The experiences of mouse parents can make their children more competitive before the offspring are even conceived, a new study from the University of Utah indicates.
Researchers found female mice who lived in a more competitive, promiscuous environment gave birth to sons with an edge in the mating game by increasing the production of sexually attractive pheromones, regardless of how the mother was living when she mated.
"Our study shows that offspring can be benefited in an inheritable way by the experiences of their mother," said Adam Nelson, first author on the study published Monday in the journal Proceedings of the National Academy of Sciences.
There was a cost, though. Pheromone production is "outrageously expensive" for mice, said U. biology professor Wayne Potts, requiring much more energy than peacocks use to grow their tails. Making all those sexy pheromones shortened the sons' life spans.
The researchers studied the mice by separating them into two groups. For eight weeks, one group of 60 mice was placed in an open enclosure where the animals could interact, mate and compete for territory. The other group was separated into 23 monogamous, nonsocial couples.
The female mice from the competitive environment had sons who produced 31 percent more mate-attracting sexual urinary proteins, the researchers found.
"That's the exciting thing about this study; it's one of the first where something the parent experiences leads to a change in the offspring that makes it more competitive," said Potts.
The effect happened regardless of whether the mice were conceived before or after the mothers' time in the competitive environment, or which environment the father came from.
In fact, if the father was from the promiscuous environment, the sons produced 5 percent fewer pheromones.
It makes sense in evolutionary terms, Potts said. For the lady mice, sexier sons ensure their genes are passed down the generations male mice with promiscuous parents produce one-third more offspring but for a father faced with competition, more sexy young things make mating harder for him.
"One important thing this shows is that not all traits are simply determined by the genes of mom and dad, but also the experiences of mom and dad," said Nelson, who was a U. doctoral student when he worked on the study and is now a postdoctoral fellow at Harvard University.
While the changes benefited the mice sexually, it hurt their live span: Only 48 percent of them lived to the end of the experiment, compared with 80 percent of the male mice whose parents lived monogamously in cages.
The study is an example of epigenetic inheritance. While the genes the mice passed to their children didn't change, the way those genes were expressed did.
Though every mouse mother passed along an ability to make the pheromone, the social mothers chemically signaled to their offspring to ramp up pheromone production.
"It really changes the way you can think about rapid adaptation," Potts said.
The mice were only in the open environment for eight weeks, after being raised in a typical, monogamous lab mouse environment for 10 generations (the original mice were caught at a restaurant in Florida).
The concept has been studied before, but typically in a rather "brute force" way, such as how exposure to a toxin affects offspring, Potts said.
The results could have applications in breeding programs for endangered animals, which often have a very low success rate. If the animals were kept in social groups rather than in lone pairs, it might increase their offspring's ability to reproduce when released into the wild.
The study was funded by the National Science Foundation and the National Institutes of Health, and also had several co-authors.
Though mice are a good analog for people, the potential impact of this study for humans isn't clear. The effect of social environments on pheromones hasn't been studied.
The emerging field of epigenetics, though, does hold possibilities for humans. It's been suggested that parents who live through famine pass on an ability to store more calories potentially detrimental when food is plentiful.
"It's really kind of a recent revelation in discovering these epigenetic mechanisms," Potts said. "I think we're just scratching the surface."