Lack of Taste Aversion in
Biology 342 Fall 06
Will McNitt and Amanda Trail
Taste Aversion, an Overview:
What is Taste Aversion?
Taste Aversion, also known as conditioned taste aversion, is the behavior in which an animal restricts its diet based on a certain stimulus. Often the stimulus is found to be visual or olfactory, although there have been many experiments to show that other stimuli, such as auditory and electrical cues, can be sucessful in triggering an aversion to a food item.
A classic example of taste aversion is found in Wight et al., 1990. These researchers found that the hermit crab Pagurus granosimanus quickly learns to reject novel food items when the crab is subsequently treated with a toxin. After one or two trials, the crabs learn to avoid these foods, such as beef, because in the past they experienced illness after consuming this item. Similar results have been reported for birds (Conover, 1984), coyotes (Cornell and Cornely, 1979), and foxes (Hanners and Southern, 1979), among the multitude of taste aversion experiments conducted in the last fourty years. One of the key aspects of taste aversion is that it is often found in animals that scavenge for food, or encounter novel food items regularly. It is theorized that these animals have evolved taste aversion in order to allow them to quickly learn not to eat food items that reduce their fitness even when they are encountering new and unique foods often.
Enter the Vampires:Desmodus rotundus, the common vampire bat, is an interesting anomaly of the bat world for many reasons. First and foremost, these bats are sanguinivores. Most bats eat fruit, or catch insects, or hunt frogs, but Desmodus and a few other species drink blood. Furthermore, they are monophagous, meaning they consume only one type of food. The do not eat a variety of insects, or many fruits, or whatever fish are just below the surface of a lake; they drink only blood. Somehow, probably as a result of this simple diet, they have lost the capability to develop taste aversion. Ratcliffe et al. found that, even after multiple trials, the bats would not develop an aversion to blood that had been tainted with citric acid despite injections of lithium chloride after feeding. This is odd because the three species of fructivirous generalist-feeding bats in the study did develop taste aversion to tainted fruit when they were subsequently injected with lithium chloride. The question of why vampire bats fail to develop taste aversion, and why other types do not, has not been thoroughly studied and at this point is still relatively unexplored. What we do know is that, when existing theories explaining the evolution of taste aversion are applied to bats, it makes some sense that vampire bats would have lost this trait because they do not often encounter novel food items.