2. DEFINITIONS OF TYPES OF SYMBIOSES
7
D. Phoresis
Phoresis is most akin to commensalism but does not involve “ eating
at the same table ”. This type of relationship is again a loose and nonobligatory one during which one organism, the host, merely provides
shelter, support, or transport for the other. Metabolic dependency is
not involved. According to this definition, those animals that are
commonly referred to as being epizootic or epizoic can be considered as
being engaged in phoretic associations with their hosts. Again, in
marine biology an example of such a relationship can be cited in the
case of fishes of the genus Fierasfer which live within the respiratory
tracts of holothurians. Fierasfer is a relatively helpless fish that is
readily preyed upon by others. Living in association with the holothurian, which is undisturbed by its presence, Fierasfer is provided
with shelter and is transported from place to place. Another example
of a phoretic relationship, but one which does not involve transport,
is that between the hydroid Clytia balceri and certain intertidal molluscs,
such as Donax gouldi and Tivela stultorum in Southern California.
The hydroid is attached to the exposed surfaces of the host’s shell and
no metabolic dependency occurs. The hydroid presumably does
benefit, since it is prevented from being washed away with the tide.
Since one of the major criteria employed to distinguish between
types of symbioses, specifically to differentiate mutualism and parasitism from commensalism and phoresis, is metabolic dependency, it
follows that definite assignments of associations can only be conclusively
brought about through physiological and biochemical analyses. Such
have been performed on relatively few species although increasingly
more information of this nature is being contributed by modern
symbiologists. Regrettably, in the case of the symbionts of marine
molluscs not much is known other than indirect and inferential
evidences. Herein lies a virtually untouched area of research for the
imaginative mind.
Having given definitions for ytegories of symbioses, it appears
appropriate at this point to re-emphasize that overlaps do occur
between the types of symbioses described. This is especially true
between parasitism and mutualism, which share the feature of the
occurrence of metabolic dependency, and between commensalism and
phoresis, which do not involve metabolic dependency. The interrelationship between all four categories of symbioses is depicted in
Fig. 2. From this diagram, it may be inferred that the greatest amount
of overlapping can be expected to occur between commensalism and
phoresis at one end, and between parasitism and mutualism at the
7
D. Phoresis
Phoresis is most akin to commensalism but does not involve “ eating
at the same table ”. This type of relationship is again a loose and nonobligatory one during which one organism, the host, merely provides
shelter, support, or transport for the other. Metabolic dependency is
not involved. According to this definition, those animals that are
commonly referred to as being epizootic or epizoic can be considered as
being engaged in phoretic associations with their hosts. Again, in
marine biology an example of such a relationship can be cited in the
case of fishes of the genus Fierasfer which live within the respiratory
tracts of holothurians. Fierasfer is a relatively helpless fish that is
readily preyed upon by others. Living in association with the holothurian, which is undisturbed by its presence, Fierasfer is provided
with shelter and is transported from place to place. Another example
of a phoretic relationship, but one which does not involve transport,
is that between the hydroid Clytia balceri and certain intertidal molluscs,
such as Donax gouldi and Tivela stultorum in Southern California.
The hydroid is attached to the exposed surfaces of the host’s shell and
no metabolic dependency occurs. The hydroid presumably does
benefit, since it is prevented from being washed away with the tide.
Since one of the major criteria employed to distinguish between
types of symbioses, specifically to differentiate mutualism and parasitism from commensalism and phoresis, is metabolic dependency, it
follows that definite assignments of associations can only be conclusively
brought about through physiological and biochemical analyses. Such
have been performed on relatively few species although increasingly
more information of this nature is being contributed by modern
symbiologists. Regrettably, in the case of the symbionts of marine
molluscs not much is known other than indirect and inferential
evidences. Herein lies a virtually untouched area of research for the
imaginative mind.
Having given definitions for ytegories of symbioses, it appears
appropriate at this point to re-emphasize that overlaps do occur
between the types of symbioses described. This is especially true
between parasitism and mutualism, which share the feature of the
occurrence of metabolic dependency, and between commensalism and
phoresis, which do not involve metabolic dependency. The interrelationship between all four categories of symbioses is depicted in
Fig. 2. From this diagram, it may be inferred that the greatest amount
of overlapping can be expected to occur between commensalism and
phoresis at one end, and between parasitism and mutualism at the