When it comes to survival of the fittest, it's all about your mother, according to a study that analyzed 24 years' worth of data from a population of North American red squirrels in Canada's Yukon and measured maternal genetic effects in squirrel offspring.  

Conclusion: Adaptive success in squirrels is often hidden in the genes of their mother. Biologists have debated "nature vs. nurture" for decades. To what extent are we born a blank slate and how much of our destiny in life is written out for us in terms of our genetics?

"Some squirrels are genetically better at being mothers than others," said Andrew McAdam, a professor in U of G's Department of Integrative Biology and co-author of the study published today in Proceedings of the Royal Society. "We provide evidence that genetic differences in the nurturing ability of red squirrels affect the fitness of their offspring."

Credit: Paulson Des Brisay

It's widely recognized that mothers make important contributions to attributes of their developing offspring, "but our study is the first to measure how important these genes in the mothers are to the evolutionary success of their offspring." 

Researchers tracked squirrels throughout their lifetime by marking each animal and using radio collars to find their nests. At first, they found no evidence for the heritability of fitness. "This is not uncommon, but it's depressing for someone interested in studying adaptation," McAdam said. But Eryn noticed that there seemed to be a difference in fitness among squirrels that depended on who their mother was, and decided to look and see whether those differences among mothers were due to genetics." 

They discovered a hidden source of adaptive potential that has not been measured before, McAdam said. "It wasn't in the genes of the offspring -- it was hidden in the genes of their mothers."

These maternal genetic effects on offspring fitness can drive evolution even when offspring genes have no direct effect on fitness, he said.

"It represents a previously undocumented source of adaptive potential in wild populations."

Although they don't know all attributes that make for a "better mother," the researchers found that genetically gifted mothers often give birth earlier in the breeding season and their pups are more successful in establishing territories. "This is just one attribute. We also know that there are still more yet to be discovered."

"What is clear is that the benefits of good mothering early in life are compounded across a whole lifetime." 

Other contributors to this paper include Eryn McFarlane of Uppsala University in Sweden,  Jamieson Gorrell and Dave Coltman from the University of Alberta, and Murray Humphries from McGill University. The research was funded in part by the Natural Sciences and Engineering Research Council, the National Science Foundation and the Ontario Ministry of Research and Innovation.