Respostas histofisiológicas de Uca maracoani (latreille, 1802-1803) frente à variação hídrica e salina
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Data
2025-08-13
Autores
Brandão, Carolina de Farias
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Universidade Federal do Espírito Santo
Resumo
Semi-terrestrial crustaceans, inhabitants of coastal regions such as the fiddler crab Uca maracoani, face recurrent variations in salinity and water availability imposed by the tidal regime, requiring physiological and structural adjustments to maintain the composition of body fluids. The maintenance of osmotic and ionic homeostasis is ensured by differential mechanisms of hyper- (salt uptake) and hypo-regulation (salt secretion) in intertidal species. Accordingly, this study investigated the histophysiological responses of U. maracoani to desiccation and submersion at different salinities (10, 30, and 50 ‰). After being collected from the São Mateus River estuary (ES, Brazil), adult crabs were maintained in the laboratory and subjected to tolerance tests in which the maximum survival time under desiccation or submersion at different salinities was determined. Based on these data and considering the influence of the tidal regime, an experimental exposure time of six hours was established. The animals were assigned to two main groups: control (maintained in a water layer at 10, 30, and 50 ‰) and fully submerged at the same salinities. An additional group was subjected to desiccation for six hours, with animals maintained in a 30 ‰S water layer used as control. Hemolymph osmolality and chloride concentration were measured, with calculations of osmo- and ionoregulatory capacities. The last pair of posterior gills (7º) was histologically analyzed for effects on gill lamella thickness. The results showed longer tolerance to submersion (with no salinity effect), with no mortality up to 240 h, whereas exposure to desiccation resulted in 100% mortality before 120 h. Total osmoregulatory capacity and the isosmotic point varied from 0.11 and 28 ‰S, respectively, under control conditions, to 0.18 and 25.6 ‰S in submerged animals, being considered strong in both cases. On the other hand, total ionoregulatory capacity for chloride ranged from 0.02 in control animals to 0.34 in submerged ones, shifting from very strong to weak ionoregulation. The iso-ionic point for chloride did not vary, remaining at ≈350 mM (≈22 ‰S). Changes in osmo- and ionoregulatory capacities were associated with reduced chloride secretion ability (hypo-ionoregulation) under high salinity. Desiccation led to a significant decrease in hemolymph osmolality and shrinkage of gill lamella thickness. In submersion experiments, there was no treatment effect (control vs. submerged), but exposure to high salinity (50 ‰) in both treatments induced thickening of the gill epithelium.Thus, it can be concluded that U. maracoani integrates morphophysiological responses that support its persistence in estuarine environments under recurrent tidal fluctuations, although it shows vulnerability to prolonged aerial exposure and reduced chloride secretion capacity under hypersaline submersion.
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Osmorregulação , Ionorregulação , Dessecação