Moths remember what they learned as caterpillars

After my visit to the Cambridge Butterfly Conservatory yesterday, I started thinking about what might be going on in the little brains of those creatures. Like bumblebees, butterflies and moths drink nectar from flowers. They have to decide where to land to get food: what is a flower and what isn’t? They have to expend energy probing flowers with their long tongues (proboscis), so they have to be choosy about there they “stick it.” It really fascinated me how the Owl Butterfly on my arm was licking my red sweater. Like bumblebees, do butterflies and moths have unlearned preferences for certain colours, like red? Or did it lick me because I smelled good? Or was it a combination of both, or something else?

I did an online search to see if any interesting nuggets are out there about butterfly and moth cognition. I found an uber cool one about moths retaining memories they made as caterpillars!

Caterpillars turn into butterflies or moths in a process called metamorphosis. Given how different a butterfly or moth looks and behaves compared to a caterpillar, it is thought that the entire caterpillar must be broken down inside the cocoon and re-arranged to form a butterfly or moth. But if butterflies and moths can remember what they learned as caterpillars, then this suggests that at least some of their neutrons (brain cells) remain intact during metamorphosis. Their bodies might have been scrambled up, but maybe at least a portion of their nervous system remains the same?

The researchers in the study I found focused on tobacco hornworm caterpillars, which transform into tobacco hornworm moths. The researchers exposed the caterpillars to a particular odour followed by a mild electrical shock. They repeated the odour-shock pairing until the caterpillars learned to avoid the odour (i.e., they would crawl away from it). Then, after the caterpillars built a cocoon and transformed into a moth, the newly emerged moths were placed one at a time in a Y-maze. A Y-maze looks exactly like it sounds: It is a big tube in the shape of a Y. The moth was placed in the vertical part in the bottom. Unscented air was piped into one arm of the Y and air scented with the odour encountered as a caterpillar was piped into the other arm. The researchers watched to see which arm of the Y-maze the moth crawled into: the unscented arm or the odour arm. 

What happened? 

Moths chose the unscented arm significantly more often than the scented arm, suggesting they were avoiding the scented arm; i.e., avoiding the odour that brought them shocks as caterpillars.

A very cool nuance in the experiment: Butterflies and moths smell with their antennae, and there are brain structures called “mushroom bodies” that receive information directly from the antennae. The researchers gave the odour-shock pairing to caterpillars of different ages, whose mushroom bodies would be at different stages of development. During the test as moths, those moths who had been exposed to the odour-shock pairing as caterpillars before their mushroom bodies would have been developed did not show avoidance of the odour. However, moths  who had been exposed to the odour-shock pairing at an age when their mushroom bodies would have been developed did show avoidance of the odour. So this suggests that a particular brain structure–or at least the synapses within them–remain intact during metamorphosis.

Amazing!

As Brandon Keim writes in his article in Wired, “wouldn’t it be poetic if scientists ended up developing treatments for dementia based on the persistence of butterfly memories?”

Food for thought, for sure.

References

         Blackiston, D. J., Casey, E. S., & Weiss, M. (2008). Retention of memory through metamorphosis: Can a moth remember what it learned as a caterpillar? PLoS ONE, 3(3): e1736. DOI: 10.1371/journal.pone.0001736.

         Keim, B. (2008). Butterflies remember what they learned as caterpillars. Wired. Retrieved October 27, 2018 from: http://www.wired.com/2008/03/butterflies-rem/.

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