By Alexander Eisenberg
Identification This article, Predator-induced morphological changes in an amphibian: predation by dragonflies affects tadpole shape and color, was authored by S.A. McCollum and J.D. Leimberger. The article was published in 1997 in the journal Oecologia.
The article begins by explaining the energy costs of different defensive mechanisms. Permanent defensive morphologies are thought to be expensive to create and sustain. As a result, these defenses may be harmful to the overall fitness of an organism. An alternative to this method of defense is inducible defenses. This type of defense is only expressed in organisms exposed to a predator. Inducible defenses are more energy efficient and are most appropriate in environments where predators are fluctuating and prey can easily sense when predators are present. This study examined the difference in color and shape of gray treefrog tadpoles exposed to tail damage, starved dragonflies, and fed dragonflies in an attempt to understand the inducible defenses of this species. The data showed that tail injury had no significant effect of tadpole size or shape. Only the predator condition had a significant impact on tadpole shape, size, and tail color. Tadpoles that had been raised with dragonflies that were fed were more likely to display black spots on their tails. Additionally, tadpoles in close proximity to dragonflies that were fed typically had deeper tails than those with unfed dragonflies. The results showed that tadpoles reared in an environment with unfed dragonflies had alterations that supported an increase in swimming velocity. These induced changes assist tadpoles in eluding dragonfly predators.
In aquatic habitats, the presence of predators is highly variable. As a result, most aquatic species have some sort of inducible defense. Inducible defenses are much more energy efficient because they are only provoked in the presence of a predator.