain a high metabolism as well as processes such as gamete production. Although group living is common, its energetic benefits for heterothermic individuals during the season of sperm production have yet to be investigated. 2. We remotely quantified the daily energy expenditures of individual parti-coloured bats (Vespertilio murinus) kept solitarily and in groups during the period of spermatogenesis, using high-resolution heart rate monitoring. 3. Data showed that the energetic benefits of group living are complex. In groups, individual daily energy expenditures were more than 50% lower. Group roosting reduced the cost of thermoregulation during normothermia and allowed for a decrease in the depth, but not the duration, of torpor. 4. Group living may enable bats to buffer unfavorable environmental conditions. Energy saved this way can then be invested into fitness-relevant processes potentially making this a driver of the evolution of male sociality.

Sea stars control hundreds of tube feet to navigate their environment with a rudimentary nervous system. Tube feet are capable of responding to stimuli without descending nervous commands and it is therefore unclear to what extent tactic orientation emerges through the collective action of the tube feet or is guided by central control. We therefore performed behavioral experiments to test models of neuromechanical control in a sea star (Protoreaster nodosus). We found that animals moved rapidly along relatively straight trajectories when exposed to light, but slowly crawled along circuitous paths in random directions in the dark. To remove mechanical interactions with the substrate, we measured the kinematics of tube feet in inverted sea stars that exhibited crawling when in contact with the water's surface. The tube feet throughout the body of these animals moved with power strokes in a similar direction when the animals were exposed to light, which is consistent with central control. This contrasts the variety of directions for power strokes exhibited without illumination. These findings support of a model of navigational control where directionless body motion emerges from collective mechanics in the dark, but is guided by the nervous system when exposed to light. In this manner, sea stars navigate through a combination of collective and central control.