Promiscuous mice bear sexier sons

House mouse with young

Female mice that compete in promiscuous environments have sexier smelling sons, research has found.

Scientists in Utah, US, studied the pheromones produced in the urine of male mice.

They found that those whose mothers competed for mates were more sexually attractive to females.

But this success was short-lived: their life spans were shorter than mice with monogamous parents.

Adam Nelson from the University of Utah completed the study alongside senior author Prof Wayne Potts.

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It is published in the journal Proceedings of the National Academy of Sciences.

“Only recently have we started to understand that environmental conditions experienced by parents can influence the characteristics of their offspring. This study is one of the first to show this kind of ‘epigenetic’ process working in a way that increases the mating success of sons,” said Prof Potts.

Epigenetics is the study of how differences in a parent’s environment can influence how its offspring’s genes are expressed.

The researchers studied domestic mice which are usually paired in a cage and therefore breed with only one partner.

To reintroduce the social competition wild mice experience, lab mice were kept in “mouse barns” which were large enclosures divided by mesh to create territories.

The mice were able to climb over the mesh to access nest boxes, feeding stations and drinking water.

Researchers purposefully made some of these territories more attractive than others to encourage the animals to compete for territories and mates.

Mouse sits on scent marked fenceThe brownish urine stain acts as a territorial scent mark

To investigate whether parents had any role in influencing their son’s attractiveness, Mr Nelson and colleagues bred mice from the mouse barn and monogamous mice in combinations.

They found that, regardless of the father’s environmental experience, sons of females from the socially competitive mouse barn produced more pheromones.

Male mice use scent to mark their territory and proteins produced in these urine patches are known as pheromones or “sex attractants”.

Female mice prefer scent marks saturated with pheromones and mate more with males that leave these marks.

“If your sons are particularly sexy, and mate more than they would otherwise, it’s helping get your genes more efficiently into the next generation,” explained Prof Potts.

In contrast, the sons of promiscuous fathers were less sexually attractive, producing 5% fewer pheromones than those with monogamous fathers.

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Production of pheromones is outrageously expensive”

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Prof Wayne Potts
University of Utah, US

“Fathers are competing with their sons and usually drive them out of the territory quickly, while they let daughters stay,” said Prof Potts.

“If you’re worried about your sons impinging on your own reproductive success, then why make them sexy?”

But the boosted production of sexually attractive pheromones appeared to come at a price.

In a further study, the team discovered that only 48% of the promiscuous mothers’ sons lived to the end of the experiment, compared with 80% of monogamous mothers’ sons.

“Production of pheromones is outrageously expensive,” Prof Potts explained.

“A single mouse’s investment in pheromone production compares with the investment that ten male peacocks make in the production of their tails, which also are used to attract females.”

Researchers suggest their findings could help breeding programmes for endangered species in captivity.

“Domestication stimulates epigenetic mechanisms that make animals less fit for nature,” Prof Potts said, underlining his findings that non-competitive environments led to less sexually successful offspring.

By breeding captive animals in social environments, with the inherent competition for mates this involves, scientists believe these animals could have greater success when reintroduced to the wild.

“It’s amazing how often reintroduction of captive-bred endangered species fails – it’s estimated to be as high as 89 percent,” said Prof Potts.

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