Adultery is for the birds

TU professors Masters & Johnson study their cheatin' hearts

Birds of a feather don't always stay together–sometimes they "cheat" on their partners. But scientists believe this adulterous behavior could give their offspring a genetic advantage.

Towson University biology professors Scott Johnson and Brian Masters have a three-year $241,777 grant from the National Science Foundation to find out if baby house wrens born to adulterous females end up with "better genes" that produce a stronger immune system. Additional funds were obtained from NSF to engage undergraduate students in the research.

The TU professors are working with three researchers at Illinois State University to sample the DNA of baby wrens in more than 600 nests to identify those offspring that females produced through the avian equivalent of "extra-marital" liaisons. They will then compare these offspring to offspring that were fathered by the female's social partner. The study is called "Extra-Pair Mating in Birds–Trading Up Genetically to Enhance Offspring Health?" The work is slated for completion in July 2006.

Like humans, male and female wrens form pairbonds, bird "marriages" of a sort, to reproduce and care for their young. And like humans, wrens sometimes mate outside of the "marriage." In birds, this is called "extra-pair mating" rather than adultery. While the benefits of extra-pair mating are clear for males – it is a fast and easy way to increase their numbers of offspring -- the advantages to females are less obvious.

One theory is that females engage in this behavior to improve the quality of the young they produce. Masters and Johnson believe that the female wrens seek matings with extra-pair males who offer genetic traits not available in their own mates. They call it the "tall, dark stranger effect." And they speculate that females may select extra-pair mates in such a way as to increase the likelihood their offspring will have stronger immune systems, and be more resistant to diseases.

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Brian Masters and Scott Johnson

Professors Brian Masters, left, and Scott Johnson, right, are engaged in one of the most comprehensive genetic selection studies ever undertaken.


Grant funds have allowed Masters and Johnson to pursue a second, related study on extra-pair mating in mountain bluebirds in northern Wyoming. They're exploring whether the male bluebird's coloration affects his paternity success – that is, are females more faithful to bright blue males because they perceive such males to be of high quality?

Related links

  • Office of Sponsored Programs & Research
  • Department of Biological Sciences
  • Scott Johnson's Web site
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