Chickadees have extraordinary memories.A new study explains why | University of Nevada, Reno

Lost your key? Have you misplaced your glasses? Can’t remember where you parked your car? You might wish you had the memory of a tit.

During the warmer months, these half-ounce birds with brains slightly larger than peas hide tens of thousands of food items, such as seeds, in the bark, lichens and crevices of mountain branches. When winter arrives, they can recall the exact location of their stash, a skill that helps them survive freezing temperatures and deep snow.

In a new study published April 17 in the journal Current Biology , researchers at the University of Nevada, Reno and the University of Colorado, Boulder discovered nearly a hundred ways that birds use spatial memory, or recall the location of objects. ability-related genes. The paper also suggests there may be a potential trade-off between having reliable long-term memories and being able to quickly discard old memories to form new ones.

These findings could help biologists better understand the evolution of spatial memory in animals, including humans.

Vladimir Pravosudov is a biology professor who has studied chickadees in the Sierra Nevada for 25 years.

“Using a field system that has been used for years to test memory spatial learning in wild birds, we worked with collaborators to parse out which genes might affect the chickadee’s ability to learn and remember spatial locations,” Pravosudov said.

To assess the spatial memory of wild tits, Pravosudov’s team devised an ingenious test. They hung multiple feeder arrays, each containing eight bird feeders filled with Sierra Nevada seeds. Each feeder has a door with a radio-frequency reader that detects tags the researchers have placed on the chickadees. The team then programmed each of the eight gates to be open only to certain birds, so that the chickadees had to remember the location of the correct feeder that was open to them.

Pravosudov and his team then measured the birds’ spatial memory – the birds with better spatial memory – by counting the number of times each chickade landed on the wrong feeder before recalling the correct feeder. The error rate is lower.

The University of Colorado Boulder team also used blood samples to sequence the entire genomes of 162 tagged chickadees that had their spatial learning and memory abilities tested using smart feeder arrays, creating the largest data collection ever Set for assessing the genetic basis of cognitive abilities in chickadees. By comparing the birds’ genomes to their performance in feeding tests, the team identified 97 genes related to spatial learning and memory in chickadees. Birds with specific genetic variations in these genes made fewer false attempts before landing at a given feeder than birds without these genes.

A large part of these genetic variations are related to the formation of neurons in the hippocampus, the part of the brain responsible for learning and memory, said co-author Sara Padula, a doctoral student on the paper. student in the Department of Ecology and Evolutionary Biology at the University of Colorado Boulder.

“Understanding the genetic basis of this trait will allow us to understand how this trait evolved,” said Scott Taylor, director of the Mountain Research Station and associate professor in the Department of Ecology and Evolutionary Biology at the University of Colorado Boulder.

According to Taylor, the common ancestor of all North American chickadees stored food. But of the seven species of chickadees currently found in North America, two don’t store food.

“They live in a milder environment, where food is generally available year-round. Now that we know the genetic region behind spatial memory, we can see what variation looks like in these species that have lost their cache,” Taylor said.

“This study significantly advances our understanding of the genetics of spatial memory and broader behavioral genetics in birds,” said Georgy Semenov, a co-author of the paper and a researcher in the Department of Ecology and Evolutionary Biology. Semenov) said.

a trade-off

Chickadees with special spatial memories can live up to eight or nine years, which is a long time for a small bird, Taylor said. But having good long-term memory can come at a price.

After running the initial task for several days, Pravosudov’s research team assigned the birds new feeders to test the birds’ ability to learn new locations after being consistently rewarded at different feeders. Item tests are commonly used to assess cognitive flexibility.

Interestingly, although chickadees from higher altitudes have better spatial learning and memory abilities than birds from lower and milder altitudes, in this “reversal” test, birds from higher altitudes Regional chickadees always seem to do worse. They seem to have difficulty letting go of their original memories and creating new ones.

“In more variable environments, our collaborators found that chickadees with good long-term memories may be at a disadvantage,” Padula said.

climate change

Like many other habitats, mountainous areas experience rapid changes in climate, characterized by rapid shifts between extreme droughts and extreme snowfalls, and it is unclear how birds adapt to this change and how this changes memory abilities.

“As a result of climate change, we might expect these selective pressures that have shaped the chickadee’s specialized memory to change significantly over thousands of years. Understanding the genetic basis of this trait will allow us to track changes in its genome over time,” Taylor said.

“Tracking genetic changes associated with spatial cognition will allow us to better understand evolutionary processes associated with climate change,” Pravosudov said.

Pravosudov will continue to work with Taylor’s team at CU Boulder. The team had already conducted the same experiment in the Rocky Mountains, home to another group of chickadees that had evolved independently of those in the Sierra Nevada over the past few million years.

The researchers will also look specifically at genes related to spatial memory and learn to understand how the frequency of certain genes, or alleles, related to cognitive ability changes with different climates.

“We can test whether selection on certain alleles is stronger in snow years and weaker in dry years, and also see changes over the years,” Pravosudov said.

Using these methods, researchers will be able to study climate-related evolutionary processes by focusing specifically on cognition and the genes underlying it.

“We have a beautiful model that can be used to study the evolution of cognition in mountainous backyards,” Pravosudov said.