34
MARINE MOLLUSOS AS HOSTS FOR SYMBIOSES
or glutamic acids to snail tissue from which the attracting substances
had been removed by solvents restores the capacity of the snail tissue
to attract and stimulate miracidia to attempt penetration.
There is little doubt from MacInnis’s results that chemotaxis does
exist between miracidia and the test agar pyramids. MacInnis has
stated that : ‘ I Some of the chemicals investigated were considered
possible components of snail mucus, or on other grounds were considered
as possible attractants.’’ Nevertheless, it would appear that further
studies are necessary to demonstrate that the attractants do occur in
the mucus or body fluids of compatible molluscs. Although there is
some indication that amino acids and amino sugars are present in snail
mucus (Wright, 1959b), these substances have not been shown conclusively to be present. Relative to short-chain fatty acids, there is no
evidence at this time that they occur in snail mucus although they may
be end-products of snail metabolism (von Brand et al., 1955). Furthermore, the question may be asked if the attraction of miracidia to
butyric acid and glutamic acid, as has been demonstrated by MacInnis,
is meaningful in nature, especially when one considers host-specificity
which may be governed, at least in part, by the chemotactic material@)
(Faust and Meleney, 1924 ; Barlow, 1925 ; Neuhaus, 1953 ; Etges and
Decker, 1963). If butyric acid is as commonly found as an end-product
of molluscan metabolism as suggested by von Brand et al. (1955), it
certainly would not serve to direct miracidia to a specific species of
snail host. Similarly, glutamic acid, which is a commonly occurring
amino acid, could not again be expected to serve as a selective guide.
On the other hand, MacInnis’s results may indicate that chemotaxis
is not always associated with host-specificity.
On the other side of the fence, there are evidences suggesting that
symbiont selection of hosts, specifically miracidia-mollusc contact, is
strictly a random phenomenon without the occurrence of attracting
factors. Mattes (1926, 1936) has reported that Fasciolu hepatica
miracidia find their host randomly and will attack almost any softbodied animal ; Stunkard (1943), in one of the very few studies of this
nature involving a marine mollusc, has reported that the miracidia of
Zoogonoides laevis are not noticeably attracted to their molluscan host
Columbella lunata (= Mitrella lunata) and that contact between the
miracidia and snails appears to be merely accidental. Similarly,
Griffiths (1939) and LaRue (1951) believed that miracidia-mollusc
contact is primarily a random phenomenon. LaRue, however, has
indicated that, although under laboratory conditions trial and error
appears to be much more important than chemotactic response in
bringing miracidium and snail together, in nature the possibility of the
MARINE MOLLUSOS AS HOSTS FOR SYMBIOSES
or glutamic acids to snail tissue from which the attracting substances
had been removed by solvents restores the capacity of the snail tissue
to attract and stimulate miracidia to attempt penetration.
There is little doubt from MacInnis’s results that chemotaxis does
exist between miracidia and the test agar pyramids. MacInnis has
stated that : ‘ I Some of the chemicals investigated were considered
possible components of snail mucus, or on other grounds were considered
as possible attractants.’’ Nevertheless, it would appear that further
studies are necessary to demonstrate that the attractants do occur in
the mucus or body fluids of compatible molluscs. Although there is
some indication that amino acids and amino sugars are present in snail
mucus (Wright, 1959b), these substances have not been shown conclusively to be present. Relative to short-chain fatty acids, there is no
evidence at this time that they occur in snail mucus although they may
be end-products of snail metabolism (von Brand et al., 1955). Furthermore, the question may be asked if the attraction of miracidia to
butyric acid and glutamic acid, as has been demonstrated by MacInnis,
is meaningful in nature, especially when one considers host-specificity
which may be governed, at least in part, by the chemotactic material@)
(Faust and Meleney, 1924 ; Barlow, 1925 ; Neuhaus, 1953 ; Etges and
Decker, 1963). If butyric acid is as commonly found as an end-product
of molluscan metabolism as suggested by von Brand et al. (1955), it
certainly would not serve to direct miracidia to a specific species of
snail host. Similarly, glutamic acid, which is a commonly occurring
amino acid, could not again be expected to serve as a selective guide.
On the other hand, MacInnis’s results may indicate that chemotaxis
is not always associated with host-specificity.
On the other side of the fence, there are evidences suggesting that
symbiont selection of hosts, specifically miracidia-mollusc contact, is
strictly a random phenomenon without the occurrence of attracting
factors. Mattes (1926, 1936) has reported that Fasciolu hepatica
miracidia find their host randomly and will attack almost any softbodied animal ; Stunkard (1943), in one of the very few studies of this
nature involving a marine mollusc, has reported that the miracidia of
Zoogonoides laevis are not noticeably attracted to their molluscan host
Columbella lunata (= Mitrella lunata) and that contact between the
miracidia and snails appears to be merely accidental. Similarly,
Griffiths (1939) and LaRue (1951) believed that miracidia-mollusc
contact is primarily a random phenomenon. LaRue, however, has
indicated that, although under laboratory conditions trial and error
appears to be much more important than chemotactic response in
bringing miracidium and snail together, in nature the possibility of the