AB 7:113-122 (2009)  -  DOI: https://doi.org/10.3354/ab00183

Evolutionary transition to freshwater by ancestral marine palaemonids: evidence from osmoregulation in a tide pool shrimp

Alessandra Augusto1, Adriana Silva Pinheiro2, Lewis Joel Greene3, Helen Julie Laure3, John Campbell McNamara2,*

1Centro de Aquicultura, Universidade Estadual Paulista, Jaboticabal, SP 14870-810, Brazil
2Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP 14040-901, Brazil
3Centro de Química de Proteínas, Faculdade de Medicina, Universidade de São Paulo, Ribeirão Preto, SP 14051-040, Brazil
*Corresponding author. Email:

ABSTRACT: The transition from marine/brackish waters to freshwater habitats constitutes a severe osmotic and ionic challenge, and successful invasion has demanded the selection of morphological, physiological, biochemical and behavioral adaptations. We evaluated short-term (1 to 12 h exposure) and long-term (5 d acclimation), anisosmotic extracellular (osmolality, [Na+, Cl]) and long-term isosmotic intracellular osmoregulatory capability in Palaemon northropi, a neotropical intertidal shrimp. P. northropi survives well and osmo- and ionoregulates strongly during short- and long-term exposure to 5–45‰ salinity, consistent with its rocky tide pool habitat subject to cyclic salinity fluctuations. Muscle total free amino acid (FAA) concentrations decreased by 63% in shrimp acclimated to 5‰ salinity, revealing a role in hypoosmotic cell volume regulation; this decrease is mainly a consequence of diminished glycine, arginine and proline. Total FAA contributed 31% to muscle intracellular osmolality at 20‰, an isosmotic salinity, and decreased to 13% after acclimation to 5‰. Gill and nerve tissue FAA concentrations remained unaltered. These tissue-specific responses reflect efficient anisosmotic and anisoionic extracellular regulatory mechanisms, and reveal the dependence of muscle tissue on intracellular osmotic effectors. FAA concentration is higher in P. northropi than in diadromous and hololimnetic palaemonids, confirming muscle FAA concentration as a good parameter to evaluate the degree of adaptation to dilute media. The osmoregulatory capability of P. northropi may reflect the potential physiological capacity of ancestral marine palaemonids to penetrate into dilute media, and reveals the importance of evaluating osmoregulatory processes in endeavors to comprehend the invasion of dilute media by ancestral marine crustaceans.

KEY WORDS: Freshwater invasion · Marine–freshwater transition · Physiological adaptation · Osmotic and ionic regulation · Free amino acids · Palaemonid shrimp · Palaemon northropi

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Cite this article as: Augusto A, Silva Pinheiro A, Greene LJ, Laure HJ, McNamara JC, (2009) Evolutionary transition to freshwater by ancestral marine palaemonids: evidence from osmoregulation in a tide pool shrimp. Aquat Biol 7:113-122. https://doi.org/10.3354/ab00183

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