Maternal food restriction during pregnancy affects offspring development and swimming performance in a placental live-bearing fish

How pregnant mothers allocate limited resources to different biological functions such as maintenance, somatic growth, and reproduction can have profound implications for early life development and survival of offspring. Here we examined the effects of maternal food restriction during pregnancy on offspring in the matrotrophic (i.e. mother-nourishment throughout gestation) live-bearing fish species Phalloptychus januarius (Poeciliidae). We fed pregnant females either with a ‘low-food’ or ‘high-food’ ration for six weeks and quantified the consequences for offspring size and body fat at birth and one week after birth. We further measured fast-start escape performance of offspring at birth, as well as swimming kinematics during prey capture at zero, two, and seven days after birth. We found that the length of maternal food restriction during pregnancy negatively affected offspring dry mass and lean dry mass at birth, as well as body fat gain during the first week after birth. Moreover, it impacted the locomotor performance of offspring during prey capture at, and during the first week after, birth. We did not observe an effect of food restriction on fast-start escape performance of offspring. Our study suggests that matrotrophic poeciliid fish are maladapted to unpredictably fluctuating resource environments, because sudden reductions in maternal food availability during pregnancy result in smaller offspring with slower postnatal body fat gain and an inhibition of postnatal improving swimming skills during feeding, potentially leading to lower competitive abilities after birth.

Stress hormone-mediated antipredator morphology improves escape performance in amphibian tadpoles

Complete functional descriptions of the induction sequences of phenotypically plastic traits (perception to physiological regulation to response to outcome) should help us to clarify how plastic responses develop and operate. Ranid tadpoles express several plastic antipredator traits mediated by the stress hormone corticosterone, but how they influence outcomes remains uncertain. We investigated how predator-induced changes in the tail morphology of wood frog (Rana sylvatica) tadpoles influenced their escape performance over a sequence of time points when attacked by larval dragonflies (Anax junius). Tadpoles were raised with no predator exposure, chemical cues of dragonflies added once per day, or constant exposure to caged dragonflies crossed with no exogenous hormone added (vehicle control only), exogenous corticosterone, or metyrapone (a corticosteroid synthesis inhibitor). During predation trials, we detected no differences after four days, but after eight days, tadpoles exposed to larval dragonflies and exogenous corticosterone had developed deeper tail muscles and exhibited improved escape performance compared to controls. Treatment with metyrapone blocked the development of a deeper tail muscle and resulted in no difference in escape success. Our findings further link the predator-induced physiological stress response of ranid tadpoles to the development of an antipredator tail morphology that confers performance benefits.

Solving post-prandial reduction in performance by adaptive regurgitation in a freshwater fish

Foraging animals must balance benefits of food acquisition with costs induced by a post-prandial reduction in performance. Eating to satiation can lead to a reduction in locomotor and escape performance, which increases risk should a threat subsequently arises, but limiting feeding behaviour may be maladaptive if food intake is unnecessarily reduced in the prediction of threats that do not arise. The efficacy of the trade-off between continued and interrupted feeding therefore relies on information about the future risk, which is imperfect. Here, we find that black carp ( Mylopharyngodon piceus ) can balance this trade-off using an a posteriori strategy; by eating to satiation but regurgitating already ingested food when a threat arises. While degrees of satiation (DS) equal to or greater than 60% reduce elements of escape performance (turning angle, angular velocity, distance moved, linear velocity), at 40% DS or lower, performance in these tasks approaches levels comparable to that at 0% satiation. After experiencing a chasing event, we find that fish are able to regurgitate already ingested food, thereby changing the amount of food in their gastrointestinal tract to consistent levels that maintain high escape performance. Remarkably, regurgitation results in degrees of satiation between 40 and 60% DS, regardless of whether they had previously fed to 40, 60 or 100% DS. Using this response, fish are able to maximize food intake, but regurgitate extra food to maintain escape performance when they encounter a threat. This novel strategy may be effective for continual grazers and species with imperfect information about the level of threat in their environment.

The Physiological Experimental Study on the Effect of Different Color of Safety Signs on a Virtual Subway Fire Escape—An Exploratory Case Study of Zijing Mountain Subway Station

Safety signs play a very important role in people’s evacuation during emergencies. In order to explore the appropriate color for subway safety signs, four safety signs of different color combinations are designed, and the virtual reality, eye-tracking technology, and physiological indicator measurement are used in a virtual subway fire escape experiment. A total of 96 participants with equal distribution in gender and four different color combination groups were recruited. Participants’ eye-tracking and physiological data (heart rate, skin conductance) were real-time recorded through ErgoLAB V3.0 in the whole experiment. The relationship between Color_of_safety_sign and escape performance, eye-tracking indicators, and physiological indicators is discussed respectively through SPSS. The results show that “Green and black” group has the best evacuation escape performance, low cognitive load, high search efficiency on safety signs, and the highest stress level and immersion and “Green and black” can be the most appropriate color for safety sign. This research is of certain significance for improving the function of subway fire-fighting infrastructure and the resilience of the metro system. Moreover, it can provide references and advice on risk management, emergency evacuation, and so on.

Unpredictable hummingbirds: Flight path entropy is constrained by speed and wing loading

ABSTRACTUnpredictable movement can provide an advantage when animals avoid predators and other threats. Previous studies have examined how varying environments can elicit unpredictable movement, but the intrinsic causes of complex, unpredictable behavior are not yet known. We addressed this question by analyzing >200 hours of flight performed by hummingbirds, a group of aerial specialists noted for their extreme agility and escape performance. We used information theory to calculate unpredictability based on the positional entropy of short flight sequences during 30-min and 2-hour trials. We show that a bird’s entropy is repeatable, with stable differences among individuals that are negatively correlated with wing loading: birds with lower wing loading are less predictable. Unpredictability is also positively correlated with a bird’s overall acceleration and rotational performance, and yet we find that moment-to-moment changes in acceleration and rotational velocities do not directly influence entropy. This indicates that biomechanical performance must share an underlying basis with a bird’s ability to combine maneuvers into unpredictable sequences. Contrary to expectations, hummingbirds achieve their highest entropy at relatively slow speeds, pointing to a fundamental trade-off whereby individuals must choose to be either fast or unpredictable.

Parasite infection directly impacts escape response and stress levels in fish

ABSTRACTParasites can account for a substantial proportion of the biomass in marine communities. As such, parasites play a significant ecological role in ecosystem functioning via host interactions. Unlike macropredators, such as large piscivores, micropredators, such as parasites, rarely cause direct mortality. Rather, micropredators impose an energetic tax, thus significantly affecting host physiology and behaviour via sublethal effects. Recent research suggests that infection by gnathiid isopods (Crustacea) causes significant physiological stress and increased mortality rates. However, it is unclear whether infection causes changes in the behaviours that underpin escape responses or changes in routine activity levels. Moreover, it is poorly understood whether the cost of gnathiid infection manifests as an increase in cortisol. To investigate this, we examined the effect of experimental gnathiid infection on the swimming and escape performance of a newly settled coral reef fish and whether infection led to increased cortisol levels. We found that micropredation by a single gnathiid caused fast-start escape performance and swimming behaviour to significantly decrease and cortisol levels to double. Fast-start escape performance is an important predictor of recruit survival in the wild. As such, altered fitness-related traits and short-term stress, perhaps especially during early life stages, may result in large scale changes in the number of fish that successfully recruit to adult populations.

Mitigating memory effects during undulatory locomotion on hysteretic materials

While terrestrial locomotors often contend with permanently deformable substrates like sand, soil, and mud, principles of motion on such materials are lacking. We study the desert-specialist shovel-nosed snake traversing a model sand and find body inertia is negligible despite rapid transit and speed dependent granular reaction forces. New surface resistive force theory (RFT) calculation reveals how wave shape in these snakes minimizes material memory effects and optimizes escape performance given physiological power limitations. RFT explains the morphology and waveform-dependent performance of a diversity of non-sand-specialist snakes but overestimates the capability of those snakes which suffer high lateral slipping of the body. Robophysical experiments recapitulate aspects of these failure-prone snakes and elucidate how re-encountering previously deformed material hinders performance. This study reveals how memory effects stymied the locomotion of a diversity of snakes in our previous studies (Marvi et al., 2014) and indicates avenues to improve all-terrain robots.

Modeling escape success in terrestrial predator–prey interactions

Synopsis Prey species often modify their foraging and reproductive behaviors to avoid encounters with predators; yet once they are detected, survival depends on out-running, out-maneuvering, or fighting off the predator. Though predation attempts involve at least two individuals—namely, a predator and its prey—studies of escape performance typically measure a single trait (e.g., sprint speed) in the prey species only. Here, we develop a theoretical model in which the likelihood of escape is determined by the prey animal’s tactics (i.e., path trajectory) and its acceleration, top speed, agility, and deceleration relative to the performance capabilities of a predator. The model shows that acceleration, top speed, and agility are all important determinants of escape performance, and because speed and agility are biomechanically related to size, smaller prey with higher agility should force larger predators to run along curved paths that do not allow them to use their superior speeds. Our simulations provide clear predictions for the path and speed a prey animal should choose when escaping from predators of different sizes (thus, biomechanical constraints) and could be used to explore the dynamics between predators and prey.