Cannibalism is not common in
lissamphibia and is only known to occur in only 5 anuran families and 1 urodele family. Ambystoma is the only salamander family
to display cannibalism. In the tiger salamander (A. tigrinum) there are two behaviorally and morphologically
distinct morphs: a cannibal and non-cannibal form. The present study evaluated
the effect of pathogens on the instance of cannibalism in the tiger salamander.
The
experimenters compared two samples of tiger salamanders from two plateaus in
Arizona, one with a high instance of the cannibal morph and the other with a
high instance of the non-cannibal morph. Samples of each morph were obtained
and reared in separate aquaria. Each type of morph contained diseased animals
to evaluate the effect of pathogens on each type of morph.
The two
plateaus had significantly different frequencies of each morph. Even when
raised in identical conditions, salamanders from the plateau containing the non-cannibal
morph were less likely to become cannibalistic. The difference in distribution
of cannibal morphs was attributed to the distribution of diseased ponds in each
plateau environment. There were significantly less diseased ponds on the
plateau containing the cannibal morph. In the laboratory population,
non-cannibal morphs did not consume the diseased salamanders. The cannibal
morph did consume the diseased salamanders and all salamanders within the
cannibal population died. Within a separate control group, cannibals fed
healthy tiger salamanders were not affected by disease. The cannibal morph was
also found to have higher levels of parasites within its digestive system.
This
study suggests that disease may be a limiting factor on the degree of
cannibalism in lissamphibia. Cannibal morphs of the tiger salamander were found
to have higher levels of pathogens and higher susceptibility to disease in the
laboratory environment. Cannibal morphs are also correlated with a low occurrence
of diseased ponds in the natural environment. The optimal environment that
would favor evolution of cannibalism is one in which there are few pathogens
and a high density of conspecifics. However as the threat of pathogens rises, cannibalism
may be increasingly less adaptive.
2 comments:
Fascinating research! Avoidance of pathogens may also be the reason for the taboo on human cannibalism.
For more about cannibalistic amphibians, see Joey's post: http://ourherpclass.blogspot.com/2012/04/you-are-what-you-eat-parasite-transfer.html
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