Adaptive shifts in osmoregulatory strategy and the invasion of freshwater by brachyuran crabs: evidence from Dilocarcinus pagei (Trichodactylidae)
✍ Scribed by Alessandra Augusto; Lewis J. Greene; Helen J. Laure; John C. Mcnamara
- Book ID
- 102339446
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 2007
- Tongue
- English
- Weight
- 196 KB
- Volume
- 307A
- Category
- Article
- ISSN
- 1932-5223
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✦ Synopsis
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‰, 750 mOsm/kg H~2~O, 350 mm Na^+^, 400 mM Cl^−^). Adults hyper‐regulate hemolymph osmolality up to isosmoticity at 744 mOsm kg/H~2~O (24‰), [Na^+^] and [Cl^−^] becoming isoionic at 449 (22‰) and 256 mM (16‰), respectively. Hemolymph (420±39 mOsm/kg H~2~O) and urine (384±44 mOsm/kg H~2~O) are isosmotic in adults held in freshwater, and after 5‐days exposure to 25‰ (787±9 mOsm/kg H~2~O and 777±43 mOs/kg H~2~O, 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‰, total FAA increase by ≈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. J. Exp. Zool. 307A:688–698, 2007. © 2007 Wiley‐Liss, Inc.