By far the most important context in which an animal needs to learn quickly is when a behavioral choice has put that animal's life in danger. Eating a poisonous or tainted meal can lead to the formation of a specific aversion to that type of food based on a single experience. While food-based aversions are the most common type, animals may also form aversions to locations which have put them at high risk for predation. Emesis, the process of vomiting a poisonous food item, costs an animal not only that specific meal, but other food items and often the ability to eat for a period of time. For animals that are on tight energy budgets, this loss can be fatal; thus selection has favored a route for quickly learning to avoid foods which make an animal ill, and for retaining this information as strong, long-lasting memory.
Specific aversions facilitate the evolution of chemical defense by plants and animals. A plant or animal which can produce or obtain a toxin which causes emisis has an excellent chance of avoiding being eaten, as its potential consumers will develop specific aversions to the food type. Perhaps the best-studied examples of this is bird responses to poison-carrying butterflies (Brower and Fink 1985, Malcolm and Brower 1989, Ritland 1995) and rats (eg Galef 1989).
The ability to form specific aversions is widespread in the animal kingdom. While mice vary in their ability to taste and respond to aversive stimuli (Glendenning 1992), some species demonstrate an ability to form strong specifc aversions. Poisonous marine larvae can elicit specific aversions in their predators (Lindquist and Hay 1995). Interestingly, vampire bats, which feed on blood and would not normally encounter toxic food, do not demonstrate an ability for aversive learning to unpalatible food (Ratcliffe et al. 2003). Ratcliffe et al. (2003) present a summary of the literature on which animal species are known to form specific aversions.
Brower L P, Fink L S 1985 A natural toxic defense system - cardenolides
in butterflies versus birds Annals New York Academy Of Sciences 443 :
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