title: Adaptive shifts in osmoregulatory strategy and the invasion of freshwater by brachyuran crabs: evidence from Dilocarcinus pagei (Trichodactylidae).
abstract: To evaluate putative adaptive changes underpinning the invasion of freshwater by the Brachyura, this investigation examines anisosmotic extra and isosmotic intracellular osmoregulatory capabilities in Dilocarcinus pagei, a neotropical, hololimnetic crab, including its embryonic and juvenile phases. All ontogenetic stages show a remarkable ability to survive a high salinity medium (25 per thousand, 750 mOsm/kg H2O, 350 mm Na+, 400 mM Cl-). Adults hyper-regulate hemolymph osmolality up to isosmoticity at 744 mOsm kg/H2O (24 per thousand), [Na+] and [Cl-] becoming isoionic at 449 (22 per thousand) and 256 mM (16 per thousand), respectively. Hemolymph (420+/-39 mOsm/kg H2O) and urine (384+/-44 mOsm/kg H2O) are isosmotic in adults held in freshwater, and after 5-days exposure to 25 per thousand (787+/-9 mOsm/kg H2O and 777+/-43 mOs/kg H2O, respectively); D. pagei does not produce dilute urine. Total free amino acid (FAA) concentrations in embryos (14.9+/-1.2), juveniles (32.8+/-0.1) and adult muscle (10.9+/-2.1 mmol/kg wet weight) in freshwater are 30-fold less than in brackish/marine Crustacea, suggesting that FAA constitute a useful parameter to evaluate adaptation to freshwater. On acclimation to 25 per thousand, total FAA increase by approximately 100% in embryos and in adult muscle and nerve tissue and hemolymph, owing to large increases in proline, arginine and/or alanine. However, effective FAA contribution to intracellular osmolality increases only in embryos, from 3 to 4.5%. These findings suggest that gill-based, anisosmotic extracellular regulation has supplanted isosmotic intracellular regulatory mechanisms during the conquest of freshwater by the Brachyura, and indicate that D. pagei may be an old, well-adapted inhabitant of this biotope.
authors.affiliation: Departamento de Biologia, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Augusto
authors.forename: Lewis J
authors.initials: LJ
authors.lastname: Greene
authors.forename: Helen J
authors.initials: HJ
authors.lastname: Laure
authors.forename: John C
authors.initials: JC
authors.lastname: McNamara
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D033364:Decapoda / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004625:Embryo, Nonmammalian / Q000187:drug effects / Q000502:physiology; D005260:Female; D005618:Fresh Water; D005880:Gills / Q000737:chemistry / Q000187:drug effects; D006458:Hemolymph / Q000737:chemistry / Q000187:drug effects; D007814:Larva / Q000187:drug effects / Q000502:physiology; D008136:Longevity / Q000187:drug effects; D009132:Muscles / Q000737:chemistry / Q000187:drug effects; D009417:Nerve Tissue / Q000737:chemistry / Q000187:drug effects; D012965:Sodium Chloride / Q000494:pharmacology; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D012965:Sodium Chloride