Thursday, February 16, 2017

A sheep in wolf's clothing: thoughts on mimicry in Las Cruces

            Without a doubt, symmetry and identicality are aesthetically stimulating. Clones, impersonations, and disguises figure prominently in plots of thrillers. But humans are not the only species that uses identicality to confuse and mislead others. Most people are familiar with mimicry, the evolutionary phenomenon by which two or more species resemble one another, often due to selective pressures from predators. Many people have heard the rhyme “Red next to yellow, kill a fellow; red next to black, friend of Jack”, to distinguish coral snakes from their less dangerous mimics, or have seen the owl-like eye spots that appear on the wings of many moth species.
            Shortly before arriving in Costa Rica, I had been talking with a friend about coral snakes and similar-looking species. It suddenly occurred to me that I only knew about visual examples of mimicry: insects that resemble sticks, milkweed butterflies that look like monarchs, cuckoos that sneak similar-looking eggs into nests of other species, and flowers that mimic bees to lure unsuspecting pollinators.
But many animals rely primarily on senses other than sight. Dogs, for example, have fewer color-sensitive cones than humans, but make up for it with their powerful ears and noses. A prey species evolving to fool a dog would do well to mimic another species’s sound or scent, not its appearance. And some animals use senses that humans don’t have at all. Is it possible that a species could evolve to mimic signals from magnetic fields to fool sea turtles, or thermal radiation signatures to hide from the infrared detection of snakes?
I was curious, but I didn’t have an answer yet. These thoughts were in the back of my mind as I arrived at Las Cruces Biological Station, the first field site I would visit in my semester abroad program with the Organization of Tropical Studies. In many of our early lectures and field outings, we discussed examples of visual mimicry—in such a biodiverse area as Costa Rica, it’s no surprise that many species evolve to resemble each other. In the Wilson Botanical Garden of Las Cruces, for example, I found passionfruit plants. Butterflies lay eggs on passionfruit leaves, which hatch into caterpillars that eat the leaves. As a defense against these butterflies, some passionfruit species produce egg-like spots on its leaves or tendrils, making it look like a butterfly has already laid eggs on this plant. Butterflies avoid plants that already have eggs, because their offspring would have to face resource competition—and possibly cannibalism—from the other caterpillars. I was still wondering whether mimicry occurs in other sensory modalities besides vision. During a class lecture on butterflies, I unexpectedly found an answer to my question.
Caterpillars of the genus Maculinea trick Myrmica ants by secreting pheromones that are chemically similar to those of Myrmica larvae. The ants take the caterpillar back to the nest and care for it, even at the expense of their own larvae, which often starve to death in the process. Once in the nest, the caterpillar also uses acoustic mimicry to mimic the sound of the queen, elevating its status in the nest. The well-fed caterpillar pupates, emerges as a butterfly, and flies out of the nest, enjoying the benefits of a free upbringing from the ants.
So it is true that non-visual mimicry exists to fool animals that communicate through other sensory modalities. Why had I only heard of visual mimicry before now? Given what I know about sensory perception in other species, I would guess that it is not because visual mimicry is that much more common, but rather because it is easier for humans to detect and study. In other words, there may be many other instances of mimicry, or other ecological phenomena, that are invisible or less apparent to us because of the way we perceive the world.
So what does that mean for me? I hope to become a biological researcher. I am used to thinking of scientific research as objective and impersonal. But scientific studies are motivated by questions, and questions stem from observations, and observations are limited by the blind spots of the observers. Learning about chemical mimicry in Maculinea and imagining how many other instances of mimicry we may be missing has reinforced my desire to incorporate fieldwork into my research career. It is important to me that I spend time with my study system, in order to break down my blind spots and understand the world that it experiences.

Reena Debray, Duke University

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