A rare discovery of long-term memory in wild frog-eating bats: 4 years after first exposure, bats remember ringtone’s connection to food

Frog-eating bats trained by researchers to associate a ringing phone with a tasty treat were able to remember what they learned over four years in the wild, new research has found.

The study familiarized 49 bats with a series of tones that caught their attention and trained them to associate flight to just one of the tones with a reward: a snack of baitfish.

Between one and four years later, eight of these bats were recaptured and re-exposed to the food-related ringing. All flew to the sound, and six flew to the speaker and grabbed the food reward, meaning they expected to find food. Control bats without prior sound training were relatively unresponsive to exposure to unfamiliar sounds.

“I was surprised – I started to think that at least a year would be a reasonable time for them to remember, given all the other things they need to know and given that long-term memory has real costs. me as long to retain a sound you may never hear again,” said lead author May Dixon, postdoctoral researcher in evolution, ecology and organismal biology at State University. from Ohio.

Dixon conducted this study at the Smithsonian Tropical Research Institute in Panama while a graduate student at the University of Texas at Austin.

“The environment that previous generations have experienced can be vastly different from the environment an animal was born into – and it can also change throughout an animal’s lifetime,” she said. “Trying to understand how animals use learning and memory is a way to understand how they will cope in a life full of changes in the modern world.”

The study is published today (June 20, 2022) in Current biology.

In the first phase, frog-eating bats captured for a series of cognitive tests were exposed to a highly attractive sound in the laboratory: the mating call of the male túngara frog, one of the bats’ favorite prey. species of bats. Flying at this sound was rewarded with a piece of baitfish placed on a net above the speaker.

Over time, the sound got mixed up and gradually replaced by ringing, but the reward was the same. The researchers then introduced three other ringtones, none of which were related to a food reward. The bats were trained to discern the differences and eventually stopped flying towards the unrewarded sounds. Each bat got at least 40 snacks while flying to the trained ringer for 11-27 days. All bats were microchipped and returned to the wild.

Starting a year later and for three more years, Dixon captured bats and identified eight of them in the initial test by their microchips. In a follow-up test of their response to the original award-winning ringtone, the eight trained bats quickly moved towards the sound and were able to tell the difference between that ringtone and a regular new tone, although many bats had flew to an unrewarded sound from the initial formation.

When 17 untrained bats were exposed to these sounds, they mostly twitched their ears in response to the sounds, but did not fly towards them.

“The study taught us a lot because there are relatively few studies of long-term memory in wild animals and we don’t yet have a systematic understanding of long-term memories in nature,” Dixon said. “If we can collect additional data on different bat species, we could separate them and see which life histories select for long memories.”

The paper lists 39 previous studies that have documented memory in species ranging from fish, birds and bats to goats and primates. Some of the longest of these experiments – documenting the memory of sea lions for 10 years, turtles for nine years and dolphins for 20 years – have all been conducted on animals that have lived in captivity the entire time.

“Being able to study memory in nature is important,” said study co-author Gerald Carter, assistant professor of evolution, ecology and organismal biology at Ohio State. “You can’t necessarily extrapolate from the wealth of data we have on animals in the lab to what they face in the wild, where there are a lot more things they need to remember. The environment is different and the brain is different in nature versus captivity.”

Despite the human tendency to assume that a long memory gives our species the advantage of intelligence, nature shows us that memory flexibility – also called adaptive forgetting – can be important for survival.

“It is not always true that being the smartest or having the longest memory is actually advantageous. Research has shown that fruit flies bred to improve their memory cannot compete as well with other fruit flies. “Dixon said. “Just because it’s helpful for humans to be so smart and have such great memories doesn’t necessarily mean it’s the best thing for other animals.

“That’s why we want to figure out when these skills will actually help the animals and when they might be a liability.”

This work was supported by the National Science Foundation and the Smithsonian Tropical Research Institute (STRI). Co-authors include Patricia Jones of Bowdoin College, Michael Ryan of STRI and UT Austin, and Rachel Page of STRI.

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