46
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
necessary for demonstration of attraction [italics added] under experimental
conditions, The decreased attraction could have resulted either from a
gradient or a highly diffusible nature of the attractant.
Sastry and Menzel have also demonstrated that if Pinnotheres
macubtus is given a choice between the bay scallop, Aequipecten
irradians, and the penshell, Atrina rigida, no preference for one host
over another occurs. Furthermore, the crabs are not attracted to empty
A. irradians shells with epiphoronts attached, thus indicating that the
source of the attractant is the soft parts of the scallops. It was also
found that adult male crabs are as equally attracted to their molluscan
hosts as females.
It is of interest to emphasize that Pinnotheres maculatus is not
attracted by the empty shells of the scallop, thus differing from the
relationship between Calliactis parasitica and Buccinum undatum as
reported by Ross and Sutton (1961). It would thus appear that the
" host factor '' or attractant can differ, depending on the specific host
and symbiont.
It should be mentioned at this point, although briefly, that whereas
host attractants are generally believed to be chemical as the result of
available evidences, there are some indications which suggest that
certain physical properties may be attractive to certain symbionts.
Specifically, Sasa et al. (1960) have demonstrated that the larvae of
several species of parasitic nematodes will respond positively to certain
concentrations of COz in the air, and Kawashima et al. (1961a) have
reported the attraction of Paragonimus ohirai miracidia to slightly
acidic solutions.
D. Contact injluenced by other natural taxes
Since chemotaxis, as has been pointed out, is only operative within
short distances, it would appear possible that other mechanisms exist
that tend to bring the symbiont and its host into the proximity of one
another from greater distances. In this regard, Laing (1937) appears to
have been the first to establish the principle that symbionts may be
attracted to the environment in which their hosts are found. She
stated :
The conclusion to be drawn . . . is that some parasites do first seek out a
particular environment, in which they afterwards proceed to seek their hosts.
The analysis of the process by which the parasite finds its host into two
parts-the finding of the environment and the finding of the host in that
environment-is, therefore, not merely a convenient theoretical division, but
corresponds to an actual difference in the behavior of the parasite.
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
necessary for demonstration of attraction [italics added] under experimental
conditions, The decreased attraction could have resulted either from a
gradient or a highly diffusible nature of the attractant.
Sastry and Menzel have also demonstrated that if Pinnotheres
macubtus is given a choice between the bay scallop, Aequipecten
irradians, and the penshell, Atrina rigida, no preference for one host
over another occurs. Furthermore, the crabs are not attracted to empty
A. irradians shells with epiphoronts attached, thus indicating that the
source of the attractant is the soft parts of the scallops. It was also
found that adult male crabs are as equally attracted to their molluscan
hosts as females.
It is of interest to emphasize that Pinnotheres maculatus is not
attracted by the empty shells of the scallop, thus differing from the
relationship between Calliactis parasitica and Buccinum undatum as
reported by Ross and Sutton (1961). It would thus appear that the
" host factor '' or attractant can differ, depending on the specific host
and symbiont.
It should be mentioned at this point, although briefly, that whereas
host attractants are generally believed to be chemical as the result of
available evidences, there are some indications which suggest that
certain physical properties may be attractive to certain symbionts.
Specifically, Sasa et al. (1960) have demonstrated that the larvae of
several species of parasitic nematodes will respond positively to certain
concentrations of COz in the air, and Kawashima et al. (1961a) have
reported the attraction of Paragonimus ohirai miracidia to slightly
acidic solutions.
D. Contact injluenced by other natural taxes
Since chemotaxis, as has been pointed out, is only operative within
short distances, it would appear possible that other mechanisms exist
that tend to bring the symbiont and its host into the proximity of one
another from greater distances. In this regard, Laing (1937) appears to
have been the first to establish the principle that symbionts may be
attracted to the environment in which their hosts are found. She
stated :
The conclusion to be drawn . . . is that some parasites do first seek out a
particular environment, in which they afterwards proceed to seek their hosts.
The analysis of the process by which the parasite finds its host into two
parts-the finding of the environment and the finding of the host in that
environment-is, therefore, not merely a convenient theoretical division, but
corresponds to an actual difference in the behavior of the parasite.