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Butterflies may keep memories of caterpillar youth

March 6, 2008
Courtesy Public Library of Science
and World Science staff

But­ter­flies and moths are well known for their strik­ing met­amor­phosis from cater­pil­lars to winged adults. The dras­tic changes—not only in body, but al­so in lifestyle, di­et and sen­so­ry re­spons­es—might make one think the adults for­get an­y­thing they learned as a cat­er­pil­lar.

A moth or but­ter­fly may be able to re­mem­ber what it learned as a cat­er­pil­lar, re­search­ers say. Above, the the to­bac­co horn­worm ca­ter­pil­lar, Man­duca sex­ta. 
But one would be wrong. At least, that’s the con­clu­sion of a new stu­dy by sci­en­tists at George­town Uni­ver­s­ity in Wash­ing­ton. They found that with­in lim­its, a moth can in­deed re­mem­ber what it learn­ed as a cat­er­pil­lar, which is es­sen­tially a lar­va.

The re­search­ers trained to­bac­co horn­worm cater­pil­lars to avoid par­tic­u­lar smells by de­liv­er­ing them along with a mild shock. As adults, the moths al­so avoided the odors, show­ing the mem­o­ry stayed, the in­ves­ti­ga­tors said.

Si­m­i­lar mem­o­ry ca­pacity may well ex­ist in but­ter­flies, their ev­o­lu­tion­ary cousins in an or­der of in­sects called Lep­i­dop­tera, ac­cord­ing to the sci­en­tists.

“The in­tri­guing idea that a cat­er­pil­lar’s ex­pe­ri­ences can per­sist in the adult but­terfly or moth cap­tures the ima­gina­t­ion, as it chal­lenges a broadly-held view of met­amor­phosis—that the lar­va es­sen­tially turns to soup and its com­po­nents are en­tirely re­built as a but­terfly,” said George­town bi­olo­g­ist Mar­tha Weiss, sen­ior au­thor of the stu­dy. 

The find­ings are pub­lished in the March 5 is­sue of the re­search jour­nal PLoS One.

“Sci­en­tists have been in­ter­est­ed in wheth­er mem­o­ry can sur­vive met­amor­phosis for over a hun­dred years,” added first au­thor Doug Black­iston, who did the re­search while earn­ing a doc­tor­ate at George­town. What has prompted doubts on this, he said, is that cater­pil­lars’ brains and nerv­ous sys­tems are dra­mat­ic­ally re­or­gan­ized dur­ing the pu­pal or co­coon stage, which comes be­tween be­tween the lar­val and winged stages.

But moths’ youth­ful educa­t­ions only take them so far. Adults could not recall in­form­a­tion they learned when they were cat­er­pil­lars less than three weeks of age, the re­search­ers found.

* * *

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Butterflies and moths are well known for their striking metamorphosis from crawling caterpillars to winged adults. The drastic changes—not only in body, but also in lifestyle, diet and sensory responses—might make one think the adults forget anything they learn as a caterpillar. But one would be wrong, according to a new study. Scientists at Georgetown University in Washington found that within certain limits, a moth can indeed remember what it learned as a caterpillar, which is essentially a larva. The researchers trained tobacco hornworm caterpillars to avoid particular smells by delivering them along with a mild shock. As adults, the moths also avoided the odors, showing the memory stayed, the investigators said. Similar memory capacity may well exist in butterflies, the evolutionary cousins of moths in an order of insects called Lepidoptera, according to the scientists. “The intriguing idea that a caterpillar’s experiences can persist in the adult butterfly or moth captures the imagination, as it challenges a broadly-held view of metamorphosis—that the larva essentially turns to soup and its components are entirely rebuilt as a butterfly,” said Georgetown biologist Martha Weiss, senior author of the study. The findings are published in the March 5 issue of the research journal PLoS One. “Scientists have been interested in whether memory can survive metamorphosis for over a hundred years,” added first author Doug Blackiston, who did the research while earning a doctorate at Georgetown. What has prompted doubts on this, he said, is that caterpillars’ brains and nervous systems are dramatically reorganized during the pupal or cocoon stage, which comes between between the larval and winged stages. But moths’ youthful educations only took them so far. Caterpillars younger than three weeks of age could not recall learned information as adults, the researchers found.