A SURVEY OF THE EFFECT OF OSMOTIC DILUTION ON FREE AMINO ACIDS OF VARIOUS POLYCHAETES

¹ Friday Harbor Laboratories, Department of Zoology, University of Washington, Seattle, Washington

1. Ten species of polychaetes were exposed to 75% and 50% sea water for 1 to 4 days, and measurements of amino-acid levels in the coelomic fluid and body wall were made. Individuals of all species, both intertidal and subtidal, survived the experimental period at both dilutions.

2. Osmotic stress at lowered salinities results in a decrease in intracellular amino-acid levels. This is primarily due to tissue hydration, although in some species, especially Nephtys ciliata and Abarenicola pacifica, hydration is minimal or absent and "active" movement of amino acids contributes a larger share of the decrease.

3. In several species osmotic dilution causes a rise in coelomic fluid amino-acid levels, suggesting direct transfer of amino acids from tissues to body fluid. In one species, Thelepus crispus, there is a 50 to 75% fall in coelomic fluid amino-acid level, although this is not true in two closely related species. The data indicate that polychaetes may use a variety of mechanisms to regulate their amino-acid levels during osmotic stress. It remains to be seen whether the distribution of regulative mechanisms among polychaete species can be correlated either with type of habitat or with phylogenetic relationships.

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