4. ANALYSIS O F FACTORS INVOLVED IN SYMBIOSIS
105
These investigators have suggested that this may be the explanation
for their inability to withstand long periods under anaerobic conditions
since polysaccharide metabolism is the main source of energy under
anaerobic conditions. This finding may be significant when considering
parasitized marine pelecypods. It has been suggested by Korringa and
others that marine pelecypods, especially oysters, live in essentially an
anaerobic condition when their valves are closed. Thus, the life-span of
parasitized pelecypods, which are continuously closed for one reason
or another, could be expected to be shorter.
There are other aspects of trematode-induced pathology in molluscs
which are for the most part unexplained. For example, Hurst and
Walker (1933, 1935) have reported that the body temperature of parasitized Lymnaea stagnalis is 2.7 times higher than that of uninfected
snails. No explanation for this is yet available other than that the
temperature rise most probably reflects some metabolic change.
Duerr (1965) has studied the effect of trematode parasitization on the
respiratory rate of the same pulmonate gastropod. By employing a
Warburg constant volume respirometer maintained at 25°C) he has
demonstrated that snails infected with trematodes (germinal sacs of
Cotylurus Jlabelliformis, metacercariae of C . jlabelliformis, and an
unidentified xiphidiocercaria) not only have a lower oxygen consumption slope (logarithm of body weight plotted against the natural logarithm
of oxygen consumption) but as a group are more variable when compared
to laboratory reared uninfected snails. Duerr’s results again indicate
marked physiological effects of parasitism. Vernberg and Vernberg
(1963) have demonstrated another physiological manifestation of
parasitization by trematodes. The investigators have found that the
upper lethal thermal limits uf the mud-flat snail, Nassarius obsoletus,
heavily parasitized by trematodes (Lepocreadium ovalis or Zoogonus
rubellus) are significantly lower than those of uninfected snails.
Another study, this one by Kendall (1964), also has revealed yet
unexplained pathological alterations. It has been pointed out earlier
(Section 11, A, 2) that there is generally considerable host cellular
response when trematodes are introduced into unnatural molluscan
hosts. Kendall has reported that if young Lymnaea palustris, L.
glabra and L. stagnalis, all semi-suitable hosts, are successfully infected
with Fasciola hepatica, some become stunted, their shells ar0 distorted,
and the snails show signs of “ ill-health ”.
Wound healing. Little is known about wound healing following
parasite-inflicted damage. F. G. Rees (1931) and Fretter and Graham
(1962) have indicated that if the infection is terminated, the host
105
These investigators have suggested that this may be the explanation
for their inability to withstand long periods under anaerobic conditions
since polysaccharide metabolism is the main source of energy under
anaerobic conditions. This finding may be significant when considering
parasitized marine pelecypods. It has been suggested by Korringa and
others that marine pelecypods, especially oysters, live in essentially an
anaerobic condition when their valves are closed. Thus, the life-span of
parasitized pelecypods, which are continuously closed for one reason
or another, could be expected to be shorter.
There are other aspects of trematode-induced pathology in molluscs
which are for the most part unexplained. For example, Hurst and
Walker (1933, 1935) have reported that the body temperature of parasitized Lymnaea stagnalis is 2.7 times higher than that of uninfected
snails. No explanation for this is yet available other than that the
temperature rise most probably reflects some metabolic change.
Duerr (1965) has studied the effect of trematode parasitization on the
respiratory rate of the same pulmonate gastropod. By employing a
Warburg constant volume respirometer maintained at 25°C) he has
demonstrated that snails infected with trematodes (germinal sacs of
Cotylurus Jlabelliformis, metacercariae of C . jlabelliformis, and an
unidentified xiphidiocercaria) not only have a lower oxygen consumption slope (logarithm of body weight plotted against the natural logarithm
of oxygen consumption) but as a group are more variable when compared
to laboratory reared uninfected snails. Duerr’s results again indicate
marked physiological effects of parasitism. Vernberg and Vernberg
(1963) have demonstrated another physiological manifestation of
parasitization by trematodes. The investigators have found that the
upper lethal thermal limits uf the mud-flat snail, Nassarius obsoletus,
heavily parasitized by trematodes (Lepocreadium ovalis or Zoogonus
rubellus) are significantly lower than those of uninfected snails.
Another study, this one by Kendall (1964), also has revealed yet
unexplained pathological alterations. It has been pointed out earlier
(Section 11, A, 2) that there is generally considerable host cellular
response when trematodes are introduced into unnatural molluscan
hosts. Kendall has reported that if young Lymnaea palustris, L.
glabra and L. stagnalis, all semi-suitable hosts, are successfully infected
with Fasciola hepatica, some become stunted, their shells ar0 distorted,
and the snails show signs of “ ill-health ”.
Wound healing. Little is known about wound healing following
parasite-inflicted damage. F. G. Rees (1931) and Fretter and Graham
(1962) have indicated that if the infection is terminated, the host