Sensory specializations drive octopus and squid behaviour.

The evolution of new traits enables expansion into new ecological and behavioural niches. Nonetheless, demonstrated connections between divergence in protein structure, function and lineage-specific behaviours remain rare. Here we show that both octopus and squid use cephalopod-specific chemotactile receptors (CRs) to sense their respective marine environments, but structural adaptations in these receptors support the sensation of specific molecules suited to distinct physiological roles. We find that squid express ancient CRs that more closely resemble related nicotinic acetylcholine receptors, whereas octopuses exhibit a more recent expansion in CRs consistent with their elaborated 'taste by touch' sensory system. Using a combination of genetic profiling, physiology and behavioural analyses, we identify the founding member of squid CRs that detects soluble bitter molecules that are relevant in ambush predation. We present the cryo-electron microscopy structure of a squid CR and compare this with octopus CRs1 and nicotinic receptors2. These analyses demonstrate an evolutionary transition from an ancestral aromatic 'cage' that coordinates soluble neurotransmitters or tastants to a more recent octopus CR hydrophobic binding pocket that traps insoluble molecules to mediate contact-dependent chemosensation. Thus, our study provides a foundation for understanding how adaptation of protein structure drives the diversification of organismal traits and behaviour.

Squid male alternative reproductive tactics are determined by birth date.

Alternative reproductive tactics (ARTs) are discontinuous phenotypes associated with reproduction, observed in males of many species. Typically, large males adopt a tactic of competing with rivals for mating, while small males adopt a tactic of stealing fertilization opportunities from the large males. The 'birth date hypothesis', proposing that the date of birth influences the determination of each male's reproductive tactic, has been tested only in teleost fish to date. Here, the birth date hypothesis was tested in ARTs of Japanese spear squid Heterololigo bleekeri (consort/sneaker) by analysing statolith growth increments. The birth date significantly differed between consorts (early-hatched) and sneakers (late-hatched). However, no differences were detected in growth history up to 100 days from hatching. Most immature males caught during the reproductive season were larger than sneakers, and their hatch date was similar to that of consorts, suggesting that these immature males had already been following a life-history pathway as a consort. These results indicate that ARTs of H. bleekeri are determined based on their hatch date in early life. This study firstly suggests that the birth date hypothesis applies to aquatic invertebrates, suggesting that the mechanism by which birth date determines the individual phenotype is a phenomenon more common than previously believed.

State-dependent dynamics of cuttlefish mantle activity.

Cuttlefish skin is a powerful rendering device, capable of producing extraordinary changes in visual appearance over a broad range of temporal scales. This unique ability is typically associated with camouflage; however, cuttlefish often produce skin patterns that do not appear connected with the surrounding environment, such as fast large-scale fluctuations with wave-like characteristics. Little is known about the functional significance of these dynamic patterns. In this study, we developed novel tools for analyzing pattern dynamics, and demonstrate their utility for detecting changes in feeding state that occur without concomitant changes in sensory stimulation. Under these conditions, we found that the dynamic properties of specific pattern components differ for different feeding states, despite no measurable change in the overall expression of those components. Therefore, these dynamic changes are not detectable by conventional analyses focusing on pattern expression, requiring analytical tools specifically targeted to pattern dynamics.

Elucidating the control and development of skin patterning in cuttlefish.

Few animals provide a readout that is as objective of their perceptual state as camouflaging cephalopods. Their skin display system includes an extensive array of pigment cells (chromatophores), each expandable by radial muscles controlled by motor neurons. If one could track the individual expansion states of the chromatophores, one would obtain a quantitative description-and potentially even a neural description by proxy-of the perceptual state of the animal in real time. Here we present the use of computational and analytical methods to achieve this in behaving animals, quantifying the states of tens of thousands of chromatophores at sixty frames per second, at single-cell resolution, and over weeks. We infer a statistical hierarchy of motor control, reveal an underlying low-dimensional structure to pattern dynamics and uncover rules that govern the development of skin patterns. This approach provides an objective description of complex perceptual behaviour, and a powerful means to uncover the organizational principles that underlie the function, dynamics and morphogenesis of neural systems.

Modulations of ocean-atmosphere interactions on squid abundance over Southwest Atlantic.

Anthropogenic shifts in seas are reshaping fishing trends, with significant implications for aquatic food sources throughout this century. Examining a 21-year abundance dataset of Argentine shortfin squids Illex argentinus paired with a regional oceanic analysis, we noted strong correlations between squid annual abundance and sea surface temperature (SST) in January and February and eddy kinetic energy (EKE) from March to May in the Southwest Atlantic. A deeper analysis revealed combined ocean-atmosphere interactions, pinpointed as the primary mode in a rotated empirical orthogonal function analysis of SST. This pattern produced colder SST and amplified EKE in the surrounding seas, factors crucial for the unique life stages of squids. Future projections from the CMIP6 archive indicated that this ocean-atmosphere pattern, referred to as the Atlantic symmetric pattern, would persist in its cold SST phase, promoting increased squid abundance. However, rising SSTs due to global warming might counteract the abundance gains. Our findings uncover a previously unrecognized link between squids and specific environmental conditions governed by broader ocean-atmosphere interactions in the Southwest Atlantic. Integrating these insights with seasonal and decadal projections can offer invaluable information to stakeholders in squid fisheries and marine conservation under a changing climate.

Bioluminescent backlighting illuminates the complex visual signals of a social squid in the deep sea.

Visual signals rapidly relay information, facilitating behaviors and ecological interactions that shape ecosystems. However, most known signaling systems can be restricted by low light levels-a pervasive condition in the deep ocean, the largest inhabitable space on the planet. Resident visually cued animals have therefore been hypothesized to have simple signals with limited information-carrying capacity. We used cameras mounted on remotely operated vehicles to study the behavior of the Humboldt squid, Dosidicus gigas, in its natural deep-sea habitat. We show that specific pigmentation patterns from its diverse repertoire are selectively displayed during foraging and in social scenarios, and we investigate how these behaviors may be used syntactically for communication. We additionally identify the probable mechanism by which D. gigas, and related squids, illuminate these patterns to create visual signals that can be readily perceived in the deep, dark ocean. Numerous small subcutaneous (s.c.) photophores (bioluminescent organs) embedded throughout the muscle tissue make the entire body glow, thereby backlighting the pigmentation patterns. Equipped with a mechanism by which complex information can be rapidly relayed through a visual pathway under low-light conditions, our data suggest that the visual signals displayed by D. gigas could share design features with advanced forms of animal communication. Visual signaling by deep-living cephalopods will likely be critical in understanding how, and how much, information can be shared in one of the planet's most challenging environments for visual communication.

The cytokine MIF controls daily rhythms of symbiont nutrition in an animal-bacterial association.

The recent recognition that many symbioses exhibit daily rhythms has encouraged research into the partner dialogue that drives these biological oscillations. Here we characterized the pivotal role of the versatile cytokine macrophage migration inhibitory factor (MIF) in regulating a metabolic rhythm in the model light-organ symbiosis between Euprymna scolopes and Vibrio fischeri As the juvenile host matures, it develops complex daily rhythms characterized by profound changes in the association, from gene expression to behavior. One such rhythm is a diurnal shift in symbiont metabolism triggered by the periodic provision of a specific nutrient by the mature host: each night the symbionts catabolize chitin released from hemocytes (phagocytic immune cells) that traffic into the light-organ crypts, where the population of V. fischeri cells resides. Nocturnal migration of these macrophage-like cells, together with identification of an E. scolopes MIF (EsMIF) in the light-organ transcriptome, led us to ask whether EsMIF might be the gatekeeper controlling the periodic movement of the hemocytes. Western blots, ELISAs, and confocal immunocytochemistry showed EsMIF was at highest abundance in the light organ. Its concentration there was lowest at night, when hemocytes entered the crypts. EsMIF inhibited migration of isolated hemocytes, whereas exported bacterial products, including peptidoglycan derivatives and secreted chitin catabolites, induced migration. These results provide evidence that the nocturnal decrease in EsMIF concentration permits the hemocytes to be drawn into the crypts, delivering chitin. This nutritional function for a cytokine offers the basis for the diurnal rhythms underlying a dynamic symbiotic conversation.

Transitioning to confined spaces impacts bacterial swimming and escape response.

Symbiotic bacteria often navigate complex environments before colonizing privileged sites in their host organism. Chemical gradients are known to facilitate directional taxis of these bacteria, guiding them toward their eventual destination. However, less is known about the role of physical features in shaping the path the bacteria take and defining how they traverse a given space. The flagellated marine bacterium Vibrio fischeri, which forms a binary symbiosis with the Hawaiian bobtail squid, Euprymna scolopes, must navigate tight physical confinement during colonization, squeezing through a tissue bottleneck constricting to ∼2 µm in width on the way to its eventual home. Using microfluidic in vitro experiments, we discovered that V. fischeri cells alter their behavior upon entry into confined space, straightening their swimming paths and promoting escape from confinement. Using a computational model, we attributed this escape response to two factors: reduced directional fluctuation and a refractory period between reversals. Additional experiments in asymmetric capillary tubes confirmed that V. fischeri quickly escape from confined ends, even when drawn into the ends by chemoattraction. This avoidance was apparent down to a limit of confinement approaching the diameter of the cell itself, resulting in a balance between chemoattraction and evasion of physical confinement. Our findings demonstrate that nontrivial distributions of swimming bacteria can emerge from simple physical gradients in the level of confinement. Tight spaces may serve as an additional, crucial cue for bacteria while they navigate complex environments to enter specific habitats.

The mechanical properties of the mantle muscle of European cuttlefish (Sepia officinalis).

The circular muscles surrounding the mantle cavity of European cuttlefish (Sepia officinalis) generate the mechanical power to compress the cavity, forcing a jet of water out of the funnel, propelling the animal during jet propulsion swimming. During ontogeny, jetting frequency decreases in adults compared with juveniles, and this is expected to be reflected in the contractile properties of the locomotory muscles. To develop greater insight into how the locomotion of these animals is powered during ontogeny, we determined the mechanical properties of bundles of muscle fascicles during isometric, isotonic and cyclic length changes in vitro, at two life stages: juveniles and adults. The twitch kinetics were faster in juveniles than in adults (twitch rise time 257 ms compared with 371 ms; half-twitch relaxation 257 ms compared with 677 ms in juveniles and adults, respectively); however, twitch and tetanic stress, the maximum velocity of shortening and curvature of the force-velocity relationship did not differ. Under cyclic conditions, net power exhibited an inverted U-shaped relationship with cycle frequency in both juveniles and adults; the frequency at which maximum net power was achieved was shifted to lower cycle frequencies with increased maturity, which is consistent with the slower contraction and relaxation kinetics in adults compared with juveniles. The cycle frequency at which peak power was achieved during cyclical contractions in vitro was found to match that seen in vivo in juveniles, suggesting power is being maximised during jet propulsion swimming.

Critical symbiont signals drive both local and systemic changes in diel and developmental host gene expression.

The colonization of an animal's tissues by its microbial partners creates networks of communication across the host's body. We used the natural binary light-organ symbiosis between the squid Euprymna scolopes and its luminous bacterial partner, Vibrio fischeri, to define the impact of colonization on transcriptomic networks in the host. A night-active predator, E. scolopes coordinates the bioluminescence of its symbiont with visual cues from the environment to camouflage against moon and starlight. Like mammals, this symbiosis has a complex developmental program and a strong day/night rhythm. We determined how symbiont colonization impacted gene expression in the light organ itself, as well as in two anatomically remote organs: the eye and gill. While the overall transcriptional signature of light organ and gill were more alike, the impact of symbiosis was most pronounced and similar in light organ and eye, both in juvenile and adult animals. Furthermore, the presence of a symbiosis drove daily rhythms of transcription within all three organs. Finally, a single mutation in V. fischeri-specifically, deletion of the lux operon, which abrogates symbiont luminescence-reduced the symbiosis-dependent transcriptome of the light organ by two-thirds. In addition, while the gills responded similarly to light-organ colonization by either the wild-type or mutant, luminescence was required for all of the colonization-associated transcriptional responses in the juvenile eye. This study defines not only the impact of symbiont colonization on the coordination of animal transcriptomes, but also provides insight into how such changes might impact the behavior and ecology of the host.

Embryonic development of the camouflaging dwarf cuttlefish, Sepia bandensis.

BACKGROUND: The dwarf cuttlefish Sepia bandensis, a camouflaging cephalopod from the Indo-Pacific, is a promising new model organism for neuroscience, developmental biology, and evolutionary studies. Cuttlefish dynamically camouflage to their surroundings by altering the color, pattern, and texture of their skin. The skin's "pixels" (chromatophores) are controlled by motor neurons projecting from the brain. Thus, camouflage is a visible representation of neural activity. In addition to camouflage, the dwarf cuttlefish uses dynamic skin patterns for social communication. Despite more than 500 million years of evolutionary separation, cuttlefish and vertebrates converged to form limbs, camera-type eyes and a closed circulatory system. Moreover, cuttlefish have a striking ability to regenerate their limbs. Interrogation of these unique biological features will benefit from the development of a new set of tools. Dwarf cuttlefish reach sexual maturity in 4 months, they lay dozens of eggs over their 9-month lifespan, and the embryos develop to hatching in 1 month. RESULTS: Here, we describe methods to culture dwarf cuttlefish embryos in vitro and define 25 stages of cuttlefish development. CONCLUSION: This staging series serves as a foundation for future technologies that can be used to address a myriad of developmental, neurobiological, and evolutionary questions.

Hybrid Histidine Kinase BinK Represses Vibrio fischeri Biofilm Signaling at Multiple Developmental Stages.

The symbiosis between the Hawaiian bobtail squid, Euprymna scolopes, and its exclusive light organ symbiont, Vibrio fischeri, provides a natural system in which to study host-microbe specificity and gene regulation during the establishment of a mutually beneficial symbiosis. Colonization of the host relies on bacterial biofilm-like aggregation in the squid mucus field. Symbiotic biofilm formation is controlled by a two-component signaling (TCS) system consisting of regulators RscS-SypF-SypG, which together direct transcription of the symbiosis polysaccharide Syp. TCS systems are broadly important for bacteria to sense environmental cues and then direct changes in behavior. Previously, we identified the hybrid histidine kinase BinK as a strong negative regulator of V. fischeri biofilm regulation, and here we further explore the function of BinK. To inhibit biofilm formation, BinK requires the predicted phosphorylation sites in both the histidine kinase (H362) and receiver (D794) domains. Furthermore, we show that RscS is not essential for host colonization when binK is deleted from strain ES114, and imaging of aggregate size revealed no benefit to the presence of RscS in a background lacking BinK. Strains lacking RscS still suffered in competition. Finally, we show that BinK functions to inhibit biofilm gene expression in the light organ crypts, providing evidence for biofilm gene regulation at later stages of host colonization. Overall, this study provides direct evidence for opposing activities of RscS and BinK and yields novel insights into biofilm regulation during the maturation of a beneficial symbiosis. IMPORTANCE Bacteria are often in a biofilm state, and transitions between planktonic and biofilm lifestyles are important for pathogenic, beneficial, and environmental microbes. The critical nature of biofilm formation during Vibrio fischeri colonization of the Hawaiian bobtail squid light organ provides an opportunity to study development of this process in vivo using a combination of genetic and imaging approaches. The current work refines the signaling circuitry of the biofilm pathway in V. fischeri, provides evidence that biofilm regulatory changes occur in the host, and identifies BinK as one of the regulators of that process. This study provides information about how bacteria regulate biofilm gene expression in an intact animal host.

Diet, trophic interactions and possible ecological role of commercial sharks and batoids in northern Peruvian waters.

The Peruvian sea represents one of the most productive ocean ecosystems and possesses one of the largest elasmobranch fisheries in the Pacific Ocean. Ecosystem-based management of these fisheries will require information on the trophic ecology of elasmobranchs. This study aimed to understand the diet, trophic interactions and the role of nine commercial elasmobranch species in northern Peru through the analysis of stomach contents. A total of 865 non-empty stomachs were analysed. Off northern Peru, elasmobranchs function as upper-trophic-level species consuming 78 prey items, predominantly teleosts and cephalopods. Two distinctive trophic assemblages were identified: (a) sharks (smooth hammerhead shark Sphyrna zygaena, thresher shark Alopias spp. and blue shark Prionace glauca) that feed mainly on cephalopods in the pelagic ecosystem; and (b) sharks and batoids (Chilean eagle ray Myliobatis chilensis, humpback smooth-hound Mustelus whitneyi, spotted houndshark Triakis maculata, Pacific guitarfish Pseudobatos planiceps, copper shark Carcharhinus brachyurus and school shark Galeorhinus galeus) that feed mainly on teleosts and invertebrates in the benthonic and pelagic coastal ecosystem. This study reveals for the first time the diet of T. maculata and the importance of elasmobranchs as predators of abundant and commercial species (i.e., jumbo squid Dosidicus gigas and Peruvian anchovy Engraulis ringens). The results of this study can assist in the design of an ecosystem-based management for the northern Peruvian sea and the conservation of these highly exploited, threatened or poorly understood group of predators in one of the most productive marine ecosystems.

Suction adhesion in the gliding joint of a cephalopod.

We have discovered features of the nuchal joint in the squid, Doryteuthispealeii, that are unique compared with moveable joints in other animals. The joint's function is unclear but it allows the head to glide toward and away from the mantle. The head glides along the joint with ease yet disarticulating the joint perpendicular to the axis of movement requires considerable force. After disarticulation, the joint components can be repositioned and full function restored immediately. Thus, an unknown attachment mechanism prevents the joint from being disarticulated yet permits gliding. We show that the joint was formed by the articulation of the nuchal cartilage and a heretofore-undescribed organ that we named the nuchal 'joint pad'. The joint pad is composed predominantly of muscle, connective tissue and cartilage organized into two distinct regions: a ventral cartilaginous layer and a dorsal muscular layer. Disarticulating the nuchal joint at a displacement rate of 5 mm s-1 required 1.5 times greater stress (i.e. force per unit area) than at 1 mm s-1 The force required to disarticulate the joint increased with nuchal cartilage area0.91 and with nuchal cartilage length1.88 The stress required to shear the nuchal joint was nearly three orders of magnitude lower than that required to disarticulate the joint. Stimulation of the joint pad dorso-ventral musculature resulted in significantly greater shear force required to move the joint (P=0.004). Perforating the nuchal cartilage decreased the stress required to disarticulate the joint to nearly zero. The results support the hypothesis that suction is the attachment mechanism.

Specialization for rapid excitation in fast squid tentacle muscle involves action potentials absent in slow arm muscle.

An important aspect of the performance of many fast muscle fiber types is rapid excitation. Previous research on the cross-striated muscle fibers responsible for the rapid tentacle strike in squid has revealed the specializations responsible for high shortening velocity, but little is known about excitation of these fibers. Conventional whole-cell patch recordings were made from tentacle fibers and the slower obliquely striated muscle fibers of the arms. The fast-contracting tentacle fibers show an approximately 10-fold greater sodium conductance than that of the arm fibers and, unlike the arm fibers, the tentacle muscle fibers produce action potentials. In situ hybridization using an antisense probe to the voltage-dependent sodium channel present in this squid genus shows prominent expression of sodium channel mRNA in tentacle fibers but undetectable expression in arm fibers. Production of action potentials by tentacle muscle fibers and their absence in arm fibers is likely responsible for the previously reported greater twitch-tetanus ratio in the tentacle versus the arm fibers. During the rapid tentacle strike, a few closely spaced action potentials would result in maximal activation of transverse tentacle muscle. Activation of the slower transverse muscle fibers in the arms would require summation of excitatory postsynaptic potentials over a longer time, allowing the precise modulation of force required for supporting slower movements of the arms.

Transient pressure modeling in jetting animals.

There are many marine animals that employ a form of jet propulsion to move through the water, often creating the jets by expanding and collapsing internal fluid cavities. Due to the unsteady nature of this form of locomotion and complex body/nozzle geometries, standard modeling techniques prove insufficient at capturing internal pressure dynamics, and hence swimming forces. This issue has been resolved with a novel technique for predicting the pressure inside deformable jet producing cavities (M. Krieg and K. Mohseni, J. Fluid Mech., 769, 2015), which is derived from evolution of the surrounding fluid circulation. However, this model was only validated for an engineered jet thruster with simple geometry and relatively high Reynolds number (Re) jets. The purpose of this manuscript is twofold: (i) to demonstrate how the circulation based pressure model can be used to analyze different animal body motions as they relate to propulsive output, for multiple species of jetting animals, (ii) and to quantitatively validate the pressure modeling for biological jetting organisms (typically characterized by complicated cavity geometry and low/intermediate Re flows). Using jellyfish (Sarsia tubulosa) as an example, we show that the pressure model is insensitive to complex cavity geometry, and can be applied to lower Re swimming. By breaking down the swimming behavior of the jellyfish, as well as that of squid and dragonfly larvae, according to circulation generating mechanisms, we demonstrate that the body motions of Sarsia tubulosa are optimized for acceleration at the beginning of pulsation as a survival response. Whereas towards the end of jetting, the velar morphology is adjusted to decrease the energetic cost. Similarly, we show that mantle collapse rates in squid maximize propulsive efficiency. Finally, we observe that the hindgut geometry of dragonfly larvae minimizes the work required to refill the cavity. Date Received: 10-18-2019, Date Accepted: 99-99-9999 *kriegmw@hawaii.edu, UHM Ocean and Res Eng, 2540 Dole St, Honolulu, HI 96822.

An encounter between a pelagic shark and giant cephalopod.

An oceanic whitetip shark (Carcharhinus longimanus) was observed off the coast of Kona, Hawaii, with scars caused by the tentacles of a large cephalopod. While the exact species could not be confirmed, candidate species include the giant squid (Architeuthis dux) or species from the genera Thysanoteuthis (flying squids) and Megalocranchia (glass squids). Telemetry shows C. longimanus will dive within the mesopelagic zone and may interact with or even forage for large cephalopods.

The importance of microbes in animal development: lessons from the squid-vibrio symbiosis.

Developmental biology is among the many subdisciplines of the life sciences being transformed by our increasing awareness of the role of coevolved microbial symbionts in health and disease. Most symbioses are horizontally acquired, i.e., they begin anew each generation. In such associations, the embryonic period prepares the animal to engage with the coevolved partner(s) with fidelity following birth or hatching. Once interactions are underway, the microbial partners drive maturation of tissues that are either directly associated with or distant from the symbiont populations. Animal alliances often involve complex microbial communities, such as those in the vertebrate gastrointestinal tract. A series of simpler-model systems is providing insight into the basic rules and principles that govern the establishment and maintenance of stable animal-microbe partnerships. This review focuses on what biologists have learned about the developmental trajectory of horizontally acquired symbioses through the study of the binary squid-vibrio model.

Quantifying the swimming gaits of veined squid (Loligo forbesii) using bio-logging tags.

Squid are mobile, diverse, ecologically important marine organisms whose behavior and habitat use can have substantial impacts on ecosystems and fisheries. However, as a consequence in part of the inherent challenges of monitoring squid in their natural marine environment, fine-scale behavioral observations of these free-swimming, soft-bodied animals are rare. Bio-logging tags provide an emerging way to remotely study squid behavior in their natural environments. Here, we applied a novel, high-resolution bio-logging tag (ITAG) to seven veined squid, Loligo forbesii, in a controlled experimental environment to quantify their short-term (24 h) behavioral patterns. Tag accelerometer, magnetometer and pressure data were used to develop automated gait classification algorithms based on overall dynamic body acceleration, and a subset of the events were assessed and confirmed using concurrently collected video data. Finning, flapping and jetting gaits were observed, with the low-acceleration finning gaits detected most often. The animals routinely used a finning gait to ascend (climb) and then glide during descent with fins extended in the tank's water column, a possible strategy to improve swimming efficiency for these negatively buoyant animals. Arms- and mantle-first directional swimming were observed in approximately equal proportions, and the squid were slightly but significantly more active at night. These tag-based observations are novel for squid and indicate a more efficient mode of movement than suggested by some previous observations. The combination of sensing, classification and estimation developed and applied here will enable the quantification of squid activity patterns in the wild to provide new biological information, such as in situ identification of behavioral states, temporal patterns, habitat requirements, energy expenditure and interactions of squid through space-time in the wild.

Hypoxia tolerance of giant axon-mediated escape jetting in California market squid (Doryteuthis opalescens).

Squids display a wide range of swimming behaviors, including powerful escape jets mediated by the giant axon system. For California market squid (Doryteuthis opalescens), maintaining essential behaviors like the escape response during environmental variations poses a major challenge as this species often encounters intrusions of cold, hypoxic offshore waters in its coastal spawning habitats. To explore the effects of hypoxia on locomotion and the underlying neural mechanisms, we made in vivo recordings of giant axon activity and simultaneous pressure inside the mantle cavity during escape jets in squid exposed to acute progressive hypoxia followed by return to normal dissolved oxygen (DO) concentration (normoxia). Compared with those in normoxia (>8 mg l-1 DO), escape jets were unchanged in moderate hypoxia (4 and 2 mg l-1 DO), but giant axon activity and associated mantle contractions significantly decreased while neuromuscular latency increased under severe hypoxia (0.5 mg l-1 DO). Animals that survived exposure to severe hypoxia reliably produced escape jets under such conditions and fully recovered as more oxygen became available. The reduction in neuromuscular output under hypoxia suggests that market squid may suppress metabolic activity to maintain sufficient behavioral output, a common strategy in many hypoxia-tolerant species. The ability to recover from the deleterious effects of hypoxia suggests that this species is well adapted to cope with coastal hypoxic events that commonly occur in Monterey Bay, unless these events become more severe in the future as climate change progresses.