First or best? Contrasting approaches reveal different outcomes in tadpole (Hypsiboas lundii) escape performance under acute chlorpyrifos exposure.

Parts cleaner: Better Engineering Mfg. Inc. Baltimore

The escape response of food-deprived cod larvae ( Gadus morhua L.)

Summary 1. The life stage suffering the highest predation rate is expected to have the highest escape performance unless developmental or functional constraints interfere. Peak aquatic escape performance in ephemeral pond‐breeding amphibians is expected to develop early in the larval period, and metamorphosis is expected to reduce or completely disrupt aquatic escape performance. In anurans, exceptionally low escape performance during metamorphosis creates selection favouring rapid metamorphosis – which minimizes the time individuals spend in the vulnerable transition between tadpole and frog. 2. We investigated the development of aquatic escape performance in the spotted salamander, Ambystoma maculatum (Shaw, 1802), from embryonic development through metamorphosis. We expected performance to peak early in the larval period as hatchlings face high rates of predation but embryos must first develop escape behaviours. We also tested whether escape performance during metamorphosis was intermediate, as predicted by tail fin resorption, or lower than larvae and adults indicating a major physiological disruption. 3. Escape performance shows a complex ontogeny that is first positively influenced by embryonic and early larval development and then negatively correlated with tail resorption and body size. Escape distance was the only performance metric not affected by life stage. In contrast, both escape velocity and duration showed ontogenetic peaks early in the larval period with the lowest performance found in early embryos and adults and intermediate performance during metamorphosis. 4. This pattern suggests that metamorphosis does not impose a major physiological disruption on escape performance. Because spotted salamanders do not pass through a frog‐like ‘ontogenetic performance valley’ during metamorphosis, they may be less subject than anurans to selection favouring rapid metamorphosis. 5. Functional implications of phenotypic variation should be considered in an ontogenetic framework because the relationship between body size and escape performance can be reversed on either side of an ontogenetic performance peak. The assumption that metamorphosis radically disrupts basic functions such as predator evasion does not seem universally warranted and suggests examination of ontogenetic performance trajectories in a diversity of animals with complex life cycles.

The prevailing shark nursery paradigm suggests that high survival in these habitats is primarily driven by reduced predator encounters: so-called pre-encounter risk. In this study, we propose an alternative or complementary mechanism: that some nurseries may lower post-encounter risk by providing environmental conditions that maximize escape performance. To test this hypothesis, we examined how temperature, depth and habitat complexity influence the escape performance of newborn blacktip reef sharks (Carcharhinus melanopterus) in Mo′orea, French Polynesia. In a controlled setting, we exposed 48 newborn sharks to four temperature treatments (25, 27, 29 and 31°C) and measured fast-start acceleration, turning rate and latency to respond to a stimulus. We also calculated aerobic scope at 27, 29 and 31°C, as greater aerobic scope is associated with faster recovery from burst swimming. Our results show that warmer temperatures improve escape performance, with 29% higher acceleration, 9% faster turning rates and 48% shorter reaction times at elevated temperatures. Furthermore, aerobic scope remained ≥80% of its maximum capacity between 27.5 and 30.8°C, suggesting that newborn sharks can sustain high metabolic performance within this thermal window. Field measurements at nursery habitats revealed that daily thermal fluctuations generally remained within this optimal aerobic scope range, meaning that newborns can maintain high escape performance for most of the day. Additionally, high-resolution mapping confirmed that previously reported home ranges were associated with shallow (median depth = 0.74 m), structurally complex reef flats dominated by coral substrate. The combination of reduced hydrodynamic drag in shallow water and increased manoeuvrability in complex habitats likely enhances predator evasion. However, extreme warming events that exceed critical thermal limits may trigger behavioural trade-offs that compromise escape performance and elevate predation risk. Our findings suggest that these nurseries provide habitat-specific advantages for predator evasion, reinforcing their critical role in the survival of newborn sharks.

Escape theory predicts that a prey should start escaping (flight initiation distance = FID) from a predator when the costs of fleeing and the cost staying are equal or until future fitness is maximized. Consequently, prey escape performances and current reproductive asset can affect FID. We tested effects of body condition, morphology, and whether the tail was regenerated or original on FID in the Balearic lizard (Podarcis lilfordi) by ourselves simulating predators. Lizards with better body condition had longer FID and lizards with longer intact tails had shorter FID. Lizards with regenerated tail presented shorter FID than lizards with intact tails. These results suggest that impaired escape performance is counterbalanced by fitness costs of tail regeneration or by alteration of escape behaviour. The weak association between morphology, body condition and FID suggest that escape performances and asset protection have relatively small effect on P. lilfordi escape decisions.

1. Many lizards use caudal autotomy as a defensive strategy. However, subsequent costs related to the alteration of locomotor abilities might decrease the fitness of individuals. In this paper, the movement patterns of spontaneously moving Psammodromus algirus lizards and their escape performance running at high speed were compared before and after tail loss. A control tailed group was also studied to assess the repeatability of locomotor patterns between trials. 2. Tail loss had a significant effect on spontaneous movement patterns. Tailless individuals moved at significantly slower speeds during bursts of locomotion, and distances moved within bursts were significantly reduced. The overall time spent pausing increased, and, as a result, overall speeds decreased to an even greater extent than burst speeds. However, mean durations of individual locomotor bursts and mean pause durations did not change significantly after tail loss. 3. Loss of the tail decreased mean stride length, although the positive relation between stride length and speed was retained. 4. Escape performance was also greatly affected; loss of the tail resulted in substantially reduced attained, maximal and overall escape speeds. These changes resulted in shorter escape distances (the time of the first pause after the initiation of the escape response) because the mean duration of escape responses did not change. 5. The relevance of these alterations for the ecology of this species, and how individuals may compensate for the costs of tail loss, favouring autotomy as an escape strategy, are discussed.

Prey can respond to predation risk through developmental plasticity, generating anti-predator phenotypes. These inducible defenses arise from changes to the stress axis, and neuroendocrine-triggered gene regulation is a likely mechanism influencing such phenotypes. As tadpoles, amphibians improve their escape performance by modifying tail shape in response to perceived predation risk (PPR), and this process should involve tissue and developmentally specific gene regulation. We exposed Lithobates pipiens tadpoles to PPR from Aeshnidae predators and measured tail morphology and transcriptomic response across different tissues (head and tail) and development (pre-metamorphosis to pro-metamorphosis). We found that PPR induced plasticity in tail shape, and this response was suppressed when tadpoles were also exposed to a glucocorticoid synthesis inhibitor. Differential gene expression was associated with predation stress across head and tail tissue, and developmental stage. Predator-exposed tadpoles exhibited up-regulation of genes responsible for muscle tissue and nervous system development, primarily in tail tissue and in pre-metamorphosis. PPR broadly influenced pathways across tissues and metamorphosis, including developmental, endocrine, and immune system pathways. This study provides an important step in understanding transcriptomic responses during predator induced morphological change, and demonstrates that gene expression, as induced by perceived predation risk, is a prominent mechanism of developmental plasticity.

Only two (C57BL, CBA) of six mouse strains improved their escape time in a simple water-escape task on five successive trials (days). The remaining four strains (BALB/c, C3H, 101, NMRI) did not learn in this test situation. The two most extreme inbred strains, C57BL (high escape performance, good learners) and BALB/c (low escape performance, nonlearners), were intercrossed to produce F1, F2, and two backcross (B1, B2) generations of both reciprocal crosses. The learning curves constructed by plotting log escape time against trial number were found to posses significant slopes and to fit straight lines for C57BL and CBA as well as for all four intercross generations. Accordingly, the inhertiance of learning ability to escape water could be explained in terms of an additive-dominance model without nonallelic interactions. Neither significant sex differences nor maternal influences were found in the six strains studied for the four strain crosses. F1 mice escaped faster and their learning curves were significantly different from those of the other genotypes (F2, B1, B2, parental strains), indicating behavioral heterosis. Albino mice of the segregating generations showed a poorer water-escape performance than their pigmented sibs.

1. The addition of mass to an animal may reduce its locomotory capabilities and thus increase the predation risk. The effects of recent feeding on locomotor and escape performance of juvenile Psammodromus algirus lizards were examined. The consequences of a full stomach on the movement rate and locomotor patterns of lizards when walking spontaneously, and on their escape response from a simulated predator, were specifically analysed to determine whether juvenile lizards were able to compensate through modifications of behaviour for the possible locomotory difficulties derived from a full stomach. 2. The results indicated that feeding did not significantly affect the rate of spontaneous movements. However, voluntary locomotor patterns were partially affected. Thus, after feeding, individuals moved to significantly slower burst speeds, and also decreased significantly the frequency of pauses. 3. The escape performance was also significantly affected by feeding. In an individual escape run, lizards decreased their initial speed, although their burst speed did not change, and escaped over longer periods, stopping at greater distances. The endurance of the escape response in a continuous predator attack also decreased significantly after feeding, and lizards ran on less occasions and for shorter periods before becoming exhausted and hiding. 4. The possible consequences of reduced locomotory abilities on fitness are discussed. It is proposed that, by changing their behaviour, juveniles may reduce these costs. This may allow them to consume large amounts of food at a time without incurring a higher predation risk.

Ectoparasites modify escape behaviour, but not performance, in a coral reef fish

Several animals advertise their escape performance toward potential predators and convey their unprofitability as prey by exhibiting pursuit-deterrent displays. Foot shakes, which are exhibited by lizards in response to potential predators, are considered as a pursuit-deterrent signal. This pursuit-deterrent signal is thought to be either perception advertisement, indicating the detection of a predator, or quality advertisement, informing the individualʼs condition. However, it remains unclear what foot shakes advertise to predators. To address this, we conducted a field experiment using the Japanese grass lizard Takydromus tachydromoides, which is known to perform foot shakes. To simulate a predator, we approached the lizards, and measured our distance from the lizards when first spotted (starting distance) as well as the distance between the lizards and us when they fled (flight initiation distance). We also recorded the presence or absence of foot shakes and their distance from us when they initiated the display (display distance). Tested lizards were captured whenever possible and snout-vent length (SVL), sex and body temperature (Tb) were recorded. In 151 approaches, 43 lizards exhibited foot shakes. Approximately half of the lizards displayed foot shakes with display distance between 1 m and 2 m, but none at closer distance. These results align with those observed in foot shakes of other lizards, which are considered as a pursuit-deterrent signal, and are consistent with pursuit-deterrent theory. SVL and Tb had a positive correlation with the probability of foot shakes, and males performed foot shakes more frequently than females. Because SVL and Tb are well known to influence the escape performance of lizards, and sex potentially influences the performance, our results suggest that foot shakes of T. tachydromoides advertises the quality of the lizard rather than the perception of predators. Keywords: predator-prey interaction, pursuit-deterrence, antipredator signal, visual display, Lacertidae

Predatory reef fishes regularly visit mutualistic cleaner fish (Labroides dimidiatus) to get their ectoparasites removed but show no interest in eating them. The concept of compensated trait loss posits that characters can be lost if a mutualistic relationship reduces the need for a given trait. Thus, selective pressures on escape performance might have relaxed in L. dimidiatus due to its privileged relationship with predators. However, the cost of failing to escape a predatory strike is extreme even if predation events on cleaners are exceptionally rare. Additionally, cleaners must escape from non-predatory clients that regularly punish them for eating mucus instead of parasites. Therefore, strong escape capabilities might instead be maintained in cleaner fish because they must be able to flee when in close proximity to predators or dissatisfied clients. We compared the fast-start escape performance of L. dimidiatus with that of five closely related wrasse species and found that the mutualistic relationship that cleaners entertain with predators has not led to reduced escape performance. Instead, conflicts in cleaning interactions appear to have maintained selective pressures on this trait, suggesting that compensated trait loss might only evolve in cases of high interdependence between mutualistic partners that are not tempted to cheat.

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 behavior of an agent may be simple or complex depending on its role. Behavioral simulation using agents can have multiple approaches that have different advantages and disadvantages. By combining different behaviors in a hierarchical model, situational inefficiencies can be compensated. This paper proposes a behavioral hierarchy model that combines different mechanisms in behavior plans. The study simulates the social behavior in an office environment during an emergency using collision avoidance, negotiation, conflict solution, and path-planning mechanisms in the same multi-agent model to find their effects and the efficiency of the combinational setups. Independent agents were designed to have memory expansion, pathfinding, and searching capabilities, and the ability to exchange information among themselves and perform evasive actions to find a way out of congestion and conflict. The designed model allows us to modify the behavioral hierarchy and action order of agents during evacuation scenarios. Moreover, each agent behavior can be enabled or disabled separately. The effects of these capabilities on escape performance were measured in terms of time required for evacuation and evacuation ratio. Test results prove that all mechanisms in the proposed model have characteristics that fit each other well in situations where different hierarchies are needed. Dynamic memory management (DMM), together with a hierarchical behavior plan, achieved a performance improvement of 23.14% in escape time without providing agents with any initial environmental information.

Subterranean rodents are often considered as ecosystem engineers because they physically modify the surrounding environment due to their burrowing and foraging activities. Understanding the modifications that ecosystem engineering species exert on the environment are of crucial importance in ecology studies, since they may affect the structure and population dynamics of several species, including lizards. Thus, the objective of the present study is to test the effect that Ctenomys mendocinus exert in the abundance of Liolaemus ruibali and its escape behaviour, in a high‐elevation desert. Lizard abundance was estimated using observation transects and escape behaviour was studied with an experiment where the observer was considered by lizards as a potential predator and distance before the lizard flees was measured. All the variables were compared between areas disturbed by C. mendocinus and undisturbed ones. We found that L. ruibali was favoured by C. mendocinus activity. By creating burrow systems that serve as refuges for lizards, this rodent species increases the abundance of L. ruibali and reduces its flight distance, thereby improving its escape performance. We may suggest that C. mendocinus, through the construction of burrow systems, would be acting as an ecosystem engineer in Puna desert, affecting L. ruibali ecology.