Wednesday, July 21, 2010

Second Glance: Mimicry and Speckled Alder Syndrome

Nature is full of little tricks. Just when you think you know something, it turns out that the one you are looking at is something else. It’s enough to drive a naturalist nutty, but it’s also the driving influence that will force a naturalist to hone his/her observation skills.

Back in my undergraduate days, we had a professor who described the whole look-at-only-one-characteristic-and-draw-a-conclusion scenario as Speckled Alder Syndrome, stated with one’s hand open, palm facing one’s face about an inch from one’s nose. In other words, you are only seeing one thing and ignoring everything else that will help you make a correct identification.

I admit it: I suffer from Speckled Alder Syndrome.

In all fairness, however, Mother Nature does conspire against us. And by “us” I mean all living things in general. From plants to reptiles, butterflies to parasites, the world is full of mimicry – living things that copy the looks of other living things all in an effort to deceive.

Mimicry comes in a variety of flavors: Batesian, Mullerian, Emsleyan, Wasmannina, Gilbertian, Browerian…and more. Most of us learn the basics of mimicry in high school biology, and usually by graduation we’ve forgotten all of it, except perhaps some of the examples, like monarch and viceroy butterflies.

What American child hasn’t grown up knowing about monarch butterflies? These large orange and black flappers are easy to identify and are the stuff of many an elementary school lesson on metamorphosis. Almost any child can recognize a monarch caterpillar, chrysalis and butterfly at a hundred paces. Well, maybe ten paces, but you get the idea.

Enter the viceroy. This is the butterfly we all learn about in biology as the one that mimics the monarch. There are a few differences that the trained eye can pick up, such as the smaller size, the extra black line across the hind wings, and the row of white spots that dot the black border band of those hind wings.

To the untrained eye, however, they look the same. This is mimicry at its best. Up until only a few years ago (the 1990s), everyone believed that the viceroy, thought to be a tasty morsel, was mimicking the monarch. We knew that monarch caterpillars ate milkweed, and that the sap from the milkweed made them taste bad. As adults, the bright orange and black coloration served to warn predators to leave them alone or suffer an upset stomach, or maybe even death.

What tasty morsel wouldn’t want to copy this? Why, if I taste good to predators, I’d want to make them think I taste bad so they would leave me alone. What better way to do so than to copy something that tastes bad? This is known as Batesian mimicry: something harmless mimicking something harmful.

As it turns out, however, viceroys also taste bad! As larvae, they feed on trees in the willow family (willows, poplars, cottonwoods). These trees contain salicylic acid, the stuff from which aspirin is made. Birds, or other predators, that eat a viceroy get the same reaction that some people get when taking regular aspirin: it tastes bitter and can cause an upset stomach. There are no buffered viceroys out there. One taste, and the predator will never again eat something that is orange and black. Mission accomplished.

This kind of mimicry, where you have two harmful species that look similar, is called Mullerian mimicry.

The viceroy’s mimicry doesn’t end here, though. As a caterpillar, and as a pupa, it takes on the appearance of a bird dropping. That’s right. The caterpillars are green and white, while the pupae are brown and white. What bird is going to snack on the previously digested remains of some other bird?

Then you have Emsleyan mimicry, where something deadly looks like something that is slightly less harmful. How can we be sure this isn’t just another case of Batesian, where something harmless looks like something dangerous? It all comes down to learning. If I eat something deadly and thus perish, how will I ever learn not to eat that thing? On the other hand, if I eat something that only makes me sick, I am likely to avoid anything that looks like the offending food. Therefore, by mimicking something less harmful, the deadly species increases its chance of being left alone.

Some forms of mimicry apply only to plants, some apply only within a single species. It’s enough to make the mind whirl.

I am learning not to take everything at face value. Most of the time I am not in such a hurry that I cannot take the time to take a second glance. Good observation skills are worth their weight in gold. You never know – you might just discover something new, even if it is only new to you.

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Ellen Rathbone

Ellen Rathbone is by her own admission a "certified nature nut." She began contributing to the Adirondack Almanack while living in Newcomb, when she was an environmental educator for the Adirondack Park Agency's Visitor Interpretive Centers for nearly ten years.

Ellen graduated from SUNY ESF in 1988 with a BS in forestry and biology and has worked as a naturalist in New York, New Jersey, and Vermont.

In 2010 her work took her to Michigan, where she currently resides and serves as Education Director of the Dahlem Conservancy just outside Jackson, Michigan.

She also writes her own blog about her Michigan adventures.





3 Responses

  1. Woodswalker says:
  2. Ellen Rathbone says:

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