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Cold-blooded: Salamander Cannibalism


(cannibal morph (bottom) vs typical morph (top))


We recently posted a tiger-salamander dissection video (which you can check out here), where we explained the anatomy and physiology of these fascinating amphibians. However, despite their adorable stripes and endearing little eyes, did you know that tiger salamanders are in fact cannibals that frequently feast on other members of their species?


Cannibalism is defined as ‘the practice of eating the flesh of one’s own species.’ Although cannibalism is a huge taboo among humans, it is actually surprisingly common in the animal kingdom. Some reasons why an animal might engage in cannibalism is to reduce competition, nourish one’s young, or quite simply out of hunger. Tiger salamanders are one of the few vertebrates that frequently engage in cannibalism, and their primary reason for doing so is to reduce competition in situations of limited resources.


A tiger salamander larvae can take one of two forms– a typical morph or a cannibal morph. The smaller typical morphs feed on small aquatic invertebrates, while the cannibal morphs –as the name suggests– feed on the smaller typical morphs. (The cannibal morphs have larger bodies, wider mouths, broader heads, jutting lower jaws, and teeth 3x the size of that of typical morphs, allowing their cannibalistic behaviors) Interestingly, studies have shown that a larvae develop into cannibal morphs only when there is a large number of larvae concentrated in one area. (limiting resources, and increasing competition) The tactile, visual, and chemical stimuli provided in crowded environments trigger a larvae into developing into a cannibal morph, and surprisingly, once one cannibal morph forms within a group of larvae, the chances of other larvae developing into cannibal morphs as well, is significantly heightened. By eating other tiger salamander morphs, the cannibal morphs are catching two birds with one stone, reducing competition and gaining nutrients. However, cannibal morphs can reverse back to typical morphs if the crowded conditions change within a certain critical period.


Adding on, studies have shown that tiger salamander larvae/morphs are able to distinguish relatives from non-relatives, and only cannibalize on the individuals they do not recognize as a relative. Through such selective cannibalism, cannibal morphs can ensure that they are not eliminating salamanders that have similar genes as them, but rather helping them, by reducing (i.e. eating) the competition. Although scientists are not entirely sure how tiger salamanders distinguish relatives from non-relatives, they hypothesize that tiger salamanders do so through smell.


After all, nature is wild sometimes, but we’re not judging.




Sources:

https://www.reed.edu/biology/professors/srenn/pages/teaching/web_2006/AMGJTG_Cannibals/competitive.html

https://www.wired.com/2015/01/animal-cannibalism/

https://askabiologist.asu.edu/explore/he-aint-tasty-hes-my-brother


Photo credit:

https://twitter.com/scott06thomas/status/1268541113155149829





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