In animal behaviour, escape response, escape reaction, or escape behaviour is a rapid series of movements performed by an animal in response to possible predation. Some types of escape response may include camouflage, freezing behaviour, and fleeing, among others It is an anti-predator behaviour that varies from species to species. In fact, variation between individuals is linked to increased survival. In addition, it is not merely increased speed that contributes to the success of the escape response; other factors, including reaction time and the individual's context can play a role. The individual escape response of a particular animal can vary based on an animal's previous experience and current state
The escape response, a particular type of anti-predator behaviour, is vital to the survival of species. Individuals that are able to execute an escape response quickly are more likely to flee from predators and avoid predation.
Arjun et al. (2017) found that it is not necessarily the speed of the response itself, but the greater distance between the targeted individual and the predator when the response is executed. In addition, the escape response of an individual is directly related to the threat of the predator. Predators that pose the biggest risk to the population will evoke the greatest escape response. Therefore, it may be an adaptive trait selected for by natural selection.
Law & Blake (1996) argue that many morphological characteristics could contribute to an individual's efficient escape response, but the escape response has undoubtedly been molded by evolution. In their study, they compared more recent sticklebacks to their ancestral form, the Paxton Lake stickleback, and found that the performance of the ancestral form was significantly lower. Therefore, one may conclude that this response has been ripened by evolution.
The neurobiology of the escape response varies from species to species, but some consistencies exist. In fish and amphibians, the escape response appears to be elicited by Mauthner Cells, two giant neurons located in the rhombomere 4 of the hindbrain.
In larval zebrafish (Danio rerio), they sense predators using their lateral line system. When larvae are positioned lateral to a predator, they will escape in a likewise lateral direction. According to game theory, zebrafish who are positioned lateral and ventral to the predator are more likely to survive, rather than any alternate strategy. Finally, the faster (cm/s) the predator is moving, the faster downward the fish will move to escape predation.
In vertebrates, the avoidance behaviour appears to be processed in the telencephalon. This has been shown repeatedly in goldfish, as individuals with ablated telencephalons were significantly impaired in acquiring avoidance behaviour. As a result, some researchers conclude that damage to the telencephalon can interfere with the emotion internal fear to produce an avoidance response.
Researchers will often evoke an escape response to test the potency of hormones and/or medication and their relationship to stress. As such, the escape response is fundamental to anatomical and pharmacological research
The role of learning in the escape responseEdit
Research has found that habituation, the process that allows individuals to learn to identify harmless events, has a significant impact on the perception of fear in the presence of a predator. Habituation allows animals to discriminate between false alarms and real, dangerous events. While many do not consider habituation a form of learning, many researchers are beginning to suggest that it could be a form of associative learning. For example, zebra danios who are habituated to predators are more latent to flee than those who were not habituated to predators. However, habituation did not affect the fish's angle of escape from the predator.
If an animal engages in an escape response, but is repeatedly unable to escape, they will eventually cease to escape. This is known as learned helplessness. In Drosophila melanogaster, the frequency of an escape reaction will decrease in an individual who is subjected to uncontrollable shocks. However, this learning is context-dependent, as when these flies are placed in a new environment, they will again exhibit the escape response
Escape response in birdsEdit
Avian species also display unique escape responses. The escape response of birds may be particularly important when considering aircraft and vehicle traffic. In one experiment by Devault et al. (1989), brown-headed cowbirds (Molothrus ater) were exposed to a demonstration of traffic travelling at speeds between 60 – 360 km/hr. When approached by a vehicle travelling at 120 km/h, the birds only allotted 0.8s to escape before a possible collision. This study showed that fast traffic speeds may not allow enough time for birds to initiate an escape response.
Escape response in fishEdit
Generally, when faced with a dangerous stimuli, fish will contract their axial muscle, resulting a C-shaped contraction away from the stimulus. This response occurs in two separate stages: a muscle contraction that allows them to speed away from a stimulus (stage 1), and a sequential contralateral movement (stage 2). This escape is also known as a "fast-start response".  The majority of the fish respond to an external stimulus (pressure changes) within 5 to 15 milliseconds, while some will exhibit a slower response taking up to 80 milliseconds. While the escape response generally only propels the fish a small distance away, this distance is long enough to prevent predation. While many predators use water pressure to catch their prey, this short distance prevents them from feeding on the fish via suction.
Particularly in the case of fish, it has been hypothesized that the differences in escape response are due to the evolution of neural circuits over time. This can be witnessed by observing the difference in the extent of stage 1 behaviour, and the distinct muscle activity in stage 2 of the C-start or fast-start response.
Recent research in guppies has shown that familiarity can affect the reaction time involved in the escape response. Guppies that were placed in familiar groups were more likely to respond than guppies who were assigned to unfamiliar groups. Wolcott et al. (2017) suggest that familiar groups may lead to reduced inspection and aggression among conspecifics. The theory of limited attention states that the brain has a limited amount of information processing, and, as an individual is engaged in more tasks, the less resources it can provide to one given task. As a result, they have more attention that they can devote toward anti-predator behaviour.
Escape response in insectsEdit
When house flies (Musca domestica) encounter an aversive stimulus, they jump rapidly and fly away from the stimulus. A recent research suggests that the escape response in Musca domestica is controlled by a pair of compound eyes, rather than by the ocelli. When one of the compound eyes was covered, the minimum threshold to elicit an escape response increased. In short, the escape reaction of Musca domestica is evoked by the combination of both motion and light.
Cockroaches are also well known for their escape response. When individuals sense a wind puff, they will turn and escape in the opposite direction. The sensory neurons in the paired caudal cerci (singular: cercus) at the rear of the animal send a message along the ventral nerve cord. Then, one of two responses are elicited: running (through the ventral giant interneurons) or flying/running (through the dorsal giant interneurons)
Escape response in mammalsEdit
Higher-order mammals often evoke a withdrawal reflex. A withdrawal reflex is defined as a type of spinal reflex designed to protect the body from damaging stimuli, and involves pulling the body part away from the dangerous stimuli
In one study, Stankowich & Coss (2007) studied the flight initiation distance of Columbian black-tailed deer. According to the authors, the flight initiation distance is the distance between prey and predator when the prey attempts an escape response. They found that the angle, distance, and speed that the deer escaped was related to the distance between the deer and its predator, a human male in this experiment
Squids have developed a multitude of anti-predator escape responses, including: jet-driven escape, postural displays, inking and camouflage. Inking and jet-driven escape are arguably the most salient responses, in which the individual squirts ink at the predator as it speeds away. These blobs of ink can vary in size and shape; larger blobs can distract the predator while smaller blobs can provide a cover under which the squid can disappear. Finally, the released ink also contains hormones such as L-dopa and dopamine that can warn other conspecifics of danger while blocking olfactory receptors in the targeted predator.
Cuttlefish (Sepia officinalis) are also well known for their escape responses. Unlike squids, who may engage more salient escape responses, the cuttlefish has few defences so it relies on more conspicuous means: jet-driven escape and freezing behaviour. However, it appears that the majority of cuttlefish use a freezing escape response when avoiding predation. When the cuttlefish freeze, it minimizes the voltage of their bioelectric field, making them less susceptible to their predators, mainly sharks
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