Promiscuous species may have stronger immune systems.

From Science Daily:

Monogamy and the Immune System: Differences in Sexual Behavior Impact Bacteria Hosted and Genes That Control Immunity

In the foothills of the Santa Cruz Mountains two closely related species of mice share a habitat and a genetic lineage, but have very different social lives. The California mouse (Peromyscus californicus) is characterized by a lifetime of monogamy; the deer mouse (Peromyscus maniculatus) is sexually promiscuous.

Researchers at the University of California Berkeley recently showed how these differences in sexual behavior impact the bacteria hosted by each species as well as the diversity of the genes that control immunity. The results were published in the May 2012 edition of PLoS One.

Monogamy is a fairly rare trait in mammals, possessed by only five percent of species. Rarely do two related, but socially distinguishable, species live side-by-side. This makes these two species of mice interesting subjects for Matthew MacManes, a National Institutes of Health-sponsored post-doctoral fellow at UC Berkeley.

Through a series of analyses, MacManes and researchers from the Lacey Lab examined the differences between these two species on the microscopic and molecular levels. They discovered that the lifestyles of the two mice had a direct impact on the bacterial communities that reside within the female reproductive tract. Furthermore, these differences correlate with enhanced diversifying selection on genes related to immunity against bacterial diseases.


Based on a comparison of the two species' genotypes he confirmed that the promiscuous mice had much more diversity in the genes related to their immune system.

"The promiscuous mice, by virtue of their sexual system, are in contact with more individuals and are exposed to a lot more bacteria," MacManes said. "They need a more robust immune system to fend off all of the bugs that they're exposed to."

The results, published in PLoS One, match findings in humans and other species with differential mating habits. They show that differences in social behavior can lead to changes in the selection pressures and gene-level evolutionary changes in a species.

Read the rest of the article here.