Tiger salamander larvae normally eat invertebrates. Under high density, and with cues from the size and kinship of nearby larvae, some individuals develop into a distinct cannibal morph with a broader head, a larger gape and elongated vomerine teeth suited to seizing other larvae. The morph grows faster and can metamorphose earlier, an advantage in ponds that dry.
Experiments have shown the switch is environmentally induced rather than genetically fixed in individuals: rearing density and diet change the proportion of cannibals produced. Studies have also found that cannibal morphs are less likely to consume siblings than unrelated larvae, consistent with kin recognition reducing the cost to inclusive fitness.
Cannibalism carries a real penalty. Larvae that eat conspecifics face a higher risk of acquiring pathogens, including ranavirus, from the animals they consume. The morph is therefore best understood as a conditional gamble, not a superior form, and it does not appear in every population.