Primary and secondary defences of squid to cruising and ambush fish predators: variable tactics and their survival value

Ritualized ink use during visual courtship display by males of the sexually dimorphic cuttlefish Sepia andreana

Visual display is a crucial aspect of courtship, and their success relies on both display quality and the surrounding environment, such as the visual background. Cephalopods may release ink when attacked by predators or during aggressive interactions with conspecifics. Here, we report that ink is used as a part of the courtship display by males of the cuttlefish species Sepia andreana. Males of this species engage in a highly ritualized multimodal courtship using a pair of markedly long sexually dimorphic arms. At the climax of the courtship, the male releases a diffuse backdrop of ink near himself and then performs the specific courtship display by extending his sexually dimorphic arms and altering his body pattern to pale in front of this ink backdrop, and then proceeds to mate. This novel use of cephalopod ink could make the surroundings darker and more homogeneous, potentially serving as a temporary modification of the visual environment for courtship display.

Rapid Shifts in Visible Carolina Grasshopper (Dissosteira carolina) Coloration During Flights

Some brightly colored structures are only visible when organisms are moving, such as parts of wings that are only visible in flight. For example, the primarily brown Carolina grasshopper (Dissosteira carolina) has contrasting black-and-cream hindwings that appear suddenly when it takes off, then oscillate unpredictably throughout the main flight before disappearing rapidly upon landing. However, the temporal dynamics of hindwing coloration in motion have not previously been investigated, particularly for animals that differ from humans in their temporal vision. To examine how quickly this coloration appears to a variety of non-human observers, we took high-speed videos of D. carolina flights in the field. For each of the best-quality takeoffs and landings, we performed a frame-by-frame analysis on how the relative sizes of the different-colored body parts changed over time. We found that in the first 7.6 ± 1.5 ms of takeoff, the hindwings unfurled to encompass 50% of the visible grasshopper, causing it to roughly double in size. During the main flight, the hindwings transitioned 6.4 ± 0.4 times per second between pauses and periods of active wing-beating (31.4 ± 0.5 Hz), creating an unstable, confusing image. Finally, during landings, the hindwings disappeared in 11.3 ± 3.0 ms, shrinking the grasshopper to 69 ± 9% of its main flight size. Notably, these takeoffs and landings occurred faster than most recorded species are able to sample images, which suggests that they would be near-instantaneous to a variety of different viewers. We therefore suggest that D. carolina uses its hindwings to initially startle predators (deimatic defense) and then confuse them and disrupt their search images (protean defense) before rapidly returning to crypsis.

The Case for Octopus Consciousness: Temporality

Temporality is one of the criteria that Birch has advanced for areas of cognitive ability that may underlie animal sentience. An ability to integrate and use information across time must be more than simply learning pieces of information and retrieving them. This paper looks at such wider use of information by octopuses across time. It evaluates accumulation of information about one’s place in space, as used across immediate egocentric localization by cuttlefish and medium distance navigation in octopuses. Information about useful items in the environment can be incorporated for future use by octopuses, including for shelter in antipredator situations. Finding prey is not random but can be predicted by environmental cues, especially by cuttlefish about future contingencies. Finally, the paper examines unlimited associative learning and constraints on learning, and the ability of cephalopods to explore and seek out information, even by play, for future use.

Squid adjust their body color according to substrate

Coleoid cephalopods camouflage on timescales of seconds to match their visual surroundings. To date, studies of cephalopod camouflage-to-substrate have been focused primarily on benthic cuttlefish and octopus, because they are readily found sitting on the substrate. In contrast to benthic cephalopods, oval squid (Sepioteuthis lessoniana species complex) are semi-pelagic animals that spend most of their time in the water column. In this study, we demonstrate that in captivity, S. lessoniana Sp.2 (Shiro-ika, white-squid) from the Okinawa archipelago, Japan, adapts the coloration of their skin using their chromatophores according to the background substrate. We show that if the animal moves between substrates of different reflectivity, the body patterning is changed to match. Chromatophore matching to substrate has not been reported in any loliginid cephalopod under laboratory conditions. Adaptation of the chromatophore system to the bottom substrate in the laboratory is a novel experimental finding that establishes oval squid as laboratory model animals for further research on camouflage.

The effect of unexpected rewards on decision making in cuttlefish

Despite numerous studies demonstrating the cognitive ability of cephalopods, there is currently no study showing an emotion-like behavior in this group of animals. To examine whether cuttlefish have different internal states, we developed a behavioral paradigm to assess if prior surprised events are able to alter the choice made by cuttlefish. By presenting unexpected food rewards to cuttlefish before the test, we investigated whether the reaction time of choosing between two shrimps, an intuitive response toward the prey without previous learning, at three different levels of discriminative tests (easy, difficult, and ambiguous), are different compared to the one without an unexpected reward. This behavioral paradigm serves to demonstrate whether cuttlefish are aware of ambiguous situations, and their choice outcome and reaction time are dependent of their internal states. The results show that the response latency was significantly shortened in the difficult and ambiguous tests when choosing from two shrimps that are either moderately different in size or similar sizes, respectively, when cuttlefish have received unexpected rewards before the test. These results were compared with tests during which the cuttlefish did not receive any reward in advance. Furthermore, this shortening of latency did not result in a difference in choice outcome during the difficult and ambiguous tests. Interestingly, even when cuttlefish have obtained the expected food rewards or simply made tentacular strike without prey capture each time before test, these prior experiences were sufficient to shorten the response latency in the difficult and ambiguous tests. However, different from the result of unexpected rewards, food consumption alone or prey capture failure did affect the choice outcome during the simple and difficult tests. Taken together, our findings suggest that pre-test treatments of unexpected and expected rewards or simply unsuccessful visual attack seem to induce cuttlefish to adopt different foraging behaviors. This context dependent decision making suggests that cuttlefish’s foraging strategies are influenced by the previously surprised event and their internal states. It also shows a speed-accuracy tradeoff in difficult and ambiguous situations when foraging for prey. This observation may lead to a future investigation of the presence of emotional state in cephalopods.

Bipedal locomotion in Octopus vulgaris: A complementary observation and some preliminary considerations

Lacking an external shell and a rigid endoskeleton, octopuses exhibit a remarkable flexibility in their movements. Bipedal locomotion is perhaps the most iconic example in this regard. Until recently, this peculiar mode of locomotion had been observed only in two species of tropical octopuses: Amphioctopus marginatus and Abdopus aculeatus. Yet, recent evidence indicates that bipedal walking is also part of the behavioral repertoire of the common octopus, Octopus vulgaris. Here we report a further observation of a defense behavior that encompasses both postural and locomotory elements of bipedal locomotion in this cephalopod. By highlighting differences and similarities with the other recently published report, we provide preliminary considerations with regard to bipedal locomotion in the common octopus.

An elaborate behavioural sequence reinforces the decoy effect of ink during predatory attacks on squid

The characteristic inking behaviour of cephalopods is a secondary defence mechanism that helps them to escape predation. However, although it has been postulated that ink creates a decoy by disrupting the visual information received by the predator, the underlying mechanisms by which ink helps squid to escape from predators remain unknown. Therefore, we observed the inking behaviour of the Japanese pygmy squid (Idiosepius paradoxus). Field observations showed the squid intermittently and linearly ejected ink while rapidly swimming backwards in response to a predator and also changed their bodies to a light colour. This behaviour was then followed by a sudden and sharp change in swimming direction or sometimes a sudden break from swimming with a concurrent change in body colour to black. We also recorded the escape behaviour with inking under captive conditions in response to predatory sculpins, which allowed the successful escape from a predatory attack. Furthermore, the greater the number of ink ejections, the higher the probability that the sculpins would initiate a predatory attack on the ink rather than the squid. Together, these results suggest that squid inking behaviour exhibits a substantial decoy effect on predators and is associated with a series of complex, spatio-temporally regulated behaviours. Digital video images related to the article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo200107ip01a, http://www.momo-p.com/showdetail-e.php?movieid=momo200107ip03a, and http://www.momo-p.com/showdetail-e.php?movieid=momo200107ip04a.

Electrophysiological and Motor Responses to Chemosensory Stimuli in Isolated Cephalopod Arms

While there is behavioral and anatomical evidence that coleoid cephalopods use their arms to "taste" substances in the environment, the neurophysiology of chemosensation has been largely unexamined. The range and sensitivity of detectable chemosensory stimuli, and the processing of chemosensory information, are unknown. To begin to address these issues, we developed a technique for recording neurophysiological responses from isolated arms, allowing us to test responses to biologically relevant stimuli. We tested arms from both a pelagic species (Doryteuthis pealeii) and a benthic species (Octopus bimaculoides) by attaching a suction electrode to the axial nerve cord to record neural activity in response to chemical stimuli. Doryteuthis pealeii arms showed anecdotal responses to some stimuli but generally did not tolerate the preparation; tissue was nonviable within minutes ex vivo. Octopus bimaculoides arms were used successfully, with tissue remaining healthy and responsive for several hours. Arms responded strongly to fish skin extract, glycine, methionine, and conspecific skin extract but not to cephalopod ink or seawater controls. Motor responses were also observed in response to detected stimuli. These results suggest that chemosensory receptor cells on O. bimaculoides arms were able to detect environmentally relevant chemicals and drive local motor responses within the arm. Further exploration of potential chemical stimuli for O. bimaculoides arms, as well as investigations into the neural processing within the arm, could enhance our understanding of how this species uses its arms to explore its environment. While not successful in D. pealeii, this technique could be attempted with other cephalopod species, as comparative questions remain of interest.

Continuous Inking Affects the Biological and Biochemical Responses of Cuttlefish Sepia pharaonis

Several marine mollusks, including cephalopods (cuttlefish, squid, and octopus) and gastropods (e.g., sea hares), can release a colored ink secretion when chased by predators or stimulated. Ink release is part of a defensive response, but the threshold for the biochemical responses caused by stimulation is unknown. The present study aimed to reveal antipredator responses of cuttlefish, such as escaping via inking and/or jetting, and to investigate its biological and biochemical responses to continuous ink release. Results showed that the behavioral responses to continuous ink release mainly manifested as blazing body pattern changes. Cuttlefish escaped from predators covered by jetting/inking and warned the potential threats by displaying a unique body pattern. Moreover, persistent inking in the presence of an overt stimulus caused uncontrollable ink release from the ink duct/anal canal (loss of control). This study first verified the characteristics of the cuttlefish ink solution, prepared a standard curve of ink solution concentrations, and fitted the relationship function between the release frequency and the released ink weight. Biological statistics indicated that cuttlefish has the ability to continuously release ink (releasing ∼90% of the ink from the ink sac) and that the individuals adapted well during the recovery period. However, re-releasing ink would result in "overexploitation" and high mortality. Hexokinase (HK), pyruvate kinase (PK), and superoxide dismutase (SOD) activities, as well as malondialdehyde (MDA) concentration increased or remained stable in different tissues after releasing ink. The expression of heat shock protein 90 and arginine kinase (AK) were upregulated by stimuli in all tissues. Biochemical changes indicated that continuous inking not only consumed considerable energy but also damaged the tissues. In summary, cuttlefish released almost 90% of their ink for active defense against predators, and it took ∼30 days for the ink sac to be refilled, but "overexploitation" resulted in serious physiological damage. These findings will be helpful to further study the defense and ink release mechanisms and to consider animal health and welfare when using cephalopods as experimental animals and for aquaculture practices.

Inexperienced preys know when to flee or to freeze in front of a threat

Using appropriate antipredatory responses is crucial for survival. While slowing down reduces the chances of being detected from distant predators, fleeing away is advantageous in front of an approaching predator. Whether appropriate responses depend on experience with moving objects is still an open question. To clarify whether adopting appropriate fleeing or freezing responses requires previous experience, we investigated responses of chicks naive to movement. When exposed to the moving cues mimicking an approaching predator (a rapidly expanding, looming stimulus), chicks displayed a fast escape response. In contrast, when presented with a distal threat (a small stimulus sweeping overhead) they decreased their speed, a maneuver useful to avoid detection. The fast expansion of the stimulus toward the subject, rather than its size per se or change in luminance, triggered the escape response. These results show that young animals, in the absence of previous experience, can use motion cues to select the appropriate responses to different threats. The adaptive needs of young preys are thus matched by spontaneous defensive mechanisms that do not require learning.

Tactical Tentacles: New Insights on the Processes of Sexual Selection Among the Cephalopoda

The cephalopods (Mollusca: Cephalopoda) are an exceptional class among the invertebrates, characterised by the advanced development of their conditional learning abilities, long-term memories, capacity for rapid colour change and extremely adaptable hydrostatic skeletons. These traits enable cephalopods to occupy diverse marine ecological niches, become successful predators, employ sophisticated predator avoidance behaviours and have complex intraspecific interactions. Where studied, observations of cephalopod mating systems have revealed detailed insights to the life histories and behavioural ecologies of these animals. The reproductive biology of cephalopods is typified by high levels of both male and female promiscuity, alternative mating tactics, long-term sperm storage prior to spawning, and the capacity for intricate visual displays and/or use of a distinct sensory ecology. This review summarises the current understanding of cephalopod reproductive biology, and where investigated, how both pre-copulatory behaviours and post-copulatory fertilisation patterns can influence the processes of sexual selection. Overall, it is concluded that sperm competition and possibly cryptic female choice are likely to be critical determinants of which individuals' alleles get transferred to subsequent generations in cephalopod mating systems. Additionally, it is emphasised that the optimisation of offspring quality and/or fertilisation bias to genetically compatible males are necessary drivers for the proliferation of polyandry observed among cephalopods, and potential methods for testing these hypotheses are proposed within the conclusion of this review. Further gaps within the current knowledge of how sexual selection operates in this group are also highlighted, in the hopes of prompting new directions for research of the distinctive mating systems in this unique lineage.

Nest usurpation: a specialised hunting strategy used to overcome dangerous spider prey

Hunting other predators is dangerous, as the tables can turn and the hunter may become the hunted. Specialized araneophagic (spider eating) predators have evolved intriguing hunting strategies that allow them to invade spiders’ webs by adopting a stealthy approach or using aggressive mimicry. Here, we present a newly discovered, specialized hunting strategy of the araneophagic spider Poecilochroa senilis (Araneae: Gnaphosidae), which forces its way into the silk retreat of the potential spider prey and immobilizes it by swathing gluey silk onto its forelegs and mouthparts. Poecilochroa senilis has been reported from the nests of a several, often large, spider species in the Negev desert (Israel), suggesting specialization on spiders as prey. Nevertheless, in laboratory experiments, we found that P. senilis has a wider trophic niche, and fed readily on several small insect species. The specialized nest-invading attack was used more frequently with large spiders, and even small juvenile P. senilis were able to attack and subdue larger spiders. Our observations show that specific hunting tactics, like nest usurpation, allow specialized predators to overcome defences of dangerous prey.

Grow Smart and Die Young: Why Did Cephalopods Evolve Intelligence?

Intelligence in large-brained vertebrates might have evolved through independent, yet similar processes based on comparable socioecological pressures and slow life histories. This convergent evolutionary route, however, cannot explain why cephalopods developed large brains and flexible behavioural repertoires: cephalopods have fast life histories and live in simple social environments. Here, we suggest that the loss of the external shell in cephalopods (i) caused a dramatic increase in predatory pressure, which in turn prevented the emergence of slow life histories, and (ii) allowed the exploitation of novel challenging niches, thus favouring the emergence of intelligence. By highlighting convergent and divergent aspects between cephalopods and large-brained vertebrates we illustrate how the evolution of intelligence might not be constrained to a single evolutionary route.

In Vivo Recording of Neural and Behavioral Correlates of Anesthesia Induction, Reversal, and Euthanasia in Cephalopod Molluscs

Cephalopod molluscs are among the most behaviorally and neurologically complex invertebrates. As they are now included in research animal welfare regulations in many countries, humane and effective anesthesia is required during invasive procedures. However, currently there is no evidence that agents believed to act as anesthetics produce effects beyond immobility. In this study we demonstrate, for the first time, that two of the most commonly used agents in cephalopod general anesthesia, magnesium chloride and ethanol, are capable of producing strong and reversible blockade of afferent and efferent neural signal; thus they are genuine anesthetics, rather than simply sedating agents that render animals immobile but not insensible. Additionally, we demonstrate that injected magnesium chloride and lidocaine are effective local anesthetic agents. This represents a considerable advance for cephalopod welfare. Using a reversible, minimally invasive recording procedure, we measured activity in the pallial nerve of cuttlefish (Sepia bandensis) and octopus (Abdopus aculeatus, Octopus bocki), during induction and reversal for five putative general anesthetic and two local anesthetic agents. We describe the temporal relationship between loss of behavioral responses (immobility), loss of efferent neural signal (loss of “consciousness”) and loss of afferent neural signal (anesthesia) for general anesthesia, and loss of afferent signal for local anesthesia. Both ethanol and magnesium chloride were effective as bath-applied general anesthetics, causing immobility, complete loss of behavioral responsiveness and complete loss of afferent and efferent neural signal. Cold seawater, diethyl ether, and MS-222 (tricaine) were ineffective. Subcutaneous injection of either lidocaine or magnesium chloride blocked behavioral and neural responses to pinch in the injected area, and we conclude that both are effective local anesthetic agents for cephalopods. Lastly, we demonstrate that a standard euthanasia protocol—immersion in isotonic magnesium chloride followed by surgical decerebration—produced no behavioral response and no neural activity during surgical euthanasia. Based on these data, we conclude that both magnesium chloride and ethanol can function as general anesthetic agents, and lidocaine and magnesium chloride can function as local anesthetic agents for cephalopod molluscs.

Escape behavior of Side-blotched Lizards (Uta stansburiana) in response to model predators

Few field studies have tested for geographic variation in escape behavior and even fewer have examined responses of prey to multiple predators despite most prey occurring in multipredator environments. We performed 458 escape trials on Side-blotched Lizards (Uta stansburiana Baird and Girard, 1852) from 10 populations that differed in predator abundances. We quantified escape behavior of Side-blotched Lizards when approached with one of two model predators: a lizard (Great Basin Collared Lizard (Crotaphytus bicinctores N.M. Smith and Tanner, 1972)) or a snake (Western Yellow-bellied Racer (Coluber mormon Baird and Girard, 1852)). Our results suggest that the escape responses of Side-blotched Lizards (flight initiation distance, distance fled, refuge entry) do not differ when approached by either a model predatory lizard or a model predatory snake. Nor do the escape responses of individual Side-blotched Lizards differ in relation to the abundances of predatory lizards or snakes in the local environment. Rather, only the directness of fleeing toward a refuge differed based on model predator type with Side-blotched Lizards fleeing more directly toward a refuge in response to a model lizard. These findings suggest that Side-blotched Lizards tend to use a more generalized escape response to approaching predators.

Changeable camouflage: how well can flounder resemble the colour and spatial scale of substrates in their natural habitats?

Flounder change colour and pattern for camouflage. We used a spectrometer to measure reflectance spectra and a digital camera to capture body patterns of two flounder species camouflaged on four natural backgrounds of different spatial scale (sand, small gravel, large gravel and rocks). We quantified the degree of spectral match between flounder and background relative to the situation of perfect camouflage in which flounder and background were assumed to have identical spectral distribution. Computations were carried out for three biologically relevant observers: monochromatic squid, dichromatic crab and trichromatic guitarfish. Our computations present a new approach to analysing datasets with multiple spectra that have large variance. Furthermore, to investigate the spatial match between flounder and background, images of flounder patterns were analysed using a custom program originally developed to study cuttlefish camouflage. Our results show that all flounder and background spectra fall within the same colour gamut and that, in terms of different observer visual systems, flounder matched most substrates in luminance and colour contrast. Flounder matched the spatial scales of all substrates except for rocks. We discuss findings in terms of flounder biology; furthermore, we discuss our methodology in light of hyperspectral technologies that combine high-resolution spectral and spatial imaging.

Freezing behaviour facilitates bioelectric crypsis in cuttlefish faced with predation risk

Cephalopods, and in particular the cuttlefish Sepia officinalis, are common models for studies of camouflage and predator avoidance behaviour. Preventing detection by predators is especially important to this group of animals, most of which are soft-bodied, lack physical defences, and are subject to both visually and non-visually mediated detection. Here, we report a novel cryptic mechanism in S. officinalis in which bioelectric cues are reduced via a behavioural freeze response to a predator stimulus. The reduction of bioelectric fields created by the freeze-simulating stimulus resulted in a possible decrease in shark predation risk by reducing detectability. The freeze response may also facilitate other non-visual cryptic mechanisms to lower predation risk from a wide range of predator types.

Multiple sensory modalities used by squid in successful predator evasion throughout ontogeny

Squid rely on multiple sensory systems for predator detection. In this study we examine the role of two sensory systems, the lateral line analogue and vision, in successful predator evasion throughout ontogeny. Squid Doryteuthis pealeii and Lolliguncula brevis were recorded using high-speed videography in the presence of natural predators under light and dark conditions with their lateral line analogue intact or ablated via a pharmacological technique. Paralarval squid showed reduced escape responses when ablated; however, no differences were found between light and dark conditions in non-ablated paralarvae, as was previously shown in juveniles and adults, indicating that the lateral line analogue is integral for predator detection early in life. However, vision does play a role in survival because ablated squid in dark conditions had lower levels of survival than all other treatments. Throughout ontogeny, squid oriented themselves anteriorly towards the oncoming predator, maximizing sensory input to the lateral line analogue system and providing better positioning for tail-first escape jetting, the preferred escape mode. Ablated juveniles and adults had lower response times, escape velocities and peak acceleration than non-ablated individuals, indicating that the lateral line analogue enables squid to respond quicker and with more powerful jets to a predator and maximize escape success. Our findings reveal that the lateral line analogue plays a role in predator detection and successful escape response at the earliest life stages, and continues to contribute to successful evasion by aiding visual cues in juvenile and adult squid.

Peripheral injury alters schooling behavior in squid, Doryteuthis pealeii

Animals with detectable injuries are at escalated threat of predation. The anti-predation tactic of schooling reduces individual predation risk overall, but it is not known how schooling behavior affects injured animals, or whether risks are reduced equally for injured animals versus other school members. In this laboratory study we examined the effects of minor fin injury on schooling decisions made by squid. Schooling behavior of groups of squid, in which one member was injured, was monitored over 24h. Injured squid were more likely to be members of a school shortly after injury (0.5-2h), but there were no differences compared with sham-injured squid at longer time points (6-24h). Overall, the presence of an injured conspecific increased the probability that a school would form, irrespective of whether the injured squid was a member of the school. When groups containing one injured squid were exposed to a predator cue, injured squid were more likely to join the school, but their position depended on whether the threat was a proximate visual cue or olfactory cue. We found no evidence that injured squid oriented themselves to conceal their injury from salient threats. Overall we conclude that nociceptive sensitization after injury changes grouping behaviors in ways that are likely to be adaptive.

Effects of Visual Cues of a Moving Model Predator on Body Patterns in Cuttlefish Sepia pharaonis

We examined the effects of predator-prey distance (PPD) and trajectory of the predator on the body patterns that the pharaoh cuttlefish, Sepia pharaonis, shows in response to a predator. A model predator moving in three different trajectories was presented to the cuttlefish: T1, approached the cuttlefish but bypassed above; T2, approached directly toward the cuttlefish; T3, bypassed the cuttlefish both vertically and horizontally. We divided the body patterns that the cuttlefish expressed into seven categories, i.e., "uniform light", "disruptive", "center circle", "dark square", "vertical stripe", "all dark" and "eyespots". In T1, the number of individuals that showed "dark square" increased as the model approached the cuttlefish, whereas the number of individuals that showed "disruptive" decreased. In T2, the number of individuals that showed "all dark" and "eyespots" increased as the model approached the cuttlefish. In T3, the number of individuals that showed "dark square" and "vertical stripe" increased as the model approached the cuttlefish, and it tended to decrease as the model receded from the cuttlefish. These results demonstrate that S. pharaonis changes its body patterns according to PPD and the trajectory of the predator, which would affect predation risk and/or predator perception.

Skin toxins in coral-associated Gobiodon species (Teleostei: Gobiidae) affect predator preference and prey survival

Predation risk is high for the many small coral reef fishes, requiring successful sheltering or other predator defence mechanisms. Coral-dwelling gobies of the genus Gobiodon live in close association with scleractinian corals of the genus Acropora. Earlier studies indicated that the low movement frequency of adult fishes and the development of skin toxins (crinotoxicity) are predation avoidance mechanisms. Although past experiments showed that predators refuse food prepared with goby skin mucus, direct predator-prey interactions have not been studied. The present study compares the toxicity levels of two crinotoxic coral gobies - Gobiodon histrio, representative of a conspicuously coloured species, and Gobiodon sp.3 with cryptic coloration - using a standard bioassay method. The results show that toxin levels of both species differ significantly shortly after mucus release but become similar over time. Predator preferences were tested experimentally in an aquarium in which the two gobies and a juvenile damselfish Chromis viridis were exposed to the small grouper Epinephelus fasciatus. Video-analysis revealed that although coral gobies are potential prey, E. fasciatus clearly preferred the non-toxic control fish (C. viridis) over Gobiodon. When targeting a goby, the predator did not prefer one species over the other. Contrary to our expectations that toxic gobies are generally avoided, gobies were often captured, but they were expelled quickly, repeatedly and alive. This unusual post-capture avoidance confirms that these gobies have a very good chance of surviving attacks in the field due to their skin toxins. Nonetheless, some gobies were consumed: the coral shelter may therefore also provide additional protection, with toxins protecting them mainly during movement between corals. In summary, chemical deterrence by crinotoxic fishes seems to be far more efficient in predation avoidance than in physical deterrence involving body squamation and/or strong fin spines.

Does predation risk affect mating behavior? An experimental test in dumpling squid (Euprymna tasmanica)

Introduction

One of the most important trade-offs for many animals is that between survival and reproduction. This is particularly apparent when mating increases the risk of predation, either by increasing conspicuousness, reducing mobility or inhibiting an individual's ability to detect predators. Individuals may mitigate the risk of predation by altering their reproductive behavior (e.g. increasing anti-predator responses to reduce conspicuousness). The degree to which individuals modulate their reproductive behavior in relation to predation risk is difficult to predict because both the optimal investment in current and future reproduction (due to life-history strategies) and level of predation risk may differ between the sexes and among species. Here, we investigate the effect of increased predation risk on the reproductive behavior of dumpling squid (Euprymna tasmanica).

Results

Females, but not males, showed a substantial increase in the number of inks (an anti-predator behavior) before mating commenced in the presence of a predator (sand flathead Platycephalus bassensis). However, predation risk did not affect copulation duration, the likelihood of mating, female anti-predator behavior during or after mating or male anti-predator behavior at any time.

Conclusions

Inking is a common anti-predator defense in cephalopods, thought to act like a smokescreen, decoy or distraction. Female dumpling squid are probably using this form of defense in response to the increase in predation risk prior to mating. Conversely, males were undeterred by the increase in predation risk. A lack of change in these variables may occur if the benefit of completing mating outweighs the risk of predation. Prioritizing current reproduction, even under predation risk, can occur when the chance of future reproduction is low, there is substantial energetic investment into mating, or the potential fitness payoffs of mating are high.

Projected near-future CO2 levels increase activity and alter defensive behaviours in the tropical squid Idiosepius pygmaeus

Carbon dioxide (CO2) levels projected to occur in the oceans by the end of this century cause a range of behavioural effects in fish, but whether other highly active marine organisms, such as cephalopods, are similarly affected is unknown. We tested the effects of projected future CO2 levels (626 and 956 µatm) on the behaviour of male two-toned pygmy squid, Idiosepius pygmaeus. Exposure to elevated CO2 increased the number of active individuals by 19-25% and increased movement (number of line-crosses) by nearly 3 times compared to squid at present-day CO2. Squid vigilance and defensive behaviours were also altered by elevated CO2 with >80% of individuals choosing jet escape responses over defensive arm postures in response to a visual startle stimulus, compared with 50% choosing jet escape responses at control CO2. In addition, more escape responses were chosen over threat behaviours in body pattern displays at elevated CO2 and individuals were more than twice as likely to use ink as a defence strategy at 956 µatm CO2, compared with controls. Increased activity could lead to adverse effects on energy budgets as well as increasing visibility to predators. A tendency to respond to a stimulus with escape behaviours could increase survival, but may also be energetically costly and could potentially lead to more chases by predators compared with individuals that use defensive postures. These results demonstrate that projected future ocean acidification affects the behaviours of a tropical squid species.

Cephalopod ink: production, chemistry, functions and applications

One of the most distinctive and defining features of coleoid cephalopods—squid, cuttlefish and octopus—is their inking behavior. Their ink, which is blackened by melanin, but also contains other constituents, has been used by humans in various ways for millennia. This review summarizes our current knowledge of cephalopod ink. Topics include: (1) the production of ink, including the functional organization of the ink sac and funnel organ that produce it; (2) the chemical components of ink, with a focus on the best known of these—melanin and the biochemical pathways involved in its production; (3) the neuroecology of the use of ink in predator-prey interactions by cephalopods in their natural environment; and (4) the use of cephalopod ink by humans, including in the development of drugs for biomedical applications and other chemicals for industrial and other commercial applications. As is hopefully evident from this review, much is known about cephalopod ink and inking, yet more striking is how little we know. Towards closing that gap, future directions in research on cephalopod inking are suggested.

Nociceptive sensitization reduces predation risk

Sublethal injury triggers long-lasting sensitization of defensive responses in most species examined, suggesting the involvement of powerful evolutionary selection pressures [1]. In humans, this persistent nociceptive sensitization is often accompanied by heightened sensations of pain and anxiety [2]. While experimental [3] and clinical [4] evidence support the adaptive value of immediate nociception during injury, no direct evidence exists for adaptive benefits of long-lasting sensitization after injury. Recently, we showed that minor injury produces long-term sensitization of behavioral and neuronal responses in squid, Doryteuthis pealei [5, 6]. Here we tested the adaptive value of this sensitization during encounters between squid and a natural fish predator. Locomotion and other spontaneous behaviors of squid that received distal injury to a single arm (with or without transient anesthesia) showed no measurable impairment 6 hr after the injury. However, black sea bass given access to freely swimming squid oriented toward and pursued injured squid at greater distances than uninjured squid, regardless of previous anesthetic treatment. Once targeted, injured squid began defensive behavioral sequences [7, 8] earlier than uninjured squid. This effect was blocked by brief anesthetic treatment that prevented development of nociceptive sensitization [6, 9]. Importantly, the early anesthetic treatment also reduced the subsequent escape and survival of injured, but not uninjured, squid. Thus, while minor injury increases the risk of predatory attack, it also triggers a sensitized state that promotes enhanced responsiveness to threats, increasing the survival (Darwinian fitness) of injured animals during subsequent predatory encounters.

Graded behavioral responses and habituation to sound in the common cuttlefish, Sepia officinalis

Sound is a widely available and vital cue in aquatic environments yet most bioacoustic research has focused on marine vertebrates, leaving sound detection in invertebrates poorly understood. Cephalopods are an ecologically key taxon that likely use sound and may be impacted by increasing anthropogenic ocean noise, but little is known regarding their behavioral responses or adaptations to sound stimuli. These experiments identify the acoustic range and levels that elicit a wide range of secondary defense behaviors such as inking, jetting, and rapid coloration change. Secondarily, it was found that cuttlefish habituate to certain sound stimuli. The present study examined the behavioral responses of 22 cuttlefish (Sepia officinalis) to pure-tone pips ranging from 80-1000 Hz with sound pressure levels of 85–188 dB re 1 μPa rms and particle accelerations of 0-17.1 m.s-2. Cuttlefish escape responses (inking, jetting) were observed between frequencies of 80-300 Hz and at sound levels above 140 dB re 1 μPa rms and 0.01 m.s-2 (0.74 m.s-2 for inking responses). Body patterning changes and fin movements were observed at all frequencies and sound levels. Response intensity was dependent upon stimulus amplitude and frequency, suggesting that cuttlefish also possess loudness perception with a maximum sensitivity around 150 Hz. Cuttlefish habituated to repeated 200 Hz tone pips, at two sound intensities. Total response inhibition was not reached, however, and a basal response remained present in most animals. The graded responses provide a loudness sensitivity curve and suggest an ecological function for sound-use in cephalopods.

Ink from longfin inshore squid, Doryteuthis pealeii, as a chemical and visual defense against two predatory fishes, summer flounder, Paralichthys dentatus, and sea catfish, Ariopsis felis

Chemical and visual defenses are used by many organisms to avoid being approached or eaten by predators. An example is inking molluscs-including gastropods such as sea hares and cephalopods such as squid, cuttlefish, and octopus-which release a colored ink upon approach or attack. Previous work showed that ink can protect molluscs through a combination of chemical, visual, and other effects. In this study, we examined the effects of ink from longfin inshore squid, Doryteuthis pealeii, on the behavior of two species of predatory fishes, summer flounder, Paralichthys dentatus, and sea catfish, Ariopsis felis. Using a cloud assay, we found that ink from longfin inshore squid affected the approach phase of predation by summer flounder, primarily through its visual effects. Using a food assay, we found that the ink affected the consummatory and ingestive phase of predation of both sea catfish and summer flounder, through the ink's chemical properties. Fractionation of ink showed that most of its deterrent chemical activity is associated with melanin granules, suggesting that either compounds adhering to these granules or melanin itself are the most biologically active. This work provides the basis for a comparative approach to identify deterrent molecules from inking cephalopods and to examine neural mechanisms whereby these chemicals affect behavior of fish, using the sea catfish as a chemosensory model.

Defensive responses of cuttlefish to different teleost predators

We evaluated cuttlefish (Sepia officinalis) responses to three teleost predators: bluefish (Pomatomus saltatrix), summer flounder (Paralichthys dentatus), and black seabass (Centropristis striata). We hypothesized that the distinct body shapes, swimming behaviors, and predation tactics exhibited by the three fishes would elicit markedly different antipredator responses by cuttlefish. Over the course of 25 predator-prey behavioral trials, 3 primary and 15 secondary defense behaviors of cuttlefish were shown to predators. In contrast, secondary defenses were not shown during control trials in which predators were absent. With seabass-a benthic, sit-and-pursue predator-cuttlefish used flight and spent more time swimming in the water column than with other predators. With bluefish-an active, pelagic searching predator-cuttlefish remained closely associated with the substrate and relied more on cryptic behaviors. Startle (deimatic) displays were the most frequent secondary defense shown to seabass and bluefish, particularly the Dark eye ring and Deimatic spot displays. We were unable to evaluate secondary defenses by cuttlefish to flounder-a lie-and-wait predator-because flounder did not pursue cuttlefish or make attacks. Nonetheless, cuttlefish used primary defense during flounder trials, alternating between cryptic still and moving behaviors. Overall, our results suggest that cuttlefish may vary their behavior in the presence of different teleost predators: cryptic behaviors may be more important in the presence of active searching predators (e.g., bluefish), while conspicuous movements such as swimming in the water column and startle displays may be more prevalent with relatively sedentary, bottom-associated predators (e.g., seabass).

Clever strategists: Australian Magpies vary mobbing strategies, not intensity, relative to different species of predator

Anti-predator behaviour of magpies was investigated, using five species of model predators, at times of raising offspring. We predicted differences in mobbing strategies for each predator presented and also that raising juveniles would affect intensity of the mobbing event. Fourteen permanent resident family groups were tested using 5 different types of predator (avian and reptilian) known to be of varying degrees of risk to magpies and common in their habitat. In all, 210 trials were conducted (across three different stages of juvenile development). We found that the stage of juvenile development did not alter mobbing behaviour significantly, but predator type did. Aerial strategies (such as swooping) were elicited by taxidermic models of raptors, whereas a taxidermic model of a monitor lizard was approached on the ground and a model snake was rarely approached. Swooping patterns also changed according to which of the three raptors was presented. Our results show that, in contrast to findings in other species, magpies vary mobbing strategy depending on the predator rather than varying mobbing intensity.

Deceptive vibratory communication: pupae of a beetle exploit the freeze response of larvae to protect themselves

It is argued that animal signals may have evolved so as to manipulate the response of receivers in a way that increases the fitness of the signallers. In deceptive communication, receivers incur costs by responding to false signals. Recently, we reported that pupae of the soil-inhabiting Japanese rhinoceros beetle Trypoxylus dichotoma produce vibratory signals to deter burrowing larvae, thereby protecting themselves. In the present study, monitoring of vibrations associated with larval movement revealed that T. dichotoma larvae remained motionless for ca 10 min when pupal vibratory signals were played back transiently (freeze response). Furthermore, pupal signals of T. dichotoma elicited a freeze response in three other scarabaeid species, whose pupae do not produce vibratory signals. This indicates that the freeze response to certain types of vibration evolved before the divergence of these species and has been evolutionarily conserved, presumably because of the fitness advantage in avoiding predators. Pupae of T. dichotoma have probably exploited pre-existing anti-predator responses of conspecific larvae to protect themselves by emitting deceptive vibratory signals.

Peripheral injury induces long-term sensitization of defensive responses to visual and tactile stimuli in the squid Loligo pealeii, Lesueur 1821

Survivable injuries are a common yet costly experience. The ability to sense and respond to noxious stimuli is an almost universal trait, and prolonged behavioral alterations, including sensitization to touch and other stimuli, may function to ameliorate fitness costs associated with injury. Cephalopods can modify their behavior by learned association with noxious electric shock, but non-associative alterations of behavioral responses after tissue injury have not been studied. The aim of this study was to make the first systematic investigations in any cephalopod of behavioral responses and alterations elicited by explicit, minor injury. By testing responsiveness in the longfin squid, Loligo pealeii, to the approach and contact of an innocuous filament applied to different parts of the body both before and after injury to the distal third of one arm, we show that a cephalopod expresses behavioral alterations persisting for at least 2 days after injury. These alterations parallel forms of nociceptive plasticity in other animals, including general and site-specific sensitization to tactile stimuli. A novel finding is that hyper-responsiveness after injury extends to visual stimuli. Injured squid are more likely to employ crypsis than escape in response to an approaching visual stimulus shortly after injury, but initiate escape earlier and continue escape behaviors for longer when tested from 1 to 48 h after injury. Injury failed to elicit overt wound-directed behavior (e.g. grooming) or change hunting success. Our results show that long-lasting nociceptive sensitization occurs in cephalopods, and suggest that it may function to reduce predation risk after injury.