November 22, 2011
Predators Drive Evolution Of Poison Dart Frogs’ Skin Patterns
Natural selection has played a role in the development of the many skins patterns of the tiny Ranitomeya imitator poison dart frog, according to a study that will be published in an upcoming edition of American Naturalist by University of Montreal biologist Mathieu Chouteau. The researcher's methodology was rather unusual: on three occasions over three days, at two different sites, Chouteau investigated the number of attacks that had been made on fake frogs, by counting how many times that had been pecked. Those that were attacked the least looked like local frogs, while those that came from another area had obviously been targeted.
The brightly colored frogs that we find in tropical forests are in fact sending a clear message to predators: "don't come near me, I'm poisonous!" But why would a single species need multiple patterns when one would do? It appears that when predators do not recognize a poisonous frog as being a member of the local group, it attacks in the hope that it has chanced upon edible prey. "When predators see that their targets are of a different species, they attack. Over the long term, that explains how patterns and colors become uniform in an area," said Bernard Angers, who directed Chouteau's doctoral research.
Chouteau was particularly surprised by the "very small spatial scale at which the evolutionary process has taken place." Ten kilometers of separation sufficed for a clearly different adaptation to take place. "A second surprise was the learning abilities of the predator community, especially the speed at which the learning process takes place when a new and exotic defensive signal is introduced on a massive scale," Chouteau said.
This process could be at origin of the wide range of color patterns that are observed not only in frogs but also many species of butterflies, bees, and other animals. Mathieu Chouteau is in fact currently undertaking post-doctoral research into the Heliconius genus of butterfly. "Considering that this kind of project requires regular field work, I have taken up residence in the small town of Tarapoto, where I am responsible for the opening of a research centre that will facilitate the study of neotropical butterfly mimicry," he said.
Mathieu Chouteau is currently in Peru, where is undertaking postdoctoral research in collaboration with the MusÃ©um national d'Histoire naturelle in Paris.
On the Net:
- University of Montreal
- The Role of Predators in Maintaining the Geographic Organization of Aposematic Signals, American Naturalist
- DÃ©partement de sciences biologiques de l'UniversitÃ© de MontrÃ©al