Recently I was lucky enough to record a podcast for Jason Goldman’s show The Wild Life. One of the subjects that came up in our discussion was my love of mimicry, and my feeling that if the National Science Foundation proclaimed that from now on they planned to fund mimicry research and nothing else, that would make total sense to me. You see, I love everything about mimicry. I think it is probably the coolest evolutionary adaptation that has ever been described, and I just happen to be lucky enough to study the group of animals that are most closely associated with this amazing phenomenon.
There are lots of different kinds of mimicry, in lots of different taxa. There are animals that mimic each other, animals that mimic inanimate things, plants that mimic animals, plants that mimic plants- you name it, someone, somewhere in the natural world, has mimicked it. I could write dozens of posts about mimicry (and incidentally I can’t believe I haven’t already written at least one!) but for now I’ll start out with the first type of mimicry ever described, Batesian Mimicry.
This type of mimicry is forever associated with Henry Walter Bates, an English naturalist who spent 11 years in the Amazon studying and describing insects, plants, birds, and lots of other things that he saw there in the mid-19th Century. Bates noticed that some of the butterflies around his camp were very colorful and conspicuous, but never seemed to take evasive flight patterns or hide from predators. He also noticed that the birds and lizards who lived in the same areas as these butterflies ignored them, even though they would readily hunt down and eat other butterfly species. After much careful observation Bates concluded that these butterflies were laying their eggs on toxic plants, and that the caterpillars that hatched from these plants ate these poisonous plants. He surmised that because of this, the caterpillars themselves must be poisonous, and that predators either knew this innately, or learned it through trial and error. Most importantly, the predators could associate this toxicity with the bright color patterns of these butterflies. We now refer to this warning coloration as aposematism, and it’s found in lots of organisms that have some type of toxicity or other dangerous defense mechanism.
When Bates decided to collect some of these butterflies, he noticed something else: he wasn’t seeing just one species of butterfly, he was seeing several that looked alike. What’s more, some of these species were not laying eggs on toxic host plants, meaning that they and their caterpillars were perfectly edible! Bates determined that these palatable butterflies were mimicking the unpalatable ones. In mimicry terminology, we now refer to the toxic species as the model and the edible species as the mimic. This particular brand of mimicry, comprised of a noxious model and a harmless mimic, is named after the man himself- Batesian mimicry.
For many years after Bates first published his findings on mimicry, scientists accepted his rationale without actually testing it. Then, famously, in the 1950s a set of experiments were undertaken by Jane Van Zandt Brower and later by Van Zandt Brower and Lincoln Brower, testing the effectiveness of several butterfly species that were assumed to be involved in mimicry. Van Zandt Brower’s approach was simple: feed the butterflies to their predators and wait to see how the predators respond. Depending on the toxicity of the butterfly in question, and the learning abilities of the predator, predators sometimes ate the butterfly and responded negatively (e.g. vomiting); tasted but didn’t eat the butterfly; or ignored it altogether. Next, the birds (she usually used birds as predators) were given the presumed mimic and asked to respond- if the bird had learned to reject the poisonous model and, based on that experience, rejected the presumed mimic, Van Zandt Brower concluded that the latter species was indeed a mimic of the former. Over the years many researchers (including me) have relied on this basic framework to test the efficacy of mimicry systems. While some of Van Zandt Brower’s earliest results have stood the test of time, others have undergone more scrutiny and allowed us to refine the interpretations somewhat. Regardless, though, this contribution has been essential to our understanding of how mimicry works.
What kind of Batesian Mimicry systems occur in your area? I promise you they’re out there!