92
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
an initial increase of amino acids is now available and as these authors
have stated: “ . . . (this) may be related to a change in the protein
metabolism of the snails or may be indicative of enzymatic activity of
the miracidia during penetration ”.
Cheng (1963d), also using chromatographic techniques, has studied
alterations in the compositions of both the bound and free amino acids
in the tissues and plasma of three host-parasite associations ; Physa
gyrina parasitized by Glypthelmins quieta sporocysts, the pelecypod
Musculium partumeium parasitized by Gorgodera amplicava sporocysts,
and the gastropod Helisoma trivolvis parasitized by Echinoparyphium
rediae. My findings are summarized in Tables VII, VIII and IX. From
these data it is apparent that there is a decrease in detectable free
amino acids in the sera of infected molluscs. The similarity between the
bound and free amino acids in the trematode larvae, plus the finding
that there is a significant decrease in the plasma protein concentrations
in all three species of infected molluscs, together with conspicuous
decreases in the hosts’ amino acids, strongly suggest that the parasites
do utilize the hosts’ amino acids. It has been stated, however, that
some of the loss of amino acids may be accounted for by the synthesis
of some still undetermined humoral factor.
The requirement of relatively large quantities of nitrogen, most
probably in the form of essential amino acids, by intramolluscan
trematodes is not surprising since such are needed not only for growth
but also for the prolific asexual multiplication which occurs. It is
known, for example, that 10 000 cercariae may be derived from a single
miracidium of Schistosoma japonicum and more than 200 000 cercariae
may arise from a single miracidium of 8. mansoni (Paust and Hoffman,
1934). Meyerhof and Rothschild (1940) have reported that one parasitized Littorina may emit as many as 1 300 000 Cryptocotyle lingua
cercariae during the course of a year.
My studies on alterations in the amino acid composition of parasitized molluscs do not reveal the initial increase as reported by Dusanic
and Lewert, but then I did not investigate the molluscs shortly after
infection. I n fact, the infected molluscs used in my studies were
naturally infected and presumably for a considerable time since the
enclosed parasites were plentiful and well developed.
A note of caution should be interjected at this point for those
anticipating studies on the amino acid composition of uninfected and
infected marine molluscs, particularly estuarine species. Allen (196lb),
working with the brackish water clam, Rangia cuneata, has shown that
the concentrations of individual amino acids increase as the saliriity
increases. Hence, when determining quantitative differences, the in-
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
an initial increase of amino acids is now available and as these authors
have stated: “ . . . (this) may be related to a change in the protein
metabolism of the snails or may be indicative of enzymatic activity of
the miracidia during penetration ”.
Cheng (1963d), also using chromatographic techniques, has studied
alterations in the compositions of both the bound and free amino acids
in the tissues and plasma of three host-parasite associations ; Physa
gyrina parasitized by Glypthelmins quieta sporocysts, the pelecypod
Musculium partumeium parasitized by Gorgodera amplicava sporocysts,
and the gastropod Helisoma trivolvis parasitized by Echinoparyphium
rediae. My findings are summarized in Tables VII, VIII and IX. From
these data it is apparent that there is a decrease in detectable free
amino acids in the sera of infected molluscs. The similarity between the
bound and free amino acids in the trematode larvae, plus the finding
that there is a significant decrease in the plasma protein concentrations
in all three species of infected molluscs, together with conspicuous
decreases in the hosts’ amino acids, strongly suggest that the parasites
do utilize the hosts’ amino acids. It has been stated, however, that
some of the loss of amino acids may be accounted for by the synthesis
of some still undetermined humoral factor.
The requirement of relatively large quantities of nitrogen, most
probably in the form of essential amino acids, by intramolluscan
trematodes is not surprising since such are needed not only for growth
but also for the prolific asexual multiplication which occurs. It is
known, for example, that 10 000 cercariae may be derived from a single
miracidium of Schistosoma japonicum and more than 200 000 cercariae
may arise from a single miracidium of 8. mansoni (Paust and Hoffman,
1934). Meyerhof and Rothschild (1940) have reported that one parasitized Littorina may emit as many as 1 300 000 Cryptocotyle lingua
cercariae during the course of a year.
My studies on alterations in the amino acid composition of parasitized molluscs do not reveal the initial increase as reported by Dusanic
and Lewert, but then I did not investigate the molluscs shortly after
infection. I n fact, the infected molluscs used in my studies were
naturally infected and presumably for a considerable time since the
enclosed parasites were plentiful and well developed.
A note of caution should be interjected at this point for those
anticipating studies on the amino acid composition of uninfected and
infected marine molluscs, particularly estuarine species. Allen (196lb),
working with the brackish water clam, Rangia cuneata, has shown that
the concentrations of individual amino acids increase as the saliriity
increases. Hence, when determining quantitative differences, the in-