4. ANALYSIS O F FACTORS INVOLVED I N SYMBIOSIS
23
(unpublished). In brief, she has been able to demonstrate that the
polynoid polychaete Arctonoe wittata is stimulated when exposed to
sea water in which its host, the keyhole limpet, Diodora aspera, had
been placed. Wikswo has also shown that the nature of the substrate
does influence the attraction of Arctonoe vittata to Diodora aspera. If
both organisms are placed in a glass-bottomed bowl the polychaete
readily moves towards the host, but if placed in a sandy bottom bowl
it does not. Similarly, if the bottom of the bowl is lined with cheese
cloth, Arctonoe vittata rarely moves towards its host. Wikswo has also
demonstrated that Arctonoe vittata is repelled by dead Diodora aspera.
This observation confirms the finding of Davenport and Hickok (1951)
who have demonstrated that commensals, Arctonoe fragilis in their
case, are repelled by water from an aquarium that contained injured
starfish, Ewasterias, its natural host. It would thus appear that the
attractant can be either destroyed or masked by substances produced
by dead or damaged hosts. This would undoubtedly be of advantage
to symbionts in nature, since they would actively migrate from a dead
or moribund host.
Among parasites of molluscs, studies designed to determine the
attraction or non-attraction of parasites are primarily limited to those
concerned with the attraction of trematode miracidia to freshwater
gastropod intermediate hosts. Since the results of such studies, which
are still highly controversial, may contribute further insights into the
nature of host-secreted attractants (host factors), the available information is briefly reviewed herein. The pitfalls and misinterpretations by
those working with freshwater molluscs, as well as their concrete
findings, can no doubt serve as guards against similar mistakes and act
as profitable guides in future work with marine molluscan hosts. The
subject at hand has been reviewed by Wright (1959a). My review
incorporates, but extends beyond, his.
Wesenberg-Lund (1934), expounding on the behavior of trematode
miracidia, has stated: “ If we try to gain some knowledge from the
literature of the behaviour of the miracidia in their relation to the different mollusc species, it is very difficult to get a clear idea of the real
facts.” Strange as it may seem, in 1967 we are faced with the same
problem although studies published during the last few years have
tended to alleviate this situation. In brief, two schools of thought are
in existence relative to the mechanisms involved in miracidiummollusc, primarily gastropod, contact. There are those who champion
the concept that a host-elaborated attractant or stimulant exists, and
there are those who believe that host contact is strictly a random
process.
23
(unpublished). In brief, she has been able to demonstrate that the
polynoid polychaete Arctonoe wittata is stimulated when exposed to
sea water in which its host, the keyhole limpet, Diodora aspera, had
been placed. Wikswo has also shown that the nature of the substrate
does influence the attraction of Arctonoe vittata to Diodora aspera. If
both organisms are placed in a glass-bottomed bowl the polychaete
readily moves towards the host, but if placed in a sandy bottom bowl
it does not. Similarly, if the bottom of the bowl is lined with cheese
cloth, Arctonoe vittata rarely moves towards its host. Wikswo has also
demonstrated that Arctonoe vittata is repelled by dead Diodora aspera.
This observation confirms the finding of Davenport and Hickok (1951)
who have demonstrated that commensals, Arctonoe fragilis in their
case, are repelled by water from an aquarium that contained injured
starfish, Ewasterias, its natural host. It would thus appear that the
attractant can be either destroyed or masked by substances produced
by dead or damaged hosts. This would undoubtedly be of advantage
to symbionts in nature, since they would actively migrate from a dead
or moribund host.
Among parasites of molluscs, studies designed to determine the
attraction or non-attraction of parasites are primarily limited to those
concerned with the attraction of trematode miracidia to freshwater
gastropod intermediate hosts. Since the results of such studies, which
are still highly controversial, may contribute further insights into the
nature of host-secreted attractants (host factors), the available information is briefly reviewed herein. The pitfalls and misinterpretations by
those working with freshwater molluscs, as well as their concrete
findings, can no doubt serve as guards against similar mistakes and act
as profitable guides in future work with marine molluscan hosts. The
subject at hand has been reviewed by Wright (1959a). My review
incorporates, but extends beyond, his.
Wesenberg-Lund (1934), expounding on the behavior of trematode
miracidia, has stated: “ If we try to gain some knowledge from the
literature of the behaviour of the miracidia in their relation to the different mollusc species, it is very difficult to get a clear idea of the real
facts.” Strange as it may seem, in 1967 we are faced with the same
problem although studies published during the last few years have
tended to alleviate this situation. In brief, two schools of thought are
in existence relative to the mechanisms involved in miracidiummollusc, primarily gastropod, contact. There are those who champion
the concept that a host-elaborated attractant or stimulant exists, and
there are those who believe that host contact is strictly a random
process.