Sarah Zala and Dustin Penn of the Konrad Lorenz Institute of Ethology at the Vetmeduni Vienna investigated whether females would also choose to mate with healthy over infected male if given a choice. In the laboratory and in large enclosures, the females were allowed to freely choose between two males, one healthy and another challenged with a mild infection, which they previously found to alter male odor.
Female mice are not making their choices solely based on health-related odor. Credit: Photo: Susanne Hammerschmid
The majority of females, about 86 percent, were initially more attracted to the healthy males. However, unhealthy males were also chosen as mating partners. "That surprised us. We assumed that the females would opt for the healthy males. Not only would this minimize the chance of becoming infected themselves, but choosing a healthy, disease-resistant partner would also be advantageous for their offspring," Zala explains.
Polyandry not unusual for female mice
A genetic analysis of the offspring revealed that about 30 percent of the litters had two fathers, the healthy male and the unhealthy one.
"Many females apparently mate with both males, whether these are healthy or not," Zala says. "We suspect that the females do this to protect their young. A male that was rejected as a mating partner may commit infanticide in order to get another chance at siring offspring."
"The females recognize whether males are healthy or unhealthy. We saw this quite clearly. But why they still mate with the unhealthy male remains unclear," says Dustin Penn.
In the future, Zala and Penn intend to study more closely the effect of an infection on the odor of the animals.
Odor preference seems irrelevant for mate choice
"Until now, scientists generally assumed that females choose their mates depending on their males' scent or other secondary sexual traits. Our study shows that this isn't necessarily the case," says Zala.
The situation could be different in the wild. As females recognize healthy males quite well based on odor, and are more attracted to them, they may be more likely to find healthy males in the wild. In the end, odor preference could still be an important factor determining sexual selection.
Citation: Sarah M. Zala, Amber Bilak, Michael Perkins, Wayne K. Potts and Dustin J. Penn, 'Female house mice initially shun infected males, but do not avoid mating with them' by Sarah M. Zala, Amber Bilak, Michael Perkins, Wayne K. Potts and Dustin J. Penn, Behavioral Ecology and Sociobiology. DOI: 10.1007/s00265-015-1884-2