The cardiac response of the crab Chasmagnathus granulatus as an index of sensory perception

Cardiovascular physiology of decapod crustaceans: from scientific inquiry to practical applications

Until recently, the decapod crustacean heart was regarded as a simple, single ventricle, contraction of which forces haemolymph out into seven arteries. Differential tissue perfusion is achieved by contraction and relaxation of valves at the base of each artery. In this Review, we discuss recent work that has shown that the heart is bifurcated by muscular sheets that may effectively divide the single ventricle into 'chambers'. Preliminary research shows that these chambers may contract differentially; whether this enables selective tissue perfusion remains to be seen. Crustaceans are unusual in that they can stop their heart for extended periods. These periods of cardiac arrest can become remarkably rhythmic, accounting for a significant portion of the cardiac repertoire. As we discuss in this Review, in crustaceans, changes in heart rate have been used extensively as a measurement of stress and metabolism. We suggest that the periods of cardiac pausing should also be quantified in this context. In the past three decades, an exponential increase in crustacean aquaculture has occurred and heart rate (and changes thereof) is being used to understand the stress responses of farmed crustaceans, as well as providing an indicator of disease progression. Furthermore, as summarized in this Review, heart rate is now being used as an effective indicator of humane methods to anaesthetize, stun or euthanize crustaceans destined for the table or for use in scientific research. We believe that incorporation of new biomedical technology and new animal welfare policies will guide future research directions in this field.

Noise accelerates embryonic development in a key crab species: Morphological and physiological carryover effects on early life stages

Anthropogenic noise is considered one important global pollutant. The impact of noise on marine invertebrates has been less assessed. The present study evaluated the chronic effect of the motorboat noise obtained from a lagoon's soundscape, the natural habitat of the key crab Neohelice granulata, on its whole embryonic development, considering morphological and physiological carryover effects on embryos and hatched larvae. Results demonstrated that embryonic development was shortened under noise exposure. The effects on advanced embryos, larvae and adult females were: increased heartbeats and non-viable eggs, and decreased fecundity. Biochemical responses showed lipid peroxidation in embryos while antioxidant enzymes were activated in larvae and adults, indicating a counteracting effect related to the life stage. The negative effects on fitness offspring may imply ecological consequences at the population level. Results are discussed in terms of the ecosystem engineer species studied and the habitat, a MAB UNESCO Reserve lagoon, suggesting the urgent need to develop mitigation plans.

Threatening stimuli elicit a sequential cardiac pattern in arthropods

In order to cope with the challenges of living in dynamic environments, animals rapidly adjust their behaviors in coordination with different physiological responses. Here, we studied whether threatening visual stimuli evoke different heart rate patterns in arthropods and whether these patterns are related with defensive behaviors. We identified two sequential phases of crab's cardiac response that occur with a similar timescale to that of the motor arrest and later escape response. The first phase was modulated by low salience stimuli and persisted throughout spaced stimulus presentation. The second phase was modulated by high-contrast stimuli and reduced by repetitive stimulus presentation. The overall correspondence between cardiac and motor responses suggests that the first cardiac response phase might be related to motor arrest while the second to the escape response. We show that in the face of threat arthropods coordinate their behavior and cardiac activity in a rapid and flexible manner.

Threat induces cardiac and metabolic changes that negatively impact survival in flies

Adjusting to a dynamic environment involves fast changes in the body’s internal state, characterized by coordinated alterations in brain activity and physiological and motor responses. Threat-induced defensive states are a classic case of coordinated adjustment of bodily responses, cardiac regulation being one of the best characterized examples in vertebrates. A great deal is known regarding the neural basis of invertebrate defensive behaviors, mainly in Drosophila melanogaster. However, whether physiological changes accompany these remains unknown. Here, we set out to describe the internal bodily state of fruit flies upon an inescapable threat and found cardiac acceleration during running and deceleration during freezing. In addition, we found that freezing leads to increased cardiac pumping from the abdomen toward the head-thorax, suggesting mobilization of energy resources. Concordantly, threat-triggered freezing reduces sugar levels in the hemolymph and renders flies less resistant to starvation. The cardiac responses observed during freezing were absent during spontaneous immobility, underscoring the active nature of freezing response. Finally, we show that baseline cardiac activity predicts the amount of freezing upon threat. This work reveals a remarkable similarity with the cardiac responses of vertebrates, suggesting an evolutionarily convergent defensive state in flies. Our findings are at odds with the widespread view that cardiac deceleration while freezing has first evolved in vertebrates and that it is energy sparing. Investigating the physiological changes coupled to defensive behaviors in the fruit fly has revealed that freezing is costly yet accompanied by cardiac deceleration and points to heart activity as a key modulator of defensive behaviors.

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Flies show tight coupling between defensive behaviors and cardiac activity

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Flies bias cardiac pumping toward the head and thorax during defensive behaviors

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After prolonged freezing, sugar levels and resistance to starvation are decreased

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Cardiac reversal rate and rate variability are predictive of freezing intensity

Patterns of heart rate and cardiac pausing in unrestrained resting decapod crustaceans

Measurement of heart rate (HR) has been used as an important physiological indicator in a broad range of taxa. In the present study HR patterns were measured in five species of unrestrained, resting decapod crustaceans. In addition to variation in HR among individuals, it was also very variable within an individual animal. While some of this variation was related to activity, there was also a non-locomotory component. Unstressed, resting crabs exhibited intermittent heart activity, whereas HR in stressed crabs was more stable, suggesting differential control of HR in resting crabs. Once the animals settled in the experimental apparatus they exhibited regular and extended cardiac pauses (acardia) of 15-300-s duration. As with HR, there was a significant variation in the frequency and length of acardic events, which were only observed in inactive crabs. Regaining of HR, following a period of acardia, was characterized by small adjustments in position and movement of the mouthparts. This rhythmic pattern, and the fact that entry into and out of acardia was not instantaneous, suggested that these events were related to release of neurohormones and their subsequent degradation in the system, rather than direct neural control of the heart. Because HR was variable and interrupted by regular periods of acardia, caution is recommended when calculating baseline levels of HR, or using HR alone as an indicator of physiological stress. Incorporating a coefficient of variation for HR and/or measuring the periods of acardia may be a more reliable indicator of physiological stress in decapod crustaceans.

Evidence of anticipatory immune and hormonal responses to predation risk in an echinoderm

Recent efforts have been devoted to the link between responses to non-physical stressors and immune states in animals, mostly using human and other vertebrate models. Despite evolutionary relevance, comparatively limited work on the appraisal of predation risk and aspects of cognitive ecology and ecoimmunology has been carried out in non-chordate animals. The present study explored the capacity of holothuroid echinoderms to display an immune response to both reactive and anticipatory predatory stressors. Experimental trials and a mix of behavioural, cellular and hormonal markers were used, with a focus on coelomocytes (analogues of mammalian leukocytes), which are the main components of the echinoderm innate immunity. Findings suggest that holothuroids can not only appraise threatening cues (i.e. scent of a predator or alarm signals from injured conspecifics) but prepare themselves immunologically, presumably to cope more efficiently with potential future injuries. The responses share features with recently defined central emotional states and wane after prolonged stress in a manner akin to habituation, which are traits that have rarely been shown in non-vertebrates, and never in echinoderms. Because echinoderms sit alongside chordates in the deuterostome clade, such findings offer unique insights into the adaptive value and evolution of stress responses in animals.

Chemosensitivity and role of swimming legs of mud crab, Scylla paramamosain, in feeding activity as determined by electrocardiographic and behavioural observations

Swimming crabs have a characteristic fifth pair of legs that are flattened into paddles for swimming purposes. The dactyl of these legs bears a thick seta along its edge. The chemoreceptive and feeding properties of the seta are supported with scientific evidence; however, there is no available data on the sensitivity of the setae in portunid crabs. The underlying mechanisms of the chemo- and mechano-sensitivity of appendages and their involvement in feeding activities of the mud crab (Scylla paramamosain) were investigated using electrocardiography and behavioural assay, which focused on the responses of the mud crab to chemical and touch stimulus. Electrocardiography revealed the sensory properties of the appendages. The dactyls of swimming legs and the antennules were chemosensitive, but not mechanosensitive and vice versa for the antennae. However, the mouthparts, claws, and walking legs were chemo- and mechanosensitive. Only the chemosensitive appendages, including the swimming legs, were directly involved in feeding. The flattened dactyls of the swimming legs were more efficient than the pointed dactyls of the walking legs in detecting the food organism crawling on the substrate. The structural features enhanced the capacity of the crab in coming into contact with scattered food items. This study revealed that the swimming legs are important appendages for feeding in the mud crab.

Stimulus Contrast Information Modulates Sensorimotor Decision Making in Goldfish

Animal survival relies on environmental information gathered by their sensory systems. We found that contrast information of a looming stimulus biases the type of defensive behavior that goldfish (Carassius auratus) perform. Low-contrast looms only evoke subtle alarm reactions whose probability is independent of contrast. As looming contrast increases, the probability of eliciting a fast escape maneuver, the C-start response, increases dramatically. Contrast information also modulates the decision of when to escape. Although response latency is known to depend on looming retinal size, we found that contrast acts as an additional parameter influencing this decision. When presenting progressively higher contrast stimuli, animals need shorter periods of stimulus processing to initiate the response. Our results comply with the notion that the decision to escape is a flexible process initiated with stimulus detection and followed by assessment of the perceived risk posed by the stimulus. Highly disruptive behaviors as the C-start are only observed when a multifactorial threshold that includes stimulus contrast is surpassed.

Experimental setup influences the cardiovascular responses of decapod crustaceans to environmental change

The effects of different holding methods on heart rate (HR) changes in the green crab, Carcinus maenas (Linnaeus, 1758), were investigated. Green crabs were held in perforated plastic boxes (with or without a layer of sand) suspended above the bottom of the tank or strapped to a weighted plastic grate. The HR of green crabs classified as unrestrained (plastic box with or without sand) dropped more rapidly compared with restrained (hanging from band, strapped to grate) green crabs. Within 1 h, unrestrained green crabs exhibited periods of cardiac pausing accounting for between 8% and 14% of the hourly time. In contrast, restrained green crabs rarely exhibited cardiac pausing. When the green crabs were subjected to a temperature increase (10–30 °C), the HR of unrestrained green crabs reached higher levels than that of the restrained animals. The four restraining methods were also used to investigate cardiac responses to hypoxia. During progressive hypoxia (100%–20% oxygen), the HR of unrestrained green crabs declined to lower levels than that of the restrained animals. The restraining methods appeared to be more stressful for the green crabs that maintained elevated HRs and were less able to respond to environmental change compared with green crabs that could move freely within a small chamber. This suggests that even subtle changes in experimental design may alter physiological responses.

Polarized object detection in crabs: a two-channel system

Many animal species take advantage of polarization vision for vital tasks such as orientation, communication and contrast enhancement. Previous studies have suggested that decapod crustaceans use a two-channel polarization system for contrast enhancement. Here, we characterize the polarization contrast sensitivity in a grapsid crab. We estimated the polarization contrast sensitivity of the animals by quantifying both their escape response and changes in heart rate when presented with polarized motion stimuli. The motion stimulus consisted of an expanding disk with an 82 deg polarization difference between the object and the background. More than 90% of animals responded by freezing or trying to avoid the polarized stimulus. In addition, we co-rotated the electric vector (e-vector) orientation of the light from the object and background by increments of 30 deg and found that the animals' escape response varied periodically with a 90 deg period. Maximum escape responses were obtained for object and background e-vectors near the vertical and horizontal orientations. Changes in cardiac response showed parallel results but also a minimum response when e-vectors of object and background were shifted by 45 deg with respect to the maxima. These results are consistent with an orthogonal receptor arrangement for the detection of polarized light, in which two channels are aligned with the vertical and horizontal orientations. It has been hypothesized that animals with object-based polarization vision rely on a two-channel detection system analogous to that of color processing in dichromats. Our results, obtained by systematically varying the e-vectors of object and background, provide strong empirical support for this theoretical model of polarized object detection.

New evidence on an old question: is the "fight or flight" stage present in the cardiac and respiratory regulation of decapod crustaceans?

The ability to stay alert to subtle changes in the environment and to freeze, fight or flight in the presence of predators requires integrating sensory information as well as triggering motor output to target tissues, both of which are associated with the autonomic nervous system. These reactions, which are commonly related to vertebrates, are the fundamental physiological responses that allow an animal to survive danger. The circulatory activity in vertebrates changes in opposite phases. The stage where circulatory activity is high is termed the "fight or flight stage", while the stage where circulatory activity slows down is termed the "rest and digest stage". It may be assumed that highly evolved invertebrates possess a comparable response system as they also require rapid cardiovascular and respiratory regulation to be primed when necessary. However, in invertebrates, the body plan may have developed such a system very differently. Since this topic is insufficiently studied, it is necessary to extend studies for a comparative analysis. In the present review, we use our own experimental results obtained in the crab Neohelice granulata and both older and newer findings obtained by other authors in decapod crustaceans as well as in other invertebrates, to compare the pattern of change in circulatory activity, especially in the "fight or flight" stage. We conclude that the main features of neuroautonomic regulation of the cardiac function were already present early in evolution, at least in highly evolved invertebrates, although conspicuous differences are also evident.

Characterization of the cardiac ganglion in the crab Neohelice granulata and immunohistochemical evidence of GABA-like extrinsic regulation

The aim of the present work is to provide an anatomical description of the cardiac system in the crab Neohelice granulata and evidence of the presence of GABA by means of immunohistochemistry. The ganglionic trunk was found lying on the inner surface of the heart's dorsal wall. After dissection, this structure appeared as a Y-shaped figure with its major axis perpendicular to the major axis of the heart. Inside the cardiac ganglion, we identified four large neurons of 63.7 μm ± 3.7 in maximum diameter, which were similar to the motor neurons described in other decapods. All the GABA-like immunoreactivity (GABAi) was observed as processes entering mainly the ganglionic trunk and branching in slender varicose fibers, forming a network around the large neurons suggesting that GABAi processes contact them. Our findings strengthen previous results suggesting that the GABAergic system mediates the cardio-inhibitory response upon sensory stimulation.