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<br />GRANATH AND ESCH-REGULATION OF 8, ACHEILOGNATHIPOPULATIONS 1121
<br />
<br /> 100
<br /> 90
<br /> 80
<br /><( 70
<br />Cl
<br />U
<br /><( 60
<br />0:
<br />0
<br />u 50
<br />w
<br />-l
<br />f- 40
<br />0
<br />~
<br />~ 30
<br />.
<br /> 20
<br /> 10
<br /> I I
<br /> 12 24 36 48 60 72
<br />
<br />
<br /><>----020. C
<br />- 250 C
<br />0.. ....,0 300 C
<br /><>--<> 350 C
<br />
<br />,P-,
<br />,/ \"..
<br />" 'q
<br />. ,
<br />. ,
<br />. ,
<br />. ,
<br />, ,
<br />" ,
<br />, ,
<br />II ..
<br />-' '
<br />" \
<br />, 0..----0-.--.-0-.._-0-_ -0-
<br />-.......-0.... ....-0.........-0 .......0 .-.o-----o-.-.-c;--.~...._"<>'___~-
<br />108 120 132 144 156 168 180 192 204 216 220 240
<br />
<br />HOURS OF INCUBATION
<br />
<br />FiGURE 5, Percentage of motile coracidia of B, acheilognathi observed following incubation of the eggs
<br />(n - 350) for up to 240 hr at 20, 25, 30, and 35 C.
<br />
<br />son believed that the major temperature effect
<br />was on parasite mortality, with large numbers of
<br />immature and mature worms dying as temper-
<br />ature increased. He suggested that such a pattern
<br />may be regulatory in nature, by serving to reduce
<br />egg production which, in turn, would reduce the
<br />number of intermediate hosts becoming infected.
<br />The result would be a smaller pool of infective
<br />larval stages available for recruitment by the de-
<br />finitive hosts. Similar patterns of change have
<br />been reported for other pseudophyllidean and
<br />caryophyllidean cestodes by other investigators
<br />(Kennedy, 1969; Grimes and Miller, 1976; Jar-
<br />roll, 1979).
<br />The precise mechanism for causing the decline
<br />in parasite infrapopulation density is not clear.
<br />There appears to be at least four possible expla-
<br />nations, The first is one that is frequently offered
<br />for mortality among various pseudophyllidean
<br />and caryophyllidean cestodes when water tem-
<br />peratures rise. It is the so-called temperature-
<br />dependent rejection response, initially proposed
<br />by Kennedy (1969). Rejection, he asserted, was
<br />not caused by an immune response (Kennedy
<br />and Walker, 1969), According to Kennedy (1977,
<br />p. 72), "The population level was thus controlled
<br />
<br />by seasonal changes in immigration and mor-
<br />tality, both density-independent factors, and the
<br />latter at least causally related to temperature
<br />changes." Thus, while Kennedy (1969) devel-
<br />oped the concept of a temperature-dependent
<br />rejection response, he could not identify a den-
<br />sity-dependent mechanism as being involved in
<br />causing parasite mortality, relying instead on the
<br />idea of a causal relationship between mortality
<br />and temperature change.
<br />A second possibility for causing the decline in
<br />B, acheilognathi infrapopulations as tempera-
<br />tures begin to rise in the spring is related to an
<br />immune response among infected mosquitofish,
<br />While Holmes et al. (1977) suggest that the im-
<br />mune response is secondary for regulation of adult
<br />tapeworms, a number of recent studies have sug-
<br />gested that immunity to enteric cestodes has the
<br />capacity to cause worm loss (Hefus, 1974; An-
<br />dreassen and Hopkins, 1980), Hopkins (1980)
<br />has recently written, "The hypothesis may be
<br />advanced that all tapeworms evoke a response,"
<br />Although enteric cestodes of homeotherms may
<br />have the capacity to induce an immune response,
<br />the question remains as to whether such a re-
<br />sponse is effective in regulating parasite densities
<br />
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