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Functional bursting by the dracunculoid nematode Philonema oncorhynchi

Published online by Cambridge University Press:  06 April 2009

J. W. Lewis ,
D. R. Jones  and
J. R. Adams
J. W. Lewis
Affiliation:
Department of Zoology, Royal Holloway College, University of London, Englefield Green, Surrey
D. R. Jones
Affiliation:
Department of Zoology, University of British Columbia, Vancouver, Canada
J. R. Adams
Affiliation:
Department of Zoology, University of British Columbia, Vancouver, Canada
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Extract

Using biomedical techniques experimental determinations of the hydrostatic pressure in the pseudocoel of adult female Philonema oncorhynchi indicated that the rate of increase in pressure (dP/dT) and absolute pressure values (cm/H2O) shown by bursting worms in distilled water are correlated with the diameter of the nematode. At bursting pressures, wall tension in a wide size range of worms was virtually identical, indicating that the bursting process is independent of muscular contraction. That the generation of the hydrostatic pressure was an osmotic phenomenon was confirmed by measuring dP/dT in prelarvigerous and larvigerous female worms subjected to different concentrations of sodium chloride, ranging from 89 to 800 m-osmol/kg, and also to a variety of solutions of similar osmolarity (155–175 m-osmol/kg), e.g. magnesium sulphate, urea, potassium chloride, sodium chloride and sucrose. The overall rate of uptake was faster in the larger worms but, per unit surface area, small worms had an uptake rate three times that of the large individuals.

The prediction that the body wall of female P. oncorhynchi is permeable to ions such as Na+ was confirmed using radiolabelled 22Na and by bringing about changes in the osmolarity of worms subjected, for 5 min periods, to hyperosmotic solutions of sodium chloride and sucrose. The survival of P. oncorhynchi in the body cavity of sockeye salmon, Oncorhynchus nerka, is dependent upon the permeable nature of the body wall of P. oncorhynchi allowing the worm to function as an ‘osmometer', because as the anadromous O. nerka enters fresh water, the osmolarity of its blood plasma is known to decrease by about 15%. At the time of spawning in Cultus Lake, British Columbia, the body fluids of both female P. oncorhynchi and O. nerka are isosmotic, indicating that the worms are able to equilibrate to the above changes and at the same time preventing premature bursting in the body cavity of its host. However, osmotic invasion of water must occur far quicker than ionic exchange since complete release of larvae does take place when female worms pass out into the redd along with the eggs of the fish and burst.

Type
Research Article
Information
Parasitology , Volume 69 , Issue 3 , December 1974 , pp. 417 - 427
Copyright
Copyright © Cambridge University Press 1974

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References

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