Cannibalism in Ambystoma

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.