298
P. 9. MEADOWS AND J. I. CAMPBELL
with the shells they inhabit although their selection of shells may play
a part in determining their local distribution (Orians and King, 1964,
p. 305); however they do provide two examples of “ h o s t ”
recognition by the physical attributes of weight and volume that might
be applicable to other true commensal relationships (Reese, 1962 ;
Vdker, 1968). Gilpin-Brown (1969) has described the unusual way in
which Nereis fucuta (Savigny) finds its host hermit crab. He has
shown that it recognizes its host’s approach by vibrations on the
substrate, and then by contact with the surface of the shell (c.f. Herter,
1929, pp. 280-6). Hermit crabs utilize tactile stimuli in choosing their
shells, for Clibanarius misanthropus Risso prefers shells such as
Cerithium (its usual shell) and Murex that are fairly bumpy, to
smoothed Cerithium shells or to BuZZa and Gibbula shells (Hertz, 1933).
By far the most popular group of specific responses to study have
been those to chemicals produced by the host and this probably reflects
a genuine prevalence in aquatic environments. It is clear from the
literature that some commensals respond to chemicals at a distance from
the host and therefore might be able to home in (Davenport, 1955),
while others detect chemicals on contact so must encounter their host
at random or else home by some other means. The significance and
reason for these differences have not been analysed experimentally, but
will serve as an empirical basis for discussion.
Specific host chemicals that act at a distance from the host are
usually offered in one side of a Y tube choice apparatus (Davenport,
1950). During studies of this sort Davenport and Hickok (1961) and
Johnson (1952) noticed a number of commensals that were not
attracted to water that had flowed over their hosts. Evidence from
later work by Davenport (1953a, b), Davenport et al. (1961) and Ross
and Sutton (1961a, 1963, 1967) suggests these might be instances of
responses to species specific chemicals on contact, rather than at a
distance, and might be analogous to the contact chemical response of
barnaele cyprids that Crisp and Meadows (1963) recorded.
Many commensals and also some parasites respond at a distance to
chemicals emitted by their hosts. One of the earliest records and most
elegant analyses is that of Fasten (1913). The freshwater parasitic
copepod, Lernaeopoda edwardsii Olsson, is found on the gills of brook
trout but not on those of the rainbow or German brown trout. I n the
presence of isolated gills of the brook trout its larvae become very
active. On the other hand, even though the larvae come into contact
with them, they show no response to the gills of the other two species.
A specific chemical must be diffusing out from the brook trout gills.
I n order to test the ecological meaning of these experiments, Fasten
P. 9. MEADOWS AND J. I. CAMPBELL
with the shells they inhabit although their selection of shells may play
a part in determining their local distribution (Orians and King, 1964,
p. 305); however they do provide two examples of “ h o s t ”
recognition by the physical attributes of weight and volume that might
be applicable to other true commensal relationships (Reese, 1962 ;
Vdker, 1968). Gilpin-Brown (1969) has described the unusual way in
which Nereis fucuta (Savigny) finds its host hermit crab. He has
shown that it recognizes its host’s approach by vibrations on the
substrate, and then by contact with the surface of the shell (c.f. Herter,
1929, pp. 280-6). Hermit crabs utilize tactile stimuli in choosing their
shells, for Clibanarius misanthropus Risso prefers shells such as
Cerithium (its usual shell) and Murex that are fairly bumpy, to
smoothed Cerithium shells or to BuZZa and Gibbula shells (Hertz, 1933).
By far the most popular group of specific responses to study have
been those to chemicals produced by the host and this probably reflects
a genuine prevalence in aquatic environments. It is clear from the
literature that some commensals respond to chemicals at a distance from
the host and therefore might be able to home in (Davenport, 1955),
while others detect chemicals on contact so must encounter their host
at random or else home by some other means. The significance and
reason for these differences have not been analysed experimentally, but
will serve as an empirical basis for discussion.
Specific host chemicals that act at a distance from the host are
usually offered in one side of a Y tube choice apparatus (Davenport,
1950). During studies of this sort Davenport and Hickok (1961) and
Johnson (1952) noticed a number of commensals that were not
attracted to water that had flowed over their hosts. Evidence from
later work by Davenport (1953a, b), Davenport et al. (1961) and Ross
and Sutton (1961a, 1963, 1967) suggests these might be instances of
responses to species specific chemicals on contact, rather than at a
distance, and might be analogous to the contact chemical response of
barnaele cyprids that Crisp and Meadows (1963) recorded.
Many commensals and also some parasites respond at a distance to
chemicals emitted by their hosts. One of the earliest records and most
elegant analyses is that of Fasten (1913). The freshwater parasitic
copepod, Lernaeopoda edwardsii Olsson, is found on the gills of brook
trout but not on those of the rainbow or German brown trout. I n the
presence of isolated gills of the brook trout its larvae become very
active. On the other hand, even though the larvae come into contact
with them, they show no response to the gills of the other two species.
A specific chemical must be diffusing out from the brook trout gills.
I n order to test the ecological meaning of these experiments, Fasten