4. ANALYSIS O F FACTORS INVOLVED I N SYMBIOSIS
35
occurrence of some chemical stimulus operating over very short
distances may exist.
Abdel-Malek (1950), who specifically looked for attraction, reported
that Schistosoma mansoni miracidia will attack any object including
empty snail shells and particles of fine gravel. When in the presence of
Biomphalaria boissyi, a suitable intermediate host, Abdel-Malek
reported that the miracidia’s movements are random and that it appears
to find its host largely by chance. Similarly, Stirewalt (1951) working
with Schistosoma mansoni and Australorbis glabratus, Chu and Cutress
(1954) working with the marine avian schistosome believed to be
Azcstrobilharzia variglundis and the marine snail Littorina pintado, and
Najim (1956) working with the freshwater avian schistosome, Bigantobilharxia huronensis, and its molluscan host, Physa gyrina, have all
reported the lack of any apparent attraction. It should be mentioned
that, except in the instance of Abdel-Malek, the other earlier reports
were incidental observations not subjected to critical analyses.
More recently, Sudds (1960) has examined for the presence or
absence of chemotaxis between four different species of schistosome
miracidia (Trichobilharzia elvae, T . physellae, Schistosomatium douthitti
and Schistosoma mansoni) and a number of normal and generally
considered incompatible molluscan hosts. It is unfortunate that Sudd’s
thorough experiments were marred by the assumption that it is only in
the case of normal or compatible hosts that specific chemotaxis occurs.
It is my opinion that attraction of symbiont to host should be considered
a distinct operation from successful establishment of symbiont in or on
its host, although there are suggestions that host-symbiont contact may
influence morphogenetic changes. For example, Campbell and Todd
(1965b) have reported the in vitro metamorphosis of Fascioloides magna
miracidium into a sporocyst after a short contact with snail tissue. At
any rate, Sudds discovered that of nineteen incompatible host-parasite
combinations studied, the miracidia in six displayed “ a determined
effort to penetrate the tissues of the snails ”. According to his data,
the “ determined effort ” was in the form of either “ miracidia sticking
to snail upon contact and appear to be penetrating ” (Sudds’ type 4
behavior pattern) or “ miracidia contacting snail and moving rapidly
over the surface, sticking intermittently, swimming away, returning,
etc.” (Sudds’ type 3 behavior pattern). In eleven other incompatible
host-parasite combinations, the miraoidia were observed making brief
attempts to penetrate. As defined elsewhere in his paper, this represents
Sudds’ type 3 behavior pattern described as “ miracidia sticking briefly
to snail, swimming away, returning, etc.”. In the remaining two
incompatible host-parasite combinations, the miracidia did not appear
35
occurrence of some chemical stimulus operating over very short
distances may exist.
Abdel-Malek (1950), who specifically looked for attraction, reported
that Schistosoma mansoni miracidia will attack any object including
empty snail shells and particles of fine gravel. When in the presence of
Biomphalaria boissyi, a suitable intermediate host, Abdel-Malek
reported that the miracidia’s movements are random and that it appears
to find its host largely by chance. Similarly, Stirewalt (1951) working
with Schistosoma mansoni and Australorbis glabratus, Chu and Cutress
(1954) working with the marine avian schistosome believed to be
Azcstrobilharzia variglundis and the marine snail Littorina pintado, and
Najim (1956) working with the freshwater avian schistosome, Bigantobilharxia huronensis, and its molluscan host, Physa gyrina, have all
reported the lack of any apparent attraction. It should be mentioned
that, except in the instance of Abdel-Malek, the other earlier reports
were incidental observations not subjected to critical analyses.
More recently, Sudds (1960) has examined for the presence or
absence of chemotaxis between four different species of schistosome
miracidia (Trichobilharzia elvae, T . physellae, Schistosomatium douthitti
and Schistosoma mansoni) and a number of normal and generally
considered incompatible molluscan hosts. It is unfortunate that Sudd’s
thorough experiments were marred by the assumption that it is only in
the case of normal or compatible hosts that specific chemotaxis occurs.
It is my opinion that attraction of symbiont to host should be considered
a distinct operation from successful establishment of symbiont in or on
its host, although there are suggestions that host-symbiont contact may
influence morphogenetic changes. For example, Campbell and Todd
(1965b) have reported the in vitro metamorphosis of Fascioloides magna
miracidium into a sporocyst after a short contact with snail tissue. At
any rate, Sudds discovered that of nineteen incompatible host-parasite
combinations studied, the miracidia in six displayed “ a determined
effort to penetrate the tissues of the snails ”. According to his data,
the “ determined effort ” was in the form of either “ miracidia sticking
to snail upon contact and appear to be penetrating ” (Sudds’ type 4
behavior pattern) or “ miracidia contacting snail and moving rapidly
over the surface, sticking intermittently, swimming away, returning,
etc.” (Sudds’ type 3 behavior pattern). In eleven other incompatible
host-parasite combinations, the miraoidia were observed making brief
attempts to penetrate. As defined elsewhere in his paper, this represents
Sudds’ type 3 behavior pattern described as “ miracidia sticking briefly
to snail, swimming away, returning, etc.”. In the remaining two
incompatible host-parasite combinations, the miracidia did not appear