Washington, Mar 5 : It's well known that butterflies and moths undergo a prominent metamorphosis - from crawling caterpillars to winged adults. Now, researchers at Georgetown University have found that a physical change in appearance doesn't necessarily change memories formed at the larval or caterpillar stage.
It was found that tobacco hornworm caterpillars could be trained to avoid specific odours delivered in association with a mild shock. After emerging from the pupae, adult moths also avoided the odours, showing that they retained their larval memory.
This study, led by Martha Weiss, an associate professor of Biology at Georgetown University, is the first to demonstrate conclusively that associative memory can be retained through metamorphosis in Lepidoptera, the order of insects that includes moths and butterflies. This study also leads to further new questions about the organization and persistence of the central nervous system during metamorphosis.
"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 Weiss.
"Scientists have been interested in whether memory can survive metamorphosis for over a hundred years," says Doug Blackiston, one of the authors of the study.
During the pupal stage, the brain and nervous system of caterpillars undergo drastic reorganization and it's still not clear if memory could survive such dramatic changes.
These findings indicate that the retention of memory relies on the maturity of the developing caterpillars' brains.
Caterpillars younger than three weeks of age learned to avoid an odour, but were not able to recall the information as adults, whereas older caterpillars, conditioned in the final larval stage before pupation, learned to avoid the odour and recalled the information as adults.
Besides, these results have both ecological and evolutionary implications, as retention of memory through metamorphosis could allow a female butterfly or other insect to lay her eggs on the type of host plant that she herself had fed on as a larva. This behaviour could actually shape habitat selection and eventually lead to development of a new species.
The findings are published in the recent edition of the journal PLoS ONE.