Essay On Cannibalism

When we think of cannibalism, our minds immediately turn to gruesome pictures of humans eating other humans or fictional characters that feast upon the flesh of other living people (especially with a nice chianti and fava beans). Though cannibalism may not be a common occurrence among humans, it is a fairly widespread practice upon many other species of the animal kingdom. This paper will explore the behavior of cannibalism in the tiger salamander (Ambystoma tigrinum) a major fitness cost of cannibalism in these organisms: pathogen transmission.

Cannibalism is operationally defined as the ingestion of all or part of a conspecific, and is taxonomically widespread amongst many vertebrate and invertebrate groups; however, it is extremely infrequent in most species (Dawkins, 1976; Elgar and Crespi, 1992). It is believed that there are numerous fitness benefits to cannibalism, including better balance of nutrients from conspecifics over heterospecifics, and a competitive advantage of killing close competitors. There are also some fitness costs, which are believed to be associated with the rarity of cannibalism, including, increased risk of injury to the cannibal, diminishment of the indirect component of their inclusive fitness by killing relatives, and the heightened probability of acquiring deleterious pathogens and parasites above that experienced by non-cannibalistic predators (Dawkins, 1976; Elgar and Crespi, 1992; Hamilton, 1964; Pfennig, 1991, 1997; Sherman, 1981).

As previously mentioned, cannibalism is uncommon in many species. However, in the tiger salamander (A. tigrinum), it is a very common occurrence. Tiger salamanders have two life-history stages including a larval form and an adult form. During the larval stag...

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... is common in many salamanders and possibly the cause of these infections, the authors never actually test the water for Clostridium specifically (Pfennig et al., 1991, 1997). Thus, the pathogens within the study could be viral or bacterial, and could potentially have different transmission rates and affects on the salamanders. Another point of contention within the methodology of the study is that they did not actually test whether the deceased animals died from infection or were actually infected. Rather, they simply compared growth rate, isolation observations, and death rates of healthy to “diseased” animals (Pfennig et al., 1991, 1997). Pfennig et al. (1991) did note, from their parasite density comparisons, that though cannibals did carry more parasites than typicals simply because the cannibals were larger (no correlation of parasite number to body size).