Finicky Finches

PHOTO CREDIT: SARAH R. PRYKE

Things seem to pile on top of my desk too easily these days. When the stacks finally started tipping over today, I decided it must be time to clean. In this process, I came across a report that I had set aside to read in Science Magazine. So, of course, I abandoned all thoughts of cleaning in order to read this article. In this report, Sarah Pryke et al., describe studies conducted on female Gouldian finches (Erythrura gouldiae) examining their extra-pair mating behaviors.
Individuals in socially monogamous species, like the finches, sometimes copulate with individuals outside of the pair bond producing extra-pair offspring. For males, this may be beneficial as they can potentially produce more offspring. For females, it is not always apparent why they partipicate in this behavior.
In Gouldian finches, being a "redhead" indicates genetic incompatibility with the black headed color morphs such that the offspring typically have a very high mortality rate. The researchers in the study described in Science examined female finches that were in socially monogamous genetically compatible or incompatible pair bonds and presented them with the opportunity for extra-pair copulations with either compatible or incompatible male finches. What they found was that 77.5% of female birds actively solicited and participated in extra-pair copulations when given the opportunity. The female birds were shown to solicit the extra-pair males regardless of their own or the male's head color (i.e. compatibility).
Birds can actually store sperm from different males within their reproductive tract. This gives them the opportunity to be picky when it comes to which sperm is chosen. For female finches in genetically incompatible pair bonds, these extra-pair copulations with compatible males translate into a 38.9% increase in the survival of their offspring compared to females mating only with genetically incompatible social mates. These findings suggest that female Gouldian finches may
be able to bias paternity towards the extra-pair male when his contribution may produce viable offspring.
The full article is available in the August 20, 2010 issue of Science Magazine: Pryke SA, Rollins LA, Griffith SC. Females Use Multiple Mating and Genetically Loaded Sperm Competition to Target Compatible Genes. Science. 329: 964-967, 2010.