Journal of Experimental Biology最新文献

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.

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) using a shuttle box, agitation temperature (22.0±1.4°C) as the point where a fish exhibits a behavioural avoidance response and the CTmax (28.2±0.4°C) as the upper thermal limit for 1 yr 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 embryonic environment is critical for the development of many ectothermic vertebrates, which makes them highly vulnerable to environmental change. Changes in temperature and moisture, in particular, are known to influence embryo survival and offspring phenotypes. While most papers concerning phenotypic development of terrestrial ectotherms focus on the role of temperature on eggs and embryos, the comparatively small number of studies on the effects of substrate moisture are well suited for quantitative analysis aimed at guiding future research. To accomplish this goal, we compiled data from 37 studies on 28 different reptile species and used a meta-analytic approach to quantify the effect of substrate moisture on several offspring outcomes: hatching success (survival), incubation duration, hatchling mass and length, and sex ratio. We found that substrate moisture had a small effect across most traits but significantly affected body size (i.e., length and mass), with wetter conditions producing longer and heavier hatchlings. Temperature also moderated the effect of moisture on hatching success; with higher temperatures resulting in lower success. Additionally, the effect of moisture on hatching success and hatchling mass was enhanced by larger differences in moisture concentration between treatments, yet the effect was small. Lastly, substrate moisture affected sex ratio in turtles, but not in other squamates. Overall, these analyses provide a foundation for further research investigating the effects of moisture on oviparous reptile development. Increasing the diversity of environmental variables for which we understand their impact on animal phenotype will be beneficial in an era with wide-ranging global change.

Artificial light at night (ALAN) has emerged as a significant ecological disruptor, affecting various behavioral and physiological processes in numerous species. This study investigated the impact of ALAN on the risk-related behaviors and activity patterns of the ground-dwelling isopod, Porcellionides pruinosus. Isopods were exposed to three different illuminance conditions (<0.01 lx, 1 lx, and 10 lx) over a period of 14 consecutive nights. Behavioral assays included emergence, open-field, habituation to a looming stimulus, and spatial navigation tests. Additionally, the distribution and activity patterns of the isopods within the terraria were monitored. Our results indicate that ALAN significantly disrupted the repeatability of risk-related behaviors, suggesting individual-level behavioral alterations. At the group level, ALAN-exposed isopods exhibited prolonged freezing durations in response to a looming stimulus, increased shelter-seeking behavior and reduced dispersal in the terrarium. These findings suggest that ALAN-induced transformation of activity pattern of isopods is linked to the adoption of more prudent behaviors. A similar phenomenon may affect the activity pattern of other ground-dwelling invertebrates, leading to severe alterations of the soil invertebrate community.

The timing of metamorphosis and settlement is critical for the survival and reproductive success of marine animals with biphasic life cycles. Thyroid hormones (THs) regulate developmental timing in diverse groups of chordates, including the regulation of metamorphosis in amphibians, teleosts, lancelets, tunicates, and lampreys. Recent evidence suggests a role for TH regulation of metamorphosis outside of the chordates, including echinoderms, annelids, and molluscs. Among echinoderms, TH effects on development as well as underlying signaling mechanisms in early embryogenesis have been documented for echinoid (sea urchin) larvae, but we lack information on TH effects on metamorphic development in most other echinoderm groups, including the ophiuroids (brittle stars). Unexpectedly, we found that THs, principally 3,5,3',5'-Tetraiodo-L-thyronine (T4), reversibly inhibit metamorphic development and settlement in the brittle star (Ophiopholis aculeata; daisy brittle star). Exposure to thiourea, an inhibitor of TH synthesis, accelerated metamorphic development. We showed that these effects were highly stage specific, providing evidence for a developmental point-of-no-return in ophiuroid metamorphic development. Furthermore, starvation of O. aculeata accelerates juvenile morphogenesis and settlement. Starvation also prevents the inhibitory effect of thiourea on TH function, suggesting that TH synthesis may play a role in delaying metamorphosis under conditions of high food availability. These findings provide evidence for a function of TH signaling in ophiuroid metamorphic development and suggest that exogenous thyroid hormone sources may be involved in the regulation of metamorphic timing in O. aculeata. Together with new evidence of TH involvement in metamorphic development in a range of invertebrates, these findings further emphasize the versatile and central role of endocrine signaling in metamorphosis.

Aedes aegypti mosquitoes are the principal vectors of dengue and continue to pose a threat to human health, with ongoing urbanization, climate change, and trade all impacting the distribution and abundance of this species. Hot periods are becoming increasingly common and their impacts on insect mortality have been well established, but they may have even greater impacts on insect fertility. In this study, we investigated the impacts of high temperatures on Ae. aegypti fertility both within and across generations. Mosquitoes developing under elevated temperatures exhibited higher critical thermal maxima (CTmax) reflecting developmental acclimation, but their fertility declined with increasing developmental temperature. In females, elevated developmental temperatures decreased fecundity while in males it tended to decrease egg hatch proportions and the proportion of individuals producing viable offspring. Rearing both sexes at 35°C increased fecundity in the subsequent generation but effects of elevated temperatures persisted across gonotrophic cycles within the same generation. Moreover, exposure of adults to 35°C further decreased fertility beyond the effects of developmental temperature alone. These findings highlight sub-lethal impacts of elevated temperatures on Ae. aegypti fertility and plastic responses to thermal stress within and across generations. This has significant implications for predicting the distribution and abundance of mosquito populations thriving in increasingly warmer environments.

Eggshell recognition in parental birds is vital for nest management, defense against brood parasitism, optimal embryonic development, and minimizing disease and predation risks. This process relies on acceptance thresholds balancing the risk of rejecting own eggs against the benefit of excluding foreign ones, following signal detection theory. We investigated the role of object shape in egg rejection decisions among three host species of the brown-headed cowbird (Molothrus ater), each with a varying known response to parasitic eggs. Following previous studies on the American robin (Turdus migratorius; a robust cowbird-egg rejecter), we presented Eastern bluebirds (Sialia sialis; moderate rejecter) and red-winged blackbirds (Agelaius phoeniceus; an accepter) with 3D-printed blue model eggs varying in width or angularity. To examine the shape-color interaction, we presented Eastern bluebirds with these series in two colors and maculation: light blue (bluebird-mimetic) and white with speckles (more cowbird-like). Both species were less likely to accept blue models as their width decreased. For the blue angularity series, acceptance decreased significantly with increased angularity for the red-winged blackbird, as has been previously seen in the American robin , but not for the Eastern bluebird. For bluebirds with the white-maculated models, these patterns remained but statistical significance reversed: acceptance did not decrease significantly with width, but did decrease significantly with angularity. These results suggest that egg shape variation influences antiparasitic egg rejection behaviors is modulated by shell color and maculation patterns, and varies among different host species, highlighting the complexity of behavioral defense cues against brood parasitism.

Phenotypic plasticity can represent a vital adaptive response to environmental stressors, including those associated with climate change. Despite its evolutionary advantages, the expression of plasticity varies significantly within and among species, and is likely to be influenced by local environmental conditions. This variability in plasticity has important implications for evolutionary biology and conservation physiology. Theoretical models suggest that plasticity might incur intrinsic fitness costs, although the empirical evidence is inconsistent and there is ambiguity in the term 'cost of plasticity'. Here, we systematically review the literature to investigate the prevalence of costs associated with phenotypic plasticity in ectothermic animals. We categorized studies into those assessing 'costs of phenotype' (trade-offs between different plastic trait values) and 'costs of plasticity' (intrinsic costs of the capacity for plasticity). Importantly, the experimental designs required to detect costs of plasticity are inherently more complex and onerous than those required to detect costs of phenotype. Accordingly, our findings reveal a significant focus on costs of phenotype over costs of plasticity, with the former more frequently detecting costs. Contrary to theoretical expectations, our analysis suggests that costs of plasticity are neither universal nor widespread. This raises questions about the evolutionary dynamics of plasticity, particularly in stable environments. Our analysis underscores the need for precise terminology and methodology in researching costs of plasticity, to avoid conflating costs associated with plastic traits with costs more intrinsic to plasticity. Understanding these nuances is crucial for predicting how species might adapt to rapidly changing environments.

Aerodynamic models of bird flight, assuming power minimization, predict a quadratic relationship (i.e. U-shaped curve) between flapping frequency and airspeed. This relationship is supported by experimental bird flight data from wind tunnels, but the degree to which it characterizes natural flight, and the extent to which birds might modify it to accommodate other behaviors, is less known. We hypothesized that the U-shaped relationship would vary or vanish when minimizing power is not a primary consideration. We analyzed videos of wild cliff swallows (Petrochelidon pyrrhonota) engaged in solo and tandem (i.e. following or being followed by a conspecific) flights to collect bird flapping frequencies and airspeeds. Solo birds had a U-shaped flapping frequency to speed relationship. Birds engaged in tandem flights had the opposite pattern; their flapping frequencies varied with speed as an inverse U-shaped curve and were up to 2.1 times higher than solo birds at the same speed.

Human proficiency for bipedal locomotion relies on the structure and function of our feet, including the interplay between active muscles and passive structures acting on the toes during the propulsive phase of gait. However, our understanding of the relative contributions of these different structures remains incomplete. We aimed to determine the distinct toe-flexion torque-angle relationships of the plantar intrinsic muscles (PIMs), extrinsic muscles and passive structures, therefore offering insight into their force-generating capabilities and importance for walking and running. Torque-angle data were twice collected from nine healthy individuals (6 males, 3 females; 28±5 years) using supramaximal transcutaneous electrical stimuli applied at two tibial nerve sites to distinguish between muscle-driven and passive toe-flexion torque about the metatarsophalangeal (MTP) joint. Innervating extrinsic muscles and PIMs concurrently produced peak torques (hallux=3.05±0.70 N m, MTP angle=48.0±13.6 deg; lesser digits=3.19±0.98 N m, MTP angle=42.6±13.4 deg) exceeding by 208% (hallux) and 150% (lesser digits), respectively, those from PIM stimulation alone. Notably, MTP joint angles pertinent to gait corresponded to the ascending limb of the active torque-angle relationship, with active muscle joint torques being the dominant contributor over passive torques. The latter finding suggests that human toe flexors are well adapted to generate the MTP joint torques that are necessary for walking and running. This further supports the notion that muscles acting within the foot play an important role in the foot's mechanical function and our ability to walk and run in an upright posture.