24
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Many earlier workers believed that miracidia are attracted to
gastropod hosts by a chemotactic substance(s) secreted in the host’s
mucus or “ juice.” Faust and Meleney (1924), Faust (1924) and Faust
and Hoffman (1934), who studied the behavior of the miracidia of
three species of human-infecting schistosomes, Xchistosoma mansoni,
S. haematobium and S. japonicum, are among the first, if not the first,
to support the “ attraction theory.’’ I n the initial study by Faust and
Meleney, they observed that S. japonicum miracidia, when in the
vicinity of the snail Katayama nesophora, show powerful response to
the snail as well as to the mucus tract left by it. The response to
K. nesophora does not occur until the swimming miracidia come
“ within a few millimeters of the range of the snail.” Although no
detailed study of the specificity of this behavior was made, it was
reported that no response was elicited by two common snails from
northern China, Vivipara quadrata and Lymnaea plicatula, both of
which are not compatible hosts for these schistosomes.
Barlow (1925), who studied the miracidia of Pasciolopsis buski, and
Tubangui and Pasco (1933), who studied those of Echinostoma ilocanum,
were also among the first to support the ‘‘ attraction theory.” Barlow
reported that Fasciolopsis buski miracidia chose only two snails,
Segmentina nitidellus and Planorbis schmackeri, if these hosts were
presented among a number of other species. These are among the first
experimental demonstrations of the manner in which specificity may
be determined by precise behavior of a parasite under host influence.
As to the exact behavior pattern, the following quotation from Faust
and Hoffman (1934) gives an account of the behavior of Schistosoma
mansoni miracidia in the presence of Australorbis glabratus:
When active miracidia of Schistosoma mansoni, swimming rapidly through
the water, come within a few millimeters of the appropriate molluscan host,
they become stimulated almost immediately and c L head ” €or the snail.
The exact attraction-mechanism is unknown, but the work of Barlow on
Fasciolopsis buski and of Tubangui and Pasco on Echinostoma ilocanum
miracidia indicates that it is some fraction of the tissue juice of tho appropriate snail. The secretion of this substance into the immediate vicinity of
the snail provides the stimulus which directs the miracidium t o the snail and
‘‘ notifies ” it that such snail is its suitable intermediate host.
Recently, Davenport et al. (1962), utilizing the flying-spot microscope
technique, reported that Schistosoma mansoni miracidia, when in the
proximity of filtered extract of whole ground Australorbis glabratus,
frequently exhibit a “ whirling dance ” upon initial contact with the
extract before heading towards the site of greatest concentration.
Following the early proponents of the “ attraction theory ”, various
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Many earlier workers believed that miracidia are attracted to
gastropod hosts by a chemotactic substance(s) secreted in the host’s
mucus or “ juice.” Faust and Meleney (1924), Faust (1924) and Faust
and Hoffman (1934), who studied the behavior of the miracidia of
three species of human-infecting schistosomes, Xchistosoma mansoni,
S. haematobium and S. japonicum, are among the first, if not the first,
to support the “ attraction theory.’’ I n the initial study by Faust and
Meleney, they observed that S. japonicum miracidia, when in the
vicinity of the snail Katayama nesophora, show powerful response to
the snail as well as to the mucus tract left by it. The response to
K. nesophora does not occur until the swimming miracidia come
“ within a few millimeters of the range of the snail.” Although no
detailed study of the specificity of this behavior was made, it was
reported that no response was elicited by two common snails from
northern China, Vivipara quadrata and Lymnaea plicatula, both of
which are not compatible hosts for these schistosomes.
Barlow (1925), who studied the miracidia of Pasciolopsis buski, and
Tubangui and Pasco (1933), who studied those of Echinostoma ilocanum,
were also among the first to support the ‘‘ attraction theory.” Barlow
reported that Fasciolopsis buski miracidia chose only two snails,
Segmentina nitidellus and Planorbis schmackeri, if these hosts were
presented among a number of other species. These are among the first
experimental demonstrations of the manner in which specificity may
be determined by precise behavior of a parasite under host influence.
As to the exact behavior pattern, the following quotation from Faust
and Hoffman (1934) gives an account of the behavior of Schistosoma
mansoni miracidia in the presence of Australorbis glabratus:
When active miracidia of Schistosoma mansoni, swimming rapidly through
the water, come within a few millimeters of the appropriate molluscan host,
they become stimulated almost immediately and c L head ” €or the snail.
The exact attraction-mechanism is unknown, but the work of Barlow on
Fasciolopsis buski and of Tubangui and Pasco on Echinostoma ilocanum
miracidia indicates that it is some fraction of the tissue juice of tho appropriate snail. The secretion of this substance into the immediate vicinity of
the snail provides the stimulus which directs the miracidium t o the snail and
‘‘ notifies ” it that such snail is its suitable intermediate host.
Recently, Davenport et al. (1962), utilizing the flying-spot microscope
technique, reported that Schistosoma mansoni miracidia, when in the
proximity of filtered extract of whole ground Australorbis glabratus,
frequently exhibit a “ whirling dance ” upon initial contact with the
extract before heading towards the site of greatest concentration.
Following the early proponents of the “ attraction theory ”, various