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Making the best of a bad situation: the upside of squid injury.

Article: Crook, R. J., Dickson, K., & Hanlon, R. T. (2014). Nociceptive Sensitization Reduces Predation Risk. Current Biology, 24, 1121–1125; DOI: 10.1016/j.cub.2014.03.043


The ability to feel pain (called nociception) warns us to stop dangerous activities immediately, but the benefit of experiencing long-term pain sensitivity is not as obvious. Prolonged pain in humans causes increased sensitivity and is often paired with anxiety. Many species show increased, lasting sensitivity of defensive responses. This allows prey to react more quickly or more intensely to approaching predators. Observing squid and their fish predators gives an opportunity to test the evolutionary benefits of prolonged sensitivity after sublethal injury. The authors in this paper hypothesized that hypersensitivity to predation stimuli exists to offset an increased predation risk associated with sublethal injury.


(Source: www.whoi.edu)

The longfin inshore squid, Doryteuthis (Loligo) pealeii, has long had a place in scientific research- used as a model organism to study axons (nearly 1000 larger than typical mammal axons) and their unique and vibrant camouflaging color changes. Squid have a complex nervous system and can easily be caught near shore so also work well as a study species for pain sensation. Minor injury causes hypersensitivity to visual and tactile stimuli without affecting general activity levels or foraging behavior. The experimental predator of the longfin squid, the black sea bass (Centropristis striata), uses visual cues to find its prey.



When faced with danger squid show a predictable series of defensive behaviors in response to predatory approach as shown in Figure 1. The researchers recorded the sequence and scored the behaviors when squid were placed in the vicinity of a black sea bass predator. They compared the timing of the behaviors, distance at which they occurred and the ultimate escape success rate. The research team cut off the tip of one arm of each squid to create sublethal injury without causing impairment to normal functions or locomotion. This small injury induces a state of hypersensitivity of defensive behaviors. Anesthesia was used on some experimental groups to show the result of injury or non-injury without the associated pain and prolonged sensitivity.


Escalation Pattern in Predator-Prey Interactions between Black Sea Bass and Squid. Top: four stages of predator behavior. Orientation is the first change in direction toward a squid from an ongoing swimming trajectory, and the distance from fish to squid is the ‘‘start distance’’ of the predation attempt. Pursuit is an accelerated, direct approach toward a squid, with the fish’s dorsal, pectoral, and caudal fins folded. Attack is close-proximity ‘‘grappling,’’ with the fish’s mouth open and fins extended to facilitate rapid directional changes. Capture is definedas any part of the squid’s body caught in the mouth of the fish. Bottom: defensive responses of squid to the fish. Primary defense (avoiding detection via crypsis) escalates to secondary defenses once the squid is alerted. Crypsis, via chromatophore patterns of disruptive banding while sitting on the sub- strate or all-over beige when swimming, occurs in the absence of encounters and often during early encounter stages; it received an escalation score of0. Distance between squid and fish at the first secondary defensive behavior is the ‘‘alert distance.’’ Secondary defenses were scored based on their typical progression. Deimatic chromatophore displays that distract or startle a predator were scored 1, as were slow avoidanceswimming evoked by distant threat. Escape jetting without inking was scored 2. This typically (but not always) followed expression of behaviors scored 1. Ink release, which was almost always combined with erratic escape jetting, was scored 3. The highest escalation score was recorded for each predatory encounter.




When faced with fish predators the injured squid showed increased defensive maneuvers. This is particularly important given injured squid were attacked at greater distances than their uninjured counterparts, regardless of presence of anesthesia.

Injured squid, without anesthesia, showed longer distances at which they became alert of predators and showed a flight response. Injured squid, both anesthetized and not, showed reduced survival in an attack. Injured squid without anesthesia, reacting based on prolonged nociception, fared better than the numb, injured squid. After a 30 minute period of attack by a fish predator uninjured (U) squid showed about a 75% survivorship rate compared to close to 50% for injured squid (I) and a significantly lower, less than 25%, chance for injured squid with anesthesia preventing nociception (IA).


Fig 3 outcomes

Injured Squid Lacking Nociceptive Sensitization Had the Lowest Odds of Survival. At the conclusion of a 30 min trial with free interaction of squid and fish, squid in the I and IA groups had lower overall survival than in the U group, and IA group squid were most likely to be killed.



Increased defensive sensitivity due to prolonged feelings of pain allows injured squid to more successfully avoid predators than anesthetized injured squid. Uninjured squid remain in a superior position with fewer attacks and higher survival. This shows the potential importance of feeling pain and reacting to it long-term. The lower attack survival rates for injured squid also remind us of the potential for a large impact from a small injury. Predator-prey interactions helped shape the squid’s reactive abilities when faced with sublethal injury. Though nociception is widespread in the animal kingdom this paper is the first to show increased survival due to pain-induced hypersensitivity.

Sublethal injury is common in all animals and can make the injured prey easy targets for predators.  This research shows that animals can counteract the vulnerability through increasing their defensive efforts.


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