Journal of Experimental Biology最新文献

Developing animals are increasingly exposed to elevated temperatures as global temperatures rise as a result of climate change. Vertebrates can be affected by elevated temperatures during development directly, and indirectly through maternal effects (e.g. exposure to prenatal glucocorticoid hormones). Past studies have examined how elevated temperatures and glucocorticoid exposure during development independently affect vertebrates. However, exposure to elevated temperatures and prenatal corticosterone could have interactive effects on developing animals that affect physiology and life-history traits across life. We tested interactions between incubation temperature and prenatal corticosterone exposure in the delicate skink (Lampropholis delicata). We treated eggs with high or low doses of corticosterone and incubated eggs at 23°C (cool) or 28°C (warm). We measured the effects of these treatments on development time, body size and survival from hatching to adulthood and on adult hormone levels and mitochondrial respiration. We found no evidence for interactive effects of incubation temperature and prenatal corticosterone exposure on phenotype. However, incubation temperature and corticosterone treatment each independently decreased body size at hatching and these effects were sustained into the juvenile period and adulthood. Lizards exposed to low doses of corticosterone during development had elevated levels of baseline corticosterone as adults. Additionally, lizards incubated at cool temperatures had higher levels of baseline corticosterone and more efficient mitochondria as adults compared with lizards incubated at warm temperatures. Our results show that developmental conditions can have sustained effects on morphological and physiological traits in oviparous lizards but suggest that incubation temperature and prenatal corticosterone do not have interactive effects.

Viviparous snakes may be particularly vulnerable to predicted increases in drought due to the high hydric costs associated with embryonic development, gestation, and their reliance on limited free-standing bodies of water or rain events for hydration. Drought will have negative implications for viper populations if females become increasingly water-stressed and resorb developing embryos to conserve bodily water. We conducted a study to investigate the importance of drinking water in late-term pregnancy and its effect on cutaneous evaporative water loss (CEWL). We measured hydration and water loss in response to supplemental hydration during the final stages of embryonic development and gestation in arid-adapted Prairie Rattlesnakes (Crotalus viridis). Our goal was to assess how supplemental water affects hydration status and water loss (via CEWL) of females during and after pregnancy, and of their neonates before and after their first ecdysis. Supplemental hydration of pregnant C. viridis improved their hydration state and their neonates were also born more hydrated than those from control mothers, showing that they transfer water to neonates via the placenta even over a very short period in the late stages of pregnancy. The supplementally hydrated maternal C. viridis experienced slightly higher rates of CEWL compared to control snakes, but CEWL was primarily driven by ambient temperature and vapor pressure deficit at the time of measurement. At birth, neonate plasma osmolality and CEWL were both directly associated with their mothers' plasma osmolality and CEWL. Additionally, we found that neonate CEWL increased after the first ecdysis, suggesting that natal skin may help neonates avoid desiccation. Investigating and quantifying physiological implications of water shortage and dehydration can help us better understand the effects of drought and predict how wild populations of arid-adapted reptiles may respond to the predicted increase in frequency and severity of droughts.

Gait adaptation during bipedal walking allows people to adjust their walking patterns to maintain balance, avoid obstacles and avoid injury. Adaptation involves complex processes that function to maintain stability and reduce energy expenditure. However, the processes that influence walking patterns during different points in the adaptation period remain to be investigated. We assessed split-belt adaptation in 17 young adults aged 19-35. We also assessed individual aerobic capacity to understand how aerobic capacity influences adaptation. We analyzed step lengths, step length asymmetry (SLA), mediolateral margins of stability, positive, negative and net mechanical work rates, as well as metabolic rate during adaptation. Dual-rate exponential mixed-effects regressions estimated the adaptation of each measure over two timescales; results indicate that mediolateral stability adapts over a single timescale in under 1 min, whereas mechanical work rates, metabolic rate, step lengths and SLA adapt over two distinct timescales (3.5-11.2 min). We then regressed mediolateral margins of stability, net mechanical work rate and metabolic rate on SLA during early and late adaptation phases to determine whether stability drives early adaptation and energetic cost drives late adaptation. Stability predicted SLA during the initial rapid onset of adaptation, and mechanical work rate predicted SLA during the latter part of adaptation. Findings suggest that stability optimization may contribute to early gait changes and that mechanical work contributes to later changes during adaptation. A final sub-analysis showed that aerobic capacity levels <36 and >43 ml kg-1 min-1 resulted in greater SLA adaptation, underscoring the metabolic influences on gait adaptation. This study illuminates the complex interplay between biomechanical and metabolic factors in gait adaptation, shedding light on fundamental mechanisms underlying human locomotion.

Desiccation is a fundamental challenge confronted by all terrestrial organisms, particularly insects. With a relatively small body size and large surface-to-volume ratio, insects are susceptible to rapid evaporative water loss and dehydration. To counter these physical constraints, insects have acquired specialized adaptations, including a hydrophobic cuticle that acts as a physical barrier to transpiration. We previously reported that genetic ablation of the oenocytes - specialized cells required to produce cuticular hydrocarbons (HCs) - significantly reduced survivorship under desiccative conditions in the fruit fly, Drosophila melanogaster. Although increased transpiration - resulting from the loss of the oenocytes and HCs - was hypothesized to be responsible for the decrease in desiccation survival, this possibility was not directly tested. Here, we investigated the underlying physiological mechanisms contributing to the reduced survival of oenocyte-less (oe-) flies. Using flow-through respirometry, we show that oe- flies, regardless of sex, exhibited an increased rate of transpiration relative to wild-type controls, and that coating oe- flies with fly-derived HC extract restored the rate to near-wild-type levels. Importantly, total body water stores, including metabolic water reserves, as well as dehydration tolerance, measured as the percentage of total body water lost at the time of death, were largely unchanged in oe- flies. Together, our results directly demonstrate the critically important role played by the oenocytes and cuticular HCs to promote desiccation resistance.

Skeletal muscles change shape when they contract. Current insights into the effects of shape change on muscle function have primarily come from experiments on isolated muscles operating at maximal activation levels. However, when muscles contract and change shape, the forces they apply onto surrounding muscles will also change. The impact of an altered contractile environment (i.e. mechanical behaviour of surrounding muscle) on muscle shape change remains unknown. To address this, we altered the mechanical contributions of the human gastrocnemii during isometric plantarflexion contractions [via changing knee angle] and determined if there were associated changes in how the muscles of the triceps surae bulged in thickness during a ramped contraction. We combined B-mode ultrasound imaging with surface electromyography to quantify the neuromechanical contributions of the medial gastrocnemius (MG), lateral gastrocnemius (MG) and soleus (SOL) muscles during isometric plantarflexion contractions. Our results demonstrate that at the same SOL activity levels, altering knee angle had no influence on the magnitude of muscle shape change (thickness) in the triceps surae muscles. We observed high levels of inter-individual variability in muscle bulging patterns, particularly in the knee flexed position, suggesting a complex relationship between muscle bulging and activation strategies in the triceps surae, which may be related to differences in muscle mechanical properties between participants or across muscles. Our findings highlight the dynamics of in vivo bulging interactions among muscles within the triceps surae and provide insights for future investigations into the impact of altered contractile environments on three-dimensional muscle deformations and force production.

Fish in the wild often contend with complex flows that are produced by natural and artificial structures. Research into fish interactions with turbulence often investigates metrics such as turbulent kinetic energy (TKE) or fish positional location, with less focus on the specific interactions between vortex organization and body swimming kinematics. Here, we compared the swimming kinematics of rainbow trout (Oncorhynchus mykiss) holding station in flows produced by two different 3×5 cylinder arrays. We systematically utilized computational fluid dynamics to identify one array that produced a Kármán vortex street with high vortex periodicity (KVS array) and another that produced low periodicity, similar to a parallel vortex street (PVS array), both validated with particle image velocimetry. The only difference in swimming kinematics between cylinder arrays was an increased tail beat amplitude in the KVS array. In both cylinder arrays, the tail beat frequency decreased and snout amplitude increased compared with the freestream. The center of mass amplitude was greater in the PVS array than in only the freestream, however, suggesting some buffeting of the body by the fluid. Notably, we did not observe Kármán gaiting in the KVS array as in previous studies. We hypothesize that this is because (1) vorticity was dissipated in the region where fish held station or (2) vortices were in-line rather than staggered. These results are the first to quantify the kinematics and behavior of fishes swimming in the wake of multiple cylinder arrays, which has important implications for biomechanics, fluid dynamics and fisheries management.

Leptin is a hormone that is secreted by adipocytes and may promote energy expenditure by increasing thermogenesis. Our previous studies have shown that thermo-transient receptor potentials (thermo-TRPs) and gut microbiota are associated with thermoregulation in Mongolian gerbils, which are characterized by relative high serum leptin concentrations. Here, we tested whether leptin can stimulate non-shivering thermogenesis (NST) in Mongolian gerbils, and whether thermo-TRPs and gut microbiota are involved in leptin-induced thermogenesis. First, gerbils were given acute leptin treatment (ALT) with different doses. Results showed that ALT significantly increased the body temperature of gerbils and changed the composition of gut microbiota. Moreover, ALT groups showed a trend towards increased expression of uncoupling protein 1 (UCP1) in brown adipose tissue (BAT). Then, we investigated the effect of chronic leptin treatment (CLT) on gerbils. Surprisingly, CLT did not affect gerbils' food intake and body mass, but it significantly increased the body temperature at the end. Further, CLT did not affect the expression of thermogenic markers in BAT, white adipose tissue (WAT) or skeletal muscle. However, CLT increased the expression of leptin receptors and TRPV2 in the small intestine and affected the composition of gut microbiota. Together, our data suggest leptin may increase body temperature by regulating gut microbiota. In conclusion, serum hyperleptin in Mongolian gerbils is beneficial for adapting to cold environments, and TRPV2 and gut microbiota are involved.

Oxygen availability is central to the energetic budget of aquatic animals and may vary naturally and/or in response to anthropogenic activities. Yet, we know little about how oxygen availability is linked to fundamental processes such as ion transport in aquatic insects. We hypothesized and observed that ion (22Na and 35SO4) uptake would be significantly decreased at O2 partial pressures below the mean critical level (Pcrit, 5.4 kPa) where metabolic rate (ṀO2) is compromised and ATP production is limited. However, we were surprised to observe marked reductions in ion uptake at oxygen partial pressures well above Pcrit, where ṀO2 was stable. For example, SO4 uptake decreased by 51% at 11.7 kPa and 82% at Pcrit (5.4 kPa) while Na uptake decreased by 19% at 11.7 kPa and 60% at Pcrit. Nymphs held for longer time periods at reduced PO2 exhibited stronger reductions in ion uptake rates. Fluids from whole-body homogenates exhibited a 29% decrease in osmolality in the most hypoxic condition. The differential expression of atypical guanylate cyclase (gcy-88e) in response to changing PO2 conditions provides evidence for its potential role as an oxygen sensor. Several ion transport genes (e.g. chloride channel and sodium-potassium ATPase) and hypoxia-associated genes (e.g. ldh and egl-9) were also impacted by decreased oxygen availability. Together, the results of our work suggest that N. triangulifer can sense decreased oxygen availability and perhaps conserves energy accordingly, even when ṀO2 is not impacted.

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.