Natural selection in a nutshell

Super squirrel moms provide silver spoon beginnings

If they could, many women would likely take a page out of the red squirrel’s book. The northern animal can not only decide when its babies are born in the season but how many brothers and sisters will be in a litter, according to new research by University of Alberta scientists.

But not all female squirrels have these “super mom” capabilities whose genes are wired with these traits–there are “dud moms” in the population as well, report Dr. Stan Boutin and Dr. Andrew McAdam in the current edition of the journal Proceedings of the Royal Society of London, Series B. The research team addressed how much influence a mother has on her babies’ well-being verus the role the environment plays.

“Everybody knew that the care a mother provides was important,” said McAdam, who conducted the work in Boutin’s lab at the U of A before moving to the University of California. “But no one has been able to actually show proof of this in the wild before this. We now know which specific traits are contributing to evolution.”

The understanding of how characteristics evolve or change is often limited because measuring inheritance in the wild is difficult. Boutin was able to address this issue because he has been monitoring a large squirrel population–approximately 400 adults–since 1989 and because he was able to take some squirrels away from one mother and give them to another (cross-foster).

“We found that the growth rates in young squirrels are determined partly by genes in the offspring–nature–but mostly by the quality of care provided by their mother–nurture,” said Boutin, from the Faculty of Science. “We also found that the ability of mothers to care for their offspring is also determined partly by genes. As such, we have quantified the nature of nurture.”

Boutin likens what is happening with the red squirrel to the familiar saying that a child is born with a silver spoon in her mouth, suggesting the child is blessed with special conditions that allow her to do well for the rest of her life. The silver spoon refers to the environment during early childhood, he said.

“We questioned how much of this environment is due to luck of the draw–the young happen to be born when times are good–and how much is controlled by the mother.”

Two environmental conditions important to offspring growth were the litter size and the time of the birth (late winter or early spring). These conditions are determined by the mother and her “decisions” are affected by the food supply and the genes she carries for litter size and birth date. “In other words, there appear to be “super moms” that are capable of creating a favourable environment…they are, in effect, putting a silver spoon in their children’s mouths.

There is a catch–the super moms and their offspring are only successful when the food supply is good. When times are tough, dud moms actually have youngsters that are more successful. “In other words, the big house, big car, fast life-style works well when the economy is humming along but this may not be the best strategy when the economy slumps and conservatism is a better strategy.

“Our work suggest that there are genes that code for the fast vs slow lifestyle so decisions about how we live are affected by both the environment and our genetic make-up.”