M.C.F. Santos

Specific dynamic action and the metabolism of the brachyuran land crabs Ocypode quadrata (Fabricius, 1787), Goniopsis cruentata (Latreille, 1803) and Cardisoma guanhumi Latreille, 1825

Oxygen uptake (MO2) was measured in the terrestrial crabs Ocypode quadrata (Fabricius, 1787), Goniopsis cruentata (Latreille, 1803) and Cardisoma guanhumi Latreille, 1825 as a function of digestive state to determine the magnitude and time course of specific dynamic action (SDA). Following 5 days of feeding ad libitum on fish flesh, “steady-state” MO2 was about 2.8, 1.0 and 1.6 μm·g−1·h−1 in Ocypode(29–31 °C), Goniopsis (23–25°C) and Cardisoma (29–31 °C), respectively. After 5 days of fasting, “steady-state” MO2 was decreased greatly to 1.0 and 0.5 μm·g−1·h−1 in Ocypode and Cardisoma, respectively, but was not significantly changed from feeding values in Goniopsis. Time-course experiments indicated that the peak in MO2 following a single large meal occurred within 8 h in both Ocypode and Cardisoma. The apparent SDA persisted for longer than 50 h in Cardisoma, but less than 42 h in Ocypode. These data show that an apparent SDA of large magnitude and variable time course can occur in land crabs. However, the absence of any apparent SDA effect in Goniopsis indicates that it is not a necessary accompaniment to feeding in all terrestrial brachyurans, and must be verified on a species-by-species basis.

TRANSEPITHELIAL POTENTIAL DIFFERENCES AND SODIUM FLUXES IN ISOLATED PERFUSED GILLS OF THE MANGROVE CRAB UCIDES CORDATUS

Abstract Marked differences in transepithelial potential difference (TEP) and unidirectional sodium fluxes were observed in isolated, perfused posterior gills 5 and 6 of the hyper–hyporegulating crab Ucides cordatus . Gills were perfused with a saline which closely matched the composition of the crabs haemolymph, and bathed with 9, 17, 26 and 34‰ seawater (SW). In 26‰ SW, TEPs were small and similar in magnitude and sign for both gills, but in all other salinities TEPs were very different, exhibiting opposite polarities and different responses to the changes in external salinity. Calculated relative ionic permeabilities, P Na : P Cl , showed that gills 5 were more permeable to sodium than gills 6, while the latter were chloride permeable. In gills 5 the TEP can be regarded as a diffusion potential. This is not the case in gill 6 where ion extrusion probably takes place. Influx rates in gill 5 were larger than efflux rates in all salinities and ranged from 726.93±103.52 to 1111.47±135.55 μ M Na + g −1 h −1 . Sodium efflux varied from 337.49±56.42 to 689.03±108.87 μ M Na + g −1 h −1 . In gill 6 influx rates were orders of magnitude smaller (3.67±0.25 to 8.45±0.79 μ M Na + g −1 h −1 ), while efflux rates varied from 87.24±20.25 to 223.27±19.38 μ M Na + g −1 h −1 . Flux-ratio analysis showed active uptake of Na + in gill 5 and active extrusion in gills 6, suggesting functional differences in adjacent gills of this hyper–hyporegulating crab.

A morphological study on posterior gills of the mangrove crab Ucides cordatus.

Morphological and histological studies on posterior gills of the mangrove crab Ucides cordatus showed that the 5th gill (of 7) has a larger surface area and a greater number of lamellae compared to the 6th gill. Regular separation of gill lamellae, important when the gill is in air, is maintained by enlargements of the marginal canals. Conical, spine-like structures along the efferent vessel of both 5th and 6th gills were also observed. In addition, pillar cells, a discontinuous lamellar septum and a hypobranchial artery were observed. The presence of valve-like structures near the efferent vessel was also indicated. These structures, together with the pillar cells, may have a role in directing the hemolymph flow towards certain gills during particular physiological states. Localization of osmoregulatory epithelia in the lamellae of both gills was inferred from dimethylaminostyrylethylpyridiniumiodine staining. Apparently gills 5 and 6 have osmoregulatory epithelial cell patches of similar area, corresponding to 43% and 38% of the total lamellae area, respectively. However, their localization is quite different. Gill number 5 osmoregulatory patches seem to be restricted to the afferent region of the lamella whereas in gill number 6, they are more dispersed over the entire lamella. These differences may be related to the particular functional characteristics of these gills.

Atrial natriuretic peptide (ANP) increases in the mangrove crab Ucides cordatus when exposed to increased environmental salinity

Abstract 1. 1. Haemolymph taken from the basal joints of the walking legs of the mangrove Brazilian crab Ucides cordatus , was analysed using a very sensitive radioimmunoassay (RIA) technique, before and after specific extraction and purification methods (Vycor-Glass) for immunoreactive atrial natriuretic peptide (IR-ANP) determinations. 2. 2. The mangrove crabs ( N = 20) were randomly distributed in four groups, exposed to four different salinities, all of them included in the ecological Brazilian mangrove range: 9, 17, 26, 34%. of seawater. 3. 3. The smallest IR-ANP value, found in the 26‰ salinity (1.25 ± 0.2 pg/ml) was coincident with the isosmotic gradient for haemolymph and external medium, where the crab is not submitted to osmoregulatory disbalances. 4. 4. The IR-ANP values found in the 9 and 17‰ salinity, did not show any significant differences when compared with values obtained at the isosmotic point 26‰. 5. 5. IR-ANP level increased significantly with the external salinity level, from 26 to 34‰ (7.5 ± 5 pg/ml; N = 5). There was a significant positive Kendall Correlation Coefficient ( P = 0.035) between the IR-ANP values found at 26 and 34‰ salinity. 6. 6. ANP could participate in the osmoregulation of the Brazilian crab. U. cordatus, contributing towards NaCl extrusion in hyperosmotic environmental salinity.

Rates of water loss in four crabs from different habitats

Abstract 1. 1. The water loss was determined for both sexes in crabs from mangrove Ucides cordaius and Goniopsis cruentata , supralittoral Ocypode quadrata and intertidal Pachygrapsus transversus under aerial desiccation conditions (19.63 ± 2.77% r.h. and 25.50 ± 0.34°C) for several hours. 2. 2. The water loss rate increased linearly with exposure time. The smaller P. transversus have the faster rate, 3.50 ± 0.20 and 3.03 ± 0.25 g/100g/hr, followed by U. quadrata , 1.03 ± 0.07 and 0.65 ± 0.07 g/100 g/hr, G. cruentata , 0.53 ± 0.02 and 0.50 ± 0.04 g/100 g/hr, V. cordatus , 0.43 ± 0.03 and 0.29 ± 0.02 g/100g/hr, females and males, respectively. 3. 3. The surface-volume ratio appears to be the most important factor related to the water loss. The terrestrialness of the four species could be indirectly inferred from their water loss rates.

The short-term respiratory responses on three crabs exposed to water-air media

1. 1. The measurements of oxygen consumption (MO2) in crabs following abrupt transference of media was found to be a useful tool for comparative studies. The results are of the same magnitude as the ones found in the literature. Careful handling permitted determinations on undisturbed animals, at the minimal level of activity. 2. 2. The MO2 was measured on three species of crabs, the semi-terrestrial Goniopsis cruentata, the amphibious Ucides cordatus and the aquatic Callinectes danae. There was a highly significant increase in the rates when they were suddenly transferred from water to air. This increase was highest in the blue crabs acclimated to the dilute salinity, but the salinity effect per se was negligible. 3. 3. When U. cordatus was submerged, MO2 fell to one-tenth of its aerial value and this effect was softened with the previous acclimation in water. 4. 4. G. cruentata drowned after 210 min submerged in water. The females are more sensitive than the males, showing frequent occurrence and long duration of apnoeic periods in air, both sexes presenting behavioral depression.

Drinking and osmoregulation in the mangrove crab Ucides cordatus following exposure to benzene

Abstract In benzene-exposed Ucides cordatus acclimated for 96 h to 9 and 34‰ SW, haemolymph, urine and gastric juice are isosmotic with each other, but differ significantly in osmolality from external media. In both salinities, under benzene action, urine K + excretion and calcium absorption are increased significantly, whereas Na + absorption and Mg 2+ excretion show U/B ratios similar to control values. In 9‰ SW, some ionic exchanges via benzene-exposed gills are possibly hastened. Benzene exposure decreases significantly branchial chamber water osmolality, [Na + ] and [K + ], whereas [Ca 2+ ] and [Mg 2+ ] are unaffected. However, faster medium exchange presumably occurs in 34‰ SW, both crab groups show branchial chamber water osmotic and ionic concentrations similar to surrounding medium. Benzene exposure unaffected gastric juice composition. In both media, [Ca 2+ ] and [Mg 2 ] accumulate several times higher than surrounding media, and [Na + ] and [K + ] are significantly hypo-ionic to haemolymph. Na + and K + G/H ratios are lower in crabs acclimated to 34‰ SW than in crabs acclimated to 9‰ SW. Drinking rates are enhanced by benzene exposure and are higher at 34‰ SW than in seawater isosmotic with the haemolymph (26‰ SW). Benzene exposure affects significantly osmoregulatory capability, slowing haemolymph dilution after transfer to clean 9‰ SW. Lower haemolymph dilution rate accounts for higher osmolality, but 48 h after transfer there is no recovery like in control crabs. Haemolymph transfusion experiments suggest an interaction among effects of benzene and hormonal factors, possibly on water influx.

Relationships concerning respiratory devices in crabs from different habitats

Abstract 1. 1. Interrelations between branchial chamber volume, gill weight, carapace width and body weight in three crabs from freshwater, mangrove and intertidal habitats were studied. 2. 2. Ucides cordatus has the greatest branchial chamber volume and the least gill supply. 3. 3. The curves obtained for U. cordatus were similar to those for other gecarcinids. 4. 4. U. cordatus possesses seven pairs of gills, in a highly vascularized branchial chamber which does not bear water. Their ventilation is bilateral.

HEMOLYMPH OSMO-IONIC CONCENTRATIONS IN TERRESTRIAL CRABS FOLLOWING DESICCATION

Abstract 1. 1. The hemolymph osmotic, Na + K + , Ca ++ and Mg ++ concentrations were determined for both sexes in crabs from mangrove Ucides cordatus and Goniopsis cruentata and supralittoral Ocypode quadrala after aerial desiccation, for 10 hr. 2. 2. There was no difference between sexes in the two mangrove crabs, but in O. quadrata the females were the most significantly affected ( P 3. 3. Hemolymph osmotic Na + , Ca ++ and Mg ++ concentrations increased significantly in desiccated ghost crabs, while K + concentration was not significantly changed. In the two mangrove crabs, only hemolymph Ca ++ concentration increased significantly, after desiccation. 4. 4. The short time desiccation is suggested to be a device to study the steps of osmo-ionic regulation in terrestrial crabs.

Time course of osmoionic compensations to acute salinity exposure in the ghost crab Ocypode quadrata (Fabricius, 1787)

Abstract Intermolt males and non-ovigerous females of Ocypode quadrata (Fabricius, 1787) were collected from the surf zone of the Guaeca Beach, on the northern coast of the State of Sao Paulo, Brazil. In the laboratory, osmoionic concentrations were measured after 3-, 6- and 12-h exposure periods to media of either O . quadrata should be coordinated by use of inorganic ions and amino acid concentrations during hyposmotic stress.