Carapace movements associated with ventilation and irrigation of the branchial chambers in the semaphore crab,Heloecius cordiformis (Decapoda: Brachyura: Ocypodidae)

Summary Carapace movements in crabs are briefly reviewed. While on land and recirculating branchial water, the Australian semaphore crab Heloecius cordiformis (Decapoda: Ocypodidae), a semi-terrestrial air-breathing mangrove crab, sequentially depresses and elevates its carapace relative to its thorax (0.5–1 mm excursion) in a regular pump-like manner. In quiescent crabs each carapace-pumping cycle lasts about 4 s; carapace depression takes 3 s and elevation 1 s. Carapace movements are brought about by pressures generated within the branchial chambers by the scaphognathites, probably in combination with carapace muscles. Carapace movements are associated with bilaterally synchronised scaphognathite activity. Unilateral scaphognathite activity was not observed. During normal forward recirculation of branchial water the scaphognathites beat at about 1.5 Hz (slow-forward pumping) and the lungs (epibranchial chambers) are not ventilated. In Heloecius, the lungs are not physically separated from the gills below by an anatomical barrier. Lung ventilation is accomplished during the following sequence of events: the carapace is lowered and the scaphognathites pump in a fast-forward mode at about 2.8 Hz. This activity preferentially pumps air out of the lungs and generates suction within the branchial chambers (4–10 cm H₂O below ambient) which draws water from external body surfaces into the hypobranchial space below and around the gills. At the end of the carapace's downward travel the scaphognathites switch from fast-forward to fastreverse beating at about 4 Hz. This pumps air into the lungs and the carapace elevates. As a result, during carapace elevation the water which had previously been drawn into the branchial chambers by fast-forward pumping activity is released and flows out between the legs and into the abdominosternal cavity. When the carapace reaches its original resting or up position the scaphognathites switch from fast-reverse to slowforward beating to re-establish water recirculation through the branchial chambers. This cycle is subsequently repeated. In stationary crabs, there are 2 carapace-pumping cycles per minute, increasing to 14 per minute in active crabs (walking). When water is absent, the lungs are preferentially ventilated by slow-reverse scaphognathite pumping activity. Carapace movements do not occur in the absence of branchial water. Carapace pumping is thought to provide a mechanism which permits the scaphognathites to ventilate the lungs in the presence of recirculating branchial water, without this water interfering with lung ventilation or being lost to the environment.Abbreviations FF, FR, SF, SR fast-forward, fast-reverse, slowforward, slow-reverse scaphognathite pumping - MEA Milne Edwards aperture     

Aerial respiration in the semaphore crab,Heloecius cordiformis,with or without branchial water

• 1.1. Semaphore crabs (Heloecius cordiformis) are active in air at low tide. Their branchial chambers are lined with a vascular epithelium and are expanded above the gills (five pairs) to form air cavities which could function as lungs. Water is continuously circulated over the gills.
• 2.2. The relative contribution made by the gills and lungs to gas exchange in semaphore crabs active in air and circulating branchial water, was determined by measuring oxygen consumption (at 25°C) in crabs with and without branchial water, and in crabs with their lungs subsequently occluded.
• 3.3. Activity levels and VO₂ were unaffected by the absence of branchial water.
• 4.4. With their lungs occluded, VO₂ dropped (on average) by 61% in crabs with branchial water (i.e. gills still functional) and by 81% in crabs without branchial water (gill function impaired).
• 5.5. It is concluded that semaphore crabs are obligate air breathers while active on land, despite carrying water within their branchial chambers. Lung development and gill reduction in land crabs is discussed briefly in relation to “terrestriality”.

     

Carapace movements aid air breathing in the semaphore crab,Heloecius cordiformis (Decapoda: Brachyura: Ocypodidae)

Summary While on land and recirculating branchial water the Australian semaphore crab Heloecius cordiformis (Decapoda: Ocypodidae), a semi-terrestrial airbreathing mangrove crab, sequentially depresses and elevates its carapace in a regular pump-like manner. The functional role of these carapace movements in aerial oxygen consumption is investigated. Carapace immobilisation (reversible and non-injurious) did not appear to affect branchial water circulation. In dry crabs (branchial water removed) carapace immobilisation had no effect on the rate of oxygen consumption (VO₂), heart rate or whole-body lactate (WBL) levels. In wet crabs (with branchial water) carapace immobilisation caused VO₂ to drop by 38% from 81 to 46 l O₂ · g^-1 · h^-1, heart rate to decline by 32%, from 2.5 to 1.7 Hz, and WBL levels to increase over 2.5-fold, from 0.27 to 0.67 mg · g^-1, after 3 h of carapace immobilisation. The (VO₂) of carapace-immobilised crabs with branchial water was similar to lung-occluded crabs with branchial water. Severe hypoxia induced physiological responses similar to those of carapace-immobilised crabs with branchial water. After 3 h of severe hypoxia, heart rate had declined by 80%, from 2.2 to 0.43 Hz, and the incidence of carapace pumping slowed by 85%, from 2.4 to 0.37 cycles · min^-1. It is concluded that in the absence of carapace movements branchial water in some way inteferes with lung ventilation. Under normal circumstances water circulation and lung ventilation are mutually exclusive processes (due to their singular dependence on the scaphognathites), yet in Heloecius these processes must be carried out simultaneously. Carapace movements may alleviate this conflict.Abbreviations FF, FR, SF, SR fast-forward, fast-reverse, slow-forward, slow-reverse scaphognathite pumping - MEA Milne Edwards aperture - VO₂ rate of oxygen consumption - WBL whole-body lactate     

Functional genomics and sexual differentiation in amphibians

To succeed on land rather than in water, crabs require a suite of physiological and morphological changes, and ultimately the ability to reproduce without access open water. Some species have modified gills to assist in gas exchange but accessory gas exchange organs, usually lungs, occur in many species. In accomplished air-breathers the lung becomes larger and more vascularised with pulmonary vessels directing oxygenated haemolymph to the heart. The relative abundance of O₂ in air promotes relative hypoventilation and thus an internal hypercapnia to drive CO₂ excretion. Land crabs have a dual circulation via either lungs or gills and shunting between the two may depend on respiratory media or exercise state. During their breeding migration on Christmas Island Gecarcoidea natalis maintained arterial Po₂ by branchial O₂ uptake, while pulmonary O₂ pressure was reduced; partly because exercise doubled relative haemolymph flow through the gills. Related species rely on elevated haemocyanin concentration and affinity for O₂ to assist uptake but this compromises unloading at the tissues and thus the aerobic scope of tissues. Aquatic crabs exchange salt and ammonia with water via the gills but in land crabs this is not possible. Birgus latro has adopted uricotelism but other species excrete ammonia in either the urine or as gas. Land crabs minimise urinary salt loss using a filtration-reabsorption system analogous to the kidney. Urine is redirected across the gills where salt reabsorption occurs in systems under hormonal control, although in G. natalis this is stimulatory and in B. latro inhibitory. While crabs occupy a range of habitats from aquatic to terrestrial, these species do not comprise a physiological continuum but across the crab taxa individual species possess appropriate and specific physiological features to survive in their individual habitat.     

Bimodal breathing in the estuarine crab Chasmagnathus granulatus Dana 1851--physiological and morphological studies

Chasmagnathus granulatus is an estuarine crab which actively moves from subtidal to supratidal areas. To elucidate the possible existence of extrabranchial sites for aerial gas exchange, we measured respiratory and acid-base variables in animals with and without branchial water (controls and experimental crabs, respectively) during air exposure. An histological study of the branchiostegite was also performed. Throughout 4 h of emergence C. granulatus did not suffer venous hypoxia, even without branchial water. The rate of oxygen uptake (M(O(2))) was similar in both groups. The rate of carbon dioxide excretion (M(CO(2))) and the gas exchange ratio (R) significantly decreased during emergence in both groups, with R significantly lower for experimental crabs. Consequently, CO(2) was accumulated in the hemolymph. This variable stabilized after 90 min in control animals, but experimental crabs continued accumulating CO(2). Histological study of the branchiostegites demonstrated the presence of an attenuated and greatly perfused epithelium facing the branchial chamber lumen, with a shortest diffusion distance of 0.5 microm. Simple folds and lobulated projections increase the respiratory surface area. These results suggest that C. granulatus is a bimodal breathing crab, active both in water and air. When emerged, this species extract oxygen directly from air through branchiostegal lungs, but relies on branchial exchange to eliminate carbon dioxide.     

Gas exchange patterns of Pterostichus niger (Carabidae) in dry and moist air

Gas exchange patterns of adult male Pterostichus niger Schaller after hydration (i.e. given access to food and water) are compared in dry air [5–7% relative humidity (RH)] and moist air (90–97% RH) by means of flow‐through CO₂ respirometry combined with infrared probe actography. Of thirty beetles examined, slightly more than 50% showed continuous gas exchange and are not considered further. Of the remaining beetles, the majority (approximately 71%) display a pattern of cyclic gas exchange in both dry and moist air (i.e. CO₂ gas is released in bursts, with a low level of CO₂ release during the interburst periods). A minority of the beetles (four out of 30) are found to exhibit discontinuous gas exchange in both dry and moist air; this is characterized by three clearly separated states of the spiracles: closed (C), flutter (F) and open (O) phases. The pattern of cyclic gas exchange is associated with weak abdominal pulsations. After switching from moist to dry air, a small modulation of the discontinuous gas exchange cycles (maximum mean CO₂ production rate) occurs, providing no clear support for the hygric theory of discontinuous gas exchange in this species (i.e. that it serves to restrict respiratory water loss).     

Morphological and behavioural adaptations to the rocky substrate by the fiddler crab Uca panamensis (Stimpson, 1859): preference for feeding substratum and feeding mechanism

The fiddler crab Uca panamensis (Stimpson, 1959) inhabits rocky shores. We examined its preference for feeding substratum—sand or rock—and its manner of feeding. The crab made its burrow in the sand among rocks but preferred to feed on rocks. The feeding time decreased as the distance between the burrow and the rock increased. We consider this to be a result of exclusive interaction among the crabs because they defended their feeding area on the rocks against others.The crab wetted a small area of rock with water held in the branchial chambers before and during feeding. It pinched up the wetted surface in the minor chelipeds, which have bundles of setae on the posterior tips of the dactyl and pollex, and put the material into its buccal cavity. It never expelled sand pellets while feeding on rock, which indicates that it swallowed the food particles directly, without sorting. The bundles of setae retained water by capillary attraction, which suggests that they capture the suspended fine food particles scraped from the rock. The wetting action may prevent the fine materials from dispersing. We consider that morphological alteration of the minor chelipeds, the application of water from the branchial chambers, and direct swallowing permit the fiddler crab to feed on fine materials attached to rocks.     

Impact scenario for the invasive red king crab <Emphasis Type="Italic">Paralithodes camtschaticus</Emphasis> (Tilesius, 1815) (Reptantia,Lithodidae) on Norwegian,native, epibenthic prey

Large invasive predators like the king crab, Paralithodes camtschaticus, deserve particular attention due to their potential for catastrophic ecological impact on recipient communities. Conspicuous, epibenthic prey species, such as the slow growing commercial scallop Chlamys islandica, are particularly exposed to the risk of local extinction. A research program integrating experiments and field monitoring is attempting to predict and track the impact of invasive king crab on scallop beds and associated fauna along the north Norwegian coast. The claw gape of the crab shows no limitations in handling the flat-bodied scallop. However, the potential impact of the crab on scallop may depend on the availability of other calcified prey associated with scallop beds, such as the sea star, sea urchin, and blue mussel, all species recorded in the diet of P. camtschaticus. To address this issue, a laboratory experiment on foraging behaviour of P. camtschaticus was conducted. The experimental results show that all size classes of red king crab prefer scallops, but small juveniles and medium sized crabs demonstrate active selection for starfish (Asterias rubens) that equals or surpasses the electivity of the large crab. The selection of sea urchin (Strongylocentrotus droebachiensis) and blue mussel (Mytilus edulis) is slightly positive or neutral for the three crab size classes. These results suggest that scallop beds with a rich associated fauna are less vulnerable to red king crabs predation and possibly more resilient than beds with few associated species. Also, crab size distribution is likely relevant for invasion impact, with increasing abundance of small and medium sized crabs being detrimental for alternative calcified prey associated with scallop beds. Successive stages of crab invasion will see an acceleration of scallop mortality rates associated with (i) decreasing availability of alternative prey, due to protracted predation pressure intensified by recruitment of juvenile crabs, and (ii) increased number of large crabs. Estimates of crab density and intake rates suggest that the accelerated loss rates will eventually endanger scallop beds persistence.     

Bimodal respiration, water balance and acid-base regulation in a high-shore crab, Cyclograpsus lavauxi H. Milne Edwards

Cyclograpsus lavauxi H. Milne Edwards, 1853 occurs under boulders near the littoral fringe, where it is wetted only briefly, if at all, in each tide. Mean water content of sea-water equilibrated crabs was 62.3 % of body weight. On warm, windy days crabs on the shore lose > 17.5% of body water. Water loss for crabs of 1.6 g mean body weight was 0.29 % water content · h ⁻¹ · mm Hg saturation deficit ⁻¹, which is similar to that of species occupying positions lower on the shore. C. lavauxi is, however, able to tolerate comparatively greater losses of body water (up to 36%) compared with species from lower shore levels.

As the gills dry, the lamellae separate into regular clumps which may help to maintain gas exchange. Resting oxygen consumption (V_o2) after 3–5 h settlement was similar in water and air. During enforced activity, V_o2 increased by factors of 5.3 in water and 2.6 in air at a standardized body weight of 1.5 g, indicating an appreciable aerobic scope in both media. Loss of up to 16% of body water did not depress resting aerial V_o2 or aerobic scope.

In resting crabs there was no change in haemolymph pH after 24 h of either immersion or emersion, but haemolymph [Ca²⁺], [HCO⁻₃] + [CO²⁻₃], and calculated P_co2 all rose in air relative to aquatic values. These results suggest that cuticular or other endogenous CaCO₃ is mobilized to compensate the respiratory acidosis in air. The implications of such physiological properties for aquatic and aerial activity on the shore are discussed.     

On the mechanism of air ventilaton in anabantoids (Pisces: Teleostei)

Summary Air ventilation in most Anabantoid species is diphasic, consisting of exhalation and inhalation. Exhalation is the release of air from the accessory breathing organs (suprabranchial chambers) through the mouth either into the water near the surface (e.g.,Ctenopoma) or directly into the atmosphere (e.g.,Osphronemus goramy). Inhalation, i.e., taking in fresh air through the mouth at the surface, immediately follows exhalation. X-ray films show (Figs. 5 and 6) that evacuation of the suprabranchial chambers during exhalation is total or nearly total. This, together with the fact that these chambers can contract at most to a very small extent, led to the conclusion that gas is replaced by water entering the chambers during exhalation and that this water is replaced by fresh air during inhalation. Further analysis of films, including conventional films showing the behavior of the opercular apparatus during air ventilation (Fig. 7), leads to a theory of a double-pumping mechanism responsible for air ventilation. This mechanism consists of the buccal apparatus and the opercular apparatus. It is suggested that both of these structures are able to act as both suction and pressure pumps, and thus air ventilation may be explained as the result of alternating activity of these two pumps.In the monophasic air ventilation characteristic of (adult)Anabas testudineus, there is no exhalation phase comparable to that of other Anabantoids. Therefore, no water enters the suprabranchial chambers, which remain filled with gas during the whole ventilation process (Fig. 10). Ventilation is limited to one phase comparable to inhalation in other Anabantoids.The structure of the accessory breathing organs (Fig. 1) and its progressive complication with growth (Fig. 4) were studied inOsphronemus goramy. The arrangement of the labyrinthine plates is in accordance with the requirements of transport of water and gas through the suprabranchial chambers. One plate (the inner plate, Fig. 1) separates these chambers into atrium, ventro-caudal, and dorso-caudal compartments, each with its own opening (valve). This organization seems essential for the transport of gas and water through the suprabranchial chambers and ensures that during exhalation, water flows into the chambers from above, so that while water is filling these chambers displaced gas can be sucked through the deep-lying pharyngeal openings into the expanding buccal cavity.Supported by the Deutsche Forschungsgemeinschaft     

Ventilatory and cardiovascular modulation associated with burying behaviour in two sympatric crab species, Cancer magister and Cancer productus

Physiological parameters associated with burying were investigated in the Dungeness crab, Cancer magister, and the red rock crab, Cancer productus. Ventilation frequency of the branchial chambers increased while the crabs were burying, this was associated with the greater oxygen demand of the tissues. The number of ventilatory reversals in C. magister increased in number as well as in duration and magnitude when the crabs were buried, which functioned to clear the branchial chambers of sediment. In contrast, the number of ventilatory reversals in C. productus decreased. On the surface of the sand, cardiac parameters (heart rate, stroke volume, cardiac output) of both species remained stable. During the burial process, there was a large increase in cardiac output which was afforded primarily by an increased stroke volume of the heart. Once buried, cardiac output declined in both species; this was due to a decrease in stroke volume in C. productus, but a decreased heart rate in C. magister. There were also differences in haemolymph flows through each arterial system. During the burying process, both species increased haemolymph flow to the muscles of the limbs via the sternal artery. Once buried haemolymph flows to the limbs decreased, and increased flow to eyestalks and antennae via the anterior aorta occurred. Perfusion of the digestive organs via the anterolateral and hepatic arteries did not change when the crabs were buried. There was an increase in flow through the posterior aorta, of C. magister, but flow through this artery did not change in C. productus. Periods of spontaneous cardiac arrest were observed in both species while resting on the surface. These increased in duration in C. productus when buried, but there was no change in C. magister. Changes in ventilatory and cardiac variables were closely linked on the surface, but tended to uncouple when the animals were buried. The physiological responses of C. magister resembled those of true sand-dwelling crabs, whereas the responses of C. productus paralleled those of crabs that only bury occasionally in the substrate. Although these two species often occur sympatrically, they employ different physiological mechanisms when buried in the sediment.     

Physiological responses to emersion in the intertidal green crab,Carcinus maenas (L.)

The green shore crab, Carcinus maenas, undergoes on average 6?h periods of emersion during each low-tide cycle during the summer months. Under those conditions, the crab is cut off from its normal water environment and is exposed to potential stress from a suite of environmental and physiological changes: dehydration, compromised gas exchange and resultant internal hypoxia and hypercapnia, thermal stress, and ammonia toxicity. This study examined the comprehensive responses of the green crab in water and to a 6?h emersion period laboratory simulation of a tidal cycle followed by a 1?h re-immersion period, measuring indicators of dehydration, hemolymph osmolality, oxygen uptake, hemolymph acid–base status, heart and ventilatory rate, and hemolymph ammonia and ammonia excretion. Green crabs showed physiological responses of varying magnitude to 6?h of emersion. Individuals were found in the field exclusively under rocks and large clumps of seaweed where temperatures were approximately half those of exposed surfaces and relative humidity was about twice as high as ambient air. During emersion, crabs lost less than 5% of their wet weight, and hemolymph osmolality did not increase significantly. Oxygen uptake continued in air at about 50% of the control, aquatic values; and the gills continued to be ventilated by the scaphognathite, albeit at lower rates. Hemolymph lactate concentrations increased, indicating a shift to a greater reliance on anaerobic metabolism to support energetic needs. A slight acidosis developed in the hemolymph after 1?h of emersion, but it did not increase thereafter. Ammonia concentrations in the hemolymph were unchanged, as ammonia was volatilized by the gills and excreted into the air as NH₃ gas. These results show that the green crab copes with emersion by seeking refuge in microhabitats that mitigate the changes in the physical parameters of intertidal emersion. Physiologically, desiccation is avoided, cardio-respiratory processes are maintained at reduced levels, and hemolymph acid–base balance is minimally affected. Ammonia toxicity appears to be avoided by a shift to excreting NH₃ gas directly or indirectly to air.     

Measurement of gas exchange rates in plant tissue culture vessels

The aerial microenvironment in culture vessels has a significant effect on the growth and development of plantlets in vitro. Since the gas exchange between outside air and inner air can influence the microenvironment of culture vessel, it is necessary to measure the air exchange rate for various vessels. In this study, water vapor was used as the tracer gas, and the change of absolute humidity inside the vessel was calculated continuously by the measured values of a relative humidity sensing element. The outside environment was maintained at constant humidity level by a saturated salt solution. The RH data were transformed into absolute humidity and the specific humidity ratio. The air exchange rates of several tissue culture vessels were then calculated. The exchange rate was between 0.0145 h^–1 to 0.0376 h^–1. This technique provides an inexpensive, rapid and simple way to determine the air exchange rate of a culture vessel within a short period. The effects of the air current velocities on the exchange rates of vessels were also determined.     

Respiration and Circulation in Land Crabs: Novel Variations on the Marine Design

Both the "true" crabs (Brachyura) and hermit crabs (Anomura)include species that show numerous behavioral, morphological,and physiological specializations permitting terrestrial life.This paper examines respiratory and circulatory adaptationsfor air breathing in these land crabs. Respiratory specializationsinclude modification of gas exchange structures for air breathing(gills and elaborated branchial chamber linings), ventilatorymechanisms permitting effective air pumping, an elevated hemolymphoxygen capacity, and a primarily CO₂- rather than O₂- sensitiveventilatory control system. The qualitative aspects of hemolymphoxygen transport and metabolic rate are apparently unchangedfrom that of marine crabs. While the basic cardiovascular morphologyof land crabs appears similar to that of marine forms, thereis considerable elaboration of the vasculature of the branchialchamber lining, which in some species includes a unique doubleportal system. Cardiac output is lower in land crabs (probablyrelated to their higher hemolymph O₂ capacity), but insufficientdata on hemolymph pressures prevent comparisons with marineforms. In general, land crabs have modified (sometimes extensively)existing structures and processes found in their marine relativesrather than evolving structures for terrestrial life de novo.Accordingly, land crabs present a useful model for the evolutionof terrestriality, showing that even subtle anatomical changescan result in the large changes in physiological function necessaryfor the terrestrial invasion.     

Respiratory behaviour,oxygen consumption and relative dependence on aerial respiration in the African lungfish (Protopterus annectens,owen) and an air-breathing teleost (Clarias lazera,C.).

The relative dependence on branchial and pulmonary organs was studied in the African lungfish P. annectens and in the catfish Clarias lazera. The frequency of pulmonary ventilation varied, in the normal state, with the activity and age of the fish and followed a circadian rhythm. Small specimens of both species exhibited a higher branchial ventilatory rate than older specimens and depended largely on aquatic O₂ uptake (over 85% and 90% in Clarias and Protopterus respectively). The dependence on aerial respiration appeared to develop gradually with age in Clarias but occurred over a limited age-range (200–300 g) in Protopterus. In mature fish (over 400 g), pulmonary respiration constituted 50–60% of the total in Clarias and 80–85% in Protopterus. Partitioning of O₂ uptake between air and water depended on the O₂ content of the water and that of O₂ and CO₂ in the pulmonary organs. Protopterus and Clarias surfaced for air when the O₂ content of the respiratory organs was reduced to 90% and 85% (of that immediately following an air-breath) respectively. An increase in the pulmonary O₂ content lengthened the apnoeic period and reduced pulmonary respiration more markedly in Protopterus than in Clarias whereas an increase of that of CO₂ produced the reverse effects.     

Responses of aerial ventilation to hypoxia and hypercapnia inChanna argus,an air-breathing fish

Summary The snake-head fish (Channa argus) is an obligate air-breather inhabiting fresh waters in the temperate zone of East Asia.Ventilation of the air-breathing organ and aerial gas exchange were measured in 1 to 2 kg specimens at 15 and 25°C. Additionally, the ventilatory responses to hypoxia and hypercapnia were studied. Aerial ventilation increased from 1.1 to 2.9 mlbtps·kg^–1·min^–1 when temperature rose from 15 to 25°C. Concomitantly, O₂-uptake through airbreathing increased from 0.1 mlstpd·kg^–1·min^–1 (15°C) to 0.28 mlstpd·kg^–1·min^–1 (25°C), whereas aerial gas exchange was less important for CO₂-climination as evident from low gas exchange ratios (0.16 at 15°C, 0.29 at 25°C).Ventilation increases only slightly in response to inspiration of hypercapnic gas mixtures or to hypoxic conditions in water. By contrast, inspiration of hypoxic gas mixtures caused marked increases of ventilation in particular at the higher temperature.Aerial ventilation inChanna is low compared to values for ectothermic pulmonary breathers. However, its ventilatory responses to hypoxia strikingly resemble those of reptiles: The most marked ventilatory response to hypoxia occurs at the higher temperature where the demands for O₂ are greatest.     

Anti-predator responses of the intertidal crab Heterozius rotundifrons (Brachyura: Belliidae) in air and water

The intertidal crab Heterozius rotundifrons responds to tactile input, as occurs during a predation attempt, by hyper-extending all of its limbs and remaining in that posture for a variable length of time. We compared the duration of this anti-predator response: (1) in the day versus night (2) in two fluid media (air versus water) (3) after exposure to additional predator cues in one medium (air or water) and testing in the other medium (4) for crabs from different parts of the tidal range and (5) for females with and without eggs on their pleopods.?Crabs showed the posture at night as well as during the day. They also executed the posture when tested in air and extended the duration of the posture in air when they detected an additional predation-risk cue, shadows passing overhead. When crabs experienced input in one medium there was no effect on the duration of behavior shown in the other medium. Crabs from the lower portion of the intertidal showed a markedly longer duration of the limb-extended posture compared to crabs from the higher end of the tidal range of this crab. Berried females responded the same as females without eggs in both air and in water. Thus, crabs show this anti-predator behavior under a wide variety of conditions, but do not appear to transfer information received in one medium to behavior shown in the other media.     

Respiratory patterns in nurses of the red wood ant Formica polyctena (Hymenoptera, Formicidae)

Summary Cycles of discontinuous gas exchange (DGCs) and abdominal ventilatory movements were studied in nurses of red wood ant, Formica polyctena, using an electrolytic respirometer and an infra-red (IR) gas analyser or flow-through respirometry. Both respirometry systems were combined with an IR actographic device based on IR-emitting and IR-sensor diodes. After recovering from handling and apparatus stress, lasting 1–3 h, completely motionless intact ants displayed regular DGC. After decapitation the ants displayed DGC whose frequency was somewhat lower than that of the intact individuals (7.17 ± 0.79 mHz and 10.43 ± 01.12 mHz, respectively). In headless ants, there occurred continuous slow movements of legs. Bursts of carbon dioxide in the intact and in the headless ants always coincided with a bout of telescoping movements (contractions) of abdominal segments, which was interpreted as active ventilation. During interburst periods, the headless ants exhibited telescoping movements characterised by rapid protraction, lasting 0.07–0.09 s, followed by a slow retraction of segments, suggesting passive ventilation. The intact ants were very sensitive to the flowing air and tended to be continuously active during flow-through respirometry. The decapitated ants, on the contrary, were insensitive to the air current.Received 26 March 2003; revised 30 July 2003; accepted 6 August 2003.     

Effects of Neem EC on gas exchange, tracheal ventilation, and water loss in diapausing pupae of Pieris brassicae

Effects of Neem EC (The Indian Neem Tree Company^TM, 1% azadirachtin) on gas exchange cycles, tracheal ventilation, and water loss in diapausing pupae of the large white butterfly, Pieris brassicae L. (Lepidoptera: Pieridae), were studied using a constant volume respirometer combined with an infrared probe actograph. The non‐treated pupae displayed discontinuous gas exchange cycles (DGC) with a trend coinciding with the bursts of carbon dioxide (CO₂) release, active tracheal ventilation, and the heartbeat periods. Two independent forms of tracheal ventilation were observed, relatively vigorous abdominal shaking movements and weak abdominal pulsations. The ability to respond to mechanical excitation with abdominal movements was entirely lost on the 2nd day after treatments with Neem EC, and also a reduced tendency to use a DGC was observed. During 2–3 days after treatments, the DGCs and gas exchange microcycles were entirely lost, as was active ventilation. Before treatments, body mass loss, that is, water loss, was 0.6–0.9 mg g^?1 day^?1. After the treatments, water loss increased to 3–5 mg g^?1 day^?1. The pupae remained alive for 10–15 days after the treatments and died after having lost about 50% of their initial body mass. The absence of heartbeats measured during at least 4–5 h was the main criterion for ascertaining death of pupae. The results suggested that respiratory failures, that is, the loss of cyclic gas exchange, evoked by Neem EC were the primary cause of lethal desiccation. Thus, the hypothesis that the cyclic gas exchange is an adaptation for restricting water losses in insects was supported.     

Gas exchange pattern in the two‐spot ladybird beetle,Adalia bipunctata,differs in dry vs. moist air

Gas exchange patterns in the ladybird beetle, Adalia bipunctata (L.) (Coleoptera: Coccinellidae), were investigated using an infrared gaseous analyser (IRGA) and a coulometric O₂ respirometer (manometric–volumetric system). Before testing, the beetles were kept either in dry (dehydrated) or moist (hydrated) conditions for 1 day. Their subsequent gas exchange patterns did not depend on their state of humidity but rather were controlled by the humidity of the insect chamber during gas exchange measurement. If this chamber contained dry air, the beetles exhibited CO₂ release by burst, which we interpreted as cyclic gas exchange (CGE) with inter‐burst periods, but if the chamber was switched to contain moist air, then cyclic CO₂ release was soon abandoned and a pattern of continuous gas exchange appeared. Measurements with the coulometric respirometer in moist air showed that continuous gas exchange was often associated with weak abdominal pulsations, which we interpreted as active ventilation. Their metabolic rate was lower during gas exchange cycles than during continuous gas exchange. We revealed that in the ladybird beetle metabolic rate increased in moist air when the gas exchange pattern transitioned from cyclic to continuous.