For the little red squirrels of North America, jumping from treetop to treetop isn’t the only daring action these little rodents do. Small creatures also take significant reproductive risks which could lead to some big rewards when it comes to genetic fitness. It’s a game about how well they can pass their genes on to the next generation.
A study published January 19 in the journal Sciences It found that red squirrels that bet more in the breeding game outperformed their more cautious cousins, even if there were higher costs in the short term. the bet? That next spring would bear a barrack of seed, and having so many offspring would not be a burden since there was so much to go.
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It’s a bit like knowing the winning lottery numbers, but I have no idea when they’ll be called. While spending money on lottery tickets with these numbers may cost you money in the short term, the payoff will be greater in the future when you hit the jackpot. According to study co-author and University of Michigan Biopsychology Research Fellow Lauren Petrollo, natural selection favors female squirrels that have large litters in years when there is plenty of food.
“We were surprised that some females had large litters in years when there was not enough food available for their babies to survive the winter,” Petrollo said in a statement. “Because producing offspring is biologically costly, we wanted to know why these females are making what appears to be a mistake in their reproductive strategy.”
The study looked at red squirrels living in the Canadian Yukon during the mast year. These are spikes in a major food source every four to seven years. For the squirrels, this buffet comes in the form of seeds taken from the cones of white fir trees. Squirrels can guess whether they will be a mast year before this happens and increase their litter size and reproductive efforts in the previous months, so that there is a better future for their children to survive and a better genetic fitness for themselves.
“There is a constant push and pull between the trees and the squirrels in our study sites as each player tries to outwit the other in order to gain their own fitness,” said Petrolo.
The study used data from the Kluane Red Squirrel Project, a 34-year-old collaborative field study involving the University of Michigan, the University of Colorado, the University of Alberta, and the University of Saskatchewan. They screened 1,000 female squirrels from the project, collecting data on litter sizes and the number of fir cones the squirrels eat.
“Each year we collect data on how many baby squirrels produce and how many fir cones the squirrels eat,” Ben Danzer, co-author and associate professor of psychology, ecology and evolutionary biology at the University of Michigan, said in a statement.
The team looked at the reproduction of female squirrels during food booms and busts and found differences in their genetic fitness whether or not they gambled with their reproductive strategy.
Some played it safe by keeping litter sizes small during the lean years, while others took a more optimistic approach and had large litters even during the scarcest food years. The research showed that squirrels with a “glass half full” had greater fitness for life if they went through a year at the mast.
However, it has been proven that the squirrels are not guaranteed to win it in the end.
“In some ways, this trash-size gambling strategy is like playing with fire,” Petrullo said. “Since a squirrel has an average lifespan of 3.5 years and masts only occur every four to seven years, the female is likely to sabotage her fitness by having too many babies in her low-feeding years, hoping that when she dies the mast will die before she does.” You can’t. Mast experience at all. This could be very expensive.”
Not gambling on the breeding game at all does not appear to be a viable option for squirrels. If they miss their shot at the jackpot, those who didn’t play could pay a huge cost.
“It’s basically impossible for the female to recoup fitness costs because reproduction is not ramped up in the mast year, so the stakes are very high,” said Petroli.
According to the team, the best bet is for the squirrels to take their chances and suffer the costs of fitness in the short term to avoid the massive cost of missing the genetic fitness jackpot altogether.
[Related: Why counting Central Park’s squirrels isn’t nuts.]
It remains unclear how squirrels can predict future food production in their environments. According to Dantzer, it may be because they eat parts of the spruce that affect their physiology and alter the number of offspring they produce.
“This is exciting because it suggests that squirrels eavesdrop on trees, but we still have a lot to do to solve this mystery,” Danzer said.
Other animals, such as some migratory songbirds, use cues about the amount of food in their environment to make reproductive choices. Climate change is causing the reliability of these signals to decline, and scientists are unsure how the costs of these types of errors will change what is the best breeding strategy for squirrels.
“If the predictability of the food boom is reduced and the squirrels can no longer predict the future, this could affect the number of squirrels in the boreal forest,” Danzer said. “This could be a problem since squirrels are prey to many predators.”